MOVEMENT AND DISTRIBUTION OF THREE SPECIES OF INQUILINE INSECTS IN BOREAL BOGLANDS: PROCESS AND PATTERN AT MULTIPLE SPATIAL

SCALES

by

MAFLGARET ANNABELLE KIWWCHUK -

B, Sc. (Hon) University of Guelph, 1995

Thesis submitted in partial füinllrnent of the requirements for

the Degree of Master of Science (Biology)

Acadia University S p ~ g Convocation 200 1

O by MARGARET ANNABELLE IKRAWCHUK, 2000

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TabIe of Contents

........................... List of Tables .... ..................................................................................... vi

. . List of Figures .......................O...... ................. .................................................................. vil ...

Abstract ............ .......... .................................................................................................... vui

Acknowledgements .......................................................................................................... ix

General Introduction ............................ ......................................... 1

References ................................................................................................................ 12

Chapter 1 . Movement potential of Wyeomyio smitlzii (Diptera: Culicidae): pattern and process ....................... ... ........................................................................................ 14

Introduction .................... .... ......... ... .............................................................. 14

Methods ........................ .. ......................................................................................... 17

Results .................................................................... .................................................... 27

Discussion ............ .... ............................................................................................ 31

References ........................ ....... .................................................................................. 37

Chapter 2 . Movement potential of FIetc~zerm~iaJrefc~zeri (Diptera: Sarcophagidae): implications for the study of populations ............................ .... ..................................... 39

Introduction ............................. .................................... 39 ............................................. Methods ....................................................................................................................... 40

Results ....................... .... ..................................................................................... 42

Discussion .................................................................................................................... 43

References .................... ...... .................... ..................................................................... 45

Chapter 3 . The relative importance of habitat structure changes within a nested hierarchy of spatial scales for three species of însects .......................................... 46

........................ Introduction ... ............................................................................... 46

.................. Methods .. .............................................................................................. 49

Results ........................ ..... ........................................................................ 57

Discussion ................. ....................... ........................................................................... 64

................................................................................................................ References 71

Synopsis .................. ........................................................................... ..................... 74

Appendix 1 . Roosting behaviour by FIefcIzerimyioflefcheri (Diptera: Sarcop hagidae) ........................................................................ in Sarracenia purpurea (Sarraceniacea) 76

References ................................................................................................................ 79

List of Tables

Chapter One

Table 1-1 Variables and attributed values for the W. smithii diffusion model.. . . . . 25

Table 1-2 A summary of movement information calculated fiom W. srnithii

release-recapture experiment and diffusion modeling.. . .. . .. . .. . .. . .. .. . . 28

Table 1-3 Variance coniponents analysis of larval W. smithii abundance at

four spatial scaies.. . . . . .. . . . . . . . ..... . . . ... . . . .. . . . . . . . . . . . . . . . . . . . . 30

Chapter Two

Table 2-1 A summary of information fiom field collection and difision modelling

to estimate F. fletcheri and W- smithii movement potential. .. . .. . . . .. . . . . 43

Chapter Three

Table 3-1 A summary of larval sarnpling effort by spatial scale and sample period 50

Table 3-2 A summary of structural variables used in multi-scale sampling.. . . . . . . . 52

Table 3-3 A summary of glm output for W. smirhii .......................... .. ...... 59

Table 3-4 A summary of glrn output for M. knabi ...... ..... ... .. . . . .. . ... .. . .. .... . . 60

Table 3-5 A sumrnary of glrn output for F. fletcheri ............... .. .. . ..... .... ..... . . 61

Table 3-6 A surnmary of mixed-effects ( h e ) models for W. smirhii ....... . .. . ...... 62

Table 3-7 A s u m r n q of mixed-effects (lme) modeIs for M. knabi.. . . ... . . . . . .. . . . . 62

vii

List of Figures

Introduction

Figure 1-1 A map of Newfoundland indicating general study location.. .-.. ........ 4

Figure 1-2 A GIS representation of the no&-west area of the study sy stem.. ..... 5

.................................... Figure 1-3 The pitcher plant, Sarracenia purpzrrea. 7

Figure 1-4 Members of the Sarracenia. purpurea inquiline comrnunity .. - ......... 10

Chapter One

Figure 1-1 The proportion of Sarracenia pztrpurea plants per distance class

.......................... ....... occupied by Wyeomyia srnifhii lmae.. - 28

Chapter Three

............. .... Figure 3-1 A visual summary of study design and variables.. .-.. 53

Figure 3-2 Direction and scde of significant relationships behveen

PQeomyia smithii, iIïetriocnemz~s knabi, and Fletcherimyia fletcheri

................. . . . density and structural variables.. .. .... ... - . 63

viii

Abstract

This study explores the movement potentiai and distribution of three species of

inquiline insects, Wyeomyia smithii (Cdicidae) , Metriocnemus knabi (C hironomidae) and

Fletcherimyia fletcheri (Sarcophagidae). Movement potentiai was detennined using

empirical mark-recapture studies, mathematical diffusion models and variance

cornponents analysis, and the process of movernent was used to predict spatial scdes

relevant to individual and population dynarnics.

The larvae of ail three dipterans obligately develop within the leaves of the

pitcher plant, Sarracenia purpurea (Sarraceniaceae) providing naturally nested Ievels of

scale including leaves within plants within clusters (points) within bogs. With the

estimates of relevant spatial scales as a template, census of the three species was used to

assess the influence of habitat structure (amount and configuration of habitat) on insect

distribution within this discrete hierarchy of spatial scales. The S u e n c e of habitat

texture was estimated at a single scale. In general, species responded to amount of habitat

at relatively fuie (individual) spatial scales, and configuration of habitat at broader

(population) scales, though each responded at slightly different absolute scales. These

relationships corresponded to evolutionarily divergent attributes such as body size andlor

movement potential. This change in the importance of structure among species and scales

demonstrates that spatial scale is an imposant attribute to be considered in conservation

decisions.

Acknowledgements

Thank you to everyone! Especially Adele Mullie, Sonja Teichert, Michelle

McPherson, Julie McKnight, Sharon Midwinter, Dave Shutler, Derek Potter, Sheila

Potter, Joe Nocera, Trina Fitzgerald, Matéo Yorke, John Chardine, Soren Bondmp-

Nielsen, Marty Snyder, Andrea Kingsley. Special thanks to Matt Holder who put up with

me in close Gros Morne quarters for two whole summers, and never ceased to keep me

smiling and thinking. Also, Renée Cormier and Jen Miner for a brilliant sumrner in 1999

- run chickens nui! 1 am indebted to Brian Starzomski, Trish Turliuk and Kat Benedict

for keeping me grounded for parts of these two years. Phi1 Taylor provided so many

ideas, much encouragement and good Company - thank you'OO. Thanks M m , Dad and

Carolyn for your continuous curiosity and support.

Funding and support came ftom: Atlantic Co-operative Wildlife Ecology

Research Network (AC WERN), NSERC, Western New£oundland Mode1 Forest

(WNMF), Parks Canada (Gros Morne National Park), Environment Canada Science

Horizons Program, Newfoundland Department of Forestry Resources and Agrifoods

(Pasadena), Stephen Flemming and Scott Taylor at Gros Morne National Park, Corner

Brook Pulp and Paper Ltd, and Ransom (RAM) Myers (statistical advice).

Lastly, thanks to Leo Hynes for the wee cabin in the woods.

GeneraI Introduction

The spatial distribution of organisms is a result of many factors at multiple spatial

and temporal scales. For example, specific processes such as the movement or fecundity

of an individual typically affect broader-scale phenornena such as population persistence.

Thus, patterns of organism aggregation can be understood as emerging fiom the

collective behaviours of large ensembles of smaller scale uuits (Levin 1992). This

emergent pattern is Iimited by larger scale constraints such as competition or resource

structure (e.g., habitat or prey structure). The result is a continuous opposition between

biological potential and constraint that occurs dong a hierarchy of spatial and temporal

scales, reinforcing the view that there is no single natural scale at which ecological

phenornena should be studied (Levin 1992). One way to understand and ultimately to

predict the dynamics of natural systems, is to identie rnechanisms underlying patterns

(of distribution) and to determine what limits them and how they are constrained at a

variety of spatial scales.

Organisms typically prefer certain m e s of habitat, thus species react to variabihty

in environmental (habitat) structure. A conventional fundamental unit of structure is a

patch of habitat, whether studied at a broad (e-g., population) or fine (e-g., individual)

scale. In this context, environments can be imagined to consist of patches, defined as

follows: a discontinuity in environmental character states pertinent to the organism

(Wiens 1976); bounded, connected discontinuity in a homogeneous reference background

(Levin and Paine 1974); and, as any place in the environment where the abundance of

either resources or organisms is high or low relative to its surroundings (Roughgarden

1977). These definitions al1 incorporate the notion that there are areas that are 'more' and

'less' suitable to organisms. The habitat patch makes intuitive sense, but it is more of a

concept than an object (see Kotliar and Wiens 1990; Bowers and Matter 1997), since

absolute boundaries of a patch are often difficuIt to delineate.

One method to approxirnate a patch of habitat relevant to an individual or group

of organisms is to understand the processes which support patterns of organism

distribution in the environment (also described as an ecological neighbourhood in

Addicott et al. 1987), and thus to determine the "grain" (the srnailest scale at which an

organism responds to patch structure) and "extent" (the largest scale of heterogeneity to

which an organism responds) relevant to the organism (Kotliar and Wiens 1990). In

doing so, habitat patches are biologically meaningfid to the study organism can be

defrned. As a result, estimates of habitat, or landscape structure can be scaled

appropriately to match definitions of individual or population dynamics.

Ecological studies ranging from spatially explicit metapopulation models of

organism distribution to a simple assessrnent of habitat use by organisms, evaluate the

relationship between process and/or pattern of organisms and their environment. The

structure of the environment c m be represented theoretically by an infinity of measures,

but landscape ecologists typically describe habitat (patch) structure using a parsimonious

trio including: composition (arnount), configuration and connectivity (Dunning et ai.

1992; Taylor et al. 1993). This mems that the composition (or arnount of each patch

type) dong with its position in space, and the nature of the space between patch types,

respectively, is hcluded in the description of the landscape. In practice, a suite of

measurable features can be estimated to represent these three concepts (see Forman and

Godron 1986; Wiens et al. 1993).

In this study 1 attempt to describe and understand the observed spatial pattern of

distribution of three species of insects, Wyeomyia smithii, Metriocnemus knabi and

Flercherimyiafletcheri. I use two approaches. First, by studying the process of individual

movement and estimating movement potential (for two of the three species; Chapters One

and Two), 1 predict spatial scaies relevant to individual and population dynamics. ln

addition, 1 propose links between movement potential, behaviour, and spatial pattern.

Second, by relating the distribution of the study organisms to habitat structure at multiple

spatial scales, I explore the influence (or constraint) of amount, configuration, and texture

of habitat on both individuals, and aggregations of the study species (Chapter Three). 1

compare response to structure at different spatial scales both intra- and inter-specifically,

incorporating movement potential as a process generating these relationships.

Study system

This work was done within the watersheds of the Main and Humber Rivers in

western Newfoundland. (UTM: 5514000N 478000E Zone 21U), an area of old-growth

(pers. cornrn. John McCarthy) boreai forest east of Gros Morne National Park (GMNP)

considered part of the Gros Morne Greater Ecosystem (GMGE) mg. 1-1). Research

activity is accelerating Iargely due to proposed forestry activity in the area. The long-term

impact of forestry on the region is unknown, but it has the potential to influence the

persistence of natural populations of plants and animals, and the ecological integrity of

G W .

Figure 1-1. A map of Newfoundland, Canada indicating the general location of the study

system. Gros Morne National Park is shaded in black on the western coast of the island,

the study site is delineated in white.

Figure 1-2. A GIS representation of the north-western area of the study Iandscape. This

naturally heterogeneous forest is cornposed of discrete bogs within a "rnarrix" of boseal

forest. Bogs are represented by yellow, water by blue, 'harvestable' forest by green, and

softwood scmb by beige. Map courtesy of Corner Brook Pulp and Paper Ltd.

This boreal landscape is a naturally heterogeneous area composed of discrete

patches of bog, mature coniferous forest (Balsam fir, Abies balsamea, and Black spruce,

Picea mariana) and softwood scrub (A. bdsamea and P. mariana) with nurnerous ponds

and rivers throughout (Fig. 1-2). The bogs are primady composed of Sphagnurn spp.

rnosses and contain extensive areas of shrubs and numerous flowering plants.

Bogs provide habitat for the pitcher plant, Sarracenia purpurea L.

(Sarraceniaceae; Fig. 1-3), a camivorous, perennial plant specializing in nitrogen-poor

environments. A large body of knowledge exists pertauiing to S. pzirpzirea and the

comrnunities which exist in its fluid-filled leaves. Sarracenia purpureu are abundant in

most boreal bogs but Vary greatly in plant density, size and condition. The plants can be

clustered together or isolated by tens of meters; leaf size and the nurnber of leaves per

plant are also variable. The plant flowers in July and August and not every plant produces

a flower in a given year.

Three species of fly, a mosquito, Wyeomyia smithii Coq. (Culicidae), a midge,

Metriocnemus krzabi Coq. (Chironomidae) and a sarcophagid, Fletcherimyia fletchéri

Aldrich (Sarcophagidae) have an obligate relationship with S. purpurea (Figure 1-4). The

eggs a d o r larvae of these three species inhabit the fluid-filled leaves of the plant during

their development. A mutualistic relationship exists between the plant and these

inhabitants whereby the larvae accelerate breakdown of prey and the rate of amrnonia

production in the leaves of S. purpurea wkle the leaves infuse oxygen into the water they

contain (Bradshaw and Creelman 1994). Sarracenia pupurea does not release digestive

enzymes into the fluid within the Ieaf. Characteristics of S. purpzrrea leaves that have

been linked to inquiline abundance include leaf age, actual and potential volume of fluid,

and the amount of organic matter. However, these characteristics exphin less than half

the observed variation in larval abundance (Nastase et ai. 1995) suggesting either

excessive random variation or that additional influentid factors exist.

Figure 1-3. The pitcher plant, S. purpzrrea. The larvae of W. smithii, M. knabi and F.

Jetcheri obligately develop within the leaves of the plant (a). Adult F. ji'etcheri roost and

mate within the flowerheads of the plant (b). Line drawing taken from Peterson and

McKenny (1968).

Wyeomyia smithii is a small culicid mosquito roughly 3 mm in length. Females

are autogenous in the norîh (do not require a blood meal for ovarioIar development

(Smith and Brust 1971 ; 07Meara et al. 198 1)) and deposit small ciutches of eggs into the

leaves of the pitcher plant in rnid-summer (Mogi and Mokry 1980; 07Meara et al. 1981).

Within the leaf fluid, the eggs hatch and develop to third instar larvae before entering

diapause and over-wintering (Smith and Brust 1971). Over-wintering mortality is

increased when temperatures of less than -5°C are experienced for more than four

months, thus snow cover is necessary for over-wintering survival (Smith and Brust 1 97 1 ).

The species is univolthe in its northern range, and individuals emerge synchronous~y in

Newfoundland in late June, early July (Heard 1994a, b; Miner 1999; pers. obs.). Thus, the

population distribution resulting fiom movement of addt females emerging in mid-

summer c m be measured by looking at the distribution of larvae in late summer.

The sarcophagid fly, Ffletcheri is a larger fly (7.5 mm in length) similar in stature

to the bouse fly, Musca domestica. In previous studies the fly was referred to as

Blaesoxipha (F.)fTetcheri. We refer to it by its current scientific names. The larval stage

of F. fletcheri has been studied more thoroughly than the adult. Since larvae are intra-

specifically aggressive, occupancy in leaves does not usually exceed one lama (Forsyth

and Robertson 1975). Adult female F. fletcheri larviposit directly into the leaves of S.

pzïrpzrrea in rnid- to Iate summer. Larvae develop in the pitcher's fluid until light and

temperature cues initiate pupation. Larvae move out of the leaf in fall, and pupate, over-

wintering in the Sphagnum spp. rnoss fiom which they emerge the following sumrner

(Forsyth and Robertson 1975; Hardwick and Giberson 1996). Adults roost in S. purpurea

flowers through the night (Krawchuk and Taylor 1999) where they have also been

observed rnating (for up to three hours (pers. obs.)). The adults are easiIy sexed externally

by observing the genitalia and shape of the abdomen, females being much broader than

males (pers. obs.).

The niidge, M knabi, is a s rnd chironomid. The Ianrae have been observed in S.

purpurea leaves throughout the surnmer (Paterson and Cameron 1982, Hardwick and

Giberson 1996; Rango 1999; pers. obs.), but peaks in abundance in Newfoundland occur

in Iune and again in August (Heard 1 994a,b; Miner 1 999). Paterson and Carneron (1 982)

suggested that A4 knabi dynarnics operate within an overlapping three-year cycle

whereby females fiom a May emergence oviposit into leaves and produce a generation

which emerges in August. The progeny of the August emergence develop and do not

emerge until the following July, this generation emerges the following May. Four instars

develop withui the leaves and prepupal instars crawl up the walls of the pitcher and

pupate in a gelatinous mass (Paterson and Carneron 1982; pers. obs.) above the fluid-line

fkom which they emerge.

The comrnunity interaction between these three species has been studied

extensively and has been described as a processing chain commensalism (Heard 19946).

Midge larvae feed by chewing on solid material, while mosquito lanlae filter-feed on

particles derived fiom the decaying matter and directly on bacteria. Sarcophagid larvae

are buoyant and feed upon newly captured insects floating upon the surface (Fish and

Hall 1978). niere does not appear to be an obligate relationship between the species, nor

a competitive one. While l a n d information is abundant fkom studies of inquiline

comrnunities, little is known about adult behaviou or life history.

Figure 1-4. Community living: a schematic representation of members of the Sarracenia

purpurea inquiline community including A) Wyeomyia srnithii (adult); B ) W. smithii

(Iarva); C ) ikfetriocnemus knabi (adult); D) M. knabi (larva); E ) Fletcherimyia fletcheri

(adult); F) F. j7etcheri (lama). Diagrams represent general morphology of the family, not

the species. Line drawing were reproduced fiom McAlpine et al. (1981).

Miner (1999) provided invaluable prelirninary work on the system with a study of

relationships between both insect abundance and plant morphology, and two components

of landscape structure (bog size and closure, the height of trees surrounding the bog) in

coastal Newfoundland. Miner's (1999) study demonstrates that bog size and the degree of

protection fkom winds (measured as closure) signincantly influences plant morphology

and midge, mosquito and sarcophagid abundance. Further, Miner (1999) proposed

relevant levels of spatial scale for the study of W- smithii and M h a b i populations based

on variation in abundance within nested spatial scales.

In this study, 1 measure movement potential of W. smithii and F. fletcheri

explicitly using release, or mark recapture (respectively) experiments to confirm and

fUrther explore behavioural and spatial patterns inferred from Miner's (1999) study.

Further, 1 use three conventional measures of habitat structure: the arnount, ~onfl~pration

and connectivity (vegetation texture) of habitat to determine hou; members of the S.

purpzrren inquiline cornmunity respond to structure at multiple spatial scales.

References

Addicott, J.F., Aho, J.M., Antolin, M.F., Padilla, D.K., Richardson, J.S. and Soluk, D.A. 1987. Ecological neighborhoods: scaling environmental patterns. Oikos 49340- 346.

Bowers, M.A. and Matter, S.F. 1997. Landscape ecology o f mammals: relationships between density and patch size. J. Mamrnal. 78:999-lO 13.

Sradshaw, W.E. and Creelman, R.A.. 1984. Mutualism between the camivorous purple pitcher plant and its inhabitants. Am. Midl. Nat. 112:294-301.

Dunning, J.B., Danielson, J.B. and Pdliam, H.R. 1992. Ecological processes that affect populations in complex landscapes. Oikos 65: 169- 1 75.

Fish, D. and Hall, D.W. 1978. Succession and stratification of aquatic insects inhabiting the leaves of the insectivorous pitcher plant, Sarracenia purpurea. Am. Midl. Nat. 99:172-183.

Forman, R.T.T. and Godron, M. 1986. Landscape Ecology. Wiley, New York. Forsyth, A.B. and Robertson, R.J. 1975. K reproductive strategy and larval behavior of

the pitcher plant sarcophagid fly, Blaesoxiphafletcheri. Can. J. Zool. 53 : 174- 1 79. Hardwick, M.L. and Giberson, D.J. 1996. Aquatic insect populations in transplanted and

natural populations of the purple pitcher plant, Sarracenia purpzrrea, on Prince Edward Island, Canada. Can. J. 2001.74: 1956- 1963.

Heard, S .B. 1994a. Pitcher-plant midges and rnosquitoes: a processing chah cornmensalism. Ecology, 75: 1 647- 1660.

Heard, S.B. 1994b. Imperfect oviposition decisions by the pitcher plant mosquito (Wyeomyia smithii). Evol. Ecol. 8:493-502.

Kotliar, N.B. and Wiens, J.A. 1990. Multiple scales of patchiness and patch structure: a hierarchical framework for the study of heterogeneity. Oikos. 59:253-260.

Krawchuk, M.A. and Taylor, P.D. 1999. Roosting behaviour by Fletcherimyiafletcheri (Diptera: Sarcophagidae) in Sarracenia purpurea (Sarraceniacea). Can. Ent. 13 1:829-830.

Levin, S.A. 1992. The problem of pattern and scale in ecology. Ecology 73 : 1943-1967. Levin, S.A. and Paine, R.T. 1974. Disturbance, patch formation and community structure.

Proc. Nat. Acad. Sci. U.S.A. 7 1 :2744-2747. McAlpine, J.F., Peterson, B.V., Teskey, H.J., Vockeroth, J.R. and Wood, D.M. 198 1.

Manual of Nearctic Diptera. Canadian Governrnent Publishing Centre, Hull Quebec.

Miner, J.A. 1999. The influence of landscape structure o n the distribution and dynarnics of insect comrnunities inhabiting the leaves of the purple pitcher plant (Sarraceniapurpurea). Hons. Thesis. Acadia University, Wolfville, Nova Scotia.

Mogi, M. and Mokry, J. 1980. Distribution of Wyeomyia srnithii (Diptera, Culicidae) eggs in pitcher plants in Newfoundland, Canada. Tropic. Med. 22: 1-1 2.

Nastase, A.J., de la Rosa, C. and Newell, S.J. 1995. Abundance of pitcher-plant mosquitoes, Wyeomyia smithii (Coq.) (Diptera: Culicidae) and midges, Metriocnemus knabi Coq. (Diptera: Chironomidae), in relation to pitcher characteristics of Sarracenia purpurea L. Am. Midl. Nat. 13 3 :44-5 1.

O'Meara, G.F., Lounibos, L.P. and Brust, R.A. 1981. Repeated egg clutches without blood in the pitcher-plant mosquito. Ann. Entomol. Soc. Am. 74:68-72.

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Petersûn, R.T. and McKenny, M. 1968. A field guide to wildflowers of northeastem aad no&-central North Amenca. Houghton Mifflin Company, Boston.

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Smith, S.M. and Brust, R.A. 1971. Photoperiodic control of the maintenance and termination of larval diapause in Wyeomyia smithii (Coq.) (Diptera: Culicidae) with notes on oogenesis in the adult femaie. Can, J. 2001.49: 1065-1 073.

Taylor, P.D., Fahrig, L., Henein, K. and Memam, G. 1993. Connectivity is a vital eIement of iandscape structure. Oikos 68571-573.

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Chapter 1. Movement potential of Wyeornyiu smifltii (Diptera: Culicidae): pattern and process.

Introduction

An assessment of the movement potentid of organisms (either of individuals or

their gametes) is an important component of ecological data interpretation and prediction

(Levin 1992; Turchin 1998). Studies of processes such as movement, fecundity or habitat

selection provide valuable information on natural history and evolutionary patterns.

Collectively, incorporation of the mechanisms contributing to spatial pattern into studies

c m help us mode1 population aggregations more realisticaüy, make wiser management

decisions and design future research at appropriate spatial and temporal scales. For

example, Griinbaum (1992) used individual-based modeling of krill populations to

dernonstrate that the collective behaviour of individuds gives rise to the formation of

aggregations consistent with field observations. By exploring variable mechanisms that

generate and maintain patterns we rnove fiom a deductive observation of pattern, towards

an inductive appreciation of the underlying complexity of the system. This mechanîstic

understanding also clarifies the relative importance of processes driving patterns at

multiple spatial and temporal scales, an extremely important topic in ecology and for our

comprehension of ecosystems (Kotliar and Wiens 1990). The overall importance of this

concept is M e r highlighted by curent work in a vax-iety of disciplines inciuding

biology, physics and economics, that similarly focus on the links between process and

pattern (Levin 1 992).

Movement is a cntical process aEecting populations by increasing genetic

variability, rescuing popdations fkom extinction, allowing colonization of new habitat

and altering species interactions (Turchin 1998). Mathematical quantification of

movement enables us to simpl% the process, and to transform it into a powerful

predictive tool in population ecology. The use of diffusion models to explain movement

pathways of organisms is one of the most successfül applications of mathematics to

ecological phenomena (Levin 1992). For example, Kareiva (1983) found that the Local

dispersal of eight of twelve species of herbivorous insects in simple environments could

be adequately described by simple difision. Spatial heterogeneity tends to increase with

higher levels of scale as a result of structural patchiness in habitat. In the context of a

heterogeneous landscape, movement may be remarkably different within and between

patches of suitable habitat, reflecting the influence of habitat structure. Flexibility in the

diffusion template allows pertinent addition of mathematicai complexïty to accomodate

heterogeneity into equations at a variety of spatial scales.

Frequently, populations of organisms using a heterogeneous landscape can be

described as a metapopulation system. Metapopulation theory describes the broad-scale

pattern of organisrns within population-level habitat patches whose independent

dynamics are driven by colonization and extinction events (Levins 1970; Edwards et al.

1994; Hanski and Gilpin 1997; Thomas and Kunin 2999). Though a continuum of

metapopulation scenarios exist (Harrison 1994), each describing varying degrees of each

population's independence £tom the other, an assurnption common to al1 scenarios is that

movement arnong groups ensures the persistence of the overall metapopulation. In the

context of rnerapopulations, the measurement of an organism's rnovement potential

allows us to consider whether interaction among (spatially distributed) habitat patches is

theoretically possible. In hm, this indicates which spatiai scales are reievant to studying

population or metapopdation persistence. Thus by understanding the movement process,

we more fully understand the spatial scde of within and between patch dynamics.

Further, this information can be used to predict how organisms might respond to the

structure of their environment.

The hierarchically "patchy" resource structure of the pitcher plant mosquito,

srnithii, in the bored forest of western Newfoundland suggests that population dynamics

could be described in a metapopulation framework. This "patchiness" can be visualized

as discrete leaves on plants, plants in a cluster, multiple clusters of plants distnbuted in a

bog, with discrete bogs embedded in a "matrix" of coniferous forest. However, the

appropriate spatial scale at which to study metapopulation-type dynamics depends, in

part, on the movement potentid of W. smithii. Similarly, the relationship between these

nested levels of habitat structure and the distribution pattern of W- srnithii may be

integrally related to the ability of the mosquito to move between and within patches of

resources.

In light of these ideas, there were three objectives to this study: one, to mode1

empirically derived movement data using diffision-theory equations to determine if

simple mathematical models could adequately describe the movement patterns of W-

srnithii within patches of bog habitat; the moments fiom these equations codd be used in

future predictive modeling of the system; two, to suggest the appropriate scale for

studying (meta) population dynamics of W. srnithii using a suite of indicators including

difision equations and distribution patterns fiom large scale census data; three, to

address a gap in natural history information pertaining to the movement potential of W.

smithii. An extensive base of literature provides information concerning the three-

member uisect community inhabithg S. purpureu, including a vast amount of

information about population and community dynamics within the leaf of the plant itself.

However, to our knowledge there is no empirical irformation available on rnovement

ability of the insects.

1 addressed these objectives using two methods. 1 used a release-recapture

experiment to measure movement potential of W. smithii explicitly. These data were used

in the diffusion rnodel and as traditional statistical descfptors of movement distance. 1

used a large scale census of W- smithii distribution to infer movement using variance

components analysis.

Methods

Release-recapture field procedure

The movement potential of W. smithii was estimated using a release-recapture

experirnent designed to measure the distribution of W. smithii larvae resulting fiom

successfUl emergence, mating, movement and oviposition by adult femaies which were

deposited as larvae at the release site. This design required a bog containing no W. smithii

larvae pnor to the study period, either natwally or through the removal of existing larvae

pnor to the experiment.

An experirnental bog was chosen after initiai sampling of the inquiline

cornrnunity in 150 pitcher plants (3 leaves per plant, n=450) indicated an absence of W.

smithii larvae in the area - ideal conditions for the movement experiment. Larval W.

smithii were detected in al1 of 40 additional sample bogs in the area (see large scale

sampling that follows) fiom a sarnple effort of between six and 24 plants per bog,

suggesting that 150 plants was an adequate effort. A sarnpling grid was constnrcted

consisting of a geo-referenced release line, and three geo-referenced transects each with

sampling points extending 200 rn in both directions perpendicular fkom the release Iine

(six transects). The grid contained 78 sampling points (234 plants) in total which were

positioned at intervals between 10 and 20 m apart along the six transects. Each sample

point consisted of the three pitcher plants, the nearest three viable plants to a flagged

point (plants were always within five rneters of the flagged point). These points were

used to sample the redistribuîion of larvae.

On 6 Jdy 1999, 840 W. smithii larvae (7 20 pupae plus 130 fourth instar larvae

were coliected fiom nearby bogs within 10 km) were deposited in 84 pitcher plant Ieaves

distributed randornly along the full length of the release line. Ten individuals were placed

in each leaf to approximate densities reported in previous experimental studies of W.

smithii (Heard 1994). To determine an appropriate re-sampling date, the progression of

development and emergence of released larvae was monitored in randornly chosen

release leaves during £ive visits to the bog between the release date (6 July 1999) and the

recapture-sampling date. Three weeks after pupation of larvae was observed, recapture-

sampling was initiated at the experimental bog. RegionaI phenology of I;TI srnithii was

also monitored at a permanent sampling bog one kilometer from this experimental bog.

First and second instar larvae were detected consistently at the permanent sarnpling bog

concurrent to the re-sampling of the experimental bog, corroborating the validity of

timing for the resample.

Re-sampling occurred on 26 August 1999. Three recapture-sample leaves were

chosen from each sample plant (n=702 Ieaves) based on their age and condition. Each

leaf was the current years' cohort, held water, and had a distal opening large enough for

the entrance by adult W- smithii. Each leaf was removed fiom the plant and the contents

were poured into a sorting tray. The leaf was opened and al1 plant and animal material

was flushed to the tray with water. The abundance of larvae according to leaf, plant and

point was recorded and associated with the measured distance fkom the release line. Two

distance-distributions of larvae were recorded. The first distribution described the

perpendicular distance fiom the release line to the point of capture. The second

distribution described the maximum distance from m y point on the release line to the

capture location. The perpe~dicular distance distribution assumes that individuals move

directly out fiom the release line, a minimum; while the maximum move distance likely

over-estirnates movements closest to the release line. These two methods will provide an

approximate range in movement estimates, since direct observation of movement was not

possible.

In addition to the sarnpling scherne detailed above, two other methods of

recapturing W. srnirhii were attempted, but proved unsuccessfid. First, the interior

circdexence of leaves were coated with Tanglefoot (Bioquip, California) in an attempt

to trap adult female W. smithii while ovipositing at pitcher plants. Circular coverage of

the leaf was one centimetre (height), including and just below the level of the ventral lip

of the leaf. Only one W- srnithii specimen was captured using this technique, however,

many other specimens of Coleoptera, Hymenoptera, Diptera and Arachnida were

recovered in good condition. The second method involved covering the top surface of

cork discs (two mm high) with Tanglefoot and placing the discs to float at the surface of

fluid in purpurea leaves. Similarly, many insects, but no W. smithii, were coilected in

good condition

The diffusion mode1

The diffusion equation used to explore the K mithii recaphne-sampling data was

based on a simple model for time-integrated data discussed explicitly in Turchin and

Thoeny (1993) and Turchin (1998). The model dehes C, the total catch in a trap (as time

+ 4 as,

where D is the diffusion rate, 6 is the disappearance rate of animais (e.g., a result of

death), a is the effective sampling rate of traps, No is the total number of organisrns

released, and x is the distance fiom the release point.

Drift

For bi-directional rnovement &a f?om the release line to be combined within the

uni-directional model the assumption that no drift existed Ui the data needed to be tested.

If no drift existed, the position of recapture-sampled larvae was equally likely to occur in

either direction fi-oom the release line. 'Population' drift would cause a shift in the average

displacement from the ongin, which in tum would be refiected in the spatial distribution

of recaptures (Turchin and Tizoeny 1 993). Displacement of recapture-samples X, was

calculated as,

where C(x) is the abundance of larvae at a sampie point, x is the x coordinate of the plant

location (modified for direction as +l- displacement), and n is the number of points

sampled. We tested the hypothesis of no drift (X not different ftom zero) using a t test

(MathSofi Inc. 1999).

Mode1 fitting

Raw data fiom both distributions (perpendicular and maximum distance) were

Poisson distributed once they were pooled to be uni-directional. Due to the small number

of larvae obtained fiom the recapture-sampling, data were interpreted at the scale of the

plant and manipulated to provide a response variable representing the proportion of plants

occupied within each distance class. Based on observation of weak female £light

(Bradshaw 1983; lstock and Weisburg 1987; pers. obs.) and the abundance of plants in

the study area, each larval incidence at a plant was considered to represent an

independent fernale. Previous studies suggest that an adult female deposits one to three

eggs at each visit to a leaf (Mogi and Mokry, 1980; Heard 1994).

Since a 'trap' in the original mode1 infers that animals stop moving after

encounter, the meaning of a was rnodSed to represent the deposition of eggs by female

W. smithii. This modincation is inspired f b m work by Okubo (1980)' who madeled the

distribution of uisect eggs in space as a result of adult movement, thus accounting for

continued movement of a female after laying eggs o n h the host plant. Similar examples

of equation modifications can be faund in Williams (1961) and Broadbent and Kendall

(1953); Williams (1961) uses a two dimensionai Bessel function, as opposed to this one

dimensional form, but the logic is identical. As a result, a now represents the rate of

larval deposition (W smirhii oviposlt, but since larvae were counted, hatch rate of eggs to

larvae waç included in the calculation of a).

A further modification to the original equation was made to account for

manipulation of the response variable C(x) fiom an abundance per plant leaf at distance x

to a proportion of plants occupied within distance class (6). The working equation is,

where 4 represents the number of plants sampled in distance class d. The value of a was

determined using literature-derived infurmation (Table 1 - 1). The total number of larvae

released was known, and d was determined for each plant sampled using real-time

corrected GPS (Trimble Surveyor TDCZ, Trimble Inc. California); distance classes were

categorized in five meter intervals. The models were & using an iterative nonlinear least

squares model (nls) in S-PLUS 2000 (Venables and Ripley 1996) fiom which estimates

of the parameters 6 and D were cdculated.

The rnean and variance of move distances were predicted using the diaision

paraneters calculated in E q d o n 3. The estimate of mean move distance (for

perpendicular and maximum distance distrriutims) for W- mithii (ab., time integrated)

w=,

using the derived diffùsion rate, D. This equation predicts a two dimensional move

distance based on the dimensions of a circle, however it is still a valid calculation since D

and 6 were appropriateIy derived fiom the data, though in one dimensional space. The

variance in move distance for W: smithii was estïmated as,

In addition to fitting the data to the df i s i on model, Equation 3, they were also fit

to a generic exponential model (sensu Theony and Turchin 1993),

where C(d) is the proportion of plants occupied by Iarvae within a distance class d. The

relative fit of the two models (Equations 3 and 6) was compared quantitatively using

residual deviance.

The data were compiled fiom the release-recapture experiment using traditional

statistical descriptors to observe general patterns and lUnits in the data including the

minimum, maximum, mean, and median move distance. These values were used to v e w

and assess the diffiision rates predicted by the difhsion models.

Table 1-1. Variables and attributed values used to estimate a (rate of larval deposition)

in the W- smithii difision mode1 (Equation 3).

Variable Source Eclosion success 0.45 Kleckner and Bradshaw 199 1 Emergence success 1 .O0 Price 1958; Istock et al. 1975 Sex ratio (ma1e:fernale) 0.50 Istock et al. 1975 Mating success 0.50 estimated Mean eggs produced per fernale $ 62.00 pers. obs. (fiorn dissections) Correction factor Y 0.33 Mogi and Mokry 1980; Heard 1994 Hatch rate of eggs 0.80 Price 1958; Istock et al. 1975;

EUeckner and Bradshaw 199 1 Product of values (a) 1.84 $ Dissection, and ovariolar counts of eight fernale W. smithii were used to estirnate female fecundiv. Y Since Our response is the proportion of plants occupied per distance class (regardless of the number of larvae per plant), this value scales-dom the egg nurnber produced per female. The literature estirnates that a female commonly deposits between one and three eggs per leaf-visit.

Large scale sampling and variance components analysis

The distribution of variation from census of Iarval counts was used to estimate

movement potential of K srniihii. Vûriance components analysis (VCA) is used to

determine the distribution of variance between a variety of (random) factors in a study

design (Searle et al. 1992). In a VCA, peaks of unusually high variance are suggested to

indicate scales at which between-group differences are especiaily large, inferring the

scale of movement, natural aggregation or patchiness (Greig-Smith 1952, 1979). Here,

the f i s t purpose of the VCA tvas to determine the dominant spatial scale(s) of variation

in the W. smithii census data The second purpose was to determine if the magnitude of

scale of W. smithii movement potential inferred statistically through VCA corroborated

with movement parameters derived fiom the experimentai data and diffusion model.

Data for the VCA were collected fiom two multi-scale censuses of S. purpurea

larval cotumunities that took place concurrently to the experimental movement study

outlined above (Sample One: 5 June - 27 June 1999; Sample Two: 17 August - 25 August

1999). Briefly, the insect fauna were sarnpIed fiom the leaves of S. purpurea in 40 bogs

within 20 km2 region. Within each bog, between two and eight sampling points were

chosen dependant on the size of the bog. A point consisted of three viable purpurea

plants (nearest neighbours) and complete faunal samples were taken fiom the three leaves

of each plant using the same method as the recapture-sampling in the movement

experiment described above. These sarnples have spatial attributes of the following

factors: a leafwithin a plant, a plant within a point, a point within a bog, a bog within a

landscape. Local habitat characteristics were also measured with each leaf sample and

included: the amount of detritus in each leaf, the number of midge larvae (M. h a b i ) ,

number of sarcophagid larvae (F. ji'e'etcheri), and the actual and potential volume of fluid

within each Ieaf.

Generalized linear models (glms) in S-PLUS 2000 (MathSoft Inc. 1999) with a

Quasi-likelihood family wcre used to statisticaily "strip-away" variation of the leaf-level

habitat variables (e.g., actual fluid volume, community structure, amount of detritus) on

the abundance of W. smithii larvae in each leaf (see Chapter R e e for more details).

Sirice larval counts are an index of adult density, the residuals fiom the glrn were used as

a relative abundance (density-type) response measure in the variance cornponents

analysis (varcomp in SPLUS 2000).

Results Table 1-2 outlines the general movement parameters of the W. smithii mark-

recapture data. The raw abundance data indicated no drift in the distribution of larvae

fiom the release line using a one-sample t test (t=1.12, df=77, p=0.26) with a nul1

hypothesis that the true mean of the spatial distribution of larvae was equal to zero.

The nonlinear models (ds) of the distance-proportion data using the difision

equation (Equation 3) resulted in a reasonable fit to the field data @oth perpendicular and

maximum distance), suggesting that the estimates of values for a were adequate (Fig. 1-

1). The residual standard error after curve fitting was 0.049 (de24) for the perpendicular

distance distribution, and 0.06 1 (de241 for the maximum distance distribution. The

parameters (e-g., mean distance) calculated fiom the diffusion values matched field-

values quite closely (Table 1-2) using both distance distributions. The exponential model,

Equation 6, was fit to the perpendicular distance data using the same, nonlinear (nls)

routine for ease in comparing the fit of the two models (difision and exponential).

Again, a reasonable fit resulted Fig. 1-1). The parameter a (kl SE) was calculated as

0.72 k 0.14 ( ~ 5 . 0 0 ) ~ and b as 0.10 I 0.022 (t4- .70). The residual stmdard error after

curve fitting was 0.054 (dfX4).

Table 1-2. A summary of movement infom~.tion calculated fiom W. srnithii release-

recapture experiment and difision modeling.

Variable Value Source

Larvae introduced Leaves sampIed Larvae 'recaptured' Median distance of 'recaptures' Mean distance of 'recaptures' (41 SE) Maximum distance moved Disappearance rate (S+1 SE) Igeneration Diffusion rate @f 1 SE) / generation Mean distance moved Variance in distance moved

Recapture rate Estirnated disappearance rate

perpendicuiar 840 702 (234 plants) 37 2 m 1 0 t 3 r n 83 rn 0.0035I 0.00 1 1 0.17f 0.016 10.95 rn 74.56 rn

maximum 840 from release experiment 702 from release experïment 37 from release experiment 40 m from reIease experirnent 45k4 rn from reIease experiment 106 rn from reIease experïment 0.020k0.026 predicted by Eqn. 3 1.53+1.17 predicted by Eqn. 3 13.73 rn predicted by Eqn. 4 1 17.4 m predicted by Eqn. 5

3.7 % 3.7 % A/(B * C) 0.38 0.38 from release experiment

(1-((AE)*F)/B*c) A Number of larvae recaptured B Nurnber of larvae introduced C Rate of egg deposition and IarvaI survivorship per larva introduced (Table 1-1). E Nurnber of plants sampled (234) F Estimated r&nber of plants in the experimental bog frorn density transects.

3 4

Distance from release tine (In(rn))

B) Distance from release line (In(rn))

Figure 1-1. The proportion of S. purpurea plants per distance class occupied by

srnithii larvae (0 ) from field data collected in the release-recapture experiment. Data are

fiom A) the perpenciicular distance distribution, B) the maximum distance distribution.

Fitted values fiom the diffusion model (+; Equation 3) and the exponential model (C l ;

Equation 6) are also indicated.

Variance Components Analysis

The glms describing data collected in the two large-scale sampling sessions (June

and August 1999) suggested significant leaf-level effects of potential fluid volume, actual

fluid volume, detritus, and the interaction of potential and actud fluid volume on W.

smithii larval abundance (Table 3-3). Variance components analysis of the glm residuals

incorporating the four spatial factors hierarchically @og, point, plant, leaf) indicated an

unequal distribution of variance between these random spatial factors (Table 1-3).

Table 1-3. The percent variance in larval W. smithii relative abundance resoIved by

variance components analysis at four spatial scales: bog, point, plant, and leaf fiom a

large-scale census of their distribution. The distribution of variance was calculated for W.

smithii in two sessions (Sample 1 : 5 June to 27 June 1999; Sample 2: 17 August to 25

August 1999).

Census Bog Point Plant Leaf Sample 1 2.9% 20.5% 12.8% 63.7% Sample 2 3 -7% 12.9% 8.1 % 75.3%

Discussion

The goal of this study was to determine the movement potentiai of W- smithii

using both experirnental (release-recapture) and inferential (VCA) methods, and to

determine whether W. srnithii movement could be described by simple diffusion

equations. The imrnediate application of the movement data collected here was to

approxhate the appropriate spatial scale to study individual, population and/or

metapopdation dynamics of W. srnithii in the boreal forest region of western

Newfoundland. Parameters of move distance estimated for W. smithii by the diffusion

mode1 and basic statisticai descriptors of the field data suggest that females fiequently

move within and between patches of S. purpurea in a bog (up to 106 m), but that longer

movements through boreal forest between bogs would be infi-equent. The variance

components analysis M e r supports this scale of movement.

Diffusion equations can be extremely valuable tools in simulation experiments to

explore population and community patterns. However, they must be biologically robust if

they are to provide meaaingful output or predictive power. The data fiom the

perpendicular and maximum move distances were used to identiQ a range of movement

potential for W. srnithii. They provide an estirnate of relevant movement scale for W.

smithii of between two to 100 metres in a generation. The observed distribution of the

data fiom the perpendicular and maximum distance distributions resulted in a wide

spread of mean and median move distances, yet both distributions predicted similar mean

movement distance fiom the diffusion equations. Likely, this is due to the similar relative

distribution of observations. The fitted values fiom the equations approximated observed

within-bog movement rates fiom release-recapture data, suggesting a biological relevance

of the parameter, D (diffusion rate). This is further supported by the overlap in the range

of values for D, as indicated by the standard errors of the estirnates estimated fiom both

the perpendicular and maximum distance distributions. Though the overall fit of the

models is adequate, the parameters 6 (disappearance rate) calculated by the equation

differed fkom the observed field rate estimated fiom the release experiment by two orders

of magnitude, suggesting that M e r work be done in this area if the rate is to be used

predictively .

The fitted-values produced by the difision model using the perpendicular data

were very sirnilar to the values of the generic exponential model. Both equations appear

to represent the pattern of the field data equally well. However, while the exponential

model is more straightfonvard to produce, the biologically meaningful parameters

(diffusion and disappearance rate) derived fkom the difision model make it a

functionally superior equation.

The most variation in larval abundance existed between Ieaves, even after leaf-

level covariates representing differential habitat selection by individual females based on

leaf quality and cornrnunity structure were removed. This suggests that individual

females oviposit at a leaf, then move to a neighbouring plant, rather than ovipositing

consecutively in leaves within the sarne plant. Further, it suggests that leaf resources are

not used to capacity, and that larval numbers are somehow constrained either by an

unrneasured factor or at another scale. Less variation in larval numbers between plants at

a point than at leaves or at points within a bog m e r implies that females fkequently

move between these plants to oviposit, while the increased variation between points in a

bog suggests that the points are more independent (i.e., movement by female W. smithii

between points is not as Eequent). Though variation between bogs appears !ow in the

VCA, suggesting fiequent between bog movemrnt, bog aggregations likely operate

independently. Stronger point and le&-level aggregation outweighs variation between

bogs. Further evidence for independent dynamics between bogs is provided by genetic

analysis of W- smithii in the northem U-S,, which suggests fiee recombination at the level

of a whole bog (Istock and Weisburg 1987) and not beyond.

In concert, the data indicate that population structure of W. smithii exists at the

spatial scale of the bog, and that multiple, 'patchy' populations likely exist within bogs.

Attempts to describe real biological systems based on theoretical principles of

metapopulation dynamics have revealed that population spatial structure exists dong a

continuum (Harrison 1994; Hansson e t al. 1995; Hanski and Gilpïn 1997; Thomas =d

Kunin 1999). Degrees of rnetapopulation structures include: mainland-island systems -

considered as source-sink populations of conspecifics, separate systems - where

conspecific populations are completely isolated fYom one another, patchy systems - a

continuous population extending over multiple habitat patches, and classic systems -

involving independent populations capable of interaction (Harrison 1994). With such a

broad range of scenarios, populations of al1 species likely exist within this fiamework at

an appropriate temporal or spatial scale. Based on the preceding inference of population

structure, 'classic' metapopulation dynamics may best descnbe W: srnirhii dynamics and

distribution between bogs in this region over a broader temporal scale, while more patchy

rnetapopulation structure likely exists between points within bogs over a shorter temporal

scale.

Movement c m be broadly classified into two behaviourally distinct types;

migratory and maintenance. Maintenance represents movements for feeding,

reproduction, or cover. A generd pattern for mosquitoes is considered to be a migration

flight (if expressed) shortly after emergence and before females are repmduc tively active

( S e ~ c e 1976). If W. smithii usually expresses a longer, migration behaviour, our

recaptwe experiment has underestimated the movement potential of the species, but has

adequately estimated the range of its maintenance moves. The potential for longer, un-

detected migration movements exists. However, the maximum move distance recorded

for W. smithii was half the extent of the re-sampling grid, suggesting that the physical

ability of the organism limited its dispersal distance. In addition, incidental obsel-vations

of adult smithii in flight uidicate it is a weak and erratic flier (Bradshaw 1983; pers.

obs.). Likely, W. smithii does not move long distances, except in unusual (perhaps wind

aided) conditions, and might move further when the density of conspecifics reaches

threshold levels. These infkequent, long-distance movements might be s a c i e n t to

maintain metapopulation dynamics among local populations restricted to individual bogs.

Further studies exploring density dependence and long-distance movement could be

performed using various marking techniques (for example Giemsa stain, Kleckner and

Bradshaw 199 1) and M e r genetic work (sensu Istock and Weisburg 1987).

The movement data were m e r explored in the context of natural history and

systematics. The pattern of distribution of JK srnithii larvae fiom the release line infers

the species does not congregate in a mating s~varm, common to many species of

mosquitoes, and that females mate in the vicinity of the plant fiom which they emerge.

Corroborating morphological evidence shows that male W. smirhii have no physical

modifications for swarrning, and that their antemae dif5er only slightly fiom the fernale's

while more sensilla on male antennae is characteristic in other species (McIver and

Hudson 1972).

The dispersal behaviour of mosquitoes has been studied extensively because of

their propensity as vectors of disease. Malaria-control operations have studied anopheline

mosquitoes (Diptera, Culicidae, Tnbe Anophelini) extensively and report movement

potential of between one and ten kilometers. Wyeomyia smithii is classified within the

Tribe Culicinï (Diptera, Culicidae, Culicini, Group Sabethes), with species of Aedes

(Group Aedes) and CzrZex (Group Culex). A mark-recapture study of A. cornmunis

reported a maximum move of 1600 m (Joslyn and Fish l986), whiie a study of A. rzrsticus

in Gemany concluded that snow-melt mosquitoes tend to remain within 50 m of their

breeding sites (Schafer et al, 1997). Culex annulirostris moved up to 9000 m in an

Australian study (09Donnell et al. 1992). The recapture rate in this experiment was

relatively high (3.7%) for insect studies, suggesting that observed distances were

representative of typical move distances. Thus, the variation in the movement potential of

similarly-sized mosquitoes seems quite broad within the tribe and genera, and is likely

related to habitat requirements. Strong habitat selection by W. smithii for S. purpzrrea

may have resulted in selection for decreased flight abilities, enforced by the lethality of

intervening territory (forest) among subpopulations (bogs) (Tstock and Weisburg 1987),

and slow change or infrequent disturbance (e-g., succession or fire) within bogs.

In summary, understanding movement of organisms is an important step towards

understanding the dynamics of populations and ecosystems. Here, the movernent

potential of W. srnithii was used to indicate relevant spatial scales for M e r study of

individual and population dynamics. In addition, the study determined that simple

diffusion models can adequately describe the movement of W. smithii, thus facilitating

future avenues for modeling the dynamics of this species mathematically.

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Wyeomyia mosquitoes. J. Med. Ent. 9:337-345.

Mogi, M. and Molay, J. 1980. Distribution of Wyeornyia srnithii (Diptera, Culicidae) eggs in pitcher plants in Newfoundlmd, Canada. Trop. Med. 22: 1 - 12.

OYDonnell, M.S., Berry, G., Carvan, T- and Bryan, J.H. 1992. Dispersal of adult females of Cdex annulirastris in GrifTith, New South Wales, Austrdia. J. Am. Mosq. Control Assoc. 8: 159- 165.

Okubo, A. 1980. Some examples of animal diffusion. In: Diffusion and Ecologicd Problems: Mathematical Models. Springer-Verlag, New York.

Price, R.D. 1958. Notes on the biology and laboratory colonization of Wyeornyia srnithii (Coquillett) @iptera:Culicidae). Can. Ent. 90:473-478.

Searle, S R , Casella, G. and McCuIloch, C.E. 1992. Variance Components. John Wiley and Sons, Inc, New York.

Service, M.W. 1976. Mosquito ecology. Field sampling methods. Applied Science Publishers, London.

Schafer, M., Storch, V., Kaiser, A., Beck, M. and Becker, N. 1997. Dispersal behavior of adult snow melt rnosquitoes in the Upper Rhine Valley, Germany. J. Vector Ecology 22: 1-5.

Thomas, C.D. and Kunin, W.E. 1999. The spatial structure Ecol. 68:647-657.

Turchin, P. 1998. Quantitative Analysis of Movement. population redistribution in animals and plants. Sunderland MA.

of populations. J. of Anirn.

Measuring and modelhg Simauer Associates, Inc.

Turchin, P. and Thoeny, W.T. 1993. Quantifj4ng dispersal of southern pine beetles with mark-recapture experiments and a diffusion model. Ecol. Applic. 3 : 18% 198.

Venables, W.N. and Ripley, B.D. 1996. Modem applied statistics with S-PLUS. Springer-Verlag New York, Inc. New York.

WilIiams, E.J. 196 1. The distribution of larvae of randomly moving insects. Aust. J. Biol. Sci, 12598-604.

Chapter 2. Movement potential of Flefclrermjia_fZefclreri (Diptera: Sarcophagidae): implications for the study of populations.

Introduction

Plant-insect communities are inieresting ecological systems due to the tight

interaction between pairs of species (Feeny 1976; Futuyma 1983). In the pitcher plant

(Sarraceniapurpurea) inquiline community, three species of fly, Wyeomyia smithii,

Metriocnemus knubi and Fletcherimyiafletcheri, are obligately related to the plant for

larval developrnent, adding three-fold complexity- Heard (1994) has coined the term

"resource chah commensalism" for this local-level l a r d community structure within the

leaves of S. purpurea, meaning that the behaviour of one species facilitates resource

acquisition of the other, with no benefit or h m to itself. At a larger spatial scale,

interaction of a comuni ty of adults of the rnosquito, W. smithii, the midge, M. knabi,

and the sarcophagid, F. fletcheri exists. Though the three species use the same resource

for larval development, distribution of adults, and thus population structure, is potentially

quite different due to unique life history strategies and habitat requirernents of each.

A valuable tool in quantitative analysis of communities is to lump together

species as an approach to simplieing phenomena and generalizing patterns of species

response (Levin 1992). However, it is as important to know what detail to ignore as it is

to know what detail to include Cudwig and Walters 1985). In other words, outstanding

characteristics of organisms can suggest unique processes and should be noted and

explored. Morphologically, F. flefcheri is lârge in cornparison to W. smil'hii and LM knabi.

Behavioural differences include the movement of F. fletcheri larvae fiom the S. purpurea

leaf to the surrounding Sphagnum spp. moss for ovenuintering as pupae (Forsyth and

Robertson 1975), and the use of S. purpurea flower heads by adults for roosting and

mating (Krawchuk and Taylor 1999; Appendix One). These char~cteristncs suggest that

individual assessrnent of component species of the tightly linked pitcher plant community

may yield significant dzerences in distribution and strategy of organisrrns in the system.

A mark-recapture study was designed to estirnate the movernent wotential of F.

fletcheri. These data were used to compare movement estimates with thobse derived in a

previous experiment for W. smithii, and to hypothesize how population s:tructure might

differ between the two species as a resuit of differences in this process.

Methods

Field procedure

The bog used for the F. fletcheri mark-recapture experiment was chosen for the

abundance of flowering purpurea plants it supported and its accessibiility. A recapture

grid was marked across the six ha bog using geo-referenced (Trimble Surveyor TDCI,

Trimble Inc. California) identification flags (n=l14) placed at each sam:_ple plant, chosen

as the closest flowering S. purpurea plant (hereafter plant or flower) to a standardized 25

m interval grid. At the centre of the bog, a 20 m2 zone contained 22 floweing plants

which were checked at three-day intervais, and used as the capture-mark area.

Aduits were marked and recaptured while roosting in flowerheadls (see Krawchuk

and Taylor 1999; Appendix One). The subjects were found by placing cl handheld aerial

insect net over the plant, pinching it closed around the base of the flawer's stalk and

manipulating the flower through the net such that the contents could be viewed. If a

sarcophagid was observed, the flower was shaken gently until the fly fell into the aerial

net nie nies were reshained by holding the thorax between the thumb and index finger

and a two-wing code unique for each census day was applied to the wings using a Sharpie

waterproof marker. Marked individuals were placed back on or in the flower fkom which

they were taken,

A c e m s of the entire grid took place between 0500 and 0700 hrs on eight

occasions between 8 JuIy and 28 July 1999. The flowers were checked for roosting adult

F. fletcheri using the net method described, above. If F. fletcheri were present, the view

was manipulated to determine if the wings were marked. The location of re-sighted,

marked individuals was recorded, and a straight line distance between this location and

the center of the capture-mark area was calculated using Pathfhder Pro GPS software

(Trimble, Inc. California).

Calcuiation of movement potential

The same diflbion equation could not be fit to these data as were fltted with the

K smithii data (Chapter One) since incidental observations made up more than haLf of

the re-sightings (Le., the entire trapping grid was not sampled on every occasion which

marked F. fletchen were observed). Instead, diffusion rate was estimated using a

procedure for individual mark-recapture data outlined in Turchin (1998), where D is a

mo vement measure of m2/t ime interval:

where x = the iength of move, and t = the duration for the move. D was calculated using

the distance moved per day for each capture (i.e., distance/days since marking) as x, and

assigned e l for al1 mcves (e-g., one day). .

Sirnilar to the general statistical descnptors of W. smithii movement in Chapter

One, the mean, variance, maximum, and minimum move distances were cdculated. Since

t h e was explicitly measured throughout the experiment, the mean time (in days)

between captures, daily mean move distance, and the relationship between move distance

and time were also calculated.

Results

The diffusion rate was estimated to be 114 rn2/day. The square root of this

measure produces a one-dimensional daily rate of movernent of 11 dday . There was no

relationship between move distance and the time elapsed since initial capture (r2 = 0.02,

n=9, p=0.7). Simple details of the experiment were tabuiated to iIlustrate general trends

of the data (Table 2-1). A cornparison between movement measures f?om F. fletcheri and

W. srnithii indicates an order of magnitude difference in their movernent potentiai (Table

2-1).

Table 2-1. A summary and cornparison o f information fiom field collection and

diffusion modelling used to estimate F. fletcheri and W. smithii (Chapter One) movement

potential.

Variable F. jletcheri W. smithii Source Number rnarkedkeleased 35 840 from release experiment Number recaptured 9 37 fiom release experiment Maximum net move distance (m) 184 Mean move distance (m) 34 Mean move distance per day 12

83 from release experiment 1 O fiom release experirnent n.a. kom release experiment

Mavimum time betwèen captures (days) 5 n.a. fiom re1ease experiment - -

Mean time between capm& (days) 3 n.a. frorn release exbenment Diffusion rate !14m2(-lldday) O.17m/ from dif is ion equation

generation

Discussion

The calculated diffusion rate per day (Table 2-1) from the modei of a tempordly

explicit, uncorrelated random walk corroborated with movement values calculated fiom

standard statistical procedures of the field data. This suggests the simpie equation could

adequately describe the magnitude of F. fletcheri movement potential within the scale of

a bog. nie calculated movement potential of 11 4 mL per day (diffusion rate) implies that

a dynamically synchronized population of F. fletcheri exists within the confines of a bog

- men a very large one. Further, movement between discrete bogs would be more

fiequent than with W. srnithii, whose mean observed move distance was 10 m over the

entire recapture period (difision rates, D, are not directly comparable between W. srnithii

and F. fletcheri due to diffèrent modeling procedures; Chapter One). In addition, the

results fiom the F. fleicheri mark-recapture experirnent show no relationship between

move distance and time, M e r implying that F. cfletcheri is a strong nier capable of

baversing the entire bog with ease. An observed movement distance can be a result of

landscape structure rather than an animal's maximum movement ability in mark-

recapture studies (Porter and Dooley 1993; Kindvall 1999). The maximum move distance

in the experùnent was recorded at the edge of the bog (and our re-sampling grid),

suggesting that this distance was imposed by bog structure, not by the ability of F.

fletcheri to continue moving. Alternatively, individuais might also remain in the vicinity

of a S. purpurea flower for extended time periods for mating and roosting if nectar

sources are located nearby to maintain energy stores.

The relative difference in body size between W. smithii (3 mm) and F. fletcheri

(7.5 mm) is substantial enough to suggest that the latter could make longer, more directed

moves. Though these two species share the same habitat, the Sphagnum spp. bog, and are

obligate to the same ovi/larviposition site, S. purpurea, their observed move distances

differ rnarkedly. This suggests that the parallel difference in movement potential and

body size is fbrther expressed as a difference in population spatial structure. An

interactive relationslip between animal body size (or body-mass) and landscape structure

has previously been suggested to structure ecosystems across temporal and spatial scales.

This relationship implies that changes in landscape structure may affect animals in

different ways, according to animal size and the spatial grain of the habitat (Holling

1992). Furthemore, Roland and Taylor (1997) have demonstrated that four parasitoid

insects responded to anthropogenic forest fragmentation at four different spatial scales

which corresponded to their relative body sizes. A neutral density-configuration response

of F. cfletcheri at the bog scale (Chapter Three) supports this conjecture that inter-bog

movement does not restrain population persistence, whereas a negative response was

detected for the smaller, W. srnithii, suggesting an effect of increased bog isolation on

population persistence.

References

Feeny, P. 1976. Plant apparency and chernical defense. In: Wallace, J. and ManseIl, R. (eds) Biochernical interaction between plants and insects. Am. Rev. Phytochem. 1O:l-40.

Forsyth, A.B. and Robertson, R.J. 1975. K reproductive strategy and larval behavior of the pitcher plant sarcophagid fly, BIaesoxiphafletcheri. Can. J. 2001. 53 : 174- 179.

Futuyma, D. J. 1983. Evolutionary interactions among herbivorous insects and plants. In: Dutuyma, D. J. and Slatkin, M. (eds) Coevolution. Sinauer, SunderIand, Massachusetts, U S .A.

Heard, S.B. 1994. Pitcher-plant rnidges and mosquitoes: a processing chah cornmensalism. Ecology 75: 1647- 1660.

Kolling, C. S. 1 992. Cross-scale morphology, geometry, and dynamics of ecosystems. Ecol. Monogr. 62:447-502.

Kindvall, O. 1999. Dispersal in a metapopulation of the bush cricket, Metrioptera bicolor (Orthoptera: Tettigoniidae). J. Anim. EcoI. 68: 172- 185.

Krawchuk, M.A. and Taylor, P.D. 1999. Roosting behaviour by FZetcherimyinfIetcheri (Diptera: Sarcophagidae) in Sarracenia purpztrea (Sarraceniacea). Can. Ent. 13 1 :829-830.

Levin, S.A. 1992. The problem of pattern and scaie in ecology. Ecology. 73 : 1943 - 1967. Ludwig, D. and Walters, C. J. 1985. Are age-structured models appropriate for catch-

effort data? Cm. J. Fish. Aquat. Sci. 42:1066-1072. Porter, J.H. and Dooley, J.L. 1993. Animal dispersai patterns: a reassessment of simple

mathematical models. Ecology 78:243 6-2443. Roland, J. and Taylor, P.D. 1997. Insect parasitoid species respond to foresr structure at

different spatial scales. Nature 3 86:ï 1 0-7 1 3. Turchin, P. 1998. Quantitative Analysis of Movement. Measuring and modeling

population redistribution in anirnals and plants. Sinnauer Associates, Inc. Sunderland MA.

Chapter 3. The relative importance of habitat structure changes within a nested hierarchy of spatial scales for three species of insects.

Introduction

Ecologicd pattern and process are manifest within a hierarchy of spatial scales

across the landscape (Kotliar and Wiens 1990; Levin 1992). Simply put, process (such as

movement or recruitment) drives patterns of distribution, and structure (such as amount

of suitable habitat) constrains them (Levin 1992). The relationships found between

structural properties of habitat and population or community responses at various scales

suppoa the concept that the physical environment influences ecosystem dynarnics (e.g.,

Bender et al. 1998; Trzcinski et al. 1999). Recent interest in broad, ecosystem and

landscape-Ievel spatial heterogeneity and its underlying mechanisms is illustrated by

studies of "lumpiness" in ecological systems (e-g., Holling 1992), density-area

relationships (Andrén 1994; Bowers and Matter 1997; Bender et al. 1998; Comor et al.

2000; Matter 2000), metapopulation dynamics (Harrison 1994; Hanski 1999), effects of

Iandscape fragmentation (McGarigal and McComb 1995; Robinson et al. 1995; With and

Crist 1995; Fahrig 1997; Villard et al. 1999; Trzcinski et al. 1999; Drolet et al. 1999) and

ecosystem rnodeling (e.g., Walters et al. 2000). Yet, a cross-scale translation of local-

level patterns attributed to habitat requirements, home range size, and community

interaction to organization at these broader spatial scales has proven to be challenging

(Addicott et al. 1987; Wiens 1989; Holling 1992, Wiens et al. 1997, Comor et al. 2000).

Explicitly hierarchical studies have begun to adàress this challenge (Senft et al.

1987; Rukke and Midtgaard 1998; Bowers and Dooley 1999; Turner et al. 1999; Kehler

and Bondrup-Nielsen 1999; Fauchald et al. 3000; Nielsen and Ims 2000) by relating a

variety of responses (e-g., predation or incidence) to measures of structure (e-g., prey or

habitat). Results fiom these works suggest that correlations among variables at small

scales rnay change in magnitude, disappear or even change sign when the scale is

extended (e-g., Wiens 1989; Fuhlendorf and Smeins 1999).

Ecologists fiequently refer to habitat structure parsimoniously using two

variables: the amount of habitat (quality of area) and its configuration (spatial pattern,

geometry, isolation) (Taylor et al. 1993; but see Hanski and Ovaskainen 2000). In the

context of habitat loss and fragmentation, the importance of these two components for

population persistence has been explored both theoretically (Fahrig 1997, 1998) and

empirical ly (Andrén 1994; McGarigal and McComb 1995; Bender et al- 19%; Trzcinski

et ai. 1999; Villard et al. 1999). The amount of habitat has repeatedly been claimed to be

the primary concem for conservation (McGarigal and McComb 1995; Bender et al. 1998;

Fahrig 1998; Drolet et al. 1999; Trzcinski et al. 1999). However, the importance of

configuration (e.g., fiagmentation, nearest neighbour distance) may be far fiom negligible

(Villard et al. 1999) for some species (McGarigal and McComb 1995; Fahrig 1998;

Rukke and Midtgaard 1998; Villard et al. 1999) at some spatial and temporal scales (e-g.,

metapopulation dynamics (Hanksi 1999)). In particular, it has been s h o w that there are

thresholds where the relative impact of configuration increases drarnatically as the

amount of habitat decreases (Andrén 1994; Fahrig 1997; Trzcinski et al 1999; Villard et

al. 1999). Since habitat destruction and fiagrnentation is of global concem (Margules and

Pressey 2000), there is an urgent need to clan@ the importance of these two broad

measures of habitat structure in conservation strategies.

Previous studies e x p l o ~ g these two structural concepts (amount and

configuration of habitat) are limited because they examine either single spatial scales

(McGarigal and McComb 1995; Fahrig 1997, 1998; Drolet et al. 1999; Trzcinski et al.

1999; Villard et al. 1999)' hierarchical scales with low replication (Nielsen and Ims 2000)

or without the discrete treztment of amount and configuration at each scale (Andren

1994; Fabrig 1997; Rukke and Midtgaard 1998; Bowers and Dooley 1999), and (or) have

only a single species' response (Rukke and Midtgaard 1998; Bowers and Dooley 1999).

These limitations provide a template for designing a more comprehensive assessment of

organism response to habitat structure.

Since movement between resources is critical to habitat use and population

survival (Taylor et al. 1993) i t is important to consider another element of structure:

connectivity. Landscape connectivity is the degree to which the landscape facilitates or

impedes movement among resvurce patches (Taylor et al. 1993). Since the environment

between suitable patches of habitat is often heterogeneous, this cari influence an

organism's ability to reach and therefore use this habitat, in addition to the amount or

configuration of habitat. The degree of between-patch ("matrix") heterogeneity will

dictate the influence of this structural measure on distribution. Cntical thresholds in

connectivity have been s h o w to differ for species with varying habitat specialization and

dispersal range (With and Crist 1995). Thus, this additional structural measure will Vary

in its importance and influence on organism distribution across spatial or temporal scales.

With these concepts in mùid, three main ideas are explored here. This chapter

addresses the relative importance of amount and configuration of habitat in a hierarchical

analysis of the distribution of W- smithii, M. knubi and F. fletcheri, al1 of which have the

same discrete habitat requirement, namely S. purpurea. Second, it compares responses to

habitat structure between the three species of insects. Third, this chapter explores the

influence of habitat texture (as a variable influencing comectivity) on distribution at a

single spatial scale.

Methods

Field methods

Census of W. smithii, M. knabi and F. fletcheri larvae in S. purpurea Ieaves was

conducted in the Main River Watershed (UTM: 55 14000N 478000E Zone 2173 lOkm

outside the border of Gros Morne National Park in western Newfoundland, Canada (Fig.

1-1). As described in the general introduction, this area of boreal forest is composed of

discrete patches of bog withui mature coniferous forest and softwood scmb (Fig. 1-2).

Data were collected during two sampling sessions, the f ~ s t between 6-27 June and the

second between 17-25 August, 1999. These two periods were chosen to census over-

wintered larvae before pupation and emergence as adults (first sample in June), and

distribution of the current year's larval cohort (second sample in late August). W. snzithii

normally have clutch sizes of between one (Mogi and Mokry 1980; Heard 1994a) and

three eggs (Bradshzw 1983): F. fletcheri deposit a single iarva into each pitcher (Forsyth

and Robertson 1975), and M. knabi fernales consistently lay eggs in large numbers

(Heard 1994a). Because of this consistent ovi/larviposition behaviour, Iarval abundance

was used as an index of adult distribution and density for al1 three species. Since F.

fletcheri over-winter in Sphupum spp. moss, they were only counted in the second

(August) sample.

Field sampling was designed to coilect response data - larval counts within a leaf

for each of three insect species (Table 3-1) - as well as a nested suite of environmental

variables from a local to landscape scale (Table 3-2). Hierarchically nested levels of

sampling included leaf, plant, point, bog, landscape.

Table 3-1. A surnmary of l a r d sarnpling effort by spatial scale and sampling period.

Spatial scaIe Sample 1 Total samples Sample 2 Total samples 6-27 June 17-25 August

Landscapes 2 2 2 2 Bogs in a landscape 20 40 20 40 Patches in a bog 2-8 202 2-8 202 Plants in a patch 3 606 3 606 Leaves in a plant 3 1817 3 1817

Landscapes one and two were chosen since each 8 km2 area provided variability

in arnount and configuration of bogs. Landscape one contained 7 % bog and landscape

two contained 20 % bog (thus decreased distance between bogs and/or larger bog areas).

These values were calculated using SPANS GIS software (Intera Tydac Technologies,

Nepean, Ontario, Canada) analysis of Forest Resource Inventory Maps of the area. A

balanced sample of bogs varying in size and nearest neighbour distance were chosen with

M e r information fkom 150 000 topographical maps of the area and GIS maps provided

by Corner Brook Pulp and Paper Ltd. (Fig. 1-2).

At each of these chosen sampling bogs, structural attributes representing arnount

and configuration of habitat were measured at four scales (leaf, plant, point, bog) (Table

3-2, variables are followed by their short forms in srnall caps; Figure 3-1). The amount of

habitat (Le., patch size) was estimated at each scaie so that larval samples were associated

with: a leaf volume (PONOL), plant size (LEAVES), point density (PTDENS), and bog area

(BGAREA) and abundance (BGABUN; estimated number of plants within a bog).

Configuration of habitat was estimated at three scales so that individuai sampies were

associated with: a distance to nearest plant neighbour (NNEIGH), index of distance to

point neighbour (PTCONF), distance to next nearest bog neighbour (BGNIU'EI). In addition,

habitat texture was measured at the point scale as an influence on habitat connectivity

(CONNEC) -

The amount, configuration and connectivity of habitat, and additional

environmental covariates were measured as follows (Table 3-2). Bog area (BGAREA) and

distance to nearest neighbouring bog (BGNNEI) were measured using SPANS GIS

software on geo-referenced 150 000 aerial photos fiom August 1985. The structure of

the area has changed little since then. Abundance (BGABUN) of purpurea plants in a bog

were estimated by multiplying bog area by the mean density of the bog'; two density

transects (details befow). Bogs were considered to be discrete if they had more than 15 m

of high scrub or trees between them.

Sample points were chosen pseudo-randornly in each bog. A point is a two meter

radius sarnpling circle. Smail bogs contained between two and four points, the largest bog

contained eight points. Each point was placed no M e r t h m 20 m fYom the bog edge to

minimize edge effects since plants and their inhabitants appear to be influenced by their

distance fiom the bog edge? attributed to exposure to winds and decreased snow cover

(Heard 19946; Miner 1999), or the thickness of the Sphagnurn spp. The locations of

Table 3-2. Summary of structural variables used in the multi-scale sarnpling of ÇV.

smithii, M. knabi and F. fletcheri in leaves of S. purpurea of the Main River study area of

Newfoundland. Structural variables used to estimate amount of habitat are indicated by

'A', configuration by 'C', and texture by 'T'. Response variables are indicated by 'R'.

Additional variables descnbed in this table were included as habitat descriptors in glms

or ornitted due to collinearity.

Spatial Description of variable Variable Range Mean Range Mean scale name Sample Sarnple sample sample

One One Ttvo Two

plant

point

bog

leaf potential volume (mL) A POTVOL 1.049.0 12.0 0.5-48.0 10.0 actual volume (mL) ACTVOL 0-27 2 0-40 6 detritus (categorical) DETRiT 0-3 2 0-3 2 midpes (larval count) R MIDGES 0-90 9 0-65 6 mosquitoes (larval count) R MOSQUI 0-24 1 .O 0-3 7 1.5 sarcophagids (larval count) R SARCOP NA NA O or Z 0.05 length of leaficm) LENGTH 0.5-17.2 8.7 1.1-79.0 8.4 leaf width at hood (cm) WlDTH 0.5-5.0 2.2 0.4-6.7 2.1 nurnber of leaves A LEAVES 3-47 7 2-3 2 7 distance to nearest neighbour (m) C NNEIGH 0.02-3.5 0.5 0.03-2.7 0.4 count within 2m radius of centre A PTDENS 2-62 14 2-62 14 density (categoncal) PTDENC High, NA High, NA

Low Low bog density C PTCONF 0.14- 0.69 O. 14- 0.69 (mean of 2 transects; lm') 0.54 0.54 texture (categot-kal) T CONNEC High, NA High, NA

Low Low distance to edge (m) DIST2E 0-16 3 0-16 3 area (km') A BGAREA 0.0020- 0.039 0.0020- 0.039

O. 17 O. 17 abundance (density * area) A BGABUN 1700- 19360 1700- 19360

77540 77540 nearest neighbour (km) C BGNNEI 0.020- 0.19 0.020- 0.19

0.68 0.68 landscape LANDSC 1 o r 2 NA 1 or2 NA

Figure 3-1. A visual summary of study design and variables representing amount and

configuration of habitat. A) bog configuration (distance to nearest neighbour); 8) bog

area; C) two transects counting plant density within a bog (an index of point

configuration); D) density of plants at a point (amount of habitat); E) plant configuration

(distance to nearest neighbouring plant) for each of three plant samples at each point.; F)

amount of habitat at the plant scale (nurnber of leaves), the three youngest leaves were

sarnpled on each plant.

points were picked if their area had a miaimum of three healthy plants (at minimum three

healthy leaves capable of containing fluid). Each point was flagged and geo-referenced

using a Trimble Surveyor TDCl (Trimble Inc., California). These points were chosen to

complete a bdanced sampling of S. purpurea density (PTDMC) and texture (height of

surrounding vegetation; CONNEC) categorically as follows: high vegetation- high density;

high vegetation-low density, low vegetation-high density, low vegetation-low density.

Point density was considered high if more than six S. purpurea plants were found within

a two metre radius circle of the centre (point area), and low if less than six. Explicitly,

texture is the height of surrounding vegetation within the point area. For example, a point

among tall grasses or shnibs was considered high, while a point among only Sphagnzm

spp. was considered low. The texture of the point may influence the connectivity of

habitat. The structure of each sample point was M e r described by a continuous variable

of plant density within the point area (PTDENS). An index of the configuration (PTCONF) of

point clusters of S. purpurea in bogs was estimated fiom counts of plants within two, 1

m-wide transects which crossed each bog between randomly chosen points wherein

higher densities of plants = closer clusters.

The nearest three plants to the centre of each point were chosen for sampling. The

number of leaves per plant (LEAVES) and the distance and bearing to the nearest

neighbouring plant (NNEIGH) was recorded. The three healthiest leaves were carefblly

removed fiom each plant. A healthy leafwas considered if it had no rips and was

succulent, with a large enough opening for successful navigation by the three study

species. Liquid contents of each leaf were poured into a 20 rd, screw top vial. The vial

and the leaf were then wrapped in a plastic sample bag marked with the bog, point, plant

and leaf number. AIl samples were processed within 24 hrs of collection.

Processing involved the measurement of leaf contents fiom the vile including:

abundance of mosquito (MOSQUI), midge (MIDGE) and sarcophagid (SARCOP) larvae,

arnount of detritus (DETEUT), and the actual volume of fluid (mL) i? the leaf (ACTVOL).

Potential volume (mL) of the leaf (POTVOL) was calculated by measuring the amount of

water it contained when it was filled to capacity. Thorough census of leaf contents was

ensured by slicing the leaf open, and flushing the remaining contents into a sampling tray

for identification (sensu Nastase et al. 1995; Miner 1999). Other morphological

meâsurements of each leaf included: leaf length (LENGTH), hood width (WIDTH) and

condition.

Sarnples Etom the second census were collected fiom the sarne locations as the

first census whenever possible. When necessary, the nearest sultable location for a new

point was sarnpled.

Statistical methods

The statistical analysis of the relationship between habitat structure and insect

distribution consisted of two steps. The first step was the removal of variation in response

data fiom more local effects using generalized linear models (ghs). The second step was

to determine the relationship between these residuals (remaining variation) and measures

of structure at higher scales using mixed linear models (lmes). Generalized linear models

were built in S-PLUS 2000 (MathSoft, Inc. Seattle, Washington) to isolate, and remove

the effects of field-measured variation (Table 3-2) on larval counts of the three species of

insects. For example, at the bog scale, a glm was first built wherein counts of larval W-

srnithii were response variables, and all variables measured at the leaf, plant and point

scale (Table 3-2) were inchded as predictors. ResiduaIs fiom this mode1 were then used

as response measures to bog structure, whereas at the point scale, the gim only included

variables fiom the leaf and plant level, and residuals were then used against measures of

point structure.

A Quasi-likelihood family (link = log, variance = mu) was used in al1 cases since

the count data of W. smithii and M knabi larvae were over-dispersed in a log-linear

(Poisson) regression model and F. fletcheri data were under-dispersed using a logistic

(Binomial) regression model (response data were one or zero). Quasi-likelihood

estimation is commoniy used to estimate regression relationships k r data kvith

incomplete knowledge of the error disîribution of the response variable (McCullagh and

Nelder 1 99 1 ; MathSoft Inc. 1999), allowing the user to define both the lulk and variance

function to estimate regression coefficients.

The residuals of these Quasi-Iikelihood g h s for W. srnithii and M knabi were

normally distributed, allowing the use of linear rnixed models (Ime; Pinheiro and Bates

2000) to explore their relationship with habitat structure. The variation in adult density

may be attributed (statistically) to a mixture (hence "mixed" model) of both random

(associated with experimental units drawn at random fkom a population (MathSofi Inc.

1999)), and fixed (associated with an entire population, or with repeatable levels of

experimental factors (MathSoft Inc. 1999)) effects. Here. fixed effects were the amount,

configuration and comectivity of habitat, and random effects were associated with the

hierarchically nested smcture of sampling (a plant within a point within a bog within a

landscape),

A slightfy different process of analysis was used for FJZetcheri since bimodal

distribution of residuak Çom glm models made the ime an inappropriate next step. A

pseudo rnixed-effects model was created using a glm and fkst including a factor effect for

each sarnple at each level of scde (ive., a unique factor for each plant, or bog) to mimic

random effects (Pinheiro and Bates 2000) of a mixed model. The point factor effects

were significant, indicating differences between individuai points unassociated with

structural variables. The landscape, bog and plant factors were insignificant effects and so

were not included here for simplicity. Thus, this method addresses the pertinent issue of

generalized models of multiple mixed effects data with nested structure. A similar

statistical method resulting in the same analytical structure for di three species would be

the use of a generalized linear mixed model (such as the macro GLMMK in SAS).

Results

The glms indicated significant relationships between the abundance of larvae and

the chosen suite of environmental variables (Tables 3-3, 3-4,3-5). This variation was

removed fkom each lower spatial scale before rnodelling the influence of amount,

configuration or texture of habitat on insect distribution. Leaf-level variables LENGTH,

W ~ T H and point-bel variabies DISTE and PTDENC were not used in analysis since they

were collinear with other structural variables.

For W. smith ii and knabi, mked h e m modds ( h e ) were used on glm

residuals of larval counts to infer the relationship between adult density and habitat

structure. S irnilarly , levels of structure were added sequentially to the glrn for F. fletcheri.

The results show that response changes with spatial scaie and diffen between species

(Tables 3-4,3-5,3-6; Fi,pre 3-2). The inclusion of interaction terms in rnodels did not

significantly improve their fit, thus no evidence for significant interactions between

amount and configuration of habitat was detected. The texture of habitat at the point scale

was significant for ail three species (Tables 3-43-5,3-6), where a negative relationship

indicates higher density at points with lower surrounding vegetation, and a positive,

higher density in higher vegetation.

Table 3-3. Summary of glm output for W. smifhii. Significant relationships between

variables and Iarval abundance are in bold. The direction of coefficients is indicated as

'coef . Incremefitally higher levels of scale were included in the g h s according to the

scale being fit with successive linear mixed models me).

Scale Variable Sample 1 Sample 2 Deviance Residual P(F) coef Deviance Residual P(F) coef

d f d f NULL 5760 1816 7438 1816

leaf POTVOL 873 1815 <0.001 + 1020 1815 <0.001 + ACn'OL 246 1814 ~0 .00 1 + 56 1814 -=0.001 + D ETRIT 43 1811 0.01 + 93 1811 -=0.001 + MIDGES 5 181U 0.2 + 2 1810 0.6 + SARCOP NA NA NA NA 21 1809 0.03 + AW0L:POTVOL 181 1804 <0.001 110 1803 <O.Oo 1 ..

plant NNEIGH 0.2 1809 0.8 + 1 1808 0.7 -+

LEAVES 77 1805 <O.OO 1 - 83 1807 <O.OO 1 - point CONNEC 181 1807 43.00 1 - 61 1806 <O.OO 1 -

PTCONF 0.1 1806 0.9 44 1805 0.002 + PTDENS 24 1805 0.01 + 1770 1804 <0.001 + Dispersion 3.8 4.6 Parameter Residual 4128 1804 5770 1803

Table 3-4. Summary of glm output for M. knabi. Significant relationships between

variables and Iarval ablmdance are in bold, The direction of coeEcients is indicated as

'coef . uicrementally higher levels of scde were included in the glms according to the

scale being fit with successive linear mixed models (lme).

Scale Variable Sample 1 Sarnple 2 Deviance Residual P(F) coef Deviance Residual P(F) coef

d f d f NULL 14811 1816 13015 1816

Ieaf POTVOL A W O L DETRfT MOSQU SARCOP ACI7rOL:POTVOL

p lant W E I G H LEAVES

point CONNEC PTCONF PTDENS

Dispersion 7.0

18 15 18 14 181 1 1810 1809 1803 1 SOS 1807 1806 1803' 1804

Parameter ResiduaI II614 1804

Table 3-5. Summary of glm output for the relationship between variables and larval

abundance of F. fletdieri. The mode1 includes as.factor@ointid) to milnic a mixed-mode1

procedure. Generalized linear modek fit effects sequentidly, thus significance of effects

are calculated in the order they are included.

Scale VariabIe Deviance Residual P(F) coeff d f

NULL 578 1816 as.factor(pointid) 230 1615 eo.001

leaf POTVOL 1 1614 O. 15 + ACTVOL 2 1613 0.008 - DETRIT 7 1610 (0.00 1 +- MIDGES 5 1609 eo.00 1 - LMOSQUI 4 1608 <O.OOI + ACTV0L:POTVOL 0.1 1601 0.6 -

plant NNEIGH 2 1607 0.006 - LEAVES 2 1606 0.006 -

point PTDENS 0.1 1605 0.5 - PTCONF 0.2 1604 0.8 - CONNEC 2 1603 0.005 -

bog BGABüN 0 1602 >O -99 - BGAREA 0 1601 >0.99 + BGNNEI 0 1600 >O -99 i-

Dispersion 0.3 Parameter Residual 321 1600

Table 3-6. Summary of output f?om the mixed-effects models (he s ) representing the

relationship between W- smithii density and the amount, configuration and connectivity

of habitat at multiple spatial scdes.

Scale VariabIe Sam~le 1 Sam~le 2 ~ o e f t-value P(F) ~ o e f t-value P(F)

plant AMOUNT CONFIGURATTON

point AMOUNT CONFIGURATION CONNECTIVITY

0% AMOUNT (area) AMOüNT (abundance) CONFIGURATION

Table 3-7. Summary of output from the mixed-effects models (lmes) representing the

relationship between M. knabi density and habitat structure at multiple spatial scales

Scale VariabIe Sample 1 Sarnple 2 Coef t-value P(F) Coef t-value P(F)

plant AMOUNT O. 1 3.8 0.0006 0.2 4.1 <0.0001 CONFIGURATION 0.3 O -4 0.6 0.01 0.02 0.9

point AMOUNT -0.04 -1.5 0.1 -0.01 -0.6 0.5 CONFIGWWTION -1.0 - 1.9 0.07 -0.4 -1 .O 0.3 CONNECTNITY 2.5 4.0 0.0001 2.1 5.0 <0.0001

bof? AMOUNT (area) 7.5 1 0.3 -5.2 -0.7 0.5 AMOUNT (abundance) <0.000 1 0.7 0.5 C-0.0001 -0.3 0.8 CONFIGURATION 1-8 0.8 0.5 5.5 2.9 0.006

leaf plant point bog Spatial scale (m)

Figure 3-2. The direction and scale of significant relationships between W. smithii, A4

knabi, and F. JZetcheri density and the structural variables amount and configuration of

habitat at four nested levels of spatial scaie. In general, amount of habitat influences

density at relatively finer, and configuration at broader spatial scales, though species

respond at slightly different absolute scales correspondhg to evolutionarily divergent

attributes such as body size andor movement potential. Squares represent a significant

relationship with amount of habitat, circles represent a significant relationship with

configuration of habitat. The directions of response denved from coefficients of gims

(leaf) and lmes (plant, point, bog) are indicated as + or - within each symbol. Grey fil1

indicates a rnargindly sianificant effect. Statistical values are found in Tables 3-3 to 3-7.

Discussion

The data suggest a significant relationship between the distribution of W. smithii,

1M. knnbi, and F. fletcheri and the effects measured to represent arnount, configuration

and connectivity of habitat. The direction and magnitude of these relationships differ

between spatial scales within and between study species. Here, larvd samples one and

two are treated as joint indicators of relationships with habitat structure since their

direction rernained consistent even though levels of significance differed between the two

samples. In contrast with the findings of Andrén (1994), no evidence for interactions

between the arnount and configuration of habitat were detected to suggest thresholds

where the influence of configuration increased with decreasing amount of habitat at any

scaie, for any species in this system.

The W. srnirhii models reved a change in the direction of density response to

amount of habitat between the leaf (potential volume), plant (number of leaves) and point

scales (point density). At the bog scale, importance flips fkom amount to configuration

(distance to nearest neighbour) of habitat (Figure 3-2). Support for these density-

arnouddensity-configuration patterns is provided by movement/behaviour studies, Field

observations (Bradshaw 1983; pers. obs) describe females visiting leaves of multiple S.

purpurea plants in an area (point). Variance components analysis (Chapter One) irnplies

that a female selects a leaf within a plant for independent oviposition events, but moves

within a group of pIants (point) over her lifetime. For an individual, the point measure is

an appropriate scale of a habitat patch (sensu Addicott et aI. 1987). This study suggests

that local dynamics at a point scale are positively influenced by amount of habitat, for

example through individual recmitrnent and/or survivorship. The negative plant-lcveI

reIationship with amount of habitat (more Ieaves per plant = fewer Iarvae per leaf) was

not a result of decreased prey-base (detritus per leaf; sensu Farkas and Brust 1985) and is

likely a result of (unmeasured) constraint forcing local populations to function below

their apparent carrying capacity (Istock et al. 1975), such as overwintering mortaliv.

Release-recapture experiments of W. smithii (Chapter One) indicace that

movement occurs between the point and bog scale (1 0-100 m) and genetic work suggests

panmixis within a bog, rather than between bogs (Istock and Weisburg 1987). Thus, for a

population of individuals a patch of habitat (or ecological neighborhood) Iikely

encompasses mdtiple pokts, or an entire bog. A 'patchy' metapopulation structure may

operate between points within bogs. The negative density relationship with bog

configuration (distance to nearest neighbour) suggests that population dynamics respond

to rates of emigratiodimmigration with neighbouring bogs, and implies that a classic

metapopulation-type system (Hanski 1999) may operate at this bog scale.

The data corroborate with work by Fahrig (1998) where the circumstances under

which the breaking apart of breeding habitat (with no habitat loss, therefore a change in

configuration) would affect population persistence were predicted using a spatially

explicit simulation mode1 of fragmentation. One of these (narrow set of) conditions was

that the average between-generation movement distance of the organism be roughiy one

to three times the expected nearest distance between suitable (population) breeding sites.

Bogs within the boreai forest of western Newfoundland are separated by areas of

softwood scrub or mature softwood forest as narrow as 25 m and extending to 2000t m.

Based on Fahrig's (1998) prediction, the short movement potential (maximum of - 90 m)

of W. ssmithii (Chapter One) relative to actual distances between bogs (population

breeding sites) suggest that the configuration of bogs within this nahirally heterogeneous

boreai forest should impact population persistence.

The M. knabi data similady suggest changes in the significance of density

response to amormt and configuration of habitat. Aithough no movement information is

available for M kzabi, adults are srnaller than W. smithii and statistical inference of

movement potential using variance cornponents andysis (unpublished data; Miner 1999)

suggests that individuals have limited rnovement potential and cluster around plants,

wtiereas W. smithii cluster around the Iarger scale of points (Chapter One). In the VCA,

peaks of unusually high variance are suggested to indicate scales at which between-group

differences are especially large, inferring the scale of natural aggregation or patchiness

(Greig-Smith 1952, 1979). If we match relative scales, W. srnithii and A4 knabi respond

positively to amount of habitat locally, (point and plant scafes, respectively), and

configuration at broader scales.

Configuration at the point scale is marginally, negatively, significant in sample

one, and at the broadest, bog scale, there is a positive density-configuration relationship

for M. knabi for sample two. The former suggests metapopulation-type dynamics at the

point scale, the latter indicates that there may be some higher-level regional process at

work, which we can detect for the smallest species (M knabi) but not for the two larger

species. Biologically, the fluctuation in these configuration responses between samples

one and two might be temporal, and attributed to the unusual life cycle of M. knabi. The

life-cycle is described to encompass three generations every two years (Paterson and

Carneron 1982), where one cohort emerges in early and one in late summer. Heard

(1994a) describes Newfoundland M. knabi phenology differently, insisting there is a

single emergence event (stnctly univoltine). In this study we observed events more like

the 'two in three' described by Paterson and Cameron (1982)- As a result the sarnples are

collected fiom two independent cohorts within the same area and these aggregations may

respond to structure slightly differently. Further information on M. knabi movement

potential a d o r genetic variation would assist in interpreting these patterns.

The relationship between habitat structure and F. fletcheri density is strongest at

the smallest scales, and no bog-scale effects were detected. Configuration and amount of

habitat at the plant level are both significantly, negatively correlated to F. fletcheri

abundance, and could be associated with natural history attributes of the fly. Unlike W-

smirhii and knabi, whose larvae overwinter in S. purpwea and pupate to emerge as

adults afker the fourth instar, F. fletcheri Iarvae move out of the plant and pupate in the

surrounding Sphagnum spp. moss where they oveminter and from which they emerge as

adults (Forsyth and Robertson 1975). Information about emergence and adult behaviour

is scant. However, it is known that adult F. fletcheri roost overnight within the flower

heads of S. purpurea and use them as a mating arena (Krawchuk and Taylor 1999).

Potentially, it is beneficial for pupae to emerge near ne ighbohg plants for protection as

tenerais. This link is speculative since amount of habitat at the point scale has no

relationship to larval abundance. Female F. fletcheri Iarviposit a single offsprllig in a

purpurea leaf. If competition for resources between individuals exists (e.g., for available

flower heads) at spring emergence of tenerals, a plant with fewer leaves may provide a

less cornpetitive patch than one that could support the development of multiple

individuals in its many leaves.

Mark-recapture of F. fletcheri indicated fiequent cross-bog movement (Chapter

Two) indicating that inter-bog rnovement would be more common than with the smaller

statured W. smithii or M. knabi Correspondingly, both point and bog codiguration did

not influence F. fletcheri density, suggesting that strong movement potential can

overcome structural constraints imposed by the boreal forest matrix. This implies that

individual bogs are not independent components of a metapopulation (that may exist at

an even broader spatial scale).

A lack of evidence for "threshold" behaviour il this system that would

demonstrate an increased influence of configuration with decreased arnount of habitat,

could be attributed to a number of factors. For example, the imposed levels of scale may

be inappropnate to the phenornenon for these three species, or sampling methodology

may not be adequate to resolve more cornplex interactions in the system. Very small

habitat patches might help illustrate a compensatory response between arnount and

configuration in the bog system. However, this study did not sample extremely small bog

patches, as they were not discernable fiom GIS maps at the beginning of the study. It

seems logical that configuration rnight become more important in scenarios where habitat

is less abundant. However, previous studies proposing tfüs threshold (Andrén 1994;

Fahrig 1997; Bender et al. 1998) might also be illustrating a change in structural

relationships as we have demonstrated, with increased spatial scale. This should be

explicitly tested or controlled.

Vegetation texture at a point was measured as a factor influencing habitat

connectivity and had a significant influence on the density of al1 three study species. A

higher W. smithii density in areas with lower surrounding vegetation suggests that these

areas were more easily accessible to ovipositing females, or that thermal microclimate as

a result of increased plant exposure may be preferable in this northem, boreal system

m g s o l v e r 1979). In contraçt to W- smithii, areas with lower texture exhibited decreased

density of M knabi suggesting that either movement away fiom plants was increased by

Iower surrounding vegetation either actively, or passively as a result of wind-throw; or

that rnicrociimate provided by areas of high vegetation provided better habitat for M.

knabi. The texture between plants at a point was also significant to F. fletcheri density.

Since F. fletcheri has the potential to move across an entire bog easily (Chapter Two), the

influence of vegetation height suggests that identification of andor movement to plants

was facilitated by lower vegetation.

These relationships highlight the importance of considering "matrix", (or

cccontrast", "context", "texture") between patches of habitat as a structural measurement,

especially if it appears pertinent to the study organism based on natural history

information. For simplicity, some spatially explicit studies and rnodels often focus on

patch characteristics (With and Crist 1995; Fahrig, 1997) at the expense of matrix

variables. While this parsimony is sometimes valid, the inclusion of additional variables

could prove important in predicting organism response (Hiebeler 2000). In our system,

connectivity was only measured at the point scale. Its inclusion at the Ieaf or plant scale

did not appear Iogical (or quantifiable). The boreal forest between study bogs was equally

heterogeneous across the entire study site. However, a sirnilar study comparing hamested

(where clear-cuts exist as the matrix) and naturaI landscapes might suggest an effect of

connectivity at the bog scale.

Scaling issues have been addressed in ecology throughout this decade (Kotliar

arid Wiens 1990: Levin 1992; Wu and Loucks 1995). This study uriiquely illustrates how

inter- and intra-specific response to habitat structure is inconsisient within and across

scales, even when species are strictly linked to the same resource. The importance of

amount and confiavation of suitable habitat on organism density changes with increasing

spatial scale. The fkequency and scaie of these changes is different for various organisms

and can be linked to scales of process, such as movement. Only when pattern is scaled to

process do these similarities begin to emerge. As postulated, there is no single

appropriate spatial (or temporal) scale at which to study nature cev in 1992), or even

individual species. With this in rnind, techniques for study integration such as meta-

analysis must diligently focus on equivalent levels of spatial and temporal scale explicitly

when combining data from various studies (Bender et al. 1998; Connor et al. 2000).

Accordingly, conservation issues can not be addressed at either a single scale or with a

single structural antidote.

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paradigm shift in ecology. Quart. Rev. Biol. 70:439-466.

Synopsis

The overall significance of this study c m be considered - in keeping with the

theme of the thesis - at two different scales. 1 consider the f i s t scale to be population and

cornmunity ecology, nested within the broader scale of conservation biology. Here, 1

have devetoped a clearer understanding of the population dynamics of W. smithii, M

knabi and F. fletcheri through the exploration of their movement potential, and their

relationship with habitat structure. In the context of a cornmunity, I have illustrated that

the members of this inquiline community exhibit unique processes (movement) and

patterns, despite their similar obligate habitat requirement, the larval 'nursery' within S.

purpurea leaves. This work adds to the phenornenal amount of Soma t ion that describes

the life history and ecology of this inquiline community. This volume of is needed to

understand local-level dynamics and provide a solid base fkom which to build studies at

Iarger scales exploring regional and ecosystem dynamics.

At a broader, landscape scale the significance of this study is its demonstration of

the variation in the response of species using the sarne microhabitat to the structure of

their shared environment. This variation exists among spatial scales and species.

However these relationships appear to scde to processes, such as movement. Likely,

temporal variation in response adds further complexity. We found that the amount of

habitat is most relevant at local scales, and the configuration at 'popülation' scales. It

would be interesting to determine whether this trend exists across a broader range of taxa

and ecosystems. Since most native organisms would be sirnilady adapted to the naturally

patchy landscape, population structure of these insects may heIp predict how the region's

other flora and fauna might react to habitat structure and changes to it, as a result of

forestry or natural disturbance. Sirnilarly, since this study was performed in a 'natural'

environment, the change in response as a result of varying connectivity (e-g., f?om

forestry) between habitat patches at a number of scales seems to be a logical next step.

Further, it is ememely important to begin recognizing the @oteiitially vat ) spatial extent

of structure that influences organism distribution.

This study was developed and implemented within the Gros Morne Greater

Ecosystern, an area of boreal forest including Gros Morne National Park and the

surrounding landscape. Since this landscape is currently the issue of a debate between

conservation/ecological integrity and economic gaidforestry, it seems suitable, necessary

in fact, to place the results of this study into this context. It is inevitable that the area will

be harvested within the next few years, but forestry operators of the area are willing to

discuss ecologicdly sensitive cutting patterns. Certainly, the concepts that were

investigated with this thesis provide ideas and mornentum for conservation principles

well beyond the scope of the pitcher plant community. Why not test these results - a

hypothesis is better than no plan at all. 1 w-ould suggest the choice of a few target species,

of which our knowledge of process (such as movement and habitat requirements) is well

developed (e.g., birds). Using our knowledge of these species, and an interactive dialogue

with the harvest planners, it rnight be possible to design cut patterns that test the influence

of arnount and configuration at local and Iandscape scales (scaled to be relevant to the

target species) in an altered ecosystem.

Appendk 1. Roosting behaviour by Fletcfzerimyiafletcfzeri @iptera: Sarcophagidae) in Sarracenia piirpurea (Sarraceniacea)

The flute-shaped Ieaves of the pitcher plant Sarraceniapurpurea L., are fluid-

filied microhabitat rich in invertebrate diversity (Bradshaw 1983; Heard 1994; Hardwick

and Giberson 1996; Harvey and Miller 1996; Miller et al. 1994). They are the obligate

Iarval habitat for F'i'efcherimyiafletcheri (Aldrich) (Forsyth and Robertson 1975). Most

Literature reports of F. Jetcheri present information o d y on larval life history and

population dynamics (Fish and Hall 1978; Hardwick and Giberson 1996). Forsyth and

Robertson (1975) state anecdotdly that they observed adults feeding on flowers and other

nectar sources within their study area. We believe that our observations represent the first

report of adult F. Jletcheri roosting within the flower heads of the pitcher plant.

On 3 July 1 998, during a survey of pitcher pIant Ieaves for Iarval F. fletcheri

conducted in boglands of the Long Range Mountains of Gros Morne National Park

(49E3SYN, 58E5OYW), Newfoundland, one of us (MAIS) fust observed, at about 1900,

adults of F. fletcheri using the flower heads of S. purpurea as roosting sites. A survey

conducted immediately after that observation revealed that 51 flower heads were

occupied by F. fletcheri. Most had one or two occupants; three plants held four, four, and

six F. fletcheri, respectively. The distribution of individuals was non-random (clumped)

cX2 = 1 1.07; P<O.OOl; n=75 flower heads). Where two flies were observed, they were on

opposite sides of the flower head, facing opposite directions with no apparent interaction.

In two plants containing greater than two flies, several pairs were mating (one fly on top

of another, with abdominal tips touching). In one plant with four occupants no mating

was observed. Fuaher evening censuses were undertaken between 10 and 27 July in 20

bogs ranging fiom low coastal zones to rock barren highlands. Occupation rates varied

f?om 3/135 to 43/167 flower heads, usudy with a single fly per flower head. By August,

we no longer observed F. fletcheri roosting with any regularity, which we expect was due

to seasonal cessation of adult activity.

Observations of individual fly behaviours at pitcher plant flowers revealed the

following general patterns. Fletcherimyiafletcheri were usually observed landing on the

sepals of the flower (on the upper surface, because the flower head is nodded) shortly

before dusk (approximately 1800-1900; 2 h prior to sunset). Within 30 min of dighting,

individuals would walk into the bowl of the flower. (The shape and structure of the

flower, with its "nodding" head, provides an urnbrella-like enclosure.) When left

undisturbed they appear to remain within the flower head for the night. In a prelirninary

study, 10 occupied flower heads were marked one evening and al1 10 were still occupied

by F. fletcheri when rechecked prior to 0900 the following morning.

Between 0700 and 0900 the foIIowing morning (2 h after sunrise), roosting F.

fletcheri would move fkom the bowl of the flower ont0 the outer face of the sepds. M e r

10-30 min of basking, individuals would fly from the flower, afier which they could not

be followed. When individuals were disturbed fiom the flower heads, they dropped to the

ground and flew only short distances, alighting on and gradually ascending other

vegetation in the area. One inciividual was observed to drop kom the flower head to the

rrround and fly directly to a neighbouring flower head roughly 30 cm distant. C

Fletcherimyiaflercheri were never observed within the flower heads between 2 h after

sunrise and 2 h prior to sunset.

Why individuals roost within the flower heads is unknown. A total of 3 h over

three evenings were spent sweeping, beating, and perusing other vegetation in various

boglands. Fletcherimyiaflefcheri was never found occupying foliage other than the

pitcher plant. Thus, it appears as though the behaviour is uniquely associated with pitcher

plants. Individuals were observed apparently feeding (head buried in pollen on stamen)

on pitcher plant pollen only once, so the plant does not appear to provide a primary food

resource. As well, F. fletcheri continued using the flower heads even as the plants lost

petals and starnen. The flower head shape rnay encapsulate a microclimate different fkom

the surroundhg environment, thus protecting individuals from wind, rain, and changes in

temperature. It may also provide a refuge from predators. One likely explanation,

especially given our observations of mating, is that the flower heads provide assembly

site and perhaps some king of cue for mating.

Multiple individuals of an unknown species of Coleoptera were observed in the

flower heads fkequently for a penod of 1 week, but no other insect species were obsenred

in the pitcher plant flower head so consistently or over the extended penod of time

recorded of F. flefcheri.

The roosting habit of F. fletcheri is interesting as an adult behaviour, even more

so because of the further, obligate association of its lava to the pitcher plant.

We thank Parks Canada and the Western Newfoundland Mode1 Forest for

financial support. We are grateful to M Holder, K Menchenton, J Miner, D Potter and D

Rogers of Agriculture Canada, Kentville. BE Cooper, Canadian National Collection

(CNC), Ottawa, verifïed the identification of voucher specimens. Vouchers have been

deposited with the CNC, Ottawa.

References

Bradshaw, W.E. 1 983. Interaction between the mosquito Wyeomyia smithii, the midge Mefriocnemus knabi, and their camivorous host Sarraceniapzvpurea. In: Frank, J.H. and Lounïbos, L.P. (eds), Phytotelmata: terrestnal plants as hosts of aquatic insect communities. PIexus, Medford, N.J.

Fish, D. and Hall, D. W. 1 978. Succession and stratification of aquatic insects inhabiting the leaves of the insectivorous pitcher plant, Sarracenia purpurea. Am. Nfidl. Nat. 99:172-183.

Forsyth, A.B. and Robertson, R.J. 1975. K reproductive strategy and larval behavior of the pitcher plant sarcophagid fly, BZaesoxiphafIetcheri. Cm. J. Zool. 53 : 174-1 79.

Hardwick, M.L. and Giberson, D.J. 1996. Aquatic hsect populations in transplanted and natural populations of the purple pitcher plant, Sarraceniapurpzcrea, on Prince Edward Island, Canada- Cm. J. Zool. 74: f 956- 1963.

Harvey, E. and Miller, T.E. 1996. Variance in composition of inquiline communities in leaves of Sarracenia purpurea L. on multiple spatial scales. Oecologia 1 O8 :562- 566.

Heard, S.B. 1994. Pitcher-plant rnidges and mosquitoes: a processing chah cornmensalism. Ecology 75: 1647- 1660.

Miller, T., Cassill, D-, Johnson, C., Kindell, C., Leips, J., McInnes, D., Bevis, T., Mehlman, D. and Richard, B. 1994. Intraspecific and interspecific cornpetition of Wyeomyia smithii (Coq.) (Culicidae) in pitcher pIant communities. Am. Midi. Nat. 13 1:136-145.