Eco Morphological Structure of Bat Communities

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ECOMORPHOLOGICAL STRUCTURE OF BAT COMMUNITIES:ALTERNATIVE MODELS AND ENVIRONMENTAL GRADIENTS

byRICHARD D. STEVENS, B.S.

A THESISIN

ZOOLOGYSubmitted to the Graduate Faculty

of Texas Tech University inPartial Fulfillment ofthe Requirements forthe Degree ofMASTER OF SCIENCE

Approved

May, 1996


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ACKNOWLEDGMENTSThis thesis represents the culmination of effort of many people. In fact, if one

were to tabulate all of the contributions towards its completion, mine would, by far, bein the minority compared to those of others.

I w ould like to fu-st thank my m ajor professor. Dr. Michael W illig, for hisfriendship, criticism, enthusiasm, encouragement, emotional and financial support, anddirection. I specifically thank Mike for instilling in me the desire to improve upon myweaker idiosyncras ies and to capitalize on the stronger ones. Moreover, I am greatlyindebted to him for constant funding, which allowed m e teaching-free supportthroughout the entire time I pursued my master's.

I would like to thank Dr. Clyde Jones, Dr. Daryl Moorhead, and Dr. RobertOw en for serving on my com mittee as well as for their interaction and direction. Iwould especially like to thank Dr. Jones for allowing me to be a not-so-honorarymember of his lab , and for ensuring that I truly appreciate what it means to be amam malogist. I certainly gained a lot from interaction with and stimulation by him andhis students.

Many fellow graduate students have aided in the conceptual and methodologicaldevelopment of this thesis. First, and certainly foremost, is the contribution of Alec B.Shaner. W ithout Big Al' s computer wizardry and mathematical adroitness, my ideaswould have simply remained questions. Maryann Lynch and Kate Lyons providedmuch criticism when I lacked forethought, and much support and encouragementduring times of self-doubt. Dianne H all was exceedingly helpful not only through he reditorial reviews, but also through sharing her wisdom during the latter stages of thisthesis and reassuring me that many of the emotions I was experiencing were quitenormal. Pragna Patel, Maryann Lynch, Kate Lyons, and Dianne Hall were invaluablein proofing of data and tables. Dr. Charles Werth, Dr. Robert Hollander, Dr. G erardo

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Cam ilo, Dr. Michael Gannon, Dr. Rick Manning, Brian Croyle, Javier Alvarez,Elizabeth Sandlin, Steven C ox, Steven Presley, Michael Cramer, Michele Secrest,Franklin D elano Yancey, II, Michelle Wallace, Burhan Gharaibeh, Johnny Peppers,Celia Lop ez-Gonzales, Justin Jones, Jeff McMillen, Cakky Brawley, and GaryGreenstreet, all provided much appreciated direction, friendship, and support.

I ow e thanks to many faculty members from Texas Tech, as well as otherinstitutions. Dr. Mark McGinely provided me with much direction in my early pursuitof community ecology. Dr. Richard Strauss provided statistical expertise regardingPCA and simulation analyses. Dr. Elgene Box,fromthe University of Georgia, andDr. Michael R osenzw eig, from the University of Arizona, provided direction regardingprimary productivity and evapotranspiration.

Various people and agencies have paid my salary during thetimeI pursued mymaster's degree. Dr. John Zak as director of The Institute for Environmental Sciencesat Texas Tech University provided funding from 1992-1994. Dr. Jorge Saliva and theU.S. Fish and Wildlife Service provided funds for two summers studying bats inPuerto Rico. Finally, Dr. Tony Krzysik and the U. S. Army Corps of Engineersprovided funding during the latter stages of this thesis, not to mention insight as tostatistical methods for achieving more accurate density estimates, an appreciation ofecological phenomena at landscape scales, and many goodtimes n the Mojave Desert.

Several museums have provided specimens for examination. These include:the Field Museum of Natural History; museums at the University of Kansas andLouisiana State University; the Smithsonian Institution and United States NationalMuseum; the American Museum of Natural History; the Carnegie Museum of NaturalHistory; and The M useum, Texas Tech University. I especially want to thank thecuratorial staff at each of these institutions for their hospitality and patience during myvisits. More specifically, I want to thank Thor Holmesfromthe University of Kansas

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for not forgetting his humble beginnings and providing shelter, food, and hospitality toa poor traveling graduate student.

I would like to state my appreciation to the late Dr. J. Knox Jones, Jr. It wasunfortunate that Dr. Jones was unable to directiy influence a majority of my graduatecareer. Noneth eless, D rs. Knox and Clyde Jones are responsible for my initialinvolvement in mamm alogy, and my subsequent development certainly w ill be lessenedby the absence of Dr. J. Knox Jones, Jr.

This thesis has probably been my most selfish undertaking, and I would like toend by thanking my family. Not only has my family been very patient regarding mylack of interaction, but they have always provided unconditional support andencouragement. For this I am most thankful. I especially want to thank my mother andfather for their bravery in allowing me thefreedomto pursue what I wanted regardlessof the avenue, and can only hope that my winding road will lead to somethingcomparable to their expectations.

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TABLE OF CONTENTS

ACKNOWLEDGMENTS iiLIST OF TAB LES vi i iLIST OF FIGURES xCHAPTER

I. INTRO DUC TION 1Objectives 5M ethodological Considerations 5Literature Cited 8

II. THE RELATIONSHIP BETWEEN ABUN DANC E AN DMORPHOLOGICAL DISSIMILARITY: A MODELOF COM MUNITY STRUCTURE 12Abstract 12Introduction 13The Model 15Com petitive Scenarios 17The Comm unity 18Results 20Discussion 20Literature Cited 26

III. COMM UNITIES, INTERACTIONS, AND COMPETITIVEEXCLUSION: A SYNOPTIC EVALUATION OFSIZE ASSORTMENT 37

Abstract 37Introduction 37Methods 39

Feeding Guilds 39M orphological Structure 40

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Species Pools 41Results 43

Principal Com ponents An alyses 43Minimum Spanning Trees 44

Discussion 44Literature Cited 49

IV. COMMUNITIES, INTERACTIONS, AN D THE LACK OFCOMPETITIVE EXCLUSION: A SYNOPTIC EVALUATIONOF DENSITY COMPENSATION 76Abstract 76Introduction 78Methods 80

Communities 80Feeding Guilds 80M orph ological Structure 81Null Hyp otheses 83

Results 85Discussion 86Literature Cited 90

V. GRADIENTS IN THE STRUCTURE OF NEW WORLDBA T COMM UNITIES 100

Abstract 100Introduction 101Metiiods 104

Selection of Comm unities 104Characterization of Comm unity Structure 104Morphological Structure 105Numerical Structure 10 6

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Environmental Characterization 108Principal Com ponents An alysis 109Multiple Regression and Correlation Analyses 11 0

Results 114Environmental Axes 11 0

Principal Components An alyses I l lAxes of Structure 11 2M ultiple Regression An alyses 113Correlation Analyses 114

Discuss ion 115Literature Cited 120

VL SYN THES IS 148Literature Cited 151

APPENDICESA. LOCATION AND ANNOTATED DESCRIPTION OF

BAT COMMUNITIES 15 2B . DESCRIPTION OF FEEDING GUILDS 157C. DESCRIPTION OF MORPHOLOGICAL CHARACTERS 159D. STRUCTURE OF FIFTEEN BAT COMMUNITIES 16 0E. SIMULATION PROGRAM TO EVALUATE DENSITY

COMPENSATION 203F. SIMULATION PROGRAM TO EVALUATE SIZEASSORTMENT 209

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LIST OF TABLES2.1 Structure of the nocturnal granivore guildfromthe Sonoran Desertcommunity 313.1 Eigenvalues and percent variation accounted for by the fu-st two principalcomponents (PC) in analyses conducted on morphological charactersof spec ies in each guild, separately 533.2 Factor loadings for the first and second principal components for eachof the five feeding guilds 543.3 Pearson product-moment correlations of each of sevenecomorphological characters with the first and second principalcomp onents derived for each of the feeding guilds 553.4 Resultsfromsimulation analyses evaluating whether the mean MSTsegment lengthfroman actual feeding guild was indistinguishable fromthose under the null hypothesis of stochastic guild assembly 563.5 Results fro m simulation analyses evaluating whether the variance ofMST segment lengthsfroman actual feeding guild wasindistinguishable from those under the null hypothesis of stochasticguild assembly 613.6 Results of Fisher's test of combined probability for overall significanceregarding mean MST lengths from each of fifteen bat comm unities 663.7 Results of Fisher's test of combined probability for overall significanceof variance of MST lengths from each of fifteen bat comm unities 683.8 Results of Fisher's test of combined probability determining overallsignificance of mean MST lengths from each of five feeding guilds 703.9 Results of Fisher's test of combined probability determining overallsignificance of variance of MST lengths from each of fivefeeding guilds 714.1 Results from simulation analyses evaluating nonrandom patterns in

abundance within fifteen bat commu nities 954 .2 Results of Fisher's test assessing overall deterministic structure of batcommunities when probabilities from all feeding guildsare combined 984.3 Results from Fisher's test assessing overall, deterministic structureof each of five feeding guilds when probabilities are combined for alllocations 995.1 Bat communities used to evaluate gradients of structure 125

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5.2 Environmental parameters and their associated acronyms in parentheses ..1265.3 Latitudinal (" N or S) and precipitation (mm /mo-^ attributes of ninelocations of Ne w World bat comm unities 1285.4 Attributes of temperature ( C) of each of nine locations of New Worldbat communities 12 95.5 Attributes of productivity (g/m^) of each of nine locations of NewW orld bat comm unities 1305.6 Eigenvalues and percent variation explained by principal componentsused to characterize environmental gradients 1315.7 Factor loadings for all climatic variables on the first four environmental

principal component axes 13 25.8 Pearson product-moment correlations of each climatic variable withfour environmental principal component axes 13 35.9 Eigenvalues (Eigen) and percent variation (%Var) accounted for bysignificant principal components characterizing the relationship amongeleven measures of structure for communities and each guild, separately.. 1345.10 Factor loadings (Eigen) and degree of association as determined byPearson product-moment correlation coefficients between each of themeasures of structure and each principal component (CPC) 1355.11 Results from stepwise multiple regression analysis determining thedegree to which measures of structure are a linear function ofenvironmental gradients 1405.12 Results from Kendall rank correlation analyses evaluating the degreeof association between environmental variables and measures ofstructure 141D. 1 Species composition, abundance, and morphological attributes of batcommunities 161

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LIST OF FIGURES2.1 Theoretical expectations of the relationship between morphologicaldistance and abundance 322.2 Graphical representation of the distribution of r-valuesgenerated bychance (Ho) and the location of the rejection region dictated by thealternate hypothesis of deterministic structure 332.3 Three competitive scenarios based on considerations of morphology andabundance 342.4 Resultsfromsimulation analyses that evaluate each of three competitivescenarios for deterministic structure 353.1 Graphical representation of a minimum spanning tree (MST) 723.2 Graphical representation of faunal poo ls 733.3 Graphical representation of the null hypothesis regarding mean minimumspanning (MS T) tree segment lengths 743.4 Graphical representation of the null hypothesis regarding the variance ofthe minimu m spanning tree (MST) lengths 755.1 Scattergram of the relationship (r = 0.761) between numerical structurefor frugivores (CPC 3) and variability of temperature (EPC 2) 1435.2 Scattergram of the relationship (r = 0.782) between morphologicalstructure characterized by mean interspecific distance (CPC l) within thegleaning animalivore guild and the relative variabiUty of productivity(EPC4) 1445.3 Scattergram of the relationship (r = 0.766) between numerical structure(CPC 3) of the gleaning animalivore guild and the absolute variabihty inprecipitation and productivity (EPC 1) 1455.4 Scattergram of the relationship (r = -0.908) between numerical structure(CPC 2) of the nectarivore guild and variability in temperature (EPC2)....1465.5 Scattergram of the relationship (r ndaii = -0.674) between morphologicalstructure characterized by the mean interspecific distance within the aerialinsectivore guild and relative variability in precipitation and productivity.. 147A. 1 Graphical representation of the approximate location of each batcommunity evaluated 15 9


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CHAPTER IINTRODUCTION

The m orphological, biogeographic, and taxonomic radiation of the Chiropterais one of the most conspicuous characteristics of the class Mammalia. Bats are thesecond largest order of mammals, and include two suborders, 18 families, 186 genera,and 986 species (N owak, 1991). Chiropteran diversity is organized into a well-documented latitudinal gradient, whereby sp ecies richness increases w ith decreasinglatitude (Findley, 1993; Lyons, 1995; W illig and Lyons, in lit.; Willig and Sandlin,1991; W illig and Selcer, 1989; Wilson, 1974). Furthermore, the latitudinal gradientin bat species richness is so strong that it is the principal component inducing thelatitudinal gradient in speciesrichnessfor mammals as a whole (Findley, 1993;W ilson, 1974; however, see Kaufman, 1995). A considerable effort over the last 50years has focused on distinguishing and understanding causal factors of the latitudinalgradient. Increases in species richness with decreasing latitude are facilitated by anincrease in the number of species within ecological comm unities in tropical areas(Begon et al., 1990). Thus, understanding the factors that affect communitycomposition are of interest from a biogeographical, as well as ecological, perspecitve.

A community is defined as a group of species that co-occur in space and time(Begon et al., 1990). Entire communities often represent hundreds if not thousands ofspecies, and as such, may be complex from an ecological perspective (Simberloff andDay an, 1991) . Com munities commonly are categorized into feeding guilds, whichoften represent more germane study units than do entire comm unities (Bonaccorso,1975; Findley, 1993; Hawkins and MacMahon, 1989; Simberloff and Dayan, 1991;W illig, 1982; W illig and Moulton, 1989). Feeding guilds are groups of potentiallyinteracting species that consume similar resources in a similar fashion (Root, 1967).

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Traditionally, it was believed that biotic interactions, primarily com petition, mediatethe co-existence of species within feeding guilds and ultimately structurecom mu nities (Robinson et al., 1993; Brow n, 1989; Davidson et al., 1984; Flem ing,1984). As a result, competition theory provides much of the historical foundation ofcontemporary animal community ecology.

An im portant assum ption in community ecology is that the consumption ofresources is dependent on the size and shape of trophic apparati, and thus, the ecologyof an organism is reflected in its morphology (B onaccorso, 1975; Brown andLieberm an, 1973; Findley and Black, 1983; Findley and Wilson, 1982; Freem an,1981, 1984, 1988, 1992; Hespenheide, 1973; Mares, 1976; Smartt, 1978). Ifmorphology reflects ecology, and competition mediates the structure of feedingguilds, then there must be a limit to how similar two species can be and still coexist inthe same comm unity (A brams, 1983; MacA rthur and Levins, 1967). If two speciesare too similar, then they will experience such intense interspecific competition thateither one or both will diverge morphologically or be driven to extinction at the locallevel. Th us, character displacement and competitive exclusion w ithin feeding guildsshould produc e patterns of morphology that are more overdispersed than w ould beexpected due to chance alone (Brown and Wilson, 1956; Gause, 1934; Hardin, 1960).Indeed, this has been widely docum ented, not only for mam mals, but for a num ber ofother vertebrate taxa as well (Simberloff and Boeklen, 1981).

Hyp erdispersion of morphologies w ithin feeding guilds alternately could bethe result of stochastic processes . Throughout the 1980s, comm unity ecologistsemp loyed null mod els to demonstrate the artifactual nature of many morphologicalpatterns (Bowers and Brown, 1982; Connor and Simberioff, 1979; Simberloff, 1984;Simberloff and Boek len, 1981; Strong and Simberioff, 1981; Willig and Moulton,


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1989). As a result, evidence regarding competition and its influence on theecomorphological structure of communities is equivocal.

Tw o important oversights potentially obscure the role of competition instructuring com mu nities. First, patterns of m orphology m ay not be the onlyindicators of deterministic structure. Nonetheless, contemporary null mod els,designed to detect hyperdispersed morphologies within communities, are incapable ofevaluating other manifestations of com petitive interactions. For example, if resourceconsumption is determined by m orphology, then pairs of morphologically similarspecies should exhibit more intense competition than do pairs of species that are lesssimilar. As a result, a negative correlation should exist between morphologicalsimilarity and abundance within feeding guilds; the ultimate local extinction of aspecies is but a consequence of this process.

Second, competition need not structure all communities in all situations to beimportant. In fact, com petitive interactions should not be expected to manifest in allsituations. For example, climatically unpredictable or unstable environments imposegreater density-independent mortality than do stable environments (Andrewartha andBirch, 1954; MacArthur, 1972; Zeveloff and Boyce, 1988). As a result, populationsmay never reach density-dependence, and never experience intense interspecificcompetition. Conversely, more stable envkonments allow populations to approachdensity-dependence and interspecific competition should become more intense; insome ca ses , intense enough to induce deterministic structure. Hence, gradients in thedegree to which com munities are deterministically structured by density-dependentbiotic interactions should coincide with axes characterizing environmental variability.In isolation , single community studies offer littie insight into this scenario. Moreover,general conclusions on the structure of com munities and the causal factors of


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structure are tenuous when only one community is evaluated. Studies involving manycommunities must be conducted to assess the generality of hypotheses.

Bat communities represent exceptional systems by which gradients instructure can be investigated. Bats numerically dominate many communities(Robinson, 1971 ; Handley, 1966), are species rich in both tropical and temperateareas, and occur in all terrestrial biom es except tundra (Nowak, 1991). Furthermore,several bat communities are well-documented and have been the focus of intensiveecological investigations (Findley, 1993).

Predictable patterns exist regarding the composition of bat communities(Findley, 1993). In general, bat comm unities are composed only of aerial insectivoresat higher latitudes. As one goes toward more tropical environs, species richnessincreases within comm unities (Findley, 1993). Moreover, as structural and resourcediversity increase, so does the number of feeding guilds, from one (aerial insectivore)to no le ss than seven guilds (aerial insectivore, frugivore, gleaning animalivore,molossid insectivore, nectarivore, piscivore, sanguinivore). Consistent morphologicalpatterns within comm unities are discernible as well. Most communities aredominated by a group of morphologically similar species that form a core, whereasthe morphological periphery harbors fewer species of higher morphological disparityspecies (Findley and Black, 1983; Fleming, 1986). Few studies have attempted tonegate that observable patterns, such as this, could be a product of chance (W illig andMoulton, 1989). Moreover, no studies have determined variation in the strength ofpatterns, or whether some extrinsic component of the environment influences thedegree to wh ich comm unities are structured by deterministic processes.


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ObjectivesHerein, I statistically evaluate 15 bat comm unities in the New World to

determine whether their structure may be the product of deterministic processes (seeAppendix A ). In Chapter n , I develop a model that evaluates comm unity structurebased on patterns in abundance. In Chapter IE, I utilize a null model developed byW illig and Moulton (1989) to determine whether nonrandom morphological patternsare pervasive in the fifteen communities. In Chapter IV, I evaluate the ubiquity ofpatterns in abundance. Finally, in Chapter V, I evaluate environmental characteristicsassociated with each community to determine if the degree to which patterns arenonrandom is dependent on climatic variables. Specifically, I evaluate whethergradients exist regarding bat community structure.

Methodological ConsiderationsAlthough ecological comm unities can be defined operationally, they are often

nebulous entities. The boundaries of some communities (e.g., pond-fish comm unity,herbivores on bracken fern) strongly correspond to physical boundaries (Schluter andRick lefs, 1993 ). How ever, this may only be true for taxonomically definedcommunities representing less mobile organisms. Bats are highly vagile and two ormore plant communities may be traversed within a night's foraging by some species(W illig and Mares, 1989). As a result, bats may perceive different plant associationsas habitat patches. Discretion must be used to ensure that an appropriate area, largeenough to comprise all interacting species that co-occur, is sampled when evaluatingbat comm unity structure. Conversely, sampling from too great an area may includespecies from more than one community, leading to the inclusion of information onspecies that have no potential to interact. Special care must be taken when selectingthe areal extent from which to sample communities.

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In the ensuing investigation, several criteria were utilized to select batcommu nities. Data collection must have been from more than one particular locality(e.g ., stock tank, specific trail), but the area that comprises samphng localities m ustbe limited so that information likely was from a single bat community. This criterionwas fairly sub jective. Finally, sampling must have been conducted on a regular basis,in all seasons during which bats were active, for at least one year. This minimizes thepossib ility of missing rare species , and increases the accuracy of relative abundances.

Feeding guilds also can be defined operationally and, like ecologicalcommu nities, may be methodologically nebulous. Feeding guilds representtaxonom ic subsets o f the community that consume similar resources in similar waysand, consequentiy, are most likely to compete (Root, 1967). When addressing theimportance of competition in structuring com munities, examination of groups ofspecies with little potential to compete will bias conclusions. Thus, communitiesshould be decomposed into feeding guilds (Bonaccorso, 1975; Findley, 1993, Willig1982; W illig and Moulton, 1989). I decomposed each community into seven feedingguilds (see Appendix B for a description of each): (1) aerial insectivore, (2 )frugivore, (3) gleaning animalivore, (4) molossid insectivore, (5) nectarivore, (6)piscivore, and (7) sanguinivore (see Appendix B). A species was assigned to afeeding guild based upon food items that composed the bulk of its diet (e.g ., blood,fish , fruit, animal, nectar). For example, the diet of Artibeus jamaicensis. in mostplaces, is primarily fruit. Although this species sometimes consumes nectar andinsects, it would be placed in the frugivore guild. Additionally, insectivores werecategorized into one of three guilds based on where and how they foraged.

Other classifications have been suggested to categorize bat comm unities intofeeding guilds . Bonaccorso (1975) suggested categorizing frugivores into canopy andsub-canopy frugivores. However , included in the spatiotemporal spectrum of

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com mu nities that I evaluated are more than one comm unity that lacks a distinctionbetween canopy and sub-canopy, yet those species believed to be canopy specialists(stenoderm atines) and those believed to sub-canopy specialists (caroliines) coexist.Canopy and sub-canopy frugivores may be valid designations; however, to makecom parisons of frugivores across all locations where they exist, a more generaldesign ation w as necessa ry. In this investigation, all bats that consumed fruit as themajor component of their diet were included in the frugivore feeding guild.Mo reover, it is comm onplace to distinguish gleaning insectivores and gleaningcarnivore s. In this study, both of these groups were combined as gleaninganim alivo res. The re is insufficient ev idence to suggest that carnivores exhibitcam ivory through all seasons of the year (Willig et al., 1993). Moreover, in m anyplaces, bats that w ould be designated as carnivores exhibit omnivory (W illig et al.,1993). Th us, my operational definition of a gleaning animalivore is any species thatconsum es principally animals (whether they be vertebrates or invertebrates) that aregleaned from surfaces. Information on dietary composition of species was obtainedeither directly from docum ents describing the bat community or from other literaturesources.


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Systematics 14: 359-376.Andrewartha, H. G., and L. C. Birch. 1954. The distribution and abundance ofanimals. The University of Chicago Press, Chicago.Begon , M., J. L. Harper, and C. R. Townsend. 1990. Ecology: individuals,populations, and communities. Blackw ell Scientific Publications, Boston.Bon accorso, F. J. 1975. Foraging and reproductive ecology in a community of bats inPanama. Dissertation. University of Florida, Gainesville, Florida.Bow ers, M. A ., and J. H. Brown. 1982. Body size and coexistence in desert rodents:chance or comm unity structure? Ecology 63: 391-400.Brow n, J. H., and G. A. Lieberman. 1973. Resource utilization and coexistence ofseed-eating desert rodents in sand dune habitats. Ecology 54: 788-757 .Brown, J. S. 1989. Desert rodent community structure: a test of four mechanisms ofcoexistence. Ecological Monographs 59: 1-20.Brown, W. L., and E. O. W ilson. 1956. Character displacement. SystematicZoology 5: 49-64.Connor, E. F., and D. S. Simberloff. 1979. The assembly of species comm unities:chance or competition? Ecology 60: 1132-1140.Davidson, D. W., R. S. Inouye, and J. H. Brown. 1984. Granivory in a dessertecosystem : experimental eviden ce for indirect facilitation of ants by rodents.Ecology 65: 1780-1786.Find ley, J. S. 1993 . Bats: a community perspective. Cambridge University Press,Cambridge, Massachusetts.Findley, J. S., and H. Black. 1983. Morphological and dietary structuring of aZambian insectivorous bat community. Ecology 64: 625-630.Findley, J. S., and D. E. W ilson. 1982. Ecological significance of chiropteranmorphology. Pages 243-258 in: T. H. Kunz, Editor. Ecology of Bats.Plenum Press, New York.Flem ing, T. H. 1984. Interspecific competition in mammals: opening remarks. ActaZoologica Fennica 172: 25-26.Flem ing, T. H. 1986. The structure of neotropical bat comm unities: a preliminaryanalysis. Revista Chilena Historia Natural 59: 135-150.

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Mammalogy 74: 117-128.W ilson, J. W ., m . 1974. Analytical zoogeography of North Am erican ma mm als.Evolution 28: 124-140.Zeveloff, S. I., and M. S. Boy ce. 1988. Body size patterns in North Am ericanmam ma l faunas. Pages 123-146 in: M. S. Boyce, Editor. Evolution of lifehistories of mam ma ls: theory and pattern. Yale University Press, NewHaven, Connecticut.

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CHAPTER nTHE RELATIONSHIP BETWEEN ABUND ANCE AND MORPHOLOGICAL

DISSIMILARITY: A MODEL OF COMMUNITY STRUCTURE

AbstractThe role of interspecific competition in structuring communities has been a

highly debated issue for the last two decades. The deterministic nature ofmorphological patterns within communities has been at the center of this debate. Nullmodels, designed as a more rigorous statistical means to evaluate the effects ofcompetition on the morphology of coexisting species, have failed to provide adequateresolution. Furthermore, null models addressing comm unity-wide dispersions inmorphology may be based on too restrictive assumptions (e.g., competitiveexclusio n), and consequently, lack power to detect deterministic structure in manycommu nities. Other manifestations of the effects of competition on communitystructure should be explored. Morphological uniqueness may allow species to escapeintense competitive pressure and exhibit increased densities. Thus, a positiverelationship should ex ist between the relative morphological dissimilarity of speciesand their abundances. Species may not uniformly impose competitive effects on allothers within a feeding guild, however. Different competitive scenarios that considersubsets of species in feeding guilds that potentially experience more intenseinteractions should be evaluated specifically. Herein, I introduce a suite of modelsthat evaluate patterns in abundance from a diversity of m orphological perspectivesMoreover, I apply these analyses to an ecological community (nocturnal desertrodents) for which the effects of competition on community structure are wellestablished. Simulation analyses indicate that these models are powerful enough todetect nonrandom patterns in abundance at the feeding guild level. Moreover, these

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models reveal deterministic abundance patterns from all morphological perspectives.These models are powerful tools to explore factors influencing the role of competitionin comm unity structure.

IntroductionA considerable amount of theory and empirical evidence exists regarding the

role of interspecific competition in the structure of natural communities (Cody andDiamond, 1975; Diamond and Case, 1986; Kikkawa and Anderson, 1986; Strong etal., 1984). Non etheless, competition remains one of the most controversial issues ineco logy. Patterns in the morphology of co-occurring species have been a popularmeans to examine competitive interactions and, ultimately, community organization(Bowers and Brown, 1982; Brown and Bowers, 1985; Case et al., 1983; Dayan andSimberioff, 1994; Diamond and Case, 1986; Mares, 1976; Moulton, 1985; Moultonand Pimm, 1983, 1986a, 1986b, 1987; Schoener, 1984; Willig, 1982, 1986; Willigand Moulton, 1989). An important assumption of this approach, consistent withcompetition theory, is that the consumption of food resources is dependent onmorphology. Moreover, substantial evidence indicates that this assumption isgenerally true (Bonaccorso, 1975; Brown and Lieberman, 1973; Dayan andSimberioff, 1994; Findley and Black, 1983; Findley and Wilson, 1982; Freeman,1979, 1984, 1988; Hespenheide, 1973; Smartt, 1978). If the morphologies of tw o ormore sp ecies are not sufficiently distinct, the resources that they consume likely willbe similar, and interspecific competition will ensue. With enough time and intensity,com petitive interactions should manifest as character displacement or com petitiveexclusion (Brown and Wilson, 1956; Case and Sidell, 1983; Gause, 1934; Hardin,1960). Ultim ately, competition should give rise to a hyperdispersion of morphologieswithin ecological communities.

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Prior to the 1980s , demonstration of hyperdispersed morphologies impliedcompetitively-induced community structure (see Simberloff and Boeklen, 1981).However, null models have demonstrated boldly that many of the patterns inmorphology originally believed to be the result of interspecific competition can begenerated by chance (Connor and Simberioff, 1979; Grant and Schluter, 1984;Ricklefs and Travis, 1980; Strong et al., 1979). As a result, equivocal evidence existsregarding the nature of morphological patterns within communities. Moreover,com petitively induced community structure, based on contemporary interpretations, isnot as common as once believed (Strong et al., 1979). Subsequently, many haveabandoned the notion that competition theory provides substantial insight intounderstanding the structure of natural communities (Strong et al., 1984).

As much as null models have engendered critical andrigoroushypothesistesting, they too have failed to provide incontrovertible evidence concerning theimportance of com petition in structuring natural comm unities. These models maketwo implicit assumptions that may limit their power: (1) interactions between nearestneighbors structure communities, and (2) those interactions must lead tomorphological hyperdispersions to evince deterministic structure. To structurecommunities, competition need not affect the dispersion of morphologies throughcharacter displacement or competitive exclusion. Competitive interactions may affectrelationships betw een abundance and morphological similarity among species;current null m ode ls, based on morphology alone, are incapable of addressing thispossibility.

Nonetheless, species experiencing more competitive pressure should exhibitlower abundance and this may be another means to evaluate deterministic structure(Lotka, 1932; Volterra, 1926). If morphological similarity is a viable surrogate foreco logical similarity, then those species that are morphologically dissimilar from

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other species in the community should experience the least competitive pressure andexhibit the highest abundance. Thus, a positive relationship should exist between themorphological distance of a species with respect to potential competitors andabundance; the strength of this relationship should be greater than that produced bystochastic processes.

Ecological communities are often complex entities including hundreds, if notthousands of species (Simberloff and Dayan, 1991). Furthermore, communitiescomprise species from different feeding guilds (sensu Root, 1967) and trophic levels.As a result, competitive interactions should not be expected to exist among all specieswithin a conmiunity; competitive interactions should be most important within atrophic level, and especially within a feeding guild. Hence, the best place to beginexamining the manifestations of competitive interactions within communities, shouldbe within feeding guilds. Herein, I develop a suite of m odels, based on theecom orphological relationships of species, that is designed to detect nonrandompatterns of abundance within feeding guilds.

The ModelMy analyses are predicated on two assumptions. First, measures of

morphological dissimilarity within a guild are suitable surrogates for eco logicaldissimilarity. Second, a species with high ecomorphological similarity to one or morepotential competitors should suffer reduced density as a result of interspecificcompetition. As a consequence of such competitive effects, a quantitativerelationship should exist between the position of a species in ecomorphological spaceand its density within a guild (Fig. 2.1).

I performed simulation analyses to determine if associations betweenmorphological dissimilarity and abundance within feeding guilds are non-random.

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Morphological distances among species were calculated based on a Euclideandistance. I used Pearson product-moment and Spearman rank correlation coefficientsto describe the magnitude of the association between abundance and morphologicaldistance. Traditional tests determining significance assume that data follow aspecified distribution. For example, hypotheses tests for both Pearsonproduct-moment and Spearman rank correlation analyses assume that random variatesfollow a t-distribution (Sokal and Rohlf, 1995). If variates from the actual data do notfollow this distribution, traditional hypothesis tests may be inaccurate (Noreen, 1989).Simulation analyses, however, are not subject to these biases. By randomizing theactual data to y ield a distribution to which the observed statistics are compared, suchassumptions are not necessary, and violations of assumptions cannot jeopardize theaccuracy of hypothesis tests (Noreen, 1989).

To evaluate deterministic structure, I compared correlation coefficients fromactual guilds to those of simulated guilds. While preserving the integrity of themorphological relationships among species, random abundances were assigned toeach species, thereby yielding the structure of a simulated guild. A correlationcoefficient was then calculated between randomized abundances and actualmorphological distances of members within the simulated guild. One thousanditerations of this process yielded a probability density function for subsequenthypothesis tests. The correlation coefficient from the actual guild was compared tothe probability density function of simulated correlation coefficients. If thecoefficient for the actual guild occurred within the upper ten percent of thedistribution (p < 0.10), I concluded a non-random association between morphologyand abundance in the actual guild (Fig. 2.2).

Many factors influence the abundance of individual species (Andrewartha andBirch, 1954 , 1988; Begon et al., 1990). As such, strong positive correlations between

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morphological distance and abundance caused by competition may be obscured byautecological or other synecological processes (e.g., predation, mutualism).Consequently, caution should be used to prevent falsely rejecting com petition as animportant influence on community structure. To minimize the possibility of such aType I statistical error (rejecting a positive correlation between morphologicaldistance and abundance when it actually exists), I established the alpha level at p ^ 500 ,1 randomlyselected 500 combinations to calculate random guild statistics. When C was < 50 0,1utilized each combination only once to minimize redundancy. As a result, hypothesistests for these situations were based on sample sizes that were less than 500. Both setsof descriptive statistics from randomly assembled guilds form distributions under thenull hypothesis (random guild assembly) to which descriptive statistics from the actual

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feeding guild can be compared. If the mean segment lengthfroman actual guild wasgreater than 90 percent of the simulated values, or the variance of die spanning treelengths w as smaller than 90 percent of the simulated values, I concluded thatnonrandom m orphological combinations existed in the actual guild (Figs. 3.3 and 3.4).

ResultsPrincipal Components Analyses. Results of the five principal components

analyses were similar (Table 3.1). Eigenvalues for the first and second principalcomponents ranged from 0.022 - 0.073 and 0.003 - 0.005, respectively. Percentvariation accounted for by the fu-st and second principal components ranged from 76.8- 89.2 and 5.9 - 16.4, respectively. Factor loadings from each of the five covariancematrices appear in Table 3 .2.

Analyses were based on the same suite of morphological characters for allfeeding guilds. In all cases , principal components analyses reduced the sevenmorphological characters into two components. Nonetheless, the possibility exists thatthe contributions of each character to each principal component may be differentdepending on feeding guild. I determined the Pearson product-moment correlationcoefficient between principal components and each of the morphological characterswithin each feeding guild (Table 3.3). All characters, regardless of feeding guild, werepositively and significantly correlated with the fu-st principal component; it is hkely ameasure of overall size. With the exception of width across the post-orbitalconstriction, no pattem exists among guilds regarding significant correlations betweenvariables and the second principal component. Shape differs among species in aguild-specific fashion, and is likely a consequence of modification of structure toenhance ecologica l efficiency. Moreover, feeding guild distinctions often correspondwith profound morphological and phylogenetic differences. Thus, it is not surprisingthat differences in the relative contribution of variables to the second principal43


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component exist. Nonetheless, thefirsttwo principal components extracted from theseseven morphological variables accounted for 87.6 - 95.2 percent of the variation amongspecies witiiin a particular feeding guild (Table 3.1).

Minimum Spanning Trees. Simulation analyses strongly indicate thatnonrandom morphological pattems, consistent with competition theory, exist within batcommunities. Twelve of thefifteen ocations, and three of the five feeding guildsexhibited mean segment lengths that were significantiy greater than those derived fromrandom assembly (Table 3.4). Furthermore, segment length variances werenonrandom at eight locations and in three feeding guilds (Table 3.5). This indicatesthat when communities represent nonrandom faunal subsets, morphological pattemsmost often manifest as greater distances between species in morphological space.

N o conspicuous pattem exists as to which communities or feeding guildsexhibited nonrandom morphological stmcture. I utilized Fisher's test (Sokal andRohlf, 1995) to combine probabilities from all feeding guilds within a community aswell as within feeding guilds across locations to determine whether communities orfeeding guilds in general exhibited nonrandom morphological pattems. Sixcomm unities exhibited unusually high mean segment lengths overall (Table 3 .6),whereas four communities exhibited atypically small variances (Table 3.7). Aerialinsectivores, gleaning animalivores, and nectarivores exhibited unusually higher meansegment lengths (Table 3.8), whereas frugivores exhibited significantiy smallervariances of segment lengths (Table 3.9).

DiscussionAlthough seemingly hyperdispersed morphological pattems are not uncommon

within communities, recent statistical evaluations using neutral models have determinedthat statistically nonrandom hyperdispersions are in the minority (Simberioff andBoeklen , 1981). Recent evaluations of bat communities have corroborated tiiese44


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find ings (W illig and Moulton, 1989). Non etheless, my results identified numerousinstances in which species within feeding guilds exhibit statistically nonrandomhyperdispersions that are consistent with competition theory. Moreover, in a fewcases, entire bat communities exhibited deterministic structure. Obviously, variationexists regarding tiie degree to which feeding guilds and communities exhibithyperdispersed morphological pattems. Evaluating the stmcture of communities alonggradients may shed hght onto which environmental conditions foster the production ofnon-random structure (Chesson, 1988; Chapter V).

Morphological overdispersion is not uncommon in the bat communities Ievaluated. Nonetheless, simply observing morphological overdispersion in a sample(s^ < x) is not a sufficient demonstration of deterministic structure. Nonrandomstructure is indicated only when the sample variance is statistically smaller than themean (Sokal and Rohlf, 1995). To these ends, ascertaining the deterministic nature ofhyperdispersions by comparison with guilds created randomly from faunal pools isnecessary to warrant against wrongfully positing the operation of competitiveinteractions on community organization. Nonetheless, the utilization of faunal pools toevaluate statistical hyperdispersions is not an infallible means of evaluatingmorphological pattems (Diamond and Case, 1986; Strong et al., 1984), andinterpretations of results from faunal pools must be conservative.

Faunal pools represent different biogeographic scenarios from whichcommunities are sampled and care must be taken in choosing their appropriate size(W illig and Moulton, 1989). Know ledge of species distributions is incomplete(Patterson, 1994). Moreover, temporal heterogeneity and rescue effects probablyimpart a dynamic nature to distributional boundaries. Faunal pool 0 in thesesimulations almost certainly includes potential invaders of contemporary feeding guilds.Furthermore, faunal pools 1 and 2 probably correspond to potential pools occurring inthe ecological time of a contemporary community. From an ecological perspective,45


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however, species pools 3 and above probably are unrealistic and provide little insightinto contemporary sources of colonists. These pools undoubtedly contain species that,because of biogeographic and ecological barriers, lack the potential to invade thecomm unity. Nonetheless, the identity of the faunal pool that is the most appropriateremains uncertain, and an exhaustive scheme most likely minimizes the possibility ofderiving false conclusions. Results from all pools regarding either communities orfeeding guilds were similar. In most cases, increasing the size of faunal poolsincreases the number of candidate species for assembly into random communities, yetno consistent trend in P-values with increased faunal pool size was detectable and littlechange in P-values existed between the largest and smallest faunal pool.

Competitive interactions are density-dependent phenomena (Begon et al.,1990). Moreover, environmental variability and stochasticity can prevent populationsfrom approaching carrying capacity, and thus mediate the degree of density-dependence(Andrewartha and Birch, 1954, 1988; Chesson, 1988). To these ends, it is reasonablethat differences exist in the degree to which nonrandom morphological pattems occurand these differences may be a product of climatic differences among sites. Althoughdeterministic structure occurred in all biomes sampled, no conspicuous pattems existregarding w hich w ere likely to giveriseto deterministic stmcture.

Three feeding guilds (aerial insectivores, fmgivores, and nectarivores) exhibitedfairly ubiquitous deterministic structure at all locations, whereas the molossidinsectivore guild ubiquitously exhibited stochastic stmcture. Fmgivores exhibitedmorphological pattems that were more even than were those in faunal p ools, whereasaerial insectivores, gleaning animahvores, and nectarivores were characterized bystatistically large segment lengths. Fmgivores never exhibited mean segment lengtiisthat were unusually large, and nectarivores never exhibited variances that wereunusually small. The m orphological diversity of these groups may be constrained byother phenomenon, and the assembly of species into these guilds is determined46


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consistentiy by only one attribute: either the mean distance or the variability of thedistances between sp ecies.

Despite the detection of deterministic stmcture in many situations, nonrandommorphological pattems were not ubiquitous. The spatio-temporal circumstances inwhich com petitive interactions manifest as morphological pattems may be fairlyrestrictive. For size assortment to be pervasive in a community, com petitiveinteractions must be strong, include m ost if not all species, and be persistent (Moultonand Pimm, 1986). Considerablefluctuationsn resource levels or climatic conditionsoccur in many environments. If narrow spatio-temporal, climatic, or resourceconditions are necessary for the manifestation and persistence of size assortment, thenmuch of the observed lack of significance may indicate appreciable environmentalvariability.

Morphological pattems within feeding guilds may be the result of eitheradaptation by constituent species or evidence that community assembly has reachedequilibrium (Case and Sidell, 1983; Strong et al., 1979). The explanation for theoccurrence o f both of these phenomena is usually based on an evolutionary time frame.Bats are highly mobile organisms (Hill and Smith, 1984; Rayner and Norberg, 1987;Thomas, 1987); they may be present in a community at one time but absent at others(Bonaccorso, 1975). Morphological pattems may exist only when resource levels arelow , during which tim es competitive interactions are most intense, and only corespec ies persist within the community. At othertimes,when resources are bountiful,competitive interactions may not be intense, and invading species may occur withincommunities; when this occurs, deterministic pattems in morphology w ill not bedetectable. Evaluating community stmcture in a number of communities through manyyears, as well as at various times of the year (such as during the dry season and wetseason), would be a good means to test this hypothesis.

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Hyperdispersion in morphology was detectable in many situations, and waspervasive in som e feeding guilds and within some communities. Nonetheless, thesepattems lack ubiquity. Morphological pattems are not the only way in whichcompetitive interactions can be detected at the community level. Pattems regardingother consequences of competitive interactions may appear in the absence of sizeassortment, and may serve to be more consistent or informative metrics (see ChapterIV).

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Figure 3.1.-- Graphical representation of a minimum spanning tree (MST). MSTsconnect N points with N-1 line segments. Dots represent the centroid of speciesattributes in morphological space, whereas line segments represent the magnitudeof the differences between nearest neighbors. PCI and PC2 are axes summarizingthe morphological relationships of species in multidimensional space.

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Figure 3 .2.-- Graphical representation of faunal pools. The sohd dot represents thelocation of a hypothetical comm unity. Faunal pool 0 corresponds to all species whosedistributions overlap the hypothetical community. Faunal pools 1, 2, 3 ,4 , and 5correspond to the set o f all species w hose distributions fall in concentric rings 1, 2, 3,4, and 5, respectively. Concentric rings 1, 2, 3 ,4 , and 5 have diameters of 500, 1000,2000 ,4 000 , and 8000 kilometers, respectively. Faunal pool 6 corresponds to allspecies of bats from the mainland of the New World.

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Figure 3.3.~ Graphical representation of the null hypothesis regarding meanminimum spanning tree (MST) segment lengths. The probability density functionrepresents a randomly generated distribution of m eans from 500 M STs. If theobserved mean (dot) in a feeding guild is larger than 90% of means from therandomly-generated distribution, then species in the feeding guild areecom orphologically hyperdispersed and the feeding guild is stmctured bydeterministic processes.

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Figure 3.4 .-- Graphical representation of the null hypothesis regarding the variance ofthe minimum spanning tree (MST) segment lengths. The probability density functionrepresents a randomly generated distribution of segment variances from 500 MSTs.If the observed segment variance (dot) in a feeding guild is smaller than 90% ofvariances from the randomly-generated distribution, then species in the feeding guildare ecom orphologically hyperdispersed and the feeding guild is stmctured bydeterministic processes.

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CHAPTER IVCOM MUN ITIES, INTERACTIONS, AN D THE LACK OF

COMPETITIVE EXCLU SION: A SYNOPTICEVALUATION OF DENSITY COMPENSATION

AbstractEcom orphological approaches are a popular means of inferring resource

utiUzation, ecological interaction, and ultimately, the stmcture of naturalconm iunities. Traditionally, ecologists have explored hyperdispersed m orphologicalpattems as a means of identifying competitively induced deterministic stmcture.Recent research, however, has been equivocal in identifying nonrandommorphological pattems within comm unities. Alternative approaches for identifyingdeterministic stmcture must be explored to assess if com petitive interactionsconsisten tly affect organization. Density compensation is the phenomenon wherebythe abundances of species depends upon morphological relationships with other taxain a feeding guild. Close competitors, evinced by morphological similarity, shouldexhibit lower abundances because of increased competitive affects. As aconsequence, a statistical relationship should exist whereby the morphologicaldistance of species is positively correlated with its abundance. Density compensationexists w ithin bat feeding guilds and comm unities. Nonrandom pattems in abundanceand morphology were detected in seven conununities, in three feeding guilds, and forthree com petitive scenarios. Nonetheless, density compensation is neither a pervasivenor consistent attribute of community or guild organization. These data add to newinformation suggesting that no one measure of stmcture pervades all communities.Future studies should be directed at environmental gradients in order to understand

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the circum stances that promote or deter the production of nonrandom pattems incommunity organization.

IntroductionEcomorphological approaches in community ecology have become a popular

avenue to explore pattems that explain the coexistence of sympatric species (Findley,1993, 1976; Findley and Black, 1983; Hespenheide, 1973; Mares, 1976; Ricklefs andM iles, 1994; Smartt, 1978; Wainwright and Reilly, 1994). Reasons for theirpopularity are num erous. The mensural nature of morphological attributes yieldsquantitative data that can be scmtinized and manipulated from a statistical standpoint.Thus, more quantitative tests o f hypotheses ultimately provide morerigor nevaluating variation within and among species (Blackith and Reyment, 1971; Rohlf,1990).

Morphological variation is a populational attribute molded by natural selectionto produce phenotypic optimization (Darwin, 1859; Endler, 1986). As a result, themorphological phenotype has become a standard metric to evaluate fitness andultimately the evolution of organisms (Clarke, 1995; Jones, 1987; Leary et al., 1984;Palmer and Strobeck, 1986). Furthermore, morphology may be among the mostimportant phenotypic attributes relevant to the ecology of organisms (Wainright andReilly, 1994); implications are profound. A species ability to invade a community,and hence occur in a given area, is dependent on its morphology (Brown, 1981;Drake, 1990; Fox, 1989; Hutchinson, 1959; Law and Morton, 1993). Consequently,morphological attributes of species play important roles regarding conmiunitycomposition and stability, and ultimately affect community equilibria (Drake, 1990;Fox , 1989; Huston, 1994; Hutchinson, 1959). As such, ecomorphological approaches

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are integral in understanding higher order ecological phenomena (F indley, 1976;Findley and Wilson, 1982; Mares, 1976; Wainright and Reilly, 1994).

At the center of theory addressing community organization lies the notionthat, via optimization, natural selection drives the morphological attributes of speciespopulations to diverge within communities (Case and Sidell, 1983; Cody andDiam ond, 1975; Hutchinson, 1959; MacArthur and Levins, 1967). Morphologicalcharacteristics are important in the consumption of resources (Bonaccorso, 1975;Brown and Lieberman, 1973; Dayan and Simberioff, 1994; Findley and Black, 1983;Findley and W ilson, 1982; Freeman, 1981, 1984, 1988, 1992; Hespenheide, 1973;Smartt, 1978 ), and for species to coex ist, there should be a limit to morphologicalsimilarity (Abrams, 1983; MacArthur and Levins, 1967). If two species are similar,the resources they consume will be similar, and they should compete with suchintensity that interactions culminate in local extinction or morphological shifts o f oneor both species. From a community perspective, morphological optimization occurswhen sympatric species exhibit hyperdispersed morphologies that minimizeinterspecific competition (Cody and Diamond, 1975; Case and Sidell, 1983;Hutchinson, 1959; MacArthur and Levins, 1967; Moulton and Pimm, 1986).

The documentation of hyperdispersions along putatively importantmorphological axes is commonplace for many taxa in many contexts (see Simberloffand Boeklen, 1981 , for a review). Nonetheless, an equal mass of evidence fails tosupport hyperdispersions (Connor and Simberloff, 1978, 1979; Simberloff andBoeklen, 1981; W illig and Moulton, 1989). Such equivocal results could be the resultof either of tw o aspects of competitive interactions: (1) species within feeding guildsdo not compete at all locations, or (2) competitive interactions lack the intensity togovern the central tendency of morphological attributes of species in all cases.

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Hyperdispersions probably manifest as population densities approach carryingcapacity. For exam ple, to cause size assortment, competitive interactions must beintensive enough to produce local extinction, extensive enough to affect all speciesutihzing a limiting resource, and these effects must predominate at a specific locality;no other influences, such as disturbance or predation, may supersede the importanceof competitive interactions (Moulton and Pimm, 1986). Nonetheless, manypopulations never approach carrying capacity and density-dependent phenomena arecircumvented by factors such as environmental stochasticity, seasonality, parasatoids,or predators (Andrewartha and Birch, 1954, 1988; Petraitis et al., 1989; Strong,1984). Com petitive exclusion may not occur in these communities.

Demonstration of hyperdispersions along morphological axes need not be theonly indication of stmcture induced by competition. Density compensation also mayexist within feeding guilds (Hawkins and MacMahon, 1989; Root, 1973). Densitycompensation is the phenomenon whereby the total abundance of individuals of allspecies within a feeding guild tends toward a maximum density set by theenvironment. The distribution of abundances of constituent species, however, isdependent upon their relationships with other guild members. Those species thatexperience the greatest comp

Documents

Eco Morphological Structure of Bat Communities