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CURRENT PROBLEMS OF ECOSYSTEM ECOLOGY
AND BIODIVERSITY THEORYJanuary Weiner
Jagiellonian University
CURRENT PROBLEMS OF ECOSYSTEM ECOLOGY AND
BIODIVERSITY THEORY
COMMUNITYBIODIVERSITY
HOW MANY SPECIES MAKE AN ECOSYSTEM?
CO2
(CH O)2 n
REDUKCJAtylko Ŝyweorganizmy
UTLENIANIEorganizmy: szybkoprocesy abiotyczne: powoli
energiaenergia
DEPOZYCJA(ocean, osady)
DEPOZYCJA(złoŜa paliw)
OXYDATION:organismsabiotic processes
REDUCTION:living organismsonly
DEPOSITION: fossil fuels
energyenergy
DEPOSITION:(ocean, sediments)
Life of the biosphere = redox cycle of C
How many species are necessary?How many species can coexist?
Taxonomic composition of ecosystems (communities) –regarding biomass or number of species Heterotrophic single-species
ecosystem
Heat
Offspring
Oxidizedsubstrate
Reduced substrate
A two-species ecosystem
Heat
Oxidized substrate
Reducedbiomass
OXIDIZER(CONSUMER)
REDUCER(PRODUCER)
Energy
RECYCYLING
A multi-species ecosystem
HeatEnergy
competitionpredationparasitismmutualism
CRYPTOENDOLITHIC ECOSYSTEM FROMANTARCTIC OASIS
Biomass: 125 g/m2
(Woodward 1994)
TWO SPECIES-POORSUBANTARCTICECOSYSTEMS
(Woodward 1994)
Forest Soil Ecosystem Functioningwith regard to biotic diversity
• The Siemianice Experiment
The SiemianiceExperimental
Forest
Taxon No. sp. Spring Autumn
Scarabeidae ? 1149 326
Carabidae 58 6609 1351
Staphylinidae 97 3186 3968
Curculionidae ? 6858 902
Other Coleoptera ? 2184 549
Coleoptera larvae ? 691 404
Formicidae 12 1970 1537
Other Hymenoptera ? 991 604
Hymenoptera larvae ? 22 82
Lepidoptera larvae ? 132 39
Other Lepidoptera ? 129 4
Dermaptera ? 772 292
Other Insects ? 1208 301
Aranea 128 13997 1987
Opilionida 8 1811 4026
Acarina ?? 2546 351
Pseudoscorpionida 2 80 92
Chilopoda ? 649 168
Diplopoda ? 966 2357
Isopoda ? 9 43
Lumbricidae ? 48 7
Total 46007 19390
Total predators >300 65397
Number of speciesand individuals
in the samplesof epigeic fauna
in 30-y oldforest monocultures
(Siemianice)
PREDATORS
Total number of speciesin a wood: ≈ 103
FUNCTIONAL REDUNDANCY(WITHIN-GUILD SPECIES RICHNESS)EXAMPLE: CORAL FISH
Heron Island Reef (Australia): > 900 fish species © jw
FUNCTIONAL REDUNDANCY(WITHIN-GUILD SPECIES RICHNESS
EXAMPLE: RAIN FOREST
Amazon (border of Venezuela and Brasil): 580 trees of 283 species/1 ha (Gentry
Borneo: 1175 tree species/52 ha
Number of tree species per hain rain forests of different continents
Primack i Corlett 2005
Hutchinson, G. E. (1961) The paradox of the plankton. American Naturalist 95, 137-145.
„PARADOX OF THE PLANKTON ”
Scheffer, M & al. (2003) Why plankton communities have no equilibrium: solutions to the paradox. Hydrobiologia 491, 9-18.
1. Numerous phototrophicfreshwater plankton species coexisting inhomogenous environment
2. A few & scarce commonlyexploited resources
BIODIVERSITY PARADOX(Hutchinson’s „paradox of the plankton”)
• Extravagant number of species in ecosystems
• Apparent functional redundancy
• Limited resources
• Competition
• Competitive exclusion principle (Gause’s Law)HOW A COMMUNITY IS
ASSEMBLED?
LOCALCOMMUNITY
LIMBOSPECIATION EXTINCTION
SPECIESPOOL
evolutionarytime scale
„ ASSEMBLYRULES”
habitat filteringdispersal constraints
interactions
ecologicaltime scale
history = chance
LOCALCOMMUNITY
LIMBOSPECIATION EXTINCTION
SPECIESPOOL
evolutionarytime scale
„ ASSEMBLYRULES”habitat filtering
dispersal constraints
interactions
ecologicaltime scale
history = chance
Habitat preference
Explaining community assemblywith gradient analysis
(Whittaker)
Classical analysis ofplant communities inGreat Smoky Mountains,Tennessee (Whittaker 1956)
Species numbers distribution oftrees in moisture gradient
Distribution of speciesof grasses in pHgradient
Distribution ofmacrofaunal speciesalong oyster bed inCanada
Spatial patterns of the substrate determinewhether communities substitute each othergradually or sharply.
NICHE
ECOLOGICAL NICHE:
• GRINNEL (1917): set of species characters*that enable survival and reproduction when competing with other species.• ELTON (1927): Species position („role”) in biotic environment, determined by interactions with the otherspecies
- ODUM (1959...): „occupation of a species”• MacFadyen, HUTCHINSON (1957): a hypervolumein a multidimensional space of resources
*adaptations
ECOLOGICAL NICHE(HUTCHINSON)
niche overlap
realized niches
Morphologic nichesof passerine birdspecies(Ricklefs &Travis 1980, after Morin 1999PCA, 8 traits, 83 species
Morphological niche:a substitute for theecological niche
The use of multivariatestatistics
Niches of the pairs of Anolis sp. lizards on two islands. Realized niches’ dimensions were estimated as averages ±SD
Pacala & Roughgarden 1982
Niche separationin warblers(classical example by MacArthur, 1958)
A – Dendroica coronataB – Dendroica tigrinaC –Dendroica virensD – Dendroica fuscaE –Dendroica castanea GAUSE’S
EXPERIMENT
Populations separated
Competitive exclusion
Coexistence
Lotka – Volterra model of competition
LOCALCOMMUNITY
LIMBOSPECIATION EXTINCTION
SPECIESPOOL
evolutionarytime scale
„ ASSEMBLYRULES”habitat filtering
dispersal constraints
interactions
ecologicaltime scale
history = chance
Limited similaritySpecies packing
Equilibrium
Limited similaritySpecies packing
Equilibrium
Diamond 1975
COMPETITIVE RELEASE GALAPAGOS
Isabela
Fernandina
San Cristobal
Santa Maria Espanola
Pinta
Marchena
San Salvador
Los Hermanos
Santa Cruz
Santa Fe
Pinzon
Genovesa
Rabida BaltraDaphne
„Darwin finches”
1. Geospiza magnirostris
2. Geospiza fortis
3. Geospiza parvula
4. Certhidea olivacea
Geospiza fuliginosa
Geospiza fortis© Wikipedia
© Wikipedia
CHARACTERDISPLACEMENT
IN GeospizaFINCHES
Lack 1947Bill height (mm)
% in
sam
ple
„Darwin’s finches”
Jonathan Weiner
„The beak ofthe Finch.
A story of evolution
in our time”.
1994REGULAR DISTANCES IN BODY SIZEOF COEXISTING SPECIES
RODENTS(CALIFORNIA)
PIGEONSNew Gwinea
METHODOLOGICAL CONTROVERSIES
after Schoener, 1984
species size ratio greater/smaller.
FR
EQ
UE
NC
Y
expected
observed
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
0.015
0.1
0.05
LIMITED SIMILARITY PRINCIPLE (Hutchinson 1959)SCHOENER’S EXAMPLE, 1984 (Accipiter sp.)
FREQUENCY DISTRIBUTION OF SPECIES PAIRS
NULL MODELS
„Limited similarity”: different phenomena
• Niche separation (e.g. size ratio) = character assortment(existing species are sorted out)
• Character displacement = character adjustment(within species evolution) [Case, 1983]
• If characters are genetically fixed = „ghost of competition past” [Connel]
• Can be distinguished with molecular methods
• Niche realized vs. potential = behavioral effect (fully reversible)
• Similar (related) species should exclude each other competitively
• Similar (related) species have similar abilities to cope with a given environment, thus should tend to co-occur
• Evidence: both patterns occur
Niche theory:contradicting predictions
„Community assembly rules”(Diamond 1975)
LOCALCOMMUNITY
LIMBOSPECIATION EXTINCTION
SPECIESPOOL
evolutionarytime scale
„ ASSEMBLYRULES”habitat filtering
dispersal constraints
interactions
ecologicaltime scale
history = chance
A „checkerboard” distribution of 2 pigeonsPtilinopus sp. on islands close to New Guinea
(Diamond 1975)
„Assembly rule” or chance distribution?
Ptilinopus porphyrea
“Incidence function”
Birds in Bismarck archipelago; J = probability of occurrence of a given species on an island with S speciesA – only on the islands with many species.B – only on the islands with few species („tramp”, „super tramp”)Diamond 1975
Community interactions
• Not only competition• Predation & herbivory (!)
• Mutualism (!!)• Real communities are shaped by all interactions
(theoretical models are restricted to selected ones)
• Verification : measuring relative effect („importance”) of a species for the community (removal experiments etc.)
• Surrogate: dominance structure, diversity indices
Distribution of bird species numbers in a150-y oldoak-hornbeam forest in Niepołomice
Histogram(distribution density)
Cumulative distribution
Rank order plot („Galton ogive”) Models fitted:
„broken stick”geometric series
Number pairs per ha Number pairs per ha
Cum
ulat
ednu
mbe
rof
spec
ies
Num
ber
ofsp
ecie
s
Species numbers distributionin three communities studied
breeding forest birds
plants of deciduous forest herb layer
plants of subalpine fir forest
Species numbers distributionin three communities studied
breeding forest birds; broken stick
plants of deciduous forest herb layer;log-normal
plants of subalpine fir forestgeometric series GEOMETRIC SERIES
log nx = b – axnx = kx ×n1
Each species in rank gets a constant fraction ofresources taken by the previous one
„BROKEN STICK”S random fractions of resources used (‘a stick broken in S-1 random places’)
Breeding birds, 150-y. old oak-hornbeam stand NIEPOŁOMICE
0.001
rela
tive
popu
latio
nde
nsity
, n/N
species rank
1.0
0.1
0.01
„BROKEN STICK”
GEOMETRIC SERIES
one-parameter indices
DistributionDistributionDistributionDistribution ofofofof individualsindividualsindividualsindividuals amongamongamongamong speciesspeciesspeciesspecies
S = 12N = 84
S = 12N = 84
DIVERSITYDIVERSITYDIVERSITYDIVERSITY INDICESINDICESINDICESINDICES
H’= 0,702 H’ = 2,485H’ = Σ (pi × log pi)
S
i=1
Limited similaritySpecies packing
Equilibrium
„EQUILIBRIUM COMMUNITY” – DENSELY „PACKED”
DO “EMPTY” (VACANT) NICHES ERXIST?
COMMUNITY SATURATIONIf local communities are unsaturated, their species richness linearly rises withregional diversity
[Krebs 2009]
SURVEY OF 9 TAXONSACROSS CONTINENTS(Caley & Schluter 1997):no evidence of localcommunities saturation
Evidence for empty niches
• Cosmopolitic species (e.g. ferns) may exploit resources (or be exploited) invarious ways in different regions;
• Invasive species may thrive in new communities without interfering with natives (many plant species)
A roadside bush full of invasive, American species(Bolechowice near Kraków)
A roadside bush full of invasive, foreign species(Bolechowice near Kraków)
Erigeron annuus
Solidago sp.
Reynoutria japonica
Rhus typhina
Limited similaritySpecies packing
Equilibrium
Two general approaches:
• equilibrium models: community stability, biotic coupling, competition; constant community composition, resilience; saturated; resource limitation, density dependence, optimality [?]
• nonequilibrium models: stochasticity, species independence; continuous recovery from perturbation. biotic decoupling, abiotic limitation, density independence, unsaturation, opportunism
• Real communities form a continuum, no pure examples of „equilibrium
Properties of an equilibrium community (globally stable)
• Conservation: no species losses (except strong perturbations – then recovery)
• Recovery (any community constituent disturbed will recover)
• Composition (community made up by immigration, combination of species increases up to equilibrium)
• Independence of history (past event unimportant, after sufficient time the same equilibrium state is assumed)
H. Remmert, „Oekologie”, 1980
„BALANCE OF NATURE”
University of Chicago PressChicago, 1991
?
Princeton University PressPrinceton, 2009
„Ecology’senduring myth”
Cambridge University Press, 2005
Non-equilibrium community
• Patchiness: small scale local patches can never be at equilibrium.
• Disturbance– there is no „normal” situation; conditions are
transient, fluctuating, under continuous disturbances (changes in community structure, function, availability of resources, physical environment, etc).
– differing in strength and frequency.
Classical example: coral reefs Classical example: coral reefs• „Geologically stable” (no change in 200 000 y)• In ecological time scale: unstable!• Connel (1997): 30 y. observation of one reef. 5
hurricanes.• Continuous changes due to external disturbances• Extremely high fish species diversity• Alternative explanations
– equilibrium (niche diversification hypothesis, competition, predation)
– non-equilibrium (variable recruitment hypothesis = stochastic larval recruitment success – random sample from species pool.
Hypotheses testing (falsifications)• Niche specialization/generalization
– Several sp. in one niche common
– Great habitat overlap
– Experiments with artificial „reefs” – random species composition (32% similarity only; high turnover rate in time)
• Variable recruitment– At high recruitment rates density dependence occurs,
various experiments equivocal
– „Competitive lottery” (who comes first)
Feeding specializations among 20 species ofbutterfly fishes (Chetodontidae) on a coralreef at Lizard Island (Great Barrier Reef, Australia)
[Anderson et al. 1984; after Krebs 2009]
Soft coral
Hard coral
Threadfin ButterflyfishChaetodon auriganon-corrallineinvertebrate eater
© JW
Red SeaChaetodontidae: 120 species in 10 genera; mainlyindo-pacific, many species cosmpopolitic
C. aureofasciatus
C. baronessa
Hard coral
C. plebeius
C. ornatissimus
C. rainfordi
GeneralistsNoncorallineinvertebrates
Soft coral andsome hard coral
C. citrinellus
C. ephippium
C. trifasciatus
C. ulietensis
C. vagabundus
C. auriga
C. trifascialis
Chelmon rostratus
Forcipiger falvissimus
C. kleinii
C. lineolatus
C. melannotus
C. speculum
C. unimaculatus
C. aureofasciatus
Ch. baronessa
Hard coral
C. plebeius
C. ornatissimus C. rainfordi
Soft coral and some hard coral
C. unimaculatus C. kleinii
C. melannotushttp://www.ryanphotographic.com/chaetodontidae.htm
C. lineolatus
C. speculum
Noncoralline invertebrates
C. auriga
Chelmon rostratus Forcipiger sp. (falvissimus)
C. trifascialis
http://www.animalpicturesarchive.com/ArchOLD-7/1203985664.jpg
http://www.ryanphotographic.com/chaetodontidae.htm
C. ulietensis
Generalists
C. citrinellus
C. ephippium
C. vagabundusC. trifasciatus
Each feeding specialization may be represented by several species
(niche overlap)
Feeding specializations among 20 species of butterfly fis hes(Chetodontidae) on a coral reef at Lizard Island (GreatBarrier Reef, Australia)
[Anderson et al. 1984; after Krebs 2009]
Models of non-equilibrium communitiesChesson and Case 1986; Krebs
• Fluctuating environment models– competition is major interaction, but external
fluctuations alternate the competence ranking
• Density-independent models– competition rare; chaotic population dynamics
• Directional changing environment models– long term trend in environmental fluctuations; history
is important.
• Slow competitive displacement models– competition acts, but very slowly (small differences
in competence); chance and history
How community persistence can be explained?
• Patchiness – „metacommunity”
• Non-equilibrium prevents competitive exclusion;
• HSS (1960) and trophic cascade: the role of competition depends on trophic level.
• Multiple stable states –quasinon-equilibrium
• Intermediate disturbanceLOCAL
COMMUNITY
LIMBOSPECIATION EXTINCTION
SPECIESPOOL
evolutionarytime scale
„ ASSEMBLYRULES”habitat filtering
dispersal constraints
interactions
ecologicaltime scale
history = chance
LOCALCOMMUNITY
LIMBOSPECIATION EXTINCTION
SPECIESPOOL
evolutionarytime scale
„ ASSEMBLYRULES”habitat filtering
dispersal constraints
interactions
ecologicaltime scale
history = chance
Theory of island biogeography
• Radical deviation from „niche assembly”
• Neutral, stochastic model
„Dispersal-assembly perspective”
Island biogeography model of MacArthur & Wilson
bliska
daleka
mała
duŜa
Imm
igra
tion
rate
Ext
inct
ion
rate
Number of species
near
distant
small
large
BARRO COLORADO ISLAND on PANAMA CHANNEL
Andes de Merida; El Baho, ok. 2400mEXTRAVAGANT NUMBER OF COMPETINGSPECIES: DIFFERENT NICHES???
ABUNDANCE DISTRIBUTION OF TREE SPECIES IN A 50-ha LTER PLOT
BARRO COLORADO ISLAND (BCI) IN PANAMA
Volkov et al.. 2004
Hubbell 2005DISPERSAL LIMITATIONSEEDS OF TROPICAL TREES
200 seed traps, seeds identified every week during 10 yearsOnly 12 species in 50% traps. 50% species ≤ 5 seeds.
Hubbel’s neutral theory of diversity
• Concerns guilds
• Limited resources, community saturated with individuals
• Principle of equivalence od individuals regarding „vital” parameters (b, d, m)
• At metacommunitylevel: speciation and extinction
• „Ecological drift” (zero sum)
• Full analogy with genetic drift
• Predicts:– „Rank abundance” patterns
– Species-area curves
– Beta diversity patterns
• Contradicts some facts– Niches are differentiates!
– Often does not fit empirical data
• May constitute a null hypothesis
• Needs a reconciliation with niche theory
Hubbel’s neutral theory of diversity