CURRENT PROBLEMS OF ECOSYSTEM ECOLOGY AND BIODIVERSITY THEORY January Weiner Jagiellonian University CURRENT PROBLEMS OF ECOSYSTEM ECOLOGY AND BIODIVERSITY THEORY COMMUNITY BIODIVERSITY HOW MANY SPECIES MAKE AN ECOSYSTEM? CO 2 (CH O) 2 n REDUKCJA tylko Ŝywe organizmy UTLENIANIE organizmy: szybko procesy abiotyczne: powoli energia energia DEPOZYCJA (ocean, osady) DEPOZYCJA (zloŜa paliw) OXYDATION: organisms abiotic processes REDUCTION: living organisms only DEPOSITION: fossil fuels energy energy 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 Oxidized substrate Reduced substrate
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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)
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
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