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