Ecological communities

A community is a local assembly of species that potentially interact.

Generally these species are on the same trophic level.

A community of species with similar niches is called an ecological guild

Examples of ecological communities

Insect eating birds in a forest.Fish in a pond.Butterflies on a meadow.

Counter examples

Birds in a forest form an assemblyAphids and Ladybeetles are on different trophic levels.Fish in an archipelago form meta-communities.

Assembly

CommunityGuild

Examples of communities

Plant visitors and pollinators Nepenthes pitcher plants

Deep sea bacterial communities

Calcareous grassland

Assemblages but not communities

Mutual effects of species interections:

Direct effects refer to the impact of the presence (or change in abundance) of species A on species B in a two-species interaction.Indirect effects refer to the impact of the presence (or change in abundance) of species A on species C via an intermediary species (A --> B --> C).Cascading effects are those which extend across three or more trophic levels, and can be top-down (predator --> herbivore --> plant) or (plant --> herbivore --> predator).Keystone species are those which produce strong indirect effects.

The starfish Pisaster predates on Mytilus mussels and makes space for many other species to colonise. The top predator Pistaster is a keystone species.

Kelp (brown algae) forest

Sea urchin (Echinus)

Sea otter (Enhydra)

Fisherig

__+_

_

Community

Global species pool

Regional species pools

Local species pools

Isolation filter

Abiotic filters

Abiotic filters Abiotic

filters

Abiotic and isolation filters at different spatial scales determine local species composition

Members of single communities pass these filters.

The distribution of species abundances

Relative abundances in a sequence of plant succession (Bazzaz 1975)

In natural comunities species abundances often differ by factors of more than 1000.That means that the most abundant species are 1000 times more abundant than the

rare species

Rank – abundance plot

Power function SAD Log-series SAD

Log-normal SAD

Log

abun

danc

e

Log

abun

danc

e

Log

abun

danc

e

Three types of relative abundance distributions (SAD)

𝑁=𝑒−𝑎×𝑛𝑜𝑟𝑚 (0,1)

𝑁=𝑁 0𝑖−𝑎

Species rank order i Species rank order i

Species rank order i

𝑃 (𝑁 )=𝛼 𝑋𝑛

𝑛P(N) is the probabiity that a species has exctly N individuals

Frank W. Preston (1896-1989)

Robert May of Oxford(1938-)

Ronald A. Fisher (1890-1962)Heavy tail

Power function SADLo

g ab

unda

nce

𝑁=𝑁 0𝑖−𝑎

Species rank order i

Parasitic Hymenoptera in a beech forest

Heavy tail

Power function SADs • have a high number of rare species (heavy

tail)• are input (colonization) driven

have a high degree of species turnover• often characterize species assemblages but not

true communitieshave a small number of very abundant species

• lack a larger number of intermediate abundant species

Examples• Incomplete samples• Arthropod assemblages• Disturbed habitats

Log-series SADLo

g ab

unda

nce

Species rank order i

Northern German Grassland spiders (Finch 2001)

The log series is a sample distribution. It describes the expected abundance of species in a sample from a large community. It applies to assemblages.

For fully censused assemblages it occurs most often• at early stages of succession• in disturbed habitats• in heterogeneous assemblages

𝑃 (𝑁 )=𝛼 𝑋𝑛

𝑛

Examples• Incomplete samples• Heterogeneous assemblages• Large arthropod samples

Log-normal SAD Lo

g ab

unda

nce

𝑁=𝑒−𝑎×𝑛𝑜𝑟𝑚 (0,1)

Species rank order i

Beetles in a Norwegian spruce forest (Ottesen 1996)

Lognormal SADs are derived from the central limit theorem of statistics that predict normal distributions

veil line Lognormal distributions occur most often in• closed and stable communities• undisturbed habitats• K- species dominated communities• Communities influenced by a large number

of divergent environmental factors.

High number of species with intermediate

abundance

Breeding birds of Ohio (Hicks 1935)

Often the distribution is not symmetrical having an excess of rare species.

𝑆=𝑆0𝑒−𝑎𝑅2

Diversity and evennness

A measure of diversity is the number of species

Abun

danc

e

Species

Abun

danc

e

Species

𝐻=1

∑1

𝑆

𝑝𝑖

Simpson index of diversity

𝐻=−∑1

𝑆

𝑝𝑖 ln ¿¿

Shannon index of diversity

𝑆=𝐻𝑙𝑛(1+𝑁𝐻

)

Log-series index of diversity

Evenness

𝐸=𝐻𝑙𝑛𝑆

Diversity indices are measures of encounter probability

High evenness

Lower evenness

Alpha, beta and gamma diversity

Alpha diversity refers to the local number of speciesBeta diversity refers to the change in species composition among local habitatsGamma diversity refers to the regional species pool

Area

Spec

ies

richn

ess

a

g

b

Multiplicative partitioning of diversity

Additive partitioning of diversity

𝑦=𝛼 𝐴𝛽

Beta diversity is a measure of regional habitat diversity

Species interactions or neutrality

Stephen P. Hubbell (1942-

Motoo Kimura (1924-1994)

Neutral models lack any specific biological interaction like competition, mutualism, regulation, species specific survival.

Individuals are grouped to evolutionary lineages

Species are ecologically equivalent

0 0 0 0 0 0iJ J iJ bJ eJ dJ J Zero sum multinomial

BirthDeath

Pool of individuals

Random migration

Neutral models are individual based! Ecological drift

J is the total number of individuals

Neutral models provide ecological expectations without species interaction

Mutations

1

10

100

1000

10000

0 5 10 15 20 25 30Rank order

Abun

danc

e

Core species

0.1

1

10

100

0 5 10 15 20 25 30Rank order

Abun

danc

e

Satellite species

Neutral models make explicit predictions about

Abundance rank order relationships

Diversity and evenness

Ground beetles on lake islands in Lake Mamry (Ulrich and Zalewski 2007)

Leistus rufomarginatusPhotos by Roy Anderson

Neutral models make explicit predictions about

Regional diversity patterns

0

5

10

15

20

25

30

35

1 2 4 8 15Sites occupied

Spec

ies

Ground beetles on lake islands in Lake Mamry (Ulrich and Zalewski 2007)

Dyschirius globosus

Core and satellite species

Observed Predicted

Observed

Predicted

Ecological gradients and the classification of communitiesSpecies 1pog 2pog 3pog dab ful gil guc hel kor lip mil sos swiPterostichus melanarius 0 36 13 17 187 345 60 169 1199 704 394 428 13Pterostichus oblongopunctatus 0 2 7 135 83 188 11 8 1019 180 4 141 1Pterostichus niger 0 0 3 0 191 167 135 0 137 0 0 530 3Oxypselaphus obscurus 1 0 27 96 27 166 80 0 96 7 48 278 0Harpalus 4-punctatus 0 41 17 9 29 77 0 67 555 69 0 9 0Carabus granulatus 0 11 52 11 12 110 25 11 154 113 0 59 1Patrobus atrorufus 0 6 22 81 11 348 9 0 11 37 0 35 2Pterostichus antracinus 11 1 0 0 0 21 1 11 2 2 274 0 0Platynusas similis 0 7 25 4 48 39 2 9 76 117 0 9 0Pterostichus nigrita 30 2 2 5 1 58 1 0 0 2 39 18 0Carabus hortensis 0 0 0 0 75 52 109 0 0 0 0 0 0Pterostichus strennus 0 5 3 47 13 30 5 6 28 24 22 14 4

Ground beetles from Mazuran lake lands

SpeciesPterostichusmelanariusPterostichusoblongopunctatus(Fabricius)Pterostichusniger(Schaller)Oxypselaphusobscurus(Herbst)Harpalus4-punctatusDejeanCarabusgranulatusPatrobusatrorufus(Stroem)PterostichusantracinusPlatynusassimilis(Paykull)Pterostichusnigrita(Paykull)CarabushortensisLinnaeusPterostichusstrennus(Panzer)Pterostichusmelanarius0 787.7 1363 1393 1122 1359 1494 1515 1442 1541 1550 1518Pterostichusoblongopunctatus(Fabricius)787.7 0 1004 955.5 530.5 887.8 1040 1101 975.5 1062 1066 1030Pterostichusniger(Schaller)1363 1004 0 327.5 714.1 533.9 591.8 671 586.5 591 571.9 590.6Oxypselaphusobscurus(Herbst)1393 955.5 327.5 0 563.3 281.7 328.9 418.8 344.1 324.4 339 320.4Harpalus4-punctatusDejean1122 530.5 714.1 563.3 0 415.3 618.4 628.2 488 567.8 578 538Carabusgranulatus1359 887.8 533.9 281.7 415.3 0 299.4 354.5 127.5 215.1 239.6 192Patrobusatrorufus(Stroem)1494 1040 591.8 328.9 618.4 299.4 0 438.2 338 307.4 333.9 322.6Pterostichusantracinus1515 1101 671 418.8 628.2 354.5 438.2 0 311.9 239.7 305.9 259.9Platynusassimilis(Paykull)1442 975.5 586.5 344.1 488 127.5 338 311.9 0 157.2 180.7 123Pterostichusnigrita(Paykull)1541 1062 591 324.4 567.8 215.1 307.4 239.7 157.2 0 141.3 72.41CarabushortensisLinnaeus1550 1066 571.9 339 578 239.6 333.9 305.9 180.7 141.3 0 139.6Pterostichusstrennus(Panzer)1518 1030 590.6 320.4 538 192 322.6 259.9 123 72.41 139.6 0

Distance matrix

EV 1 EV 20.648 0.4960.368 0.361-0.059 0.298-0.179 0.2400.036 0.262-0.207 0.218-0.202 0.262-0.218 0.267-0.240 0.228-0.276 0.237-0.264 0.244-0.270 0.232

The first two eigenvectors

Principal component

analysis

Principal component analysis

PCA serves to identify ecological communities

Communities as ecological indicators

Ecological indicators are used to provide information about the state and the functioning of ecological systems.

Indicators might be single species , sets of species or whole communities.

Often used indicators

Anthropogenic disturbance Indicator

Acid rain MossesEutrophication Aquatic macrophytesInvasive species BirdsSedimentation ShrubsLogging Bark beetlesHeavy metals ProtozoaUrbanization Birds, CarabidsAir pollution PlantsAir quality Lichen