Community Ecology. GeographyResources Phylogeny Community Redrawn from Fauth et al. (1996) Community...

Community Ecology

Geography Resources

Phylogeny

Community

Redrawn from Fauth et al. (1996)

Community – collection of species that occur at the same place & time, circumscribed by natural (e.g., serpentine soil), arbitrary, or artificial (e.g., 1-m2 quadrat) boundaries

Many prefer a more restrictive definition in which species must interact to be included, e.g., Whittaker (1975)

Geography Resources

Phylogeny

Taxon

Taxon – phylogenetically related group of species; a clade

E.g., Mammalian Order Rodentia

Community


Geography Resources

Phylogeny

Community Guild

Guild – a group of species “without regard for taxonomic position” that “exploit the same class of environmental resources in a similar way” (Root 1967)

E.g., granivores

Taxon


Geography Resources

Phylogeny

Community GuildLocalguild

Local guild – a group of species that share a common resource and occur in the same community (Root 1967)

E.g., Sonoran Desert granivores

Taxon


Geography Resources

Phylogeny


Assemblage

Assemblage – a group of phylogenetically related species within a community

Taxon


Geography Resources

Phylogeny


Assemblage

Assemblage – a group of phylogenetically related species within a community

a.k.a. “Taxocene” (Hutchinson 1967)

E.g., Sonoran Desert rodents

Taxon


Geography Resources

Phylogeny

Community Guild

Taxon

Ensemble

Localguild

Assemblage

Ensemble – a phylogenetically bounded group of species that use a similar set of resources within a community

E.g., Sonoran Desert granivorous rodents


Geography Resources

Phylogeny

Community Guild

Taxon

Localguild

AssemblageE.g.,

granivorous rodents,pond-breeding salamanders…

Ensemble

In this course any collection of two or

more species is “fair game” for close

scrutinyRedrawn from Fauth et al. (1996)

“Any set of organisms currently living near each other and about which it is interesting to talk” (MacArthur 1971)

Painting by D. Kaspari for M. Kaspari (2008) – anniversary reflection on MacArthur (1958)

Robert H. MacArthur’s definition of Community

Some historic landmarks

Community Ecology has matured from purely descriptive studies (i.e., description & analysis of patterns) to mechanistic studies (i.e., investigations into processes) that aim to improve our explanatory & predictive abilities

In any case, the tradition of good Natural History is not ignored by the best modern practitioners

Community Ecology

“Though I do not believe that a plant will spring up where no seed has been, I have great faith in a seed. Convince me that you have a seed

there, and I am prepared to expect wonders.” (H. D. Thoreau ~1860)


Community Ecology

Photo from WikiMedia Commons

Charles Darwin (1809 - 1882)

Ernst Haeckel (1834 - 1919) coined “oekologie” for the study of Darwin’s multifaceted “struggle for existence”

Not the first “ecologist,” but clearly recognized the importance of organisms’ interactions (intraspecific, interspecific & with their abiotic environments) for evolution by natural selection


Community Ecology



On biotic interactions:

“Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain

flowers in that district!” (Darwin 1859)


Community Ecology



On abiotic processes, e.g., abiotic disturbance:

“If turf which has long been mown… be let to grow, the most vigorous plants gradually kill

the less vigorous, though fully grown plants; thus out of 20 species growing on a little plot of mown turf (3 feet by 4 feet) nine species perished from the other species being

allowed to grow up freely…” (Darwin 1859)


Community Ecology

Photo from WikiMedia Commons; for further details see Damschen et al. (2005)

Ellen Swallow Richards (1842 - 1911)

Chemist who probably “created and taught the first ecology curriculum” in the U.S. and may have introduced the term “ecology” into the English language (from Ernst Haeckel’s “oekologie”)


Photo from http://home.grics.net...

Stephen Forbes (1844 - 1930)

Community Ecology

One of the earliest ecologists to examine multiple, cross-trophic level interactions simultaneously within an explicitly evolutionary framework

Wondered how in spite of a constant “struggle for existence” some balance is nevertheless maintained in ecosystems (see: The lake as a microcosm, 1887)


Community Ecology

Photo of Cowles from http://oz.plymouth.edu... Photo of Lake Michigan sand dune from http://ebeltz.net...

Henry Cowles (1869 - 1939)

A pioneer of “dynamic ecology,” especially on the sand dunes of Lake Michigan


Community Ecology

In the grand traditions of Alexander von Humboldt (1769 - 1859; the “father of biogeography”) & Alfred Russel Wallace (1823 - 1913)…

Clinton Hart Merriam (1855 - 1942) also noticed that geographic changes in physical conditions often coincide with changes in biota

Merriam devised Empirical Life Zones (similar biotic changes with increased elevation or latitude)


Community Ecology

Leslie Holdridge (1907 - 1999) – devised Theoretical Life Zones (1947)

Image from WikiMedia Commons


Community Ecology

Clements vs. Gleason (1920s & 1930s)

Frederic Clements (1874 - 1945) – thought succession always reached a predictable climax community; viewed communities metaphorically as “superorganisms”

Henry Gleason (1882 - 1975) – proposed the “individualistic concept” of communities; discrete populations whose patterns of distribution and abundance give rise to communities as epiphenomena

Photo from WikiMedia Commons; figures from http://ecology.botany.ufl.edu...


Community Ecology

Robert H. Whittaker (1869 - 1939) His gradient analyses helped end the Clements-Gleason debate


Community Ecology

We continue to need good descriptions of patterns, often supported by sound, quantitative techniques

See: The Ordination Web Page (http://ordination.okstate.edu)

E.g., the Ecological Society of America, The Nature Conservancy, the U.S. Geological Survey, the U.S. National Park Service & others collaborate to continue to refine the National Vegetation Classification Standard (NVCS)

E.g., Bray & Curtis (1957) introduced ordination methods to define plant communities in Wisconsin

http://ordination.okstate.edu/

Photo of Davis from U. Minnesota; photo of pollen from http://www.gl.rhbnc.ac.uk...


Community Ecology

Margaret Davis (b. 1931)Her paleo-ecological perspective hashelped increase awareness of historical contingencies

Photo from UCSB


Community Ecology

Joseph H. Connell (b. 1923)

Heralded as milestones in ecology, his studies demonstrated the utility of field experiments for answering ecological questions; empirically assessed multiple hypotheses for intertidal zonation

The concept of equifinality was formalized by Ludwig von Bertalanffy (1968; founder of General Systems Theory) – multiple hypotheses or mechanisms can equally explain or generate the same pattern


Community Ecology


Observations:

Balanus balanoides – Larger barnacle, generally found lower in the intertidal

Chthamalus stellatus – Smaller barnacle, generally found higher in the intertidal

Photo from UCSB


Community Ecology

Photo from UCSB



Why might these patterns exist?

Community Ecology


Observations:

Balanus balanoides – Larger barnacle, generally found lower in the intertidal

Chthamalus stellatus – Smaller barnacle, generally found higher in the intertidal

Photo from UCSB


Community Ecology


Hypotheses:

Differential physiological tolerances to desiccation and submersion

Interspecific competition

Predation (e.g., Thais lapillus is a predator of Balanus balanoides)

Photo from UCSB


Community Ecology


Exclusion experiments, results & conclusions:

The absence of competitors & predators produced no change in upper level of distributions

For Chthamalus, removing Balanus increased downslope survivorship & distribution

For Balanus, removing Thais increased downslope survivorship & distribution

Photo from UCSB


Community Ecology


Photo from UCSB; figure from Connell (1961; one of Connell’s 5 Science Citation Classics)


Photo from Wikipedia

Community Ecology

Robert H. MacArthur (1930 - 1972)

More than most of his predecessors, MacArthur demonstrated the utility of simplifying assumptions combined with mathematical rigor for exploring ecological problems

Criticisms: oversimplification; over-emphasized competition & equilibria


Community Ecology

G. Evelyn Hutchinson (1903 - 1991)

Photo from Yale Peabody Archives

Conceived of fundamental vs. realizedniche spaces or hyper-volumes

“Ecologists use the metaphor of the ‘ecological niche’ to express the idea that plant and animal species play certain roles in the ecological community” (Kingsland 2005, pg. 1)


Figure from Gotelli & Graves (1996, pg. x)

Community Ecology

G. Evelyn Hutchinson

The idea & disagreement over how to test it helped motivate the development of null models in ecology

E.g., Hutchinsonian ratiosA ratio of ~ 1.3 in size occurs between pairs of coexisting species, possibly owing to inter-specific competition

Community Ecology


“Null hypotheses [models] entertain the possibility that nothing has happened…” (Strong 1980)

“A null model is a pattern-generating model that is based on randomization of ecological data or random sampling from a known or imagined distribution. The null model is designed with respect to some ecological or evolutionary process of interest. Certain elements of the data are held constant, and others are allowed to vary stochastically to create new assemblage patterns. The randomization is designed to produce a pattern that would be expected in the absence of a particular ecological mechanism…” (Gotelli & Graves 1996)


Community Ecology

Photo from UCLA

Stephen P. Hubbell (b. 1942)

Neutral theory… asks how well community-level patterns conform

to predictions under the simplifying assumption that all individuals are equal (in terms of probability of recruiting, dying, and replacing themselves through reproduction)

“When we look at the plants and bushes clothing an entangled bank, we are tempted to attribute their proportional numbers and kinds to what we

call chance. But how false a view is this!” (C. Darwin 1859)

Patterns – any observable properties of the natural world, often expressed as variable quantities or distributions (since variation characterizes

every level of biological organization)

Processes – the causal mechanismsthat give rise to the patterns

See also Watt (1947) Pattern and process in the plant community – J. Ecology

Community EcologyPatterns & Processes

Physiological constraints Biogeographical events

Habitat selection Dispersal ability

Competition

SPECIESCOMPOSITION OF THE

LOCAL COMMUNITY

Predation Mutualisms

REGIONALSPECIES

POOL

Evolutionary processes

Processes that determine local community composition (most of which produce community structure that

wouldn’t be predicted by null models)

Redrawn from Morin (1999, pg. 27)



Competition


LOCAL COMMUNITY


REGIONALSPECIES

POOL


Community A Community B

What relative contributions do the various processes make (and have made) towards maintaining (and originally creating) differences between communities A and B?



Competition


LOCAL COMMUNITY


REGIONALSPECIES

POOL


Processes that determine local community composition (most of which produce community structure that

wouldn’t be predicted by null models)

Redrawn from Morin (1999, pg. 27)

Processes

Drift

Migration

Selection Abiotic environment Biotic interactions (e.g., competition, predation, etc.)

Speciation … and extinction (owing to drift & selection)

Primary patterns(across space & time)

Species diversity

Species composition (identity & traits)

Species abundances

Emergent patterns

Productivity

Stability

Food-web connectance

Etc.

Redrawn from Vellend & Orrock (2010)

These affect biological

variants, i.e., alleles or species

Parallels between Community Ecology & Population Genetics

Local community

Regional community

Global communityDrift

SelectionSpeciation

DriftSelection

Speciation

DriftSelection

Speciation

MigrationMigration

MigrationMigration



Local community A

Regional community

Global communityDrift

SelectionSpeciation

DriftSelection

Speciation

DriftSelection

Speciation

MigrationMigrationLocal

community B

DriftSelectionSpeciation



MigrationMigration

Local community A

Global community

Local community B

Parallels between Community Ecology & Evolutionary Theory

Roughgarden (2009)

Local interactions Local interactions

In a parallel fashion the “formational theory of communnity ecology” could be: “local interactions act upon the species arriving at the community’s boundary to produce a diversity

of communities”

“the central narrative of evolutionary theory is that variation originates from random mutation and

then natural selection in a local setting acts upon this variation to produce organic diversity”

Supply-sideecology

Supply-sideecology

A B

Competition

-

-

Influence of species A

Infl

ue

nce

of

Sp

eci

es

B

+ (positive)0 (neutral/null)- (negative)

A B

Amensalism

0

-A B

Antagonism(Predation/Parasitism)

+

-

A B

Commensalism

+

0A B

Neutralism(No interaction)

0

0

A B

Commensalism

0

+A B

Mutualism

+

+

A B

Amensalism

-

0

A B

Antagonism(Predation/Parasitism)

-

+

-

0

+

Pair-wise species interactions(owing to acquisition or assimilation of resources, etc.)

Redrawn from Abrahamson (1989); Morin (1999, pg. 21)

Interactions are often asymmetric, even when the sign of the interaction is the same in both directions (e.g., obligate for one

organism, but facultative for the other)

Pair-wise species interactions

Species A

Species B

+ / +_ / +

+ / __ / _

In any case, the laws of physics & chemistry apply (e.g., thermodynamics & stoichiometry)

Are there “laws” specific to Ecology, and Community Ecology in particular?

Laws in Community Ecology

To separate Ecology and Evolution into separate disciplines is somewhat artificial

Nothing in biology makes sense except in the light of evolution (T. Dobzhansky 1973)

All organisms interact with other organisms, both conspecific and heterospecific, and their environments; i.e., the

evolutionary play takes place within an ecological theater(G. E. Hutchinson 1965)

Ecologists and evolutionary biologists must recognize and embrace the complexity of natural ecosystems to understand them, and their components, much as Zen masters recognize

and embrace the interconnectedness of the universe(D. P. Barash 1973)

…just as is completely separating Community Ecologyfrom other related sub-disciplines

Community Ecology. GeographyResources Phylogeny Community Redrawn from Fauth et al. (1996) Community...

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