community ecology. geographyresources phylogeny community redrawn from fauth et al. (1996) community...
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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
Redrawn from Fauth et al. (1996)
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
Redrawn from Fauth et al. (1996)
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
Redrawn from Fauth et al. (1996)
Geography Resources
Phylogeny
Community GuildLocalguild
Assemblage
Assemblage – a group of phylogenetically related species within a community
Taxon
Redrawn from Fauth et al. (1996)
Geography Resources
Phylogeny
Community GuildLocalguild
Assemblage
Assemblage – a group of phylogenetically related species within a community
a.k.a. “Taxocene” (Hutchinson 1967)
E.g., Sonoran Desert rodents
Taxon
Redrawn from Fauth et al. (1996)
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
Redrawn from Fauth et al. (1996)
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)
Some historic landmarks
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
Some historic landmarks
Community Ecology
Photo from WikiMedia Commons
Charles Darwin (1809 - 1882)
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)
Some historic landmarks
Community Ecology
Photo from WikiMedia Commons
Charles Darwin (1809 - 1882)
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)
Some historic landmarks
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”)
Some historic landmarks
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)
Some historic landmarks
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
Some historic landmarks
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)
Some historic landmarks
Community Ecology
Leslie Holdridge (1907 - 1999) – devised Theoretical Life Zones (1947)
Image from WikiMedia Commons
Some historic landmarks
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...
Some historic landmarks
Community Ecology
Robert H. Whittaker (1869 - 1939) His gradient analyses helped end the Clements-Gleason debate
Some historic landmarks
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
Photo of Davis from U. Minnesota; photo of pollen from http://www.gl.rhbnc.ac.uk...
Some historic landmarks
Community Ecology
Margaret Davis (b. 1931)Her paleo-ecological perspective hashelped increase awareness of historical contingencies
Photo from UCSB
Some historic landmarks
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
Some historic landmarks
Community Ecology
Joseph H. Connell (b. 1923)
Observations:
Balanus balanoides – Larger barnacle, generally found lower in the intertidal
Chthamalus stellatus – Smaller barnacle, generally found higher in the intertidal
Photo from UCSB
Some historic landmarks
Why might these patterns exist?
Community Ecology
Joseph H. Connell (b. 1923)
Observations:
Balanus balanoides – Larger barnacle, generally found lower in the intertidal
Chthamalus stellatus – Smaller barnacle, generally found higher in the intertidal
Photo from UCSB
Some historic landmarks
Community Ecology
Joseph H. Connell (b. 1923)
Hypotheses:
Differential physiological tolerances to desiccation and submersion
Interspecific competition
Predation (e.g., Thais lapillus is a predator of Balanus balanoides)
Photo from UCSB
Some historic landmarks
Community Ecology
Joseph H. Connell (b. 1923)
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
Some historic landmarks
Community Ecology
Joseph H. Connell (b. 1923)
Photo from UCSB; figure from Connell (1961; one of Connell’s 5 Science Citation Classics)
Some historic landmarks
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
Some historic landmarks
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)
Some historic landmarks
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
Some historic landmarks
“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)
Some historic landmarks
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)
Physiological constraints Biogeographical events
Habitat selection Dispersal ability
Competition
SPECIESCOMPOSITION OF THE
LOCAL COMMUNITY
Predation Mutualisms
REGIONALSPECIES
POOL
Evolutionary processes
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?
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)
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
Redrawn from Vellend & Orrock (2010)
Parallels between Community Ecology & Population Genetics
Local community A
Regional community
Global communityDrift
SelectionSpeciation
DriftSelection
Speciation
DriftSelection
Speciation
MigrationMigrationLocal
community B
DriftSelectionSpeciation
Redrawn from Vellend & Orrock (2010)
Parallels between Community Ecology & Population Genetics
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