Community Ecology

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Community Ecology
Link to course web page
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Community
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)
Redrawn from Fauth et al. (1996)
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Community
Taxon phylogenetically related group of
species, e.g., a clade
Taxon
Redrawn from Fauth et al. (1996)
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Guild
Community
Guild a group of species without regard for
taxonomic position that exploit the same class
of environmental resources in a similar way
(Root 1967)
Taxon
Redrawn from Fauth et al. (1996)
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Local guild
Guild
Community
Local guild a group of species that share a
common resource and occur in the same community
(Root 1967)
Taxon
Redrawn from Fauth et al. (1996)
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Local guild
Guild
Community
Assemblage
Assemblage a group of phylogenetically related
species within a community
Taxon
Redrawn from Fauth et al. (1996)
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Local guild
Guild
Community
Assemblage
Assemblage a group of phylogenetically related
species within a community a.k.a. Taxocene
(Hutchinson 1967)
Taxon
Redrawn from Fauth et al. (1996)
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Local guild
Guild
Community
Ensemble
Assemblage
Ensemble a phylogenetically bounded group of
species that use a similar set of resources
within a community
Taxon
Redrawn from Fauth et al. (1996)
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Local guild
Guild
Community
Ensemble
Assemblage
E.g., seed-eating finches, pond-breeding
salamanders
Taxon
In this course any collection of two or more
species is fair game for close scrutiny
Redrawn from Fauth et al. (1996)
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Robert H. MacArthurs definition of Community
Ecology
any set of organisms currently living near each
other and about which it is interesting to talk
Painting by D. Kaspari for M. Kaspari (2008)
anniversary reflection on MacArthur (1958)
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Community Ecology
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 attempt to
improve our explanatory predictive abilities
Nevertheless, the tradition of good Natural
History is not ignored by the best modern
practitioners
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Community Ecology
Some historic landmarks
Charles Darwin (1809 - 1882)
Certainly not the first ecologist, but clearly
recognized the importance of organisms
interactions (intraspecific, interspecific with
their abiotic environments) for evolution by
natural selection
Ernst Haeckel (1834 - 1919) coined oekologie
for the study of the multifaceted struggle for
existence envisioned by Darwin
Photo from Wikipedia
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Community Ecology
Some historic landmarks
Charles Darwin (1809 - 1882)
Recognized the importance of 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)
Photo from Wikipedia
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Community Ecology
Some historic landmarks
Charles Darwin (1809 - 1882)
Recognized the importance of 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)
Photo from Wikipedia
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Community Ecology
Some historic landmarks
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 Haeckels
oekologie)
Photo from Wikipedia for further details see
Damschen et al. (2005)
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Community Ecology
Some historic landmarks
Stephen Forbes (1844 - 1930)
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)
Photo from http//home.grics.net/forbes01/Forbes
20history.html
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Community Ecology
Some historic landmarks
Henry Cowles (1869 - 1939)
A pioneer of dynamic ecology, especially on the
sand dunes of Lake Michigan
Photo of Cowles from http//oz.plymouth.edu/lts/e
cology/ecohistory/cowles.html photo of Lake
Michigan sand dune from http//ebeltz.net/folio/cf
ol-5.html
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Community Ecology
Some historic landmarks
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 a
scheme of Empirical Life Zones (similar biotic
changes with increased elevation or latitude)
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Community Ecology
Some historic landmarks
Leslie Holdridge devised Theoretical Life Zones
Image from Wikipedia
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Community Ecology
Some historic landmarks
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
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Community Ecology
Some historic landmarks
Robert H. Whittaker (1869 - 1939) His gradient
analyses helped end the Clements-Gleason debate
Photo from Wikipedia figures from
http//ecology.botany.ufl.edu/ecologyf03/graphics/
WhittakerGradients.gif
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Community Ecology
Some historic landmarks
We continue to need good descriptions of
patterns, often supported by sound, quantitative
techniques
E.g., Bray Curtis (1957) introduced ordination
methods to define plant communities in Wisconsin
See The Ordination Web Page (http//ordination.o
kstate.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)
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Community Ecology
Some historic landmarks
Margaret Davis (b. 1931)Her paleo-ecological
perspective hashelped increase awareness of
historical contingencies
Photo of Davis from U. Minnesota photo of pollen
from http//www.gl.rhbnc.ac.uk/palaeo/images/Polle
n_large.jpg
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Community Ecology
Some historic landmarks
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
Photo from UCSB
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Community Ecology
Some historic landmarks
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
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Community Ecology
Some historic landmarks
Joseph H. Connell (b. 1923)
Photo from UCSB
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Community Ecology
Some historic landmarks
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
Why might these patterns exist?
Photo from UCSB
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Community Ecology
Some historic landmarks
Joseph H. Connell (b. 1923)
Hypotheses Differential physiological
tolerances to desiccation and submersion Inters
pecific competition Predation (e.g., Thais
lapillus is a predator of Balanus balanoides)
Photo from UCSB
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Community Ecology
Some historic landmarks
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
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Community Ecology
Some historic landmarks
Joseph H. Connell (b. 1923)
Photo from UCSB figure from Connell (1961 one
of Connells 5 Science Citation Classics)
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Community Ecology
Some historic landmarks
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
Photo from Wikipedia
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Community Ecology
Some historic landmarks
G. Evelyn Hutchinson (1903 - 1991)
Conceived of fundamental vs. realized niche
spaces or hyper-volumes
Photo from Yale Peabody Archives
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Community Ecology
Some historic landmarks
G. Evelyn Hutchinson
E.g., Hutchinsonian ratios A ratio of 1.3 in
size occurs between pairs of coexisting
species, possibly owing to inter- specific
competition
The idea and disagreement over how to test it
helped motivate the development of null models
in ecology
Figure from Gotelli Graves (1996, pg. x)
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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)
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Community Ecology
Some historic landmarks
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)
Photo from UCLA
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Community Ecology Patterns Processes
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 mechanisms that give rise
to the patterns
See also Watt (1947) Pattern and process in the
plant community J. Ecology
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Processes that determine local community
composition (most of which produce community
structure that wouldnt be predicted by null
models)
Redrawn from Morin (1999, pg. 27)
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Processes that determine local community
composition (most of which produce community
structure that wouldnt be predicted by null
models)
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?
Redrawn from Morin (1999, pg. 27)
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Parallels between Population Genetics Community
Ecology
These affect biological variants, i.e., alleles
or species
Processes
Drift
Migration
Selection Abiotic environment Biotic
interactions (e.g., competition,
predation, etc.)
Speciation
Primary patterns(across space time)
Emergent patterns
Productivity
Species diversity
Stability
Species composition (identity traits)
Food-web connectance
Etc.
Species abundances
Redrawn from Vellend Orrock (in press)
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Parallels between Community Ecology Population
Genetics
Global community
Drift
Selection
Speciation
Migration
Migration
Regional community
Drift
Selection
Speciation
Local community
Migration
Migration
Drift
Selection
Speciation
Redrawn from Vellend Orrock (in press)
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Parallels between Community Ecology Population
Genetics
Global community
Drift
Selection
Speciation
Migration
Migration
Regional community
Drift
Selection
Speciation
Migration
Migration
Local community A
Local community B
Drift
Drift
Selection
Selection
Speciation
Speciation
Redrawn from Vellend Orrock (in press)
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Parallels between Community Ecology
Evolutionary Theory
Global community
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
In a parallel fashion the formational theory of
communnity ecology could be local
interactions act upon the species arriving at the
communitys boundary to produce a diversity of
communities
Supply-side ecology
Supply-side ecology
Local community A
Local community B
Local interactions
Local interactions
Roughgarden (2009)
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Pair-wise species interactions (owing to
acquisition or assimilation of resources, etc.)
Influence of species A
- (negative)
0 (neutral/null)
(positive)
-
Influence of Species B
0

Redrawn from Abrahamson (1989) Morin (1999, pg.
21)
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Pair-wise species interactions
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)
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Laws in Community Ecology
In any case, the laws of physics chemistry
apply (e.g., thermodynamics stoichiometry)
Are there laws specific to Ecology, and
Community Ecology in particular?
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To separate Ecology and Evolution into separate
disciplines is somewhat artificial
Just as is completely separating Community
Ecology from other related sub-disciplines
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)