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Community Ecology
Geography
Resources
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)
Phylogeny
Redrawn from Fauth et al. (1996)
Geography
Resources
Community
Taxon – phylogenetically
related group of species; a
clade
Taxon
E.g., Mammalian Order
Rodentia
Phylogeny
Redrawn from Fauth et al. (1996)
Geography
Resources
Guild
Community
Taxon
Phylogeny
Redrawn from Fauth et al. (1996)
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
Geography
Community
Resources
Local
guild
Taxon
Phylogeny
Redrawn from Fauth et al. (1996)
Guild
Local guild – a group of
species that share a common
resource and occur in the
same community
(Root 1967)
E.g., Sonoran Desert
granivores
Geography
Resources
Local
guild
Community
Guild
Assemblage
Assemblage – a group of
phylogenetically related
species within a community
Taxon
Phylogeny
Redrawn from Fauth et al. (1996)
Geography
Resources
Local
guild
Community
Guild
Assemblage
Assemblage – a group of
phylogenetically related
species within a community
Taxon
Phylogeny
Redrawn from Fauth et al. (1996)
a.k.a. “Taxocene”
(Hutchinson 1967)
E.g., Sonoran Desert
rodents
Geography
Resources
Local
guild
Community
Guild
Ensemble
Assemblage
Taxon
Phylogeny
Redrawn from Fauth et al. (1996)
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
Local
guild
Community
Guild
Ensemble
Assemblage
Taxon
Phylogeny
Redrawn from Fauth et al. (1996)
E.g.,
granivorous rodents,
pond-breeding
salamanders…
In this course any
collection of two or
more species is
“fair game” for close
scrutiny
Robert H. MacArthur’s definition of Community
“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)
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 aim to improve our explanatory
& predictive abilities
In any case, the tradition of good Natural History
is not ignored by the best modern practitioners
“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
Some historic landmarks
Charles Darwin (1809 - 1882)
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 Darwin’s multifaceted “struggle for
existence”
Photo from WikiMedia Commons
Community Ecology
Some historic landmarks
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)
Photo from WikiMedia Commons
Community Ecology
Some historic landmarks
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)
Photo from WikiMedia Commons
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 Haeckel’s “oekologie”)
Photo from WikiMedia Commons; for further details see Damschen et al. (2005)
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...
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...
Photo of Lake Michigan sand dune from http://ebeltz.net...
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 Empirical Life Zones (similar biotic
changes with increased elevation or latitude)
Community Ecology
Some historic landmarks
Leslie Holdridge (1907 - 1999) – devised
Theoretical Life Zones (1947)
Image from WikiMedia Commons
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
Community Ecology
Some historic landmarks
Robert H. Whittaker (1869 - 1939)
His gradient analyses helped end the
Clements-Gleason debate
Photo from WikiMedia Commons; figures from http://ecology.botany.ufl.edu...
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.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)
Community Ecology
Some historic landmarks
Margaret Davis (b. 1931)
Her paleo-ecological perspective has
helped increase awareness of historical contingencies
Photo of Davis from U. Minnesota; photo of pollen from http://www.gl.rhbnc.ac.uk...
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
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
Community Ecology
Some historic landmarks
Joseph H. Connell (b. 1923)
Photo from UCSB
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
Community Ecology
Some historic landmarks
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
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
Community Ecology
Some historic landmarks
Joseph H. Connell (b. 1923)
Photo from UCSB; figure from Connell (1961; one of Connell’s 5 Science Citation Classics)
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
Criticisms: oversimplification; over-emphasized
competition & equilibria
Photo from Wikipedia
Community Ecology
Some historic landmarks
G. Evelyn Hutchinson (1903 - 1991)
Conceived of fundamental vs. realized
niche 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)
Photo from Yale Peabody Archives
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 interspecific competition
The idea & disagreement over how to
test it helped motivate the development
of null models in ecology
Figure from Gotelli & Graves (1996, pg. x)
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)
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)
“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)
Photo from UCLA
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
Processes that determine local community composition
(most of which produce community structure that
wouldn’t be predicted by null models)
Evolutionary processes
Physiological constraints
Biogeographical events
REGIONAL
SPECIES
POOL
Habitat selection
Competition
Dispersal ability
Predation
SPECIES
COMPOSITION OF THE
LOCAL COMMUNITY
Redrawn from Morin (1999, pg. 27)
Mutualisms
Processes that determine local community composition
(most of which produce community structure that
wouldn’t be predicted by null models)
Evolutionary processes
Evolutionary processes
Physiological constraints
Biogeographical events
Physiological constraints
REGIONAL
SPECIES
POOL
REGIONAL
SPECIES
POOL
Habitat selection
Competition
Biogeographical events
Habitat selection
Dispersal ability
Predation
SPECIES
COMPOSITION OF THE
LOCAL COMMUNITY
Community A
Mutualisms
Competition
Dispersal ability
Predation
Mutualisms
SPECIES
COMPOSITION OF THE
LOCAL COMMUNITY
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)
Processes that determine local community composition
(most of which produce community structure that
wouldn’t be predicted by null models)
From HilleRisLambers et al. (2012, pg. 228)
Parallels between Community Ecology & Population Genetics
Processes
Drift
Migration
Selection
These affect
biological
variants, i.e.,
alleles or
species
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
Redrawn from Vellend & Orrock (2010)
Emergent patterns
Productivity
Stability
Food-web connectance
Etc.
Parallels between Community Ecology & Population Genetics
Global community
Drift
Selection
Speciation
Migration
Migration
Regional community
Drift
Selection
Speciation
Migration
Redrawn from Vellend & Orrock (2010)
Local
community
Drift
Selection
Speciation
Migration
Parallels between Community Ecology & Population Genetics
Global community
Drift
Selection
Speciation
Migration
Migration
Regional community
Drift
Selection
Speciation
Migration
Local
community A
Drift
Selection
Speciation
Redrawn from Vellend & Orrock (2010)
Local
community B
Drift
Selection
Speciation
Migration
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 community’s boundary to produce a diversity
of communities”
Supply-side
Supply-side
Local
Local
ecology
ecology
community A
community B
Local interactions
Roughgarden (2009)
Local interactions
Pair-wise species interactions
(owing to acquisition or assimilation of resources, etc.)
Influence of species A
Influence of Species B
A
-
- (negative)
0 (neutral/null)
-
0
-
A
-
B
Competition
Amensalism
-
0
A
B
0
A
B
A
B
Antagonism
(Predation/Parasitism)
+
A
B
0
0
Amensalism
Neutralism
(No interaction)
Commensalism
-
0
+
0
+
B
+ (positive)
+
A
B
+
Antagonism
(Predation/Parasitism)
A
B
+
Commensalism
Redrawn from Abrahamson (1989); Morin (1999, pg. 21)
A
+
Mutualism
B
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)
Species B
_
/+
+/+
Species A
_
/_
+/_
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?
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)