1. Community Ecology
Link to course web page

2. Robert H. MacArthur’s definition of Community Ecology
I may be particularly biased in favor of MacArthur’s definition (found in MacArthur [1971] in Farner & King, eds., Avian Biology; see J. A. Wiens [1989] The Ecology of Bird Communities, pg. 3), since it most flexibly fits the types of “communities” on which my research focuses.
“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)

3. Community Ecology 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
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 ( ) coined “oekologie”
for the study of the multifaceted “struggle for existence” envisioned by Darwin
Photo from Wikipedia

4. Community Ecology 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

5. Community Ecology 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

6. Community Ecology Historic landmark Joseph H. Connell (b. 1923)
Photo from UCSB

7. 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
Mechanistic explanations provide guidance for forecasting or predicting future patterns, which is especially important in response to anthropogenic change and in the context of restoration.
See also Watt (1947) Pattern and process in the plant community – J. Ecology

8. 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)

9. Processes that determine local community composition
(most of which produce community
structure that wouldn’t 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)

10. 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
From Vellend & Orrock (in press): “Both population and community ecology are essentially concerned with variation over space and time in the relative abundance and diversity of discrete biological variants: alleles or species, respectively. Four logically distinct processes can change the abundances and diversity of biological variants (Vellend & Geber 2005).”
Productivity
Species diversity
Stability
Species composition
(identity & traits)
Food-web connectance
Species abundances
Etc.
Redrawn from Vellend & Orrock (in press)

11. Parallels between Community Ecology & Population Genetics
Global community
Drift
Selection
Speciation
Migration
Migration
Regional community
Drift
Selection
Speciation
Local
community
Migration
Migration
From Vellend & Orrock (in press): “Both population and community ecology are essentially concerned with variation over space and time in the relative abundance and diversity of discrete biological variants: alleles or species, respectively. Four logically distinct processes can change the abundances and diversity of biological variants (Vellend & Geber 2005).”
Drift
Selection
Speciation
Redrawn from Vellend & Orrock (in press)

12. 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
From Vellend & Orrock (in press): “Both population and community ecology are essentially concerned with variation over space and time in the relative abundance and diversity of discrete biological variants: alleles or species, respectively. Four logically distinct processes can change the abundances and diversity of biological variants (Vellend & Geber 2005).”
Drift
Drift
Selection
Selection
Speciation
Speciation
Redrawn from Vellend & Orrock (in press)

13. 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
ecology
Supply-side
ecology
Local
community A
Local
community B
Local interactions
Local interactions
Roughgarden (2009)

14. Pair-wise species interactions
(owing to acquisition or assimilation of resources, etc.)
Influence of species A
- (negative)
0 (neutral/null)
+ (positive) A B
Competition - A B
Amensalism - A B
Antagonism
(Predation/Parasitism) + - - A B
Amensalism - A B
Neutralism
(No interaction) A B
Commensalism +
Influence of Species B A B
Antagonism
(Predation/Parasitism) - + A B
Commensalism + A B
Mutualism + +
Redrawn from Abrahamson (1989); Morin (1999, pg. 21)

15. 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)
I hope this brief introduction to Community Ecology convinces you that we will take a broad view of the subject: From interactions between pairs of species through global patterns of diversity.
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)