Community Ecology
Introduction: what is a community? What is community ecology?
Outline:
1. Discussion of syllabus and course content
2. Definitions: what is a community? what is community ecology?
3. Comparisons among community ecology, population ecology, and ecosystem ecology
4. Discussion of the controversy over how community is defined: it is a real entity?
Terms:
Ecology
Community (cf. population and ecosystem)
Community ecology (cf. population and ecosystem ecology)
Synecology (cf. autecology)
Intraspecific (cf. interspecific)
Abiotic (cf. biotic)
Definitions:
ecology
abiotic vs. biotic environment
community - an association or assemblage of plant and animal populations that are spatially
delimited (i.e., they live in a particular area or habitat) and are often dominated by one or more
prominent species, or by a characteristic physical attribute, e.g. the buffalograss-blue grama
community of the Llano Estacado, or the riffle community in streams, etc.
population - group of interbreeding individuals of the same species separated but not completely
isolated from other interbreeding groups of the same species.
ecosystem - sustainable natural community comprised of a definable space, its physical
characteristics, the living organisms that inhabit it, and the ways these organisms interact with
the physical space and with each other.
community ecology (cf. population and ecosystem ecology) - study of members of a multispecies
assemblage interact with each other and their surroundings; the ecology of biodiversity;
“patterns, causes, and consequences of biodiversity” (Mittelbach 2012)
synecology (cf. autecology)
interspecific vs. intraspecific interactions
Characteristics of a community:
Diversity
Relative abundance
Biotic interactions
There is much controversy over the definition of community. Why?
boundaries
emergent properties?
Community ecology addresses questions like:
Why are there this many species, not more or less?
Why do certain species co-occur but not others?
How can species coexist?
How do species interact?
How many species are necessary for a healthy ecosystem?
What factors govern how many species can be supported in a given area?
What are the consequences of biodiversity loss?
So to summarize:
A community consists of all of the organisms living within a certain geographical area. These
organisms include conspecifics as well as members of other species. These organisms interact
with each other both directly and indirectly.
Numerous (endless?) parameters affect what species are present and in what abundance.
Species presence and abundance are both causative and indicative of environmental conditions
(“health”).
Simple generalizations can rarely explain why certain species commonly occur together in
communities.
Or, more poetically:
Near or far,
Hiddenly
To each other linked are,
That one canst not stir a flower
Without troubling a star.
-Francis Thompson, The Mistress of Vision, 1897
Next lecture: history of community ecology
References:
Allen, T.F.H., and T.W. Hoekstra. 1990. The confusion between scale-defined levels and
conventional levels of organization in ecology. J. Vegetation Science 1:5-12.
Cody, M.L. 1989. Discussion: Structure and assembly of communities. Pp. 227-241 in:
Perspectives in Ecological Theory (J. Roughgarden, R.M. May, and S.A. Levin, eds.). Princeton
University Press, Princeton, NJ.
McIntosh, R.P. 1985. The Background of Ecology. Cambridge University Press, Cambridge,
UK. [Chapters 3 and 4]
Mittelbach, G.G. 2012. Community Ecology. Sinauer, Sunderland, MA.
Southwood, T.R.E. 1987. The concept and nature of the community. Pp. 3-27 in: Organization of
Communities, Past and Present (J.H.R. Gee and P.S. Giller, eds.). Blackwell Scientific
Publications, Oxford, UK.
Underwood, A.J. 1986. What is a community? Pp. 351-367 in: Patterns and Processes in the
History of Life (D.M. Raup and D. Jablonski, eds.). Springer-Verlag, Berlin, Germany.
Definitions of “community” from a variety of sources
WEBSTER: “an interacting population of different kinds of individuals (as species) constituting
a society or association or simply an aggregation of mutually related individuals in a given
location”
WHITTAKER: “an assemblage of populations of plants, animals, bacteria, and fungi that live in
an environment and interact with one another, forming together a distinctive living system with
its own composition, structure, environmental relations, development, and function”
CURTIS: “a studiable grouping of organisms which grow together in the same general place and
have mutual interactions”
McINTOSH: “a multispecies aggregation with varying degrees of integration, a more or less
specific composition, and some degree of repeatability and consistency from place to place”
McNAUGHTON & WOLF: “groups of populations co-occurring in space and time”
LEVINS & LEWONTIN: “a contingent whole in reciprocal interaction with the lower and
higher level wholes, and not completely determined by them”
RICKLEFS: “an association of interacting populations, usually defined by the nature of their
interactions or the place in which they live”
MacMAHON ET AL.: “groups of interacting populations, among which no gene exchange is
taking place but whose demography or gene pools are affected by the interaction”
ODUM: “any assemblage of populations living in a prescribed area or physical habitat; it is an
organized unit to the extent that it has characteristics additional to its individual and population
components and functions as a unit through coupled metabolic transformations”
MacARTHUR: “any set of organisms currently living near one another and about which it is
interesting to talk”
Components and problems with defining “community”
Component
1) contains several species
2) species co-occur in time and space
3) populations interact
4) assemblage is stable and self-regulating
5) composition repeatable in similar environments
6) possesses emergent properties in structure and function
Problem
1) degree of inclusiveness
2) scale of study
3) nature of interactions; and what about non-interactive species?
4) definition of equilibrium; presence of nonequilibrium
5) determination of boundaries
6) are emergent properties statistical consequences of individual components?