WLF 448: Fish & Wildlife Population Ecology

Fall 2004

Population Dynamics

II.  Competition

Definitions of Competition

• Competition occurs when animals utilize common resources that are in short supply; or if resources are not in short supply; competition occurs when the animals seeking those resources nevertheless harm one another in the process. -Birch 1957
• Interspecific competition occurs when two or more species experience depressed growth rate or equilibrium population level attributed to their mutual presence in an area. -Emlem 1973

Ecological theory of competition:

• Competitive exclusion:  Gause (1934) in his book The Struggle for Existence stated: "Complete competitors cannot coesist."

• Niche

• Character displacement

Lotka-Volterra competition model

Equations

 

 

 

 

 

 

 

 

 

 

 

 

 

Assumptions

 

 

Phase plane analysis

    To understand the result of competition we need to answer 2 questions?

1. When, as a function of species B, is there no growth in species A?

 

 

 

 

 

 

 

 

 

 

2. How does N_A change on either side of the zero growth isocline?

 

 

 

 

 

 

 

 

Coexistence or exclusion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

Ayala, F. J., M. E. Gilpin, and J. G. Ehrenfeld. 1973. Competition between species: theoretical models and experimental tests. Theor. Pop. Biol. 4:331-356.

Beuchamp, R. S. and P. Ullyett. 1932. Competitive relationships between certain species of freshwater triclads. J. Ecol. 20:200-208.

Cody, M. L. 1974. Competition and the structure of bird communities. Princeton Univ. Press, Princeton, N.J. 318pp.

Connell, J. H. 1961. The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus stellatus. Ecology 42:710-723.

Elton, C. S. 1927. Animal ecology. Sidgwich and Jackson, London.

Gause, G. F. and A. A. Witt. 1935. Behavior of mixed populations and the problem of natural selection. Amer. Natur. 69:596-604.

Grinnell, J. 1917. The niche relationships of the California thrasher. Auk 21:364-382.

Heller, H. C. 1971. Altitudinal zonation of chipmunks (Eutamias): Interspecific aggression. Ecology 52:312-319.

Horn, H. S. and R. M. May. 1977. Limits to similarity among coexisting competitors. Nature 270:660-661.

Hutchinson, G. E. 1957. Concluding remarks. Cold Spring Harbor Symp. Quant. Biol. 22:415-427.

Hutchinson, G. E. 1959. Homage to Santa Rosalia, or why are there so many kinds of animals? Am. Nat. 93:145-159.

Miller, R. S. 1964. Ecology and distribution of pocket gopher (Geomyidae) in Colorado. Ecology 45:256-272.

Miller, R. S. 1967. Pattern and process in competition. Adv. Ecol. Res. 4:1-74.

Pulliam, H. R. 1975. Coexistence of sparrows: a test of community theory. Science 189:474-476.

Tilman, David. 1982. Resource Competition and Community Structure. Monographs in Population Biology No. 17, Princeton Univ. Press, Princeton, NJ.