WLF 448: Fish & Wildlife Population Ecology

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Population Interactions - Competition (competit.cpl)

A. Outline

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

Lotka-Volterra competition model

a. Equations

b. Assumptions

c. Phase plane analysis

d. Coexistence or exclusion

Competitive exclusion

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

Gause's competitive exclusion principle."

Miller (1967) study of gophers

Niche

a. Definitions by Grinnell and Elton

Grinnell (1914) used the term niche or ecological niche to express the species position in the community in terms of habitat.

Elton (1927): role theat species plays in a community

b. Hutchinson's fundamental and realized niche

G.E. Hutchinson (1957) expanded the concept to include both aspects. Hutchinson (1957) suggested defining niche in terms of an abstract spce in which the axes represent habitat or resource factors. Example: Blue-gray gnatcatcher

Fundamental niche = The range of conditions in which the species could potentially survive.

Realized niche = The actual range of conditions occupied.

c. Character displacement

d. Limiting similarity

Case study of Sierra Nevada chipmunks (Heller)

`Example of Research on Competition:`Heller 1971, Ecology 52:312-319
The Observed Distribution:
Eutamias alpinus	Alpine Zone	(tundra, rock)
E. speciosus	Lodgepole pine	(dry granitic soil w/ little understory)
E. amoenus	Pinion pine	(clumped food)
E. minimus	Sage bunchgrass	(hot dry)

Limitations:
Species	Intraspecific Aggression	Interspecific Aggression	Cover	Physiological Limits
E. alpinus	strong	Dominant	42% Boulders	Can't take desert
E. speciosus	none	weak	42% open ground and lodgepole	Can't take desert
E. amoenus	strong	Dominant	82% Dense shrubs, rocks, logs, Pinion pine food in clumps	Can't take desert
E. minimus	none	weak	50% shrubs only	Can tolerate any zone- Most adapted to desert

Resource Competition and Community Structure

Tilman (1982) proposed a new approach to competition and community structure based on the "Monod equation" relating resource availability to per capita growth rate:

This leads to a sigmoidal pattern of population growth through time and a concommitant exponential decline in resource availability:

Multispecies-multiresource competition can be portrayed with phase planes/spaces in which ZNGI (Zero Net Growth Isocline) for each species delineates resource levels at which the species growth rate is positive. Resource production is pictured with a Renewal Vector and species consumption with a Consumption Vector. Overlapping ZNGIs for pairs or sets of species lead to predictions about results of competition and final community composition which are interesting and supported to some degree by empirical studies.

Case Study: Competition Between White-tail and Mule Deer on Colville Reservation

Dr. Garton worked with biologists from the Colville Confederated Tribes to estimate effects of competition between white-tailed and mule deer on each population as well as effects of an increasing population of elk. Chris Hennings, a student in Wlf 448, performed preliminary analyses of these data as part of his class project and a senior thesis. We have now estimated the effects of competition amongst these three cervids on each species populations under the unique conditions where they can move around North Central Washington to choose different wintering areas from year to year. The effects on each species populations differ dramatically from what we expected when the research began.

B. Student Responsibilities

Define competition and justify your definition.
Distinguish between the types of competition termed active, passive, scramble, contest, interference and give an example of each.
Be able to identify the Lotka-Volterra model of competition, define its constants, state its assumptions, and predict its results if given the appropriate constants.
What problems are there with use of the Lotka-Volterra model?
What is the principle of "competitive exclusion" and what does it mean"
Trace the development of the concept of the niche or ecological niche.
What is the difference between the fundamental and realized niche of a species?
Define character displacement and give an example of it.
What is the explanation for the pattern of mouth part sizes in co-existing congeneric species?
What did Heller conclude was the explanation for the distribution pattern of chipmunks in the eastern Sierra Nevada Mountains?
How does Tilman's approach to resource competition differ from the classic Lotka-Volterra picture?
How can there be so many species in a typical plant-animal community in the face of competitive exclusion?
How do the 3 large cervids on the reservation of the Colville Confederated Tribes affect each other's poplations?
How can the maximum rates of increase for the mule deer and white-tailed deer on the reservation be so large?

C. 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.

Revised: 25 August 2011