Other Species: Predation, Competition, Parasitism

PREDATION

Predation can also limit the distribution of a species.

The snowshoe hare and Canadian lynx populations cycle together. The lynx feeds almost exclusively on the hares.

COMPETITION

Two or more consumers may compete for a limited resource. If the consumers are of the same species then intraspecific competition is said to occur. Intraspecific competition can be for nest sites, mates, or food. The results of intraspecific competition leads to density dependent  birth and death rates (as density goes up, the birth rates drop while death rates increase).

If the consumers are different species, then interspecific competition is said to occur. Under these conditions, the birth and death rates of one population affect these rates in the second population. While intraspecific competition results in regulation of the specie's population, interspecific competition can result in one species dominating the other, even to the point where the second species will go extinct.

Competition between two species of Paramecium in the laboratory. Grown separately, both species do well. When grown together, however, P. aurelia out-competes P. caudatum; eventually leading to P. caudatum's extinction in the culture dish.

The Tricolor Blackbird and Redwing Blackbird are closely related species with similar ecological requirements. In the absence of Tricolors, the Redwing will chop up the habitat into a series of territories as shown below in figure A. If Tricolors move in, however, they are more demanding as to their territorial needs and will displace the Redwings as shown in "B". Tricolors out-compete the Redwings and limit their distribution. Other examples of competition displacing or limiting the distribution of a species are  shown below. These include an introduced plant (Kudzu) and the competition between sage and other species in a mixed grassland.

Kudzu out-competes native plants in the south.

PARASITISM

Tsetse flies (Glossinia) occupy 4 million square miles of Africa between 15° N and 28° S. The tsetse fly is a vector for African Sleeping Sickness in humans and nagana in domestic animals. Because of nagana, 1/4 of Africa can have no domestic animals other than poultry.