Ecology: Lecture 13 Interspecific Competition (finish) October 31, 2005

What evidence is required to show that competition is responsible for a particular pattern of distribution?  The distribution of the two species is inversely correlated.  The two species have been demonstrated to require the same limited resource and/or one interferes with the other’s ability to acquire resources  Removal of the “superior” competitor results in movement of the “inferior” competitor into the now unoccupied region.  It is really the presumed competitor that is responsible for the exclusion and not some correlated factor.

Definition of a niche: Theodore Giesel And NUH is the letter I use to spell Nutches, Who live in small caves, known as Niches, for hutches. These Nutches have troubles, the biggest of which is The fact there are many more Nutches than Niches. Each Nutch in a Nich knows that some other Nutch Would like to move into his Nich very much. So each Nutch in a Nich has to watch that small Nich Or Nutches who haven't got Niches will snitch. -On Beyond Zebra (1955) -On Beyond Zebra (1955)

Definition of a niche (from Hutchinson and Shelford)  For each environmental variable it faces in its world, an organism has a range of values for which it can grow and multiply

A space of n-dimensions  Fig

Defining and mapping niches (based on key characteristics)  Fig

Define niche overlap between species  Fig

Niche relationships among species x-axis: state of a particular resource (size of prey, for example) y-axis: species response/fitness (much as for Shelford’s law of tolerance) Fig

Niche overlap: mapping >1 variable  Fig

Fundamental vs. realized niche  Fig

Competitive exclusion principle  Gause: “As a result of competition, two similar species scarcely ever occupy similar niches, but displace each other in such a manner that each takes possession of certainly particular kinds of food and modes of life in which it has an advantage over its competitor.”  Hardin: “Complete competitors cannot coexist.”

Resource partitioning  Fig. 14.9

Resource partitioning: Mojave desert plants  Fig

Resource partitioning: Christmas Island terns

Other responses to competition (spatial rather than resource-based)  Niche compression  Example: Doves in New Guinea  Niche shift  Example: Sunfish in artificial ponds  Ecological release

Character displacement: Darwin’s finches  Fig