Ecology: Lecture Ecology: Lecture 1313

Interspecific Competition 2November 5, 2007

Definition of a niche:Definition of a niche:Theodore Giesel 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 Niche knows that some other Nutch

Would like to move into his Niche very much.

So each Nutch in a Niche has to watch that small Niche Or Nutches who haven't got Niches will snitch.

              -On Beyond Zebra (1955)

Definition of a nicheDefinition of a niche(from Hutchinson and Shelford)(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-dimensionsA space of n-dimensions

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

Niche relationships among Niche relationships among speciesspecies

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)

Niche overlap: Niche overlap: mapping >1 variablemapping >1 variable

Fundamental vs. realized nicheFundamental vs. realized niche

Competitive exclusion principleCompetitive 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 partitioningResource partitioning

Resource partitioning:Resource partitioning:Mojave desert plantsMojave desert plants

Resource partitioning:Resource partitioning:Christmas Island ternsChristmas Island terns

Other responses to competition Other responses to competition (spatial rather than resource-(spatial rather than resource-

based)based)

Niche compression Example: Doves in New Guinea

Niche shift Example: Sunfish in artificial ponds

Ecological release

Character displacement: Character displacement: Darwin’s finchesDarwin’s finches

So, how is it possible for so many So, how is it possible for so many similar species of tropical fish to exist?similar species of tropical fish to exist?

So, how is it possible for so many So, how is it possible for so many similar species of tropical fish to similar species of tropical fish to

exist?exist?

Explanations consistent with the competitive exclusion principle

i.e. resource partitioning, niche compression, niche shift Essentially, these suggest extreme

specialization

Multiple niche dimensions must be considered (see. Fig. 14.21) What might some of these “dimensions” be?

So, how is it possible for so many So, how is it possible for so many similar species of tropical fish to similar species of tropical fish to

exist?exist? Non-equilibrium conditions

Factor 1: Transient nature of larvae What does this mean? How could this prevent competitive exclusion?

Factor 2: Environmental disturbance (i.e. storms) Cause mortality How could this prevent competitive exclusion?

Factor 3: Predation! Predators may target the species that are most

abundant, so that less abundant species are able to increase.

How can we relate this back to the Lotka-Volterra competition equations?