Why are ecological interactions important?

Interactions can affect distribution and abundance.

Interactions can influence evolution.

Ecological effects of competition

What are the following?

Intraspecific competition –

Interspecific competition –

Ecological effects of competition

Intraspecific competition – between individuals of theSAME species

Interspecific competition – between individuals ofDIFFERENT species

Competition – two species share a requirement for alimited resource reduces fitness of one or both species

# d

eer

mic

e ca

ptu

red

0.2

.4.6

.81 k rats excluded

control

1978-80 1988-90(Heske, E. J., J. H. Brown, and S. Mistry 1994)

What is the effect of kangaroo rat competition on deer mice?

competitive exclusion principle

If two species have the same niche, the strongercompetitor will eliminate the other competitor.

“Complete competitors cannot coexist.”

Why do kangaroo rats exclude deer mice?

What if you put more seeds in the environment?

What if you added another resource to the environment?

AnswersComplete competitors cannot coexist.

Competitive exclusion is reached more slowly with higher resource abundances.

Stable coexistence requires niche differentiation, such that members of each species compete more strongly among themselves than with members of the other species. (intraspecific > interspecific)

What is the niche?set of conditions within which an organism can maintain a viable population

multi-dimensional with as many dimensions as their are limiting conditions

temperature

light intensity

okaysalinity

ecologicalniche

predict the outcome ofinterspecific competition

A classic interspecific competition experiment

two species of Paramecium

P. caudata

P. aurelia

Gause (1934)

Barnacles on a Rocky shore

1) Describe the distribution of the two species of barnacles2) Where are the harsher conditions, what are they?

Fundamental niche depends on physical (abiotic) conditions.

Realized niche depends on biotic as well as abiotic conditions.

What is the realized niche of each barnacle?What is the fundamental niche of each?

growthrate

Location in intertidal zone

low highmiddle

How can we determine the niche of each barnacle?

Where do they grow when allowed to compete?

Balanus niche

Chthamalus niche

Balanus and

Chthamalus

growthrate

Location in intertidal zone

low highmiddle

Chthamalus alone

Balanus alone

Why are these niches different?

Balanusfundamental

niche

Chthamalus fundamental niche

growthrate

Location in intertidal zone

low highmiddle

Chthamalus alone

Balanus alone

Why are these niches different?

Removal experiments – remove each species and see where the other grows

Balanusfundamental

niche

Chthamalus fundamental niche

growthrate

Location in intertidal zone

low highmiddle

Chthamalusalone

competitive release – niche of the competitively-inferior species expands in the absence of the

competitively-superior species

fundamental niche

realized niche

Chthamalus withBalanus

competitiverelease

Streams with onlyPlanaria species A

Streams with onlyPlanaria species B

Streams with bothPlanaria species

What are the fundamentaland realized niches foreach species?

The niche of a species may contract in the presence of acompetitor species.

This phenomenon leads to resource (niche) partitioning and coexistence among functionally similar species.

The narrower niche resulting from competition is calledthe realized niche.

When the dominant competitor is removed, the niche ofthe inferior competitor can expand by competitive release.