Download - ScienceShare.co.uk Shared Resource
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.