Ch. 7 Flashcards
competitive exclusion
“two species cannot exist on one limiting resource”.
David tilman quote to be familar with
“Multispecies stable equilibrial coexistence
requires interspecific tradeoffs. If a species arose
that was able to avoid such tradeoffs and be a
superior competitor relative to all other species, it
would eliminate its competitors.”
major factor influencing
community structure.
Historical perspective:
Gause (1934) conducting experiments on competitive exclusion
Lotka/Volterra (1925, 1926) independently develop mathematical theory of interspecific
competition
Interspecific competition is the
( def 1 ) grover 1997
interaction occurring between species when increased
abundance of a first species causes the population growth of a second to decrease, and
there is a reciprocal effect of the second on the first. (Grover, 1997)
Interspecific competition
( cas 2000)
Interspecific competition between two species occurs when individuals of one species
suffer a reduction in growth rate from a second species due to their shared use of limiting
resources (exploitative competition) or active interference (interference competition).
(Case, 2000)
two special cases of competition
Exploitative competition (a.k.a. resource competition)
Interference competition (a.k.a. contest competition)
Exploitative competition (a.k.a. resource competition)
When a species consumes a shared resource that limits its and other species’ population growth
making that resource less available to other species.
Interference competition (a.k.a. contest competition)
Occurs when one species restricts another species’ access to a limiting resource.
Can encompass overt aggression such as in territorial defense or just occupying the space another
individual needs.
Lotka-Volterra competition model
Adds in the term α which is a
competition coefficient and this constant reflects the effect
of an individual species on the per capita growth rate of the alternative species.
Lotka-Volterra competition model is based on what type of model
Based on logistic growth model
Lotka-Volterra competition model on density and population between species
the density of one species has a negative effect on the population
growth of the second species.
zero growth isoclines of species
see slides
Founder control
the outcome is dependent on the
initial starting abundances of species 1 and
species 2.
What is a resource?
A resource is any substance or factor which can lead to increased population growth rates as its
availability in the environment is increased, and which is consumed by an organism (Tilman,
1982).
Resources are entities which contribute positively to population growth, and are consumed in the
process (Grover, 1997).
two properties that define a resource:
A resource contributes positively to the growth rate of the consumer population
- a resource is consumed (and is thus made unavailable to other individuals or species).
Resource types
biotic and abiotic
examples of biotic resource types
Prey (for predators)
Plants (for herbivores)
Seeds (for granivores)
examples of abiotic resource types
Minerals
Light
Space (although stronger for sessile
organisms like sponges)
One consumer, one resource: R*
R* is the intersection of mortality and per capita birth rate
Presumably there is an upper limit to per capita birth rates, and is generally approached in an asymptotic fashion as limiting resources become less available.
If R > R*
Then, the consumer population will increase over time and the abundance of resources
will decline to the R* point (the equilibrium point).
see graphs
two species competing
for one resource
Conclusions from this analysis
- Two species cannot exist on one limiting resource.
- The species that can maintain population growth with the lowest resource level (R*)
will win.
what can maintain coexistence of two species then?
?
One species has relatively greater
population growth rate at low resource
levels and the other has relatively
greater population growth rate at high
resource levels.
Gleaners
– grow relatively well when
resources are scarce (here that is
species 2).
Opportunists
grow relatively well
when resources are abundant (here
that is species 1).
If resources fluctuate between high and low,
then two species might coexist because each
has an advantage under different resource conditions.
Essential resources:
required for growth and one essential resource cannot substitute for
another.
Example: plants require 20 different mineral resources (i.e. nitrogen, phosphorus, etc.)
Substitutable resources:
one resource can take the place of another.
Example: a fox predator might consume a number of different prey species to fulfill its nutritional needs
(i.e. rabbits, squirrels, or mice)
ZNGI
zero net growth isocline
ZNGI defines
an equilibrium
point at which the densities
of species 1 and species 2
are unchanging (births = deaths
for both species).
Interspecific Competition results in an inverse relationship in density between the two
competing species. This competition can come in the form of
exploitative competition
or interference competition.
C1 and C2 are
the consumption
vectors for the two species.
The equilibrium point is potentially
stable because each species consumes
more of the resource that most
limits its own growth.
R* is the point at which
per capita birth rate equals per capita death rate (know how to
find R* on a graph.
Resources are
entities that contribute positively to the consumer’s growth.
When in competition for resources, two species
cannot be maintained on the same
limiting resource & the one that can maintain itself on a lower amount of resource will
be the one that wins.
if resources fluctuate and are not stable,
it is possible that one species will
have increased growth when resources are scarce (gleaners) and the other will have
increased growth when resources are abundant (opportunists). This may lead to
coexistence.
When we expand the model further, we see that some resources may be substituted.
And, under this relaxed assumption we see that the two species may coexist when each
consumes more of the resource that limits its own growth. (Be able to point out the area
on the graph where stable coexistence could be achieved.)
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