Lecture 19: Competition Flashcards
Competition
-/-, interaction hurts both species
any use or defense of a resource by one individual that reduces the availability of that resource to other individuals
Resource
features of the environment required from growth, survival, or reproduction and which can be consumed or otherwise used to the point of depletion
can be abiotic or biotic
Aspects of the environment that are necessary for survival but not
resources?
Temperature, air quality, climate stability, oxygen
Conspecific
individuals of the same species
Competition can be:
Intraspecific: between two individuals of the same species
Interspecific: between two individuals of different species
Resources commonly important to competition
Light
Nitrogen
Phosphorus
Water
Space
Nest Sites
Limiting resource
A resource limiting the ability to grow, survive or reproduce
When added the organisms should respond in some way
Liebig’s law of minimum
Because organisms cannot perfectly match the environment
Only one resource can be limiting
Prediction: the population should only respond to resource additions of the most limiting resource
Optimal foraging for essential resource
Tilman, Givnish, Bloom, 1980s
Because an organism is wasting investment in uptake of any nonlimiting resource –> natural selection should favor movements toward colimitation
Exploitative competition
Indirect competition, competition through resource depletion
Ex. Competition for water, nitrogen, food in the environment
In exploitative competition, experimentally lowering resource availability will have the same effect on one individual as
adding the other individual into the environment
Interference competition
Direct competition, individuals compete directly for access to a resource
Allelopathy
(interference competition)
plant species releasing toxic compounds that harm other species
thought to be how some invasive plant species come to be invasive
experimental evidence is weak
Symmetric competition (individual proportional)
when both individuals/species are hurt equally by competition
Ex. belowground roots
Asymmetric competition
when one individual/species is hurt more than the other by the competition
a size (or other) difference, disproportionally advantages the winner
Ex. extinction, aboveground competition for light
Competitive exclusion principle
two species that use a limiting resource in the same way cannot coexist indefinitely
Ex. experiment with two ciliate species, P aurelia and P caudatum cannot coexist
Lotka Volterra competition model Basic assumptions
All individuals are equivalent
Species grow logistically if not in competition
Effect of competition by one species can be expressed by adding an amount of the other individuals - exploitative competition implied
When do competing species coexist?
When:
K2/β > K1 and K1/α > K2
or rearranged:
α < K1/K2 < 1/β
Competition coefficients
α – effect of species 2 on species 1
β – effect of species 1 on species 2
If α = 1,
individuals of N2 and N1 are equivalent for N1 pop dynamics.
If β = 1
individuals of N2 and N1 are equivalent for N2 pop dynamics.
If α = β = 1
stable coexistence at equilibrium is impossible
If α and β are close to 1 (0.95)
Individuals of the opposite species compete almost as intensely as individuals of the same species do with one another
Interspecific competition is almost as strong as intraspecific competition
K1 and K2 have to be very similar for stable
coexistence to be possible
If α < 1, β < 1
Individuals of the same species are worse than individuals of the
opposite species for that species’ population growth
Intraspecific competition is more intense than interspecific competition
Stable coexistence is possible
______ is the only chance for stable coexistence
α, β less than 1
Intraspecific competition must be stronger than interspecific competition for species to coexist
When do competing species coexist at equilibrium?
α < K1/K2 < 1/β
Stable coexistence requires
species differences
Character displacement
Natural Selection (NS) can favor individuals whose resource use differs from that of competitors
- niche differentiation –> will decrease α and β, making coexistence more likely.
Gause’s Paramecium experiments
P. Aurelia and P. caudatum fed on floating bacteria (no stable coexistence)
P. bursaria fed on yeast cells (stable coexistence with P. caudatum)
When do competing species coexist?
Intensity of intraspecific competition gives rare species the advantage
If a species is rare, it has few conspecific competitors and tends to increase
If a species is common, it has many conspecific competitors and tends to decrease
Rare species advantage makes coexistence stable
How to test of niche differentiation diversity: Diversity and productivity?
Experimental diversity manipulation
1- 24 species
Seeded with the same total seed weight across diversity levels
- Monocultures (1 species) 100 grams
- High diversity (24 species), each species has 100/24 grams
Stable coexistence vs unstable coexistence
Stable coexistence; rare species advantage, many mechanisms
Unstable coexistence; no difference in K’s, α, β
