Lecture 19: Competition

Question 1

Competition

Answer 1

-/-, interaction hurts both species
any use or defense of a resource by one individual that reduces the availability of that resource to other individuals

Question 2

Resource

Answer 2

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

Question 3

Aspects of the environment that are necessary for survival but not
resources?

Answer 3

Temperature, air quality, climate stability, oxygen

Question 4

Conspecific

Answer 4

individuals of the same species

Question 5

Competition can be:

Answer 5

Intraspecific: between two individuals of the same species
Interspecific: between two individuals of different species

Question 6

Resources commonly important to competition

Answer 6

Light
Nitrogen
Phosphorus
Water
Space
Nest Sites

Question 7

Limiting resource

Answer 7

A resource limiting the ability to grow, survive or reproduce
When added the organisms should respond in some way

Question 8

Liebig’s law of minimum

Answer 8

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

Question 9

Optimal foraging for essential resource

Answer 9

Tilman, Givnish, Bloom, 1980s
Because an organism is wasting investment in uptake of any nonlimiting resource –> natural selection should favor movements toward colimitation

Question 10

Exploitative competition

Answer 10

Indirect competition, competition through resource depletion
Ex. Competition for water, nitrogen, food in the environment

Question 11

In exploitative competition, experimentally lowering resource availability will have the same effect on one individual as

Answer 11

adding the other individual into the environment

Question 12

Interference competition

Answer 12

Direct competition, individuals compete directly for access to a resource

Question 13

Allelopathy

Answer 13

(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

Question 14

Symmetric competition (individual proportional)

Answer 14

when both individuals/species are hurt equally by competition
Ex. belowground roots

Question 15

Asymmetric competition

Answer 15

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

Question 16

Competitive exclusion principle

Answer 16

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

Question 17

Lotka Volterra competition model Basic assumptions

Answer 17

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

Question 18

When do competing species coexist?

Answer 18

When:
K2/β > K1 and K1/α > K2
or rearranged:
α < K1/K2 < 1/β

Question 19

Competition coefficients

Answer 19

α – effect of species 2 on species 1
β – effect of species 1 on species 2

Question 20

If α = 1,

Answer 20

individuals of N2 and N1 are equivalent for N1 pop dynamics.

Question 21

If β = 1

Answer 21

individuals of N2 and N1 are equivalent for N2 pop dynamics.

Question 22

If α = β = 1

Answer 22

stable coexistence at equilibrium is impossible

Question 23

If α and β are close to 1 (0.95)

Answer 23

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

Question 24

If α < 1, β < 1

Answer 24

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

Question 25

______ is the only chance for stable coexistence

Answer 25

α, β less than 1
Intraspecific competition must be stronger than interspecific competition for species to coexist

Question 26

When do competing species coexist at equilibrium?

Answer 26

α < K1/K2 < 1/β

Question 27

Stable coexistence requires

Answer 27

species differences

Question 28

Character displacement

Answer 28

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.

Question 29

Gause’s Paramecium experiments

Answer 29

P. Aurelia and P. caudatum fed on floating bacteria (no stable coexistence)
P. bursaria fed on yeast cells (stable coexistence with P. caudatum)

Question 30

When do competing species coexist?

Answer 30

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

Question 31

How to test of niche differentiation diversity: Diversity and productivity?

Answer 31

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

Question 32

Stable coexistence vs unstable coexistence

Answer 32

Stable coexistence; rare species advantage, many mechanisms
Unstable coexistence; no difference in K’s, α, β