Competition I

Question 1

Three types of species interactions

Answer 1

• trophic interactions
• reproductive interactions
• habitat related

Question 2

How does competition influence population dynamics?

Answer 2

something “breaks” exponential growth at K/2
- usually is it intraspecific competition responsible for this effect

Question 3

What are the two types of competition?

Answer 3

1. intraspecific - within species competition
2. interspecific competition - between species competition

Question 4

Two modes of competition

Answer 4

1. interference - direct
2. exploitative - indirect (individuals do not interact)

Question 5

Intraspecific Competition

Answer 5

• between individuals of the SAME species
• usually has a stronger effect on population growth
• leads to fitness reduction in both individuals, but the more fit individuals survive and are able to reproduce
• can be both direct and indirect
• if resources are infinite, intraspecific does not occur

Question 6

Interspecific Competition

Answer 6

• between individuals of different species
• occurs when two species share the same ecological niche
• if resources are not unlimited, fitness will suffer in at least one of the two species
• can be both direct and indirect
• usually plays less a roll in population dynamics than within-species

Question 7

What is Interference Competition?

Answer 7

direct aggressive interaction between individuals
- exhibited by both animals and plants, but most common in animals

Question 8

What is Exploitative competition?

Answer 8

• indirect competition to secure resources first
• more common in plants
• as the resources becomes limiting the two start to compete by increasing uptake efficiency and depleting the resource, to the detriment of the other competitor

Question 9

What is the Self Thinning Rule

Answer 9

predicts that plants will decrease in population density (self-thin) as the total biomass of the population increases
- as a stand of plants develops, more and more biomass composed of fewer and fewer individuals
- observed mostly in monodominant stands (e.g., plantations)

Question 10

Why is competition more common in plants?

Answer 10

1. plants exist in higher densities than animals
2. plants are sessile and can’t really move out of the way

Question 11

Phillip Grime’s Proposal (1973)

Answer 11

competition should be highest when there is high resource availability because productivity will be highest at this point, and that at low resource availability competition should be lowest

Question 12

David Tilman (1987)

Answer 12

• argued that competition should be high at both high and low resource availability
• the difference lies in where and when competition occurs

Question 13

Examples of competition influences evolutionary trajectories:

Answer 13

1. Tansley (1917): experiement with Galium Plants
2. Connell (1961a.b): experiment with barnacles

Question 14

Competitive exclusion principle

Answer 14

two species with the same niche cannot co-exist indefinitely
- aka Gause’s law
- stable coexistence rarely occurs

Question 15

When does exclusion not occur?

Answer 15

• when disease and predation are the bigger limiting factors
• in extreme, or highly variable environments (deserts, lake)

Question 16

Resource partitioning

Answer 16

• two species divide out resources
• ex. galapagos finches

Question 17

Conditional Partitioning and example

Answer 17

• occurs when species differ in their competitive ability based on varying environmental conditions
• ex. in Sonoran desert, some annual plants germinate best in wet years; others in dry years
• aka temporal niche differentiation

Question 18

What is Character Displacement?

Answer 18

changes in the characteristics of a species’ population (morphology, behaviour, etc.) as a consequence of natural selection for reduced competition in regions where species co-occur

Question 19

Testable Criteria for Character Displacement? (6 of them)

Answer 19

1. random chance should be ruled out
2. phenotypic differences must have genetic basis
3. phenotypic differences in sympatry should result from evolutionary shifts
4. phenotypic differences should relate to resource use
5. sites of sympatry and allopatry should not differ in food or other major environmental features
6. should be evidence that similar phenotypes actually compete for resource