Unit 4 Lecture 21

Question 1

What is the difference between resources relevant to competition and resources not relevant for competition?

Answer 1

• One organism can reduce access to another (food, water, light for plants when shading happens, space, refuge, nesting sites
• Affect all organisms regardless of density (temperature, pH, wind)

Question 2

What is intraspecific competition?

Answer 2

Competition WITHIN species
- Acorn barnacles for space
- Wolves for food
- Redwood trees for light

Question 3

Intraspecific competition can cause what?

Answer 3

1. Density-dependent reduction in survival: carrying capacity is an intraspecific competition and the reason why we cannot have more is because they compete with each other for survival causing a density-dependent reduction in survival
2. increase in dispersal when populations get too large
3. Natural selection

Question 4

What is interspecific competition

Answer 4

Competition between species
- Two species that use the same resource
- Competitors: limit each other’s ability to grow/survive/reproduce

Question 5

What are the 2 types of competition?

Answer 5

1. Exploitation competition: use by one species reduces resource supply for other species
2. Interference competition: One species reduces exploitation efficiency of the other (disrupt, weaken or kill other species)

Question 6

Explain an example of interspecific competition over seeds

Answer 6

Rodents and Ants both eat seeds but prefer slightly different sized seeds
- Looked at how competition was occurring in dessert rodents and ants
- Saw that ants and rodents ate the same species so they wanted to see if two different species would compete

Question 7

What were the 3 ways they tested the ant and rodent study?

Answer 7

1. Exclude rodents and track population size of ants
2. Exclude ants and track population size of rodents

Question 8

What was the result of the rodent & ant study?

Answer 8

When rodents were removed there was a 71% increase in ant population

When ants were removed, there was an 18% increase in rodents

Question 9

What kind of competition is the rodents v ants study?

Answer 9

Exploitation (they aren’t actively fighting each other for the seeds, and are just reducing the availability)

Question 10

Explain the experiment with the two diatom species

Answer 10

• Took two diatom species where they were grown in two separate vials filled with silica and measured the population over time
• Both species started at a lower population, then grew, then leveled off
• Synedra reduced the concentration of the silica more

Question 11

What happened when the two diatoms were placed in a vial together?

Answer 11

Asterionella goes extinct because when placed together they compete for silica
- This is because Synadra was able to drain the silica concentration further down than asterionella to a point where asterionella could not maintain a constant population size

Question 12

Explain the Lotka-Volterra competition model

Answer 12

dN/dt = rN (1-N/K)
- logisitic growth equation models intraspecific competition
- K represents when dN/dt = 0

Question 13

What is the equation for interspecific competition that shows the effect on population growth

Answer 13

dN/dt = rN (1- (N1+ 𝛼12 N2)/K)

𝛼12: How much each individual of species 2 affects/reduces/increases the size of species 1

Question 14

If 𝛼12 > 1, this means what?

Answer 14

Interspecific competition is stronger than intraspecific competition

-𝛼12 is the per capita impact of interspecific competition vs. per capita impact of intraspecific competition

Question 15

If 𝛼12 < 1, this means what?

Answer 15

There is still interspecific competition
- But effect of each individual of species 2 on species 1 is less than species 1 on itself
- Intra > inter

Question 16

What does it mean when dN/dt = 0

Answer 16

Population is no longer growing
- N = K

Question 17

When there is interspecific competition when is the population no longer growing?

Answer 17

K - 𝛼12(N2) = 0 or
N = K- 𝛼12(N2)

Question 18

What does competitive exclusion mean?

Answer 18

When interspecific competition drives a species extinct
- So the lotka-volterra competition equation allows us to determine when 2 species can coexist

Question 19

What is the competitive exclusion principle?

Answer 19

1. If two species share a limited resource, they will compete for that resource
2. Species best at exploiting the resource will eliminate or exclude the other
3. Complete competitions cannot coexist (species that share the same resource)

Question 20

What are the criteria for stable coexistence?

Answer 20

Both species has to be able to maintain dN/dt > 0 even when the other species is abundant

Question 21

When can species 1 persist? species 2?

Answer 21

1. When N1 = 0 or N2 = K2
   - K1/K2 > 𝛼12
2. When N2 = 0 0r N1 = K1
   - K1/K2 < 1/ 𝛼21