Competition

Question 1

What is competitions effect on sp 1 and sp 2?

Answer 1

Both negative

Question 2

What is competition?

Answer 2

Interactions in which two species negatively influence each other’s population growth rates

Question 3

3 types of competition?

Answer 3

Exploitation competition
Compete for a shared resource

Interference competition
Behaviour that reduces resource exploitation by other individuals/species

Pre-emptive competition
Compete for limited space
Barnacles on rocks

Question 4

Interspecific and infraspecific competition.

Answer 4

Intraspecific competition:
Among individuals within a population
Captured by models with density-dependence (e.g., logistic)

Interspecific competition
Among individuals of different species
Population growth is affect by other species’ population size
(e.g. Lotka-Volterra)

Question 5

Whats competition coefficients?

Answer 5

• Apha

- How much each individual of species 2 reduces carrying capacity of species 1

Question 6

Which colour box is sp 1 and sp2?

Answer 6

-Red box:
species 1 individual (size = 1)
-Blue box:
species 2 individual (size = α12)

Question 7

Whats the frame?

Answer 7

carrying capacity 
of species 1

Question 8

What does more individuals of N2 result in?

Answer 8

Less N1 at equilibrium

Question 9

What does a larger alpha result in?

Answer 9

Steeper growth isocline

Question 10

What are the 4 possible outcomes?

Answer 10

-Sp2 win- N2 isocline above N1
-Sp1 win- N1 isocline above N2
-Co existence- N1 K below N2 on x axis and N2 K below N1 on y axis
-Founder control (unstable)
N1 K above N2 on x axis and N2 K above N1 on y axis

Question 11

How to be a successful competitor?

Answer 11

• Achieve positive growth when competitor at K
• More efficient at exploiting resources
• Lessen effect of competition

Question 12

What does stable coexistence require?

Answer 12

Both species can invade one another

Question 13

Criticisms of Lotka-Volterra competition

Answer 13

Unclear “how” species compete
→ what they are competing for?

α only measure pair-wise competition, not among >2 species (“higher-order interactions”)

Hard to measure parameters

Predictions only confirmed in simple lab experiments

Question 14

“Resource competition” theory

Answer 14

Predicts what species wins without observing them together

Question 15

What s a resource?

Answer 15

• Something in the environment that
  (1) contributes positively to population growth, and
  (2) is consumed in the process

-Examples: Light, nutrients, food
Not examples: Temperature, air

Question 16

Assume per-capita biomass growth depends on what?

Answer 16

The concentration of some resource R

Question 17

What is stable competition equilibrium?

Answer 17

If R < R*, then B(biomass) ↓, consumption ↓, and R ↑

Question 18

What happens when biomass increases?

Answer 18

R is reduced to lowest R*

Question 19

Whats an example of competition for a single resource?

Answer 19

2 species of diatoms (algae) competing for Si

Question 20

Where is the optimum Growth os Species?

Answer 20

Where the growth rate intersects the R*

Question 21

What happens when there are two resources?

Answer 21

Resources not substitutable
Positive growth only if 
R1 > R1*
and 
R2 > R2*

Question 22

What happens when neither R is < R*?

Answer 22

Species at equilibrium

Question 23

Whats the consumption vector?

Answer 23

(c)
Relative rate at which species consumes R1 and R2
Points in direction from (R1,R2) to origin

Question 24

Whats the supply point?

Answer 24

(S): Total amount of R1, R2 that can exist in the environment (without consumption)

Question 25

Whats the supply vector?

Answer 25

(U): Rate of resource replenishment

Points from current (R1,R2) back to S

Question 26

Whats ZNGI?

Answer 26

Zero net growth isocline

Question 27

What happens if S is below ZNGI?

Answer 27

Species can’t persist

Question 28

What happens if S is above ZNGI

Answer 28

• Species can persist
• Equilibrium occurs along ZNGI where consumption vector is opposite supply vector (c = -U)
• Resource that is at R* at this point is the most limiting

Question 29

What does the competition of 2 sp with 2 resources depend on? Which sp will win if they don’t cross?

Answer 29

• The zero net growth isocline

- Species with lower R will win

Question 30

What happens if ZNGI cross?

Answer 30

• Outcome depends on consumption vectors and supply point
• S before any isocline- both go extinct
• S infront of sp 1 isocline- sp 1 wins
• S infront of sp 2 isocline- sp 2 wins
• S infront of both (directly infront of sp 2)- Sp 1 wins
• S infront of both (directly infront of sp 2)- Sp 2 wins

Question 31

Why is coexistence possible?

Answer 31

• Species 2 consumes more of, and is limited by, R1
• Species 1 consumes more of, and is limited by, R2
• Stronger competition with themselves than each other

Question 32

How many species can persist with one resource? 2?

Answer 32

One

Two

Question 33

When is coexistence possible?

Answer 33

Co-existence possible when:

1. Each species can survive on less of one resource than the other species
2. Environment provides adequate supply of both resources
3. Each species consumes more of the resource that is limiting to it