Lecture 23: Population Regulation, Intraspecific Competition

Question 1

What assumptions do the logistic and geometric growth models make?

Answer 1

1. Closed population
2. Per capita births/deaths are constant – unlimited food
3. No competition, predation, disease
4. No age or size structure (all equal probability of giving birth)
5. Growth depends on current pop. size, not a past pop. size

Question 2

What are the limits on population growth?

Answer 2

Density INdependent factors: affect population size regardless of density

Density DEpendent factors: affect population size in relation to population density

Question 3

What are the two types of dependence for density-dependent factors?

Answer 3

1. Negative density dependence: growth rate DECLINES with increasing density
   (ex. competition for limiting resources).
2. Positive density dependence (“Allee effects”): growth rate INCREASES with increasing density
   (ex. easier to find mates, less pollen-limitation, inbreeding less likely, lower per capita predation risk)

Question 4

What is the effect of increasing resources on carrying capacity (K)?

Answer 4

Increases K

Question 5

Logistic growth model: delayed density dependence
(ex. when births occur during one season and mating occurs during another)

Question 6

intraspecific competition: logistic growth model

negative density dependence:

Answer 6

-(negative) density dependence:
b’ = b – aN d’ = d + cN

-birth rate should decrease as N increases (competition); death rate should increase

-b and a, d and c, are constants; a and c are measures of the strength of density dependence

-when N small, actual birth rate (b’) is similar to b; actual death rate (d’) is similar to d

-when N gets larger, actual birth rate declines, death rate increases

Question 7

Using the Intraspecific competition: logistic growth model, determine when the population will increase

(dN/dt>1)

Answer 7

Question 8

Using the Intraspecific competition: logistic growth model, determine when the population will decrease?

(dN/dt <1)

Answer 8

Question 10

Intraspecific competition: logistic growth model (this looks useful)

Answer 10

Question 11

logistic growth model – delayed density dependence

Answer 11

births may be in response to earlier conditions; e.g., mating may occur in fall, but births
may only happen following spring when population size is very different.
35