Lecture 13 Flashcards
(21 cards)
Assumptions of exponential growth
- No I or E
- Constant b and d
- All individuals are the same
- No age or size or sex structure
- Continuous growth with no time lags
What does no I or E mean?
the population is closed; changes in population depend only on local births and deaths
What does Constant b and d mean?
if a population is going to grow with constant birth and death rates, an unlimited supply of space, food, and
other resources is required. b and d do not vary randomly in time.
What does all individuals are the same mean?
No genetic structure, or if there is, the genetic structure must be the same through time
What does no age or size or sex structure mean=
no differences in b and d among
individuals due to their age or body size or sex
What does continuous growth with no time lags mean?
individuals are being born and dying continuously and the rate of increase change instantly as a function of the current population size
Density Independent Growth
the per capita birth and death rates are independent of the density of the population (i.e. not a function of the population density)
Density Dependent Growth
the per capita birth and death rates are dependent on the density of
the population
What do you expect to happen to the b rates as density increases in dependent growth?
The births will go down because the number of resources is limited as the population grows
What do you expect to happen to the d rates as density increases?
The number of deaths will increase
In a population undergoing logistic growth, the change in population size slows as it approaches
a. K
b. r
c. Ro
d. b
e. b-d
a. K
What is K?
When b = d
When is dN/ dt = 0?
When b=d, so at K the resources are used up
List some biological reasons why we would see the per capita rates being a function of density for a population?
At high density…
- Intraspecific competition: resource limitation and competition for space, food, or resources
- Predation or Pathogens
How are Density independent (per capita rates)?
Exponential increase or decrease
How is Density Dependent (per capita rates?
Logistic Growth to carrying capacity
What are the 5 assumptions of logistic growth?
- Constant carrying capacity
- Linear density dependence
- No immigration or emigration
- Individuals are identical
- Changes in density effects per capita rates instantaneously
In the logistic model of population growth, if the per capita growth rate is greater than zero then…
a. The population declines
b.The population increases because there is no intraspecific competition
c.The population increases because the abundance is below the carrying capacity
d. We can’t know if the population increases or decreases because we don’t know the carrying capacity
c.The population increases because the abundance is below the carrying capacity
Allee effect
In some populations the density dependence is NOT a simple linear relationship
What is referred as the Allee effect?
At low densities, the per capita growth rate can increase as a function of density
What might cause an Allee effect? Why would the per capita growth rate increase as a function of density at low densities?
- Mate limitation
- Limits cooperation
- Plants: not attracting enough pollinators
