Ch 8: Population Change

r-selected species

High population growth rate. Small body size, early maturity, short life span, large broods, and little or no parental care.

Usually opportunists found in variable, temporary, or unpredictable environments where the probability of long-term survival is low.


Examples: mosquitoes and dandelions/weeds.

k-selected speices

Maximizes the change of surviving where the number of individuals is near the carrying capacity of the environment.

Do not produce large number of offspring, long life spans with slow development, late reproduction, large body size, and low reproductive rate.

Animals invest in the parental care of their young. K-strategists are found in relatively constant or stable environments, where they have high competitive ability.


Examples: Redwood trees.

Type I Survivorship

Those in the young/preproductive and reproductive stage have a high probability of living. The probability of survival decreases more rapidly with age. Death is concentrated later in life. 


Example: Humans and Elephants

Type III Survivorship

The probability of death is greatest early in life, and those individuals that avoid early death subsequently have a high probability of survival.


Example: many fish species and oysters. 

Type II Survivorship

Intermediate between types I and III.

Probability of survival does not change with age. 

The probability of death is likely across all age groups, resulting in a lineral decline in survivorship.

 Death usually occurs in random events, with little age bias.


Examples: lizards. 

Thomas Malthus
British economist that recognized that the human population cannot increase indefinitely.
Population Doubling Time formula
T = 70/r