In the models that describe population growth, r stands for
a) carrying capacity
b) population density
c) a time interval
d) per capita population growth rate
e) total number of individuals in the population

d) per capita population growth rate

Explanation:

Per capita growth rate of a population is symbolized as "r" in population growth models. Here, "r" is the rate of change of a population on a per capita basis. The change in the population includes both an increase and a decrease in its size.  The per capita growth rate is calculated by subtracting the birth rate of the population from its death rate. Therefore, r= b-d. Here, "b" is the birth rate of the population and "d" is the death rate.

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