Regulation of Population Growth

Population growth can’t be maintained at exponential rates indefinitely
Resources to support growth (energy, nutrients, space) are finite- eventually their supply limits the growth and sustenance of the population
key factors that contribute to lower growth rate include:
* competition
* predation
* parasitism
* climate variation/ change
*  intrinsic rate of population growth- reproductive potential, susceptibility to disease

Some control factors vary as the size of the populaton changes (density dependent), while others don’t (density independent)
Increases in density result in decreased birth rates, increased death rates, and greater dispersal from the population (emigration); lead to decreased population growth.
Density independent factors affect population growth at any population size, often leading to unpredictable changes in population size
Evidence indicates that in many populations, as density increases, birth rates decrease and/or death rates increase, which should act to regulate the growth of populations to some potentially stable size
The size of a population that can be supported by the environment is the carrying capacity
We can modify our exponential growth model to include a term with density dependent control that acts to keep the population size near the carrying capacity (K):
(K-N)/K or (1-N/K); when N is small compared to K, the term is near 1; as N approaches K, the term decreases to zero
Incorporating the density dependent term into the exponential growth model gives us logistic growth model:
dN/dt = rN (1 – N/K)
Populations often follow a logistic function after initial colonization of a site