Factors that Affect population growth
Populations experience changes in growth when organisms are added or removed through births, death, immigration or emigration. These changes are influenced by both density dependent and density independent factors described below.
Density Dependent factors limit population growth based on the size or density of a given popullation. Examples of density dependent factors include intraspecific competition and predation.
Density Independent factors limit population growth based on factors independent of population density. Exmaples include extreme changes in weather or human interventions such as pesticide use.
Population Growth Models
Population ecologists need to quantify rates of change to monitor and evaluate population dynamics. This is accomplished largely by use of three mathematical models. The geometric growth model, exponential growth model and exponential growth model
Geometric Growth Model
- Births are restricted to one part of the year “breeding season”
- - Growth rate is constant and is calculated from yearly change.
N = population number
t = time of flight ((or example, t could be the population size in year one, so t+1 would be the population size in year 2)
t = time of flight ((or example, t could be the population size in year one, so t+1 would be the population size in year 2)
Geometric Growth - Sample Problem
Exponential Growth Model
- No limit in population size
- J shape
- Grow continuously at a fixed rate in a fixed interval of time
- J shape
- Grow continuously at a fixed rate in a fixed interval of time
Exponential Growth - Sample Problem
Logistic Growth Model
- Most common pattern in nature
- Shows the effect of a limiting factor (carrying capacity)
- Shows the effect of a limiting factor (carrying capacity)
r max = maximum intrinsic growth rate
N = population size at give time
k = carrying capacity
N = population size at give time
k = carrying capacity
Logistic Growth - Sample Problem
Example of Logistic Growth - Harbour Seals
Watch this good logistc growth video