Module 8
1. Module 8
1.33. Page 3
Module 8—Populations, Individuals, and Gene Pools
Lesson Summary
This lesson focused on the following question:
- What are the factors that influence population size?
- How do these factors influence population change?
The four factors that determine population size are termed determining factors and include natality, mortality, immigration, and emigration. Natality and immigration increase population size; mortality and emigration decrease population size. Population size is represented as N.
Change in a population is symbolized as ∆N. The formula for change in population size is ∆N = (natality + immigration) – (mortality + emigration).
The determiners of population size influence population change because immigration and emigration can add or remove alleles from a population. Populations with restricted immigration and emigration, such as game reserves and wildlife parks, will have reduced genetic variability, show more genetic drift, and be less able to survive environmental change.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
emigration: number of individuals that leave the population; due to the same reasons as immigration
immigration: number of individuals entering the population from outside; can be due to abiotic factors (e.g., escape from fire, drought, flood, climate change) or biotic (e.g., increased competition)
mortality: number of deaths; due to starvation (competition), predation, or disease
natality: number of births; tends to increase with food supply and decrease with competition
population determiners: four factors that change the numbers of individuals in the population: natality, mortality, immigration, and emigration