Overview
This lecture covers population ecology, focusing on how populations are measured, described, and the factors that influence their size and distribution.
Population Basics
- A population is a group of organisms of the same species living in the same area.
- Population ecology examines interactions within a population and between the population and its environment.
Measuring Populations
- Population size can be counted, but population density (number of individuals per unit area) is more informative.
- Population density is calculated by dividing the number of organisms by the area they occupy.
- High density means many individuals in a space; low density means fewer.
Factors Affecting Population Density
- Birth (natality) and immigration (organisms moving in) increase population density.
- Death (mortality) and emigration (organisms exiting) decrease population density.
Survivorship Curves
- Survivorship curves graph the number of individuals expected to survive to different ages.
- Type I: High early and mid-life survival, most die late (e.g., humans, high parental care).
- Type II: Constant death rate across ages (e.g., some birds, rodents).
- Type III: High early death rate, few survive to old age (e.g., fish, mosquitoes).
Population Dispersion Patterns
- Dispersion describes how individuals are spread in an area: random, uniform (even), or clumped (grouped).
Population Growth Patterns
- Exponential growth: Population grows without limit.
- Logistic growth: Population grows quickly, then levels off at carrying capacity due to limited resources.
- Carrying capacity is the maximum population size an environment can support.
Limiting Factors
- Limiting factors restrict population growth and can be biotic (living, e.g., competition, predation) or abiotic (non-living, e.g., climate, disasters).
- Density-dependent factors have a bigger effect as population density increases (e.g., disease, competition).
- Density-independent factors impact populations regardless of density (e.g., weather, natural disasters).
Key Terms & Definitions
- Population — group of same-species organisms living in a specific area.
- Population density — number of individuals per unit area.
- Natality — birth rate.
- Mortality — death rate.
- Immigration — movement of individuals into a population.
- Emigration — movement of individuals out of a population.
- Survivorship curve — graph showing the number of survivors at different ages.
- Carrying capacity — maximum population an environment can support.
- Limiting factor — anything that restricts population size.
- Density-dependent — effect varies with population density.
- Density-independent — effect does not vary with population density.
Action Items / Next Steps
- Review examples of calculation for population density.
- Study types of survivorship curves and examples.
- Read about biotic and abiotic limiting factors and their impact on populations.