1. Populations are described by density, spatial distribution, and growth rate.
Population Ecology

5. Population Characteristics
Populations are groups of the same species in the same area.
Characteristics of population include:
Density
Spatial Distribution
Growth rate

6. Population density
The number of organisms per unit area is population density.

7. Spatial distribution
Dispersion is the pattern of spacing of individuals of a population within an area.
Three kinds: clumped, uniform, and random

9. Population-Limiting Factors
Limiting factors are biotic or abiotic forces that keep population from increasing indefinitely.
Limiting factors are either density-independent or density-dependent.

10. Density-independent factors
Any factor in the environment that does not depend on the number of members in a population per unit area is a density-independent factor.
Usually abiotic, and include:
Weather events
Fire
Human alteration of the landscape
Air, land, and water pollution

11. Density-dependent factors
Any factor in the environment that depends on the number of members in a population per unit area is a density-dependent factor.
Often biotic, and include:
Predation
Competition
Disease
Parasites

12. Population growth rate
The population growth rate (PGR) describes how fast a given population grows.
Natality: birthrate of a population in a given year.
Mortality: death rate of a population in a given year
Emigration: number of individuals moving away from the population
Immigration: number of individuals moving into a population

13. Deaths and emigration remove individuals from a population.
Births
Deaths
Deaths and emigration remove individuals from a population.
Births and immigration add individuals to a population.
Figure 53.3 Population dynamics.
Immigration
Emigration 13

14. Exponential growth model
Occurs when growth rate is proportional to population size.
All populations grow exponentially until they encounter a limiting factor.

15. Logistic growth model:
Occurs when a population’s growth slows or stops following exponential growth.
A population stops increasing when the number of births < number of deaths, or when emigration > immigration.

16. Carrying capacity
Carrying capacity is the maximum number of individuals of a species (pop size) that an environment can support.

17. Reproductive patterns
Species vary in the number of births per reproduction cycle, age that reproduction begins, and in the life span.
Plants and animals are placed into groups based on these patterns.