BIOLOGY Volume 1 - A Guide to General Biology - 2004

10. ORGANISMS AND THE ENVIRONMENT

10.7. Population Ecology

A population can be defined as a group of organisms of the same species living in the same area, interbreeding with one another, and isolated to a certain extent from similar groups by geographical barriers. For example, roe deer in a forest tract surrounded by farmland, frogs in a specific mountain valley, or trout in a single lake represent distinct populations. Population studies involve more than simply counting the individuals of a given species in a particular habitat at a given time. More importantly, they aim to determine: 1) how population size grows; 2) how population size is maintained at a certain level; and 3) how and why population size declines. The Study of these issues is known as population dynamics. Typically, researchers analyze such group parameters as population density, birth rate, death rate, survivorship, age Structure, Migrations, and patterns of population growth. Various curves are constructed based on these data. Interactions among populations through competition, predation, and parasitism not only regulate their numbers but also influence The structure of the entire community.

10.7.1. Natality and Mortality

Population size may increase As a result of the immigration of individuals from outside and local reproduction by its members. In mammals, natality (birth rate) is defined as the number of offspring produced per female per unit of time (usually a year).

A population may decrease as a result of emigration and the death of individuals. In population biology, mortality (death rate) is expressed as the number of deaths per hundred or thousand individuals per year.