Ecologists measure characteristics of populations: size, density, dispersion pattern, age structure, and sex ratio. Life tables are useful to calculate life expectancies of individual population members.

Survivorship curves show the number of individuals surviving at each age interval plotted versus time All species have evolved a pattern of living, called a life history strategy, in which they partition energy for growth, maintenance, and reproduction.

ecology — the study of the relationships among living organisms and their environment. life history — inherited pattern of resource allocation under the influence of natural selection and other evolutionary forces. survivorship curve — graph of the number of surviving population members versus the relative age of the member. life table — table showing the life expectancy of a population member based on its age.