Biology » Population and Community Ecology » Population Demography

Summarizing Population Demography


Populations are individuals of a species that live in a particular habitat. 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.



statistical study of changes in populations over time

life table

table showing the life expectancy of a population member based on its age

mark and recapture

technique used to determine population size in mobile organisms

mortality rate

proportion of population surviving to the beginning of an age interval that die during the age interval

population density

number of population members divided by the area or volume being measured

population size (N)

number of population members in a habitat at the same time


square made of various materials used to determine population size and density in slow moving or stationary organisms

species dispersion pattern

(also, species distribution pattern) spatial location of individuals of a given species within a habitat at a particular point in time

survivorship curve

graph of the number of surviving population members versus the relative age of the member

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