Module 9S2 Changes in Populations

Lesson 4.9.2S2

4.9.2S2 page 4

Lesson Summary

All population calculations are based on accurate counts of numbers of organisms and their phenotypes/genotypes. Formulas and methods that allow us to consistently and accurately count and analyze population counts are essential.

Most organisms can be counted by extrapolation from an average of small density samples.
Density is determined by Dp = N or Dp = N
A V
Change in population is calculated by Nfinal – Ninitial
Growth rate gives information about how fast the population is changing:

gr = delta N gr can be positive or negative.
Delta t
Per capita growth rate gives information about how much of the change each initial individual is responsible for:

cgr = delta N or Nfinal – Ninitial cgr can also be positive or negative
N Ninitial
Populations can be distributed randomly where there is low competition, organisms can be clumped in the presence of significant competition, and organisms can be distributed uniformly if there is territoriality, or if the population is artificial (e.g. agriculture)

Lesson Glossary

density: the number of individuals in a given unit of area (land) or volume (air or water)

Dp = N or Dp = N
A V

growth rate (gr): the change in the number of individuals in a unit of time

gr = delta N = final population – initial population
delta t change in time
Gr will be positive if the population size is increasing, and negative if it is decreasing.

per capita growth rate (cpr): the rate of change per individual

cgr = delta N or Nfinal – Ninitial
N Ninitial
Cgr can also be positive or negative depending on whether the initial N is.

clumped distribution: organisms grouped together; occurs in highly competitive environments

random distribution: no pattern exists in organism distribution; occurs in environments with little competition

uniform distribution: organisms are equally spaced apart; occurs in artificial environments (e.g.agriculture)