Module 8 Lesson 4 - 5

Lesson Summary

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The four determining factors of population size are natality, mortality, immigration, and emigration. Natality and immigration increase population size; mortality and emigration decrease population size. Population size is represented as N.

Change in a population is symbolized as ∆N.
The formula for change in population size is ∆N = (natality + immigration) - (mortality + emigration).

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

• Most organisms can be counted by extrapolation from an average of small density samples.
  
  
• Density is determined by D_p = N/A or D_p = N/V.
  
  
• Change in population is calculated by N_final - N_initial.
  
  
• Growth rate gives information about how fast the population is changing:
  
  gr = ∆N/∆t  (gr can be positive or negative.)
  
  
• Per capita growth rate gives information about how much of the change each initial individual is responsible for:
  
  cgr = ∆N/N or (N_final-N_initial)/N_initial   (cgr can be positive or negative.)
  
  
• Populations can be distributed randomly where low competition occurs. Organisms can be clumped in the presence of significant competition. Organisms can be distributed uniformly if there is territoriality or if the population is artificial (such as in agriculture).
  
  

Complete the Lesson 4 set of questions inAssignment 8B and Assignment 8D