Lecture Notes for Ecology

Chapter 5, Population Dynamics:

Terminology:

Exponential Growth
growth in which the population increase in a period is a fixed percentage of the size of the population at the beginning of the period; the number of individuals increases over time logarithmically (e.g. bacterial cultures).

Components of an exponential growth pattern for a given population (simple example is a bacterial culture in a closed system):
  1. Time Zero - time of establishment of a population; for bacterial culture, time that the culture was inoculated.
  2. Lag Time - time that it takes for the population to start growing; resources must be obtained; habitat and microhabitat establishment; niche definition; population prepares for reproduction (for bacterial cultures: time that the cells need to begin their specific type of metabolism before cell division can occur).
  3. Log Phase - period of exponential (logarithmic) growth.
  4. Stationary Phase - period following exponential growth where number of deaths equals the number of new individuals.
  5. Death Phase - period following the stationary phase where the population is dying due to depletion of resources and or contamination of habitat with waste products.
  6. Range expansion - in an open system, individuals can move to new locations and establish new populations.

Effects of population density on growth in open systems:

  1. Density-independent growth - size of population per given area (numbers of individuals per given area) is not a factor in determining the resulting population size overall; population size, however, stays about the same as when it began (geometric growth rather than exponential growth.
  2. Density dependent growth - size of the population per given area is a factor in determining the resulting population size overall; exponential growth can occur if adequate resources are available and range expansion can occur as in an open system.