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Population Ecology

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Population Ecology. Chapter 52. Population - group of individuals living in same area at same time. Population density - # of individuals per unit area. Population dispersion - arrangement of population in area. Dispersion patterns happen 3 ways. 1 Clumped dispersion - individuals in groups.

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Population - group of individuals living in same area at same time.
  • Population density - # of individuals per unit area.
  • Population dispersion - arrangement of population in area.
Dispersion patterns happen 3 ways.
  • 1Clumped dispersion - individuals in groups.
  • 2Uniform dispersion – individuals evenly spaced out.
  • 3Random dispersion - individuals live regardless of where other individuals live.
Demography - study of statistics of a population.
  • Life tables - show summary of specific ages of population and survival rates.
Reproductive tables - reproductive rates at various ages.
  • Focus only on females and not males in these tables.
Life history - traits that affect organism’s schedule of reproduction and survival.
  • 1Big-bang reproduction (produce large number of offspring sometimes followed by the organism’s death)
  • Known as semelparity.
2Repeated reproductive episode - organism produces smaller numbers of offspring.
  • This is also known as iteroparity.
Change in population - # of births minus # of deaths during that same time.
  • Equation : N/t = r; r= difference between birth and death rates, N= change in population size, and t= change in time.
Limitations on population growth due to resources.
  • K = carrying capacity.
  • Carrying capacity – max # of individuals an area can handle based on resources.
Logistic population growth model - incorporates affect of population density on rate of increase.
  • Carrying capacity cannot be exceeded - graph is S-shaped.

Carrying capacity

equals change in

population size




Cannot exceed

carrying capacity

Life histories - predict how population will reproduce.
  • 1K-selection - live and reproduce around K.
  • 2r-selection - high rates of reproduction, but live in environments where populations are well below K.
2 factors determine the growth of a population.
  • 1Density-dependent factors increase their effect as density increases (negative feedback)
  • 2Density-independent factors - not affected by density increase.
Negative feedback - caused by several different factors.
  • One - resources (force populations to stop reproducing if conditions are crowded)

As # of planted seeds increase,

# reproducing decreases

Competition for resources can force decreased reproduction rates.
  • Need to defend space can reduce population size.
  • Predation can decrease the size.
Human population has been steadily growing since 1650.
  • Zero transition growth # of births = # of deaths.
  • Only way to steady out population growth.
One of the difficulties with population growth is looking at the distribution of ages.
  • The problem is that the carrying capacity of Earth has not been determined.