8.3 Population Ecology

• Population

  A group of organisms comprised of the same species in a particular area
• Populations

  • Individuals interact with one another and with the environment in complex ways
  • Individuals within a population usually interbreed with one another more than interbreeding with individuals from other populations
  • Many adaptations are related to obtaining and using energy in a particular environment
• Food availability affects population size
• When food is less available, the population size decreases, less food energy is available to support individuals, reproduction rates decrease, and offspring survivability decreases
• When food is readily available, the population size increases, reproduction rates increase, more food for offspring, and survival rates increase
• Species have adaptations that aid in survival when energy availability changes (e.g. storage of fat, losing/growing leaves, migrating)
• Factors affecting population growth

  • Age at reproductive maturity
  • Number of offspring produced
  • Frequency of reproduction
  • Survival of offspring to reproductive maturity
• Population growth equation

  dn/dt = b - d (where dn is change in population size, dt is change in time, b is birth rate, and d is death rate)
• Exponential growth

  Sharp increase in the growth of a population under ideal conditions when resources are abundant
• Exponential growth occurs because the number of organisms added in each generation increases as the population gets larger, with more individuals reproducing, while the time to produce an offspring stays the same
• Exponential growth equation

  dn/dt = rN (where dn is change in population size, dt is change in time, r is the maximum per capita growth rate, and N is the population size)
• Exponential growth

  • J-shaped curve