CHAPTER 21 Summary

• Ecology is the study of the interactions between organisms and between organisms and their nonliving environment.
• Ecologists study these interactions at a number of levels, including population, community, and ecosystem.
• Living organisms may have a clumped, random, or uniform distribution pattern, depending on ecological and behavioral adaptations. Few organisms fall into strictly one category.
• Population growth is an increase in the number of individuals in a population. The growth rate of a population is defined as the birth rate minus the death rate. Growth rate is also known as the rate of natural increase.
• Exponential growth is the unrestricted growth experienced by a population growing at a constant rate. Logistic growth is the slowing of the growth of a population due to environmental factors such as crowding and lack of food.
• Carrying capacity is the maximum population size that an area can support, given its food supply and other life-sustaining resources. Populations cannot grow exponentially forever; eventually, they hit the carrying capacity for the region and stop growing.
• Population growth can be limited by a variety of factors, including biotic (living) and abiotic (nonliving) parts of the environment.
• Density-independent factors, such as a severely cold winter, can affect a population of any size.
• Density-dependent factors, such as the presence of predators, have different impacts on the population, depending on the size and crowding of individuals in the population.
• Populations in a community are interconnected, the fate of one often influencing the fate of the others.

• MORE TO EXPLORE

  1. Wolves and Moose on Isle Royale http://isleroyalewolf.org/
  2. Vucetich, J. A., and Peterson, R. O. (2013) Ecological studies of wolves on Isle Royale, Annual Report 2012–2013.
  3. PBS. (2007) Nature: In the Valley of the Wolves http://www.pbs.org/wnet/nature/episodes/in-the-valley-of-the-wolves/introduction/212/
  4. Ripple, W. J., and Beschta, R. L (2012) Trophic cascades in Yellowstone: the first 15 years after wolf reintroduction. Biological Conservation 145:205–213.
  5. Seabird Monitoring on the Isle of May, Scotland http://www.ceh.ac.uk/sci_programmes/IsleofMayLong-TermStudy.html