4.5 Chapter Resources


Populations are individuals of a species that live in a particular habitat. Ecologists measure characteristics of populations: size, density, and distribution pattern. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time. Populations with unlimited resources grow exponentially—with an accelerating growth rate. When resources become limiting, populations follow a logistic growth curve in which population size will level off at the carrying capacity. Humans have increased their carrying capacity through technology, urbanization, and harnessing the energy of fossil fuels. Unchecked human population growth could have dire long-term effects on human welfare and Earth’s ecosystems. Communities include all the different species living in a given area. The variety of these species is referred to as biodiversity. Species may form symbiotic relationships such as commensalism, mutualism, or parasitism. Community structure is described by its foundation and keystone species. Communities respond to environmental disturbances by succession: the predictable appearance of different types of plant species, until a stable community structure is established.

Review Questions

  1. Describe how a researcher would determine the size of a penguin population in Antarctica using the mark and release method.
  2. Describe the growth at various parts of the S-shaped curve of logistic growth.
  3. Give an example of how density-dependent and density-independent factors might interact.
  4. Describe the age structures in rapidly growing countries, slowly growing countries, and countries with zero population growth.
  5. Describe the competitive exclusion principle and its effects on competing species.


OpenStax College. (2013). Concepts of biology. Retrieved from http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@8.10. OpenStax CNX. Available under Creative Commons Attribution License 3.0 (CC BY 3.0).  Modified from Original.

Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0