Chapter 10 Summary

CONCEPT 10.1 Populations exhibit a wide range of growth patterns, including exponential growth, logistic growth, fluctuations, and regular cycles.

• Of the four major patterns of population growth, the first, exponential growth, can occur for a limited time when conditions are favorable.
• The second pattern, logistic growth, is found in populations that increase initially and then level off at a maximum population size, the carrying capacity.
• The third pattern, population fluctuations, is found in all populations. Some populations fluctuate greatly over time; others fluctuate relatively little.
• The fourth pattern, regular population cycles, is a special type of fluctuation in which alternating periods of high and low abundance occur after nearly constant intervals of time.

CONCEPT 10.2 Delayed density dependence can cause populations to fluctuate in size.

• There is often a time lag between a change in population density and the effect that change has on future population densities.
• A version of the logistic equation that includes a time lag suggests that delayed density dependence can produce several types of population fluctuations, including damped oscillations and stable limit cycles.
• A series of pioneering experiments by A. J. Nicholson indicated that delayed density dependence was a cause of fluctuations in laboratory blowfly populations.

CONCEPT 10.3 The risk of extinction increases greatly in small populations.

• The risk of extinction increases in populations whose growth rate (λ) varies considerably from one year to the next.
• Small populations are at much greater risk of extinction than large populations.
• Small populations can be driven to extinction by chance events associated with genetic drift and inbreeding, demographic stochasticity, environmental stochasticity, and natural catastrophes.

CONCEPT 10.4 Many species have a metapopulation structure in which sets of spatially isolated populations are linked by dispersal.

• Metapopulations are characterized by repeated extinctions and colonizations.
• A metapopulation can be doomed to extinction even when suitable habitat remains.
• Extinction and colonization rates often vary among a metapopulation’s patches.