Chapter 8 Summary

CONCEPT 8.1 Populations are dynamic entities that vary in size over time and space.

• Populations are groups of individuals of a species that live in the same area and interact with one another.
• The number of individuals in a population changes over time and from one place to another.
• Dispersal can link the populations of a species to one another.
• In species that can reproduce asexually, the members of a population can be defined in terms of genetic individuals (genets) or physiological individuals (ramets).

CONCEPT 8.2 The distributions and abundances of organisms are limited by habitat suitability, historical factors, and dispersal.

• The presence of suitable habitat limits the distribution and abundance of organisms.
• The suitability of habitat depends on abiotic and biotic features of the environment, the interaction between abiotic and biotic factors, and disturbance.
• Dispersal and events in the evolutionary and geological history of Earth also influence the distribution and abundance of organisms.

CONCEPT 8.3 Many species have a patchy distribution of populations across their geographic range.

• No species is found everywhere, since much of Earth is not suitable habitat for its populations.
• Geographic ranges vary considerably in size from one species to another.
• Populations often have a patchy structure at both small and large spatial scales.

CONCEPT 8.4 The dispersion of individuals within a population depends on the location of essential resources, dispersal, and behavioral interactions.

• The dispersion of individuals within a population may be regular, random, or clumped. In the field, clumped dispersions are most common.
• A random or clumped dispersion may match the spatial arrangement of important resources. Clumping may also result from short dispersal distances.
• Behavioral interactions in which individuals repel or attract one another can affect the dispersion of individuals within a population.

CONCEPT 8.5 Population abundances and distributions can be estimated with area-based counts, mark–recapture methods, and niche modeling.

• The most direct way to determine the number of individuals in a population is to count all of them. When this is not possible or practical, area-based counts or mark–recapture methods can be used to estimate the number of individuals in a population.
• The geographic distribution of an organism can be analyzed in terms of its ecological niche, the physical and biological conditions of the environment that the organism needs to grow, survive, and reproduce.
• Niche models can be used to estimate the distribution of an organism when we have insufficient data on its geographic range, or when we want to predict the future locations of its populations.