Chapter Summary

• Species are divided into groups of individuals, or populations, that can vary spatially across their geographic range. Review Figure 54.1A

• A group of geographically isolated populations linked together by dispersal is known as a metapopulation. A species might consist of one or multiple metapopulations, depending on its geographic range. Review Figures 54.1, 54.4

• All populations fluctuate in size over time due to the physical environment, biological interactions, and dispersal. Review Figure 54.2

• Ecologists use a variety of approaches to estimate population sizes, including full censuses, surveys using quadrats or transects, mark–recapture methods, and DNA analysis. Review Figure 54.5, Animation 54.1

• Population growth is the change in population size over time, as reflected by the number of births, deaths, and migrants in and out of the population. Review Equation 54.1

• Exponential growth occurs when the rate of change in population size is constant over time. Review Figure 54.6, Activity 54.1

• Logistic growth occurs when resources are limited, slowing growth to a population’s maximum size (carrying capacity). Review Focus: Key Figure 54.8, Activities 54.2, 54.3

• Factors limiting population growth can be density-dependent when intraspecific competition between individuals affects population growth. Density-independent factors are those that act independently of the population density, such as physical conditions.

• Life tables summarize how survival and fecundity vary with the age, size, or sex of individuals within a population, and incorporate how these demographic events affect population growth. Review Table 54.1

• Species have different types of survivorship curves that reflect mortality patterns over time. Review Figure 54.9, Activity 54.4

• Life history strategies are characterized by lifetime patterns of growth, reproduction, and survival, and can vary at the species and population levels. Review Figure 54.10

• Life history trade-offs arise from genetic and environmental constraints on optimal growth, reproduction, and survival.

• Extremes in life history strategies of species allow for high growth rates (r-strategists) or for persistence at or near the carrying capacity (K-strategists), but most species fall along a continuum between these two strategies. Review Figure 54.15

• Efforts to manage populations are more likely to be successful if they are based on an understanding of life histories and population and metapopulation dynamics.

• Biological control is the use of natural enemies to reduce the population density of an economically damaging species.

• Metapopulations can conserve endangered species if source populations, which serve as a source of individuals to sink populations, can rescue those populations from extinction. Review Figure 54.17, Activity 54.5