Chapter 52 Population Ecology

Distinguish between density and dispersion of a population Density – the number of individuals per unit area or volume Dispersion- pattern of spacing among individuals within the population

Explain how ecologists may estimate the density of a species It is almost always impractical to count all individuals in a population. They might count the number of individuals in a series of randomly located plots, calculate the average density in the samples, and extrapolate to estimate the population size in the entire area. A sampling technique that researchers commonly use to estimate wildlife populations is the mark-recapture method.

Describe conditions that may result in clumped dispersion, uniform dispersion, and random dispersion of individuals in a population. Dispersion is clumped when individuals aggregate in patches. Plants and fungi are often clumped where soil conditions favor germination and growth. Animals may clump in favorable microenvironments (such as isopods under a fallen log) or to facilitate mating interactions. Dispersion is uniform when individuals are evenly spaced. Animals often exhibit uniform dispersion as a result of territoriality, the defense of a bounded space against encroachment by others. In random dispersion, the position of each individual is independent of the others, and spacing is unpredictable. For example, plants may grow where windblown seeds land. Random patterns are not common in nature.

Describe the characteristics of populations that exhibit Type I, Type II, and Type III survivorship curves.

Explain, with examples, how limited resources and trade-offs may affect life histories Limited resources mandate trade-offs between investment in reproduction and survival. Plants and animals whose young are subject to high mortality rates often produce large numbers of relatively small offspring In other organisms, extra investment on the part of the parent greatly increases the offspring’s chances of survival.

Compare the exponential model of population growth with the logistic model

Explain how an environment’s carrying capacity affects the per capita rate of increase of a population Ecologists define carrying capacity (K) as the maximum stable population size that a particular environment can support. Population growth is greatest when the population is approximately half of the carrying capacity.

Distinguish between r-selected populations and K-selected populations r-selection tends to maximize r, the rate of increase, and occurs in environments in which population densities fluctuate well below K, or when individuals face little competition. K-selection tends to maximize population size and operates in populations living at a density near K.

Explain how density-dependent factors affect population growth. Density-dependent factors have an increased effect on a population as population density increases. This is a type of negative feedback.

Explain, with examples, how biotic and abiotic factors may work together to control a population’s growth. Resource limitation in crowded populations can reduce population growth by reducing reproductive output In animal populations, territoriality may limit density. Population density can also influence the health and thus the survival of organisms. Predation may be an important cause of density-dependent mortality for a prey species if a predator encounters and captures more food as the population density of the prey increases.

Describe boom-and-bust population cycles, explaining possible causes of lynx/hare fluctuations. Three main hypotheses have been proposed to explain the lynx/hare cycles. The cycles may be caused by food shortage during winter. The cycles may be due to predator- prey interactions. The cycles may be affected by a combination of food resource limitation and excessive predation.

Describe the history of human population growth.

Describe the problems associated with estimating Earth’s carrying capacity for the human species.