14998549-Chapter-52-Population-Ecology - Chapter 52...

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Lecture Outline Overview: Earth’s Fluctuating Populations To understand human population growth, we must consider the general principles of population ecology. Population ecology is the study of populations in relation to the environment, including environmental influences on population density and distribution, age structure, and population size. Concept 52.1 Dynamic biological processes influence population density, dispersion, and demography A population is a group of individuals of a single species that live in the same general area. Members of a population rely on the same resources, are influenced by similar environmental factors, and have a high likelihood of interacting with and breeding with one another. Populations can evolve through natural selection acting on heritable variations among individuals and changing the frequencies of various traits over time. Two important characteristics of any population are density and the spacing of individuals. Every population has a specific size and specific geographical boundaries. The density of a population is measured as the number of individuals per unit area or volume. The dispersion of a population is the pattern of spacing among individuals within the geographic boundaries. Measuring density of populations is a difficult task. We can count individuals, but we usually estimate population numbers. It is almost always impractical to count all individuals in a population. Instead, ecologists use a variety of sampling techniques to estimate densities and total population sizes. For example, 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. Such estimates are accurate when there are many sample plots and a homogeneous habitat. A sampling technique that researchers commonly use to estimate wildlife populations is the mark-recapture method. Individuals are trapped and captured, marked with a tag, recorded, and then released. After a period of time has elapsed, traps are set again, and individuals are captured and identified. The second capture yields both marked and unmarked individuals. From these data, researchers estimate the total number of individuals in the population. The mark-recapture method assumes that each marked individual has the same probability of being trapped as each unmarked individual. This may not be a safe assumption, as trapped individuals may be more or less likely to be trapped a second time. Density results from dynamic interplay between processes that add individuals to a population and those that remove individuals from it. Additions to a population occur through birth (including all forms of reproduction) and immigration (the influx
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This note was uploaded on 01/12/2012 for the course BILD 2 taught by Professor Schroeder during the Spring '08 term at UCSD.

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14998549-Chapter-52-Population-Ecology - Chapter 52...

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