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CHAPTER 53 - CHAPTER 53 POPULATION ECOLOGY Population...

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CHAPTER 53: POPULATION ECOLOGY Population Ecology – the study of populations in relation to environment, including environmental influences on density and distribute, age structures, 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 living in the same general area Density and Dispersion Density is the number of individuals per unit area or volume Dispersion is the pattern of spacing among individuals within the boundaries of the population Density: A Dynamic Perspective In most cases, it is impractical or impossible to count all individuals in a population Sampling techniques can be used to estimate densities and total population sizes Population size can be estimated Density is the result of an interplay between processes that add individuals to a population and those that remove individuals Immigration – influx of new individuals from other areas parallels with birth rate Emigration – movement of individuals out of a population parallels with death rates In a clumped dispersion , individuals aggregate in patches A clumped dispersion may be influenced by resource availability and behavior Clumped. For many animals, such as these starfish, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory. A uniform dispersion is one in which individuals are evenly distributed It may be influenced by social interactions such as territoriality Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors. In a random dispersion , the position of each individual is independent of other individuals It occurs in the absence of strong attraction or repulsions Dandelions grow from windblown seeds that land at random and later germinate. Demographics Demography is the study of the vital statistics of a population and how they change over time Death rates and birth rates are of particular interest to demographers Life Tables A life table is an age-specific summary of the survival pattern of a population It is best made by following the fate of a cohort , made by the fate of a group of individuals of same age class The life table of Belding’s ground squirrels reveals many things about this
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population Survivorship Curves A survivorship curve is a graphic way of representing the data in a life table The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate Survivorship curves can be classified into three general types: Type I, Type II, and Type III Type I - Humans – low death rates during early/middle life then increase among older age groups
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