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Unformatted text preview: 03/26/09 OUTLINE FOR LECTURES ON ECOLOGY Text : Chapters 26 through 28 of Audesirk, Audesirk and Byers. Lectures I. Population Dynamics (Chapter 26). A. A population is defined as a collection of individuals of the same species that routinely interact with each other (i.e., they are in the same geographical area at the same time). To understand the mechanics of population growth, we will consider two types of growth curves, the exponential, whose formula is G = rN, and the logistic, whose formula is: G = rN K - N K In these formulas, G = growth rate; N = number of individuals in the population; r = net reproductive rate (which is b minus d , where b = birth rate and d = death rate) and K = the carrying capacity of the populations habitat. 1. As long as the birth rate is even slightly greater than the death rate, a population will continue to grow exponentially. The exponential curve is largely theoretical since it can only be seen where K = infinity. The resources required by a population are never unlimited; thus one expects to routinely see populations following a logistic growth curve. The first part of the equation for a logistic curve represents exponential growth. The second part acknowledges the fact that K does not = infinity. As N approaches K, the growth of the population slows and it stops when b = d and N = K. 2. There are four parts to a logistic curve: the phase of exponential growth (where b >> d), the inflection point where the curve begins to depart from the exponential because resources are limited (thus b begins to decrease and d begins to increase), the phase of decelerating growth (where b is still > d) and the asymptote where b = d. 3. Each part of the logistic curve has its own characteristic age distribution. Thus a populations age distribution can be used to predict the rate at which it will grow in the near future. B. Different species have evolved different life history strategies. 1. Characteristics of an r-selected species: short life span, high reproductive potential (rapid production of many young), rapid maturation of young, and little or no parental care. 2. Characteristics of a K-selected species: long life span, low reproductive potential, slow maturation of young with lots of parental care. 3. K- and r-selection are relative terms, as will be demonstrated by comparing voles, coyotes and humans....
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- Spring '09