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Chapter52PopulationEcology[1]

Chapter52PopulationEcology[1] - BLY 122 Chapter 52...

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Chapter 52 Population Ecology 1 BLY 122 C. S. Major Chapter 52 Population Ecology I. Demography A. Population Dynamics 1. A population is a group of individuals from the same species that live in the same area at the same time. 2. Population ecology is the study of how and why the number of individuals in a population changes over time. 3. Demography is the study of factors that determine the size and structure of populations through time. Analyzing birth rates, death rates, immigration rates, and emigration rates is fundamental to demography. B. Life Tables 1. Formal demographic analyses of populations are based on a type of data set called a life table, which summarizes the probability that an individual will survive and reproduce in any given year over the course of its lifetime. a. Example: Researchers set out to estimate the life table of a low-elevation population of Lacerta vivipara in the Netherlands compared with the life table of a high-elevation population. ( Fig. 52.1 ) 2. Survivorship a. Definition: Survivorship is the proportion of offspring produced that survive, on average, to a particular age ( l x , where x represents the age class being considered. It is calculated by dividing the number of individuals in that age class by the number of individuals in the first age class. b. l x = N x / N 0 ( Box 52.1, Eq. 52.1 ) c. Type I curve—survivorship throughout life is high. ( Fig. 52.2a ) d. Type II curve—constant mortality throughout life. ( Fig. 52.2a ) e. Type III curve—high death rate early in life. ( Fig. 52.2a ) 3. Fecundity a. Definition: Fecundity is the number of female offspring produced by each female in the population. ( Box 52.1 ) b. R 0 = l x m x ( Box 52.1, Eq. 52.2 ) c. Lifetime reproduction is a function of fecundity at each age ( m x ) and survivorship to each age class ( l x ). If R 0 is greater than 1, the population is increasing. If R 0 is less than 1, the population is declining. C. The Role of Life History 1. An organism’s life history consists of how the organism allocates resources to growth, reproduction, and activities related to survival. 2. Example: It is not possible to achieve both high fecundity and high survivorship. A trade- off exists between survival and reproduction. ( Fig. 52.3 ) 3. Example: An Arabidopsis plant and an oak tree represent two ends of a broad continuum that exists in life-history characteristics. ( Fig. 52.4 ) II. Population Growth A. The fate of any population depends on four factors: 1. Birth rate 2. Death rate
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Chapter 52 Population Ecology 2 3. Immigration rate 4. Emigration rate B. Exponential Growth 1. Exponential growth occurs when r does not change over time. It does not depend on the number of individuals in the population. Therefore, it is density independent.
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