Bio Test 4 - Test 4 CHAPTER 39 POPULATION ECOLOGY 39.1...

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Test 4 CHAPTER 39: POPULATION ECOLOGY 39.1 Characteristics of Populations A. Each population - individuals of the same species - has certain characteristics: 1. Population size : number of individuals making up its gene pool 2. Age structure : relative proportions of individuals of each age - especially with respect to the reproductive years. 3. Population density : number of individuals per unit of area or volume- The Habitat 4. Population Distribution : pattern in which the population members are dispersed throughout habitat. B. Dispersal in 3 Patterns : 1. Living in Clumps is very common: a. Because suitable physical, chemical, and biological conditions are patchy , not uniform. b. Many animals form social groups. c. Offspring (esp. plants) are forced to live “where they landed.” 2. Uniform dispersion is rare in nature; it is usually the result of fierce competition for limited resources . 3. Random dispersion occurs, if environmental conditions are uniform in the habitat and members are neither attracting nor repelling each other . 39.2 Skip 39.3 Population Size and Exponential Growth A. Gains and Losses 1. Population size: depends on births, immigration (in), deaths, and emigration (out) 2. But numbers may change daily or seasonally during migrations . B. From Zero to Exponential Growth 1. Zero population growth designates a near balance of births and deaths 2. Rate of increase: R = net reproductions/ individual / unit time 3. Growth rate formula: G (growth) = R (rate) x N (number) G = R x N a. Graph of above is a J-shaped curve that becomes steeper with advancing time b. Most populations continue to grow at ever increasing rates- easily measured by noting the “ doubling time C. What is Biotic Potential ? 1. Maximum rate of increase (numbers) under ideal, nonlimiting, conditions 2. Varies from species to species because of: a. The age each generation starts producing
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b. How often production occurs c. And how many offspring are born each time 3. Actual Rate is much lower due to limiting factors. 39.4 Limits on the Growth of Populations A. What are the limiting factors ? 1. Actual Rate of increase is influenced by environmental conditions 2. Limiting factors (nutrient supply, predation, competition for space, pollution and metabolic wastes) provides environmental resistance to population growth . B. Carrying Capacity and Logistic Growth 1. Sustainable Supply of resources defines the carrying capacity for a particular population in a given environment . a. Carrying capacity can vary overtime, expressed graphically in the S-shaped curve pattern called logistic growth . 2. Logistic growth deals with density-Dependent controls a. These factors expert their effects in proportion to the number of individuals present . b. The include: competition for resources, prediation, parasitism and disease C. Density-Independent Factors 1. Weather events increase the death rate without respect to the numbers present.
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