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Bio102-Chap4Notes - Populations Themes 1 2 3 4 Population...

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Populations Themes 1. Population Attributes 2. Dynamics of Population Growth Exponential growth (Biotic potential) Logistic growth (Environ. resistance) 3. Reproductive Strategies 4. Population Demography Survivorship Age structure 1. Population attributes Population = a group of organisms of the same species that occurs in a particular area Boundaries somewhat arbitrary Members can potentially interbreed Attributes Abundance - total numbers Density - #s per unit area Dispersion - distribution of individuals in space Structure - makeup of individuals (age, sex, size, ) 2. Dynamics of Population Growth a. Exponential Growth - Growth at a constant rate of increase per unit time (= Geometric) = “J-shaped” growth Arithmetic Growth (Growth at a constant amount per unit time) Population grows as a function of its intrinsic growth rate (r): 1) N = (Births - Deaths), 2) So if, r = B irths - D eaths, 3) Then, per capita, N = r • N, If r > 0, pop. grows exponentially Population size over time: N t = N (t-1) e rt Doubling Time of a population = 70 / r (%) When pop. increases at its maximum r —> Biotic Potential Pop. increases as a % of its current size (like compound interest) Function of its genetic potential Varies with species b. Logistic Growth No pop. grows exponentially forever —> ultimately limited by its environment = Environmental Resistance Growth rates regulated by environmental factors = Logistic Growth “S-Shaped” curve Growth rate slows as population approaches its Carrying Capacity Growth of some laboratory populations fits the S-shaped curves fairly well Logistic model provides a basis to which we can compare real populations Natural populations tend to oscillate over time Population Oscillations (3 stages): Malthusian Growth (Irruptive Growth) Population explosions driven by biotic potential Overshoot - Population exceeds carrying capacity of its environment Dieback - Negative growth Severity of dieback related to the extent of overshoot
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Severe overshoot of Carrying Capacity may reduce K in future Factors Regulating Population Growth:
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