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Exam 4 Study Notes

# Exam 4 Study Notes - Exam 4 Study Notes 52 53 54 55 A...

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Exam 4 Study Notes: 52, 53, 54, 55 A population is a group of individuals of the same species that occupy the same area at the same time. A community is an assemblage of interacting species. An ecosystem is populations of organisms and their interaction with the physical or abiotic environment, connected by the movement of energy, nutrients, and organisms. Population ecology is the study of how and why the number of individuals in a population changes over time. Population size changes in response to changes in birth, death, immigration, and emigration rates. The study of these factors is demography . Biologists use a variety of mathematical and analytical tools to study population ecology/demography. Life tables summarize the probability that an individual will survive and reproduce in any given year over its entire lifetime. They show that individuals may have distinct ways of allocating energy and resources to activities that promote survival versus activities that promote reproduction. This tradeoff between survival and reproduction is the most fundamental aspect of a species’ life history. The growth rate of a population can be calculated from life-table data or from the direct observation of changes in population size over time. Exponential growth occurs when the per- capita growth rate, r , does not change over time. With discrete generations (no overlap): N t+1 = R 0 N t and N t = R 0 t N 0 where R 0 is the per capita net reproductive rate (average # of female offspring a female produces every generation. If R 0 = 1, then N does not change. If R 0 > 1, then the population is growing and if R 0 < 1, then the population is declining. With continuous generations and no immigration or emigration: r (intrinsic rate of increase) is the difference between births and deaths per time interval. ΔN/Δt = dN/dt = (b-d)N = rN, so N t+1 = e rt N 0 . If r = 0, population replaces itself. If r < 0, the population is increasing. If r > 0, the population is decreasing. This assumes no seasonality, identical organisms (no age structure), and unlimited resources. Eventually, however, growing populations approach the carrying capacity of their environment— resulting in logistic growth. As population density increases, survivorship (probability that an individual will live from time t to time t 1 ) and fecundity (number of female offspring produced per female from t to t 1 ) may decrease—leading to increased death rates, lowered birth rates, and a reduction in growth rate. Age-specific fecundity is the average number of offspring produced by a female of a given age class. Changes in population size through time may occur as a result of changes in the age structure of populations—specifically the number of juveniles in various age classes. (Few juveniles, many adults may be declining or stable in size… Many juveniles = likely rapid increase in size)

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Immigration rates and generation time (the average time between a mother’s first offspring and her daughter’s) also impact a population’s future.
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Exam 4 Study Notes - Exam 4 Study Notes 52 53 54 55 A...

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