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Chapter 45

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BIOL 1001
Tamara Kelly

Chapter 45 Population Ecology 412012 23600 PM 451 The Science of Ecology Ecology can be divided into four levels of organization Organismal ecology researchers study organism to determine genetic biochemical and behavioural adaptations to abiotic environment Population Ecology researchers focus on groups of individuals that live together how size and other characteristics change in space and time Community ecology examines populations of different species that live together in one area are sympatric Analyzes how predation competition and ecological disturbances influence a community Ecosystem ecology explores how nutrient cycle and energy flows between an ecological community and abiotic environment 452 Population Characteristics Seven characteristics can be described for any population 1 Geographic Range the overall spatial boundaries within which a population lives Every population also occupies a habitat the specific environment in which it lives characterized by its biotic and abiotic factors It can vary in its magnitude for different populations 2 Population Size and Density species with a larger body size generally have a lower population density A lower population density means that the organisms have more access to the resources 3 Population Dispersion the spatial distribution of individuals within the geographic range There are three patterns of distribution Clumped dispersion occurs in three situations suitable conditions are often patchily distributed Secondly populations of some social animals are clumped so its easier to find a mate eg elephants Third populations can be clumped when species reproduce by asexual clones that remain attached to the parents Uniform dispersion occurs when individuals repel each other due to shortage of supplies Territorial behaviour can also lead to uniform dispersion Plants and animals can develop an interrelationRandom dispersion occurs when environmental conditions do not vary much within a habitat and individuals are neither attracted nor repelled by others of their species eg spiders Dispersion can vary among animals and populations can display different types of dispersions at different times or stages of life 4 Age Structure the relative number of individuals in each age class They are classified as prereproductive reproductive or postreproductive5 Generation Time the average time between the birth of an offspring and the birth of its offspring Usually short in species that reach sexual maturity at a small body size their population grows rapidly 6 Sex Ratio the relative proportions of males and females The number of females in a population has a general impact on the number of offspring 7 Proportion Reproducing the proportion of individuals in a population that are reproducing Pg 1115 CaptureRecapture This technique is used to estimate the population of mobile animals in a restricted geographic range You capture a bunch of animals in a species mark or tag them and release them into the wild Later you take another large sample of animals and look at the ratio of marked to unmarked animals and plug it into this equation to find the ratio nx nn 12m2There are several assumptions that is critical to the accuracy 1 Being marked has no effect on survival 2 Marked and unmarked individuals mix randomly in the population 3 No migration into to or out of the population occurs during estimation 4 Marked individuals are just as likely to be captured as unmarked ones 453 Demography Demography the statistical study of the processes that change a populations size and density through time Only few individuals survive to the maximum age possible Mortality results from starvation diseases etc Life table summarizes the demographic characteristics of a population Cohort used to make the life table it is a group of individuals of similar age at birth and monitor their survival until all members of the cohort die If their lifespan is more than a few years you can just monitor them for a couple of years recording the ages at which members die and extrapolating those results over a species lifespan Lifespan is split into intervals of appropriate length Mortality can be split into two different ways 1 Agespecific mortality the proportion of individuals alive at the start of an age interval that died during that age interval 2 Agespecific survivorship the proportion of individuals alive at the start of an age interval that survived until the start of the next age interval
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