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Population Ecology Population = group of individuals of a single species living in the same general area -density: # individuals/area -dispersion: pattern of spacing between individuals 1. Clumped: Grouped together. Most common. Near required resource 2. Uniform: Evenly spaced. Usually antagonistic interactions. 3. Random: Not common in nature. Determining population size and density:-count every individual-random sampling-mark-recapture method Demography: the study of vital statistics that affect population size-additions occur through birth, subtractions occur through death-life table: age-specific summary of the survival pattern of a population-represent data w a survivorship curve: plot # of individuals in a cohort still alive at each age. --Type I curve: low death rate early in life (ex: humans) --Type II curve: constant death rate over lifespan (ex: squirrels) --Type III curve: high death rate early in life (ex: oysters) Life history: traits that affect an organism’s schedule of reproduction and survival3 variables: --age of sexual maturation --how often an organism reproduces --# of offspring during each eventImportant to know: these traits are evolutionary outcomes, not conscious decisions by organisms Semelparity = big-bang reproduction. Many offspring produced at once. Individual often dies afterwards. less stable environments. Iteroparity = repeated reproduction. Few, but large offspring. More stable environments. Survival rate of offspring and repreated reproduction when resources are limited are critical factors. Change in Population Size Change in population size = births – deathsdelta N/delta t = B – Dwhere N = pop size, t = time, B = births, D = deaths Zero population growth: B = D Exponential population growth: ideal conditions, population grows rapidly-unlimited resources are rare-Logistic model: incorporates carrying capacity (K)-K = maximum stable population which can be sustained by the environment-dN/dt = rmax((K-N)/K)-results in an S-shaped curve Factors that limit population growth:-Density-dependent factors: population matters. Like predation, disease, competition, waste accumulation, physiological factors-Density-independent factors: population NOT a factor. Like natural disasters, fire, flood, weather. K-selection: pop close to carrying capacityr-selection: maximize reproductive success K-selection characteristics:-Population lives around K. High parental care. Low birth numbers. Good survival of young. Density-dependent. Ex: humans, elephants. r-selection characteristics:-Population undergoes exponential growth. Little or no parental care. High birth numbers. Poor survival of young. Density independent. Ex: roaches. Populations can fluctuate due to biotic and abiotic factors. Predator and prey populations are often linked-boom-and-bust cycles due to predator-prey interactions -ex: lynx and snowshoe hare on 10-year cycle Human Population Growth-2 configurations for a stable human population (zero population growth): -high birth/high death -low birth/low death-Demographic transition occurs when population goes from configuration A to configuration B-Can graph/represent visually with age structure diagrams-large base/increasingly smaller toward to – indicates rapid pop growth, high births, high deaths, developing countries-slow growth or no growth – smaller base, ages evenly distributed, developed nations-Global carrying capacity: -UN predicts 7.8-10.8 billion people by the year 2050 (2012 = 7 billion)-Estimated carrying capacity – 10-15 billion???-Ecological Footprint: total land and water area needed for all the resources a person consumes in a population. -1.7 hectares per person is sustainable -US citizens use about 10 hectares per person. Well over K. -limitations, consequences, and solutions…
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