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Population Ecology & Population Limiting Factors notes.docx

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University of Toronto St. George
Paul Thompson

Population Ecology:  25% of amphibians danger of going extinct  Earths pop doubled in less than 50yrs  Pop Ecology – study of what factors affect pop and why a pop changes overtime o Study in growth, regulation, dynamics and demography o explains organism’s life history – its growth, development, reproduction and survival  Salmon, bamboos, insects die immediately after reproducing, others reproduce repeatedly  Semelparity vs Iteroparity Population Limiting Factors:  Grow at geometric or exponential rates in presence of unlimited resources o Geometric – grow through pulsed reproduction (annual deer reproduction during mating seasons) o Exponential – humans, bacteria, insects, etc – all pops have exponential growth in favorable enviros and at low pop densities  Applies to new establishing enviros, with low initial pop density  Pop growth eventually slows and ceases to increase o Logistic Growth – resources deplete, pop growth rate very slow and stops  Carrying Capacity (K) – point at which growth stops  Number of individuals of a particular pop that enviro can support – pop size become constant (birth rates = death rates), pop growth = 0  Lemmings – small rodents (arctic of Greenland) – experiences rapid fluctuations in pop density o Collard lemming – limiting factor of pop size was predation pressure (foxes, owls, stoats)  Density dependant  As lemmings increased, more predation  increase in stoat pop  collapse in lemming pop ;; collapse in stoat pop  cycle repeats Density Dependant Limitation: increase pop size reduces available resources ;; limiting growth  Disease, competition and predation – biotic factors  Can have positive or negative correlation to pop size o Positive = limiting factors increase (intensity) with the size of pop – limit growth as pop size increases  affects individuals more strongly o Negative = pop growth limited at low dens
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