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Lecture 11

Biol 3446B Lecture 11.docx

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Western University
Biology 3446B
Robert Solomon

Lecture 11 – Population Size and Reproduction Environmental factors (nutrition, weather, predation, disease) that influence reproduction often have greater impacts on reproduction when populations are large Large population = large competition for food and cover  some animals and their young end up in poorer habitats (b/c less food and less cover)  lots of crowding = lots of stress = decreased reproduction Ecological Density = # of animals relative to the quantity and quality of their habitat resources Maximum Total Reproduction (yield) occurs at an intermediate density and reproductive rate Ecological Density and Reproduction - Population density is often used as a measure of crowding, or of stress, or to indicate competition for resources - But density alone is a poor measure of these parameters Population density can be measures = # of animals/ unit area Ecological density cannot be measured exactly, so used indicators (i.e. condition of animals, reproductive rate, mortality rate) Wildlife Mortality In a stable population, # of deaths = # of births Species with high biotic potential have high birth and death rates vs. species with low biotic potential Normal Mortality These rates and type of mortality that have been common in the species’ evolutionary history Species are adapted to this mortality: - Anatomically - Physiologically - Behaviourally Most wildlife mortality is normal – and is good for population Normal mortality is an agent of natural selection  removes inferior animals, maintains genetic quality Also keeps population in balance with resources (or restores balance) Abnormal Mortality - Rates and types of mortality that have not been common in a species’ history - Abnormal mortality (introduced disease, or predator) can drastically reduce wildlife populations – even to extinction 1. Human caused destruction by overharvesting, overtrapping or poisoning; whaling, commercial fishing 2. Introduced predators, disease 3. Abnormal abundance of predators supported by abnormal food/cover – particularly bad if species’ habitat has been severely altered by man 4. Man-constructed hazards – cause accidental deaths - Mat reduce extirpate wildlife populations so i
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