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Lecture 14

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Biology 3446B
Robert Solomon

Lecture 14: Harvest Potential damages/costs should hunting/trapping be lost as a wildlife management tool in North America: - 50,000 injures/year (collisions) - $3.8 billion in auto repair costs - $1.45 billion in disease control – rabies alone - $128 million in aircraft damages - $934 million - $9.3 billion to control white-tailed deer - $132 million - $265 million to control furbearers - $3 billion/year in damage to livestock and crops (US) o $35.7 million (Canada) Hunting = form of population control Harvestable surplus: # of animals that can be removed from a population without affecting the size of the population at some later time (next breeding season/next hunting season) - For all stable of increasing populations, there is an annual population increase - Subsequent mortality returns the population to about the same size next spring - Unhunted populations: o Annual surplus dies from natural mortality before next breeding season (i.e. robins) - If harvest is compensatory, the spring breeding populations are the same with or without harvest (hunted species) o The greater the level of harvest, the greater the chance that the harvest will become additive mortality (mortality added to natural mortality and not replacing it) o Additive mortality will result in a small spring breeding population - But, a DECREASE in spring breeding population may not cause a decreased population in the next fall hunting season o Reproductive success often responds in a density dependent manner - Reducing a WTD population in fall below the number that would just barely survive would mean that survivors have more food per animal during winter  higher juvenile survival in the spring Effects of Harvest on Populations - Human activities that impact wildlife (pre-1900s) o Overharvest o Destruction of habitats - Human activities that impact wildlife (present day) o Destruction of habitat o Exotic species o Pollution o Overharvest - A stable population annually produces a surplus of young, and equivalent number of animals will die before the next breeding season - So, the biological basis for hunting is to harvest part of this surplus that would die anyway o Validity? Ratio of compensatory : additive mortality  Depends in every case upon the intensity of harvest relative to the ability of the population to compensate - A certain amount of additive mortality is not bad = may stimulate production and improve welfare of population Resident Small Game - Most species - High biotic potential - Reproduce at high rates when conditions are favourable - Have high rates of population turnover - Why don’t small game populations tend to decline when harvest is increase? o Compensatory mortality - Why don’t small game populations tend to decline when seasons are lengthened? o Law of diminishing returns  Harvest intensity is density dependent  Negative feedback Waterfowl/Migratory Birds - Mallard – most widespread duck in NA
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