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Lecture 9

ENVS 1200 Lecture 9.docx

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York University
Environmental Studies
ENVS 1200
Anders Sandberg

11/4/2013 7:23:00 AM Predators: kills and consume other organisms. May consume proportionality more of a particular prey species as prey increases in abundance (predators increasing as prey increases is a density dependent response). Parasites: lives on tissues of host. Usually weakens hosts but does not kill them. Parasitoid: insect larva that consume host, typically form the inside – only one host per individual (they kill their host) Pathogens: induce disease in host (diseases that require hosts) Book suggests we refer to all categories in the sense of ‘Exploitation’ – one organisms makes its living at the expense of another Herbivores and Pants Defense: Snow geese and subarctic salt marsh  Can influence the rate of plant growth b/c of their grazing Impacts of predators on prey populations: Lynx and the hare  At high densities, hares affect both quantity and quality of food source (plants). An experiment was set up to determine what was driving the cycle of population growth and crash (Kerb’s experiment). Included 3 control plots & 6 experimental plots Non-consumptive effects of predators (even if they are not eating prey they can have a negative effect on
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