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Lecture 3

Week 3 Soils and Vegetation.docx

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York University
GEOG 2500
Nina Hewitt

Week 3 Soils and Vegetation Symbiotic nitrogen fixation is a very important process. 1. Mutualisms are very tightly evolved relationships. Symbiosis: 2. Facilitation, it benefits one species more than the other. 2. Parasitism, benefits one species at the expense of another *pay attention in class, stop checking WSJ* Example: strangler figs have small seeds that get dispersed. These seeds land in the branch of the canopy, and then germinate. Parasites are not a big control on the population of the species, because this is usually an evolved relationship. If parasites kill all the members of the species, they will have to recondition the relationship, and these parasites will go extinct. Exotic Pests American chestnut{chestnut blight} -It came from Asia and was imported on logs that didn’t have bark on them. It was a native disease to chestnuts in area, but it did affect N A. -Dutch elm disease; -it is a type of fungus, and it has replaced the elm population with red elms and slippery elms that are not as large-growing. It came in unpeeled veneer logs from Europe, it is a fungus, and it spreads herbivores: they tend to eat diff
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