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Lecture 11

Biology Lecture 11 Article 1.docx

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University of Toronto St. George
Scott Browning

BIOLOGY LECTURE 11 The Maintenance of Species Diversity Differences in how species interact with their environment counter the inevitable los of biodiversity that occurs when better competitors overrun their inferior counterparts Biodiversity valued or many reasons:  Crops + livestock we rely on for food are derived from wild species long ago domesticated  Future improvements to agricultural productivity and sustainability depend on genes derived from wild pop instead of domesticated  Large fraction of meds prescribed today contain chemical compounds originally isolated from wild orgs (aspirin = willow trees)  Diverse habitats are increasingly understood to be more stable in provisioning ecosystem services: clean water + pollination of agriculture crops *Speciation: the evolutionary process by which new species are formed  Needed for ultimate generation of species diversity over time  Mystery of species coexistence is rooted in competitive exclusion principle: “2 species competing for the same resources can’t coexist, species better at gaining limiting resource will eventually eliminate the inferior competitor” o Differences in competitive ability of different species cause their abundance to diverge over time = one species becoming more common while the other become less common o If the difference in the competitive ability of species is large, the poorer competitor will be rapidly excluded o If these differences are small, exclusion will be slow  Differences between species in their competitive ability drive the superior to dominance and inferior to exclusions  Prediction of the competitive exclusion principle, elimination of all but the best competitor, contrasts with what we see as coexistence  Other species properties must prevent the elimination of the inferior competitors AKA NICHE DIFFERENCES!  *Niche Differences: species differences that maintain diversity by preventing competitive exclusions  Defines how a species interacts with its environment Ex) Mouse diet: the quantity + size of seeds eaten o Arises when one tends to consume larger seeds o Imagine this: eating large seeds so common that competitor becomes rate. Shift in abundance will cause a deficit of large seeds and abundance in small seeds that will benefit the small seed consuming species Defining feature of a niche difference is that it causes each species to limit individuals of its own species ore than it limits competitor ones Niche differences thereby disfavors species that become common and advantage those that are rare, which hinders competitive exclusion and maintains
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