16 - Extinction and Conservation Reading-Freeman, Chapter...

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Unformatted text preview: Extinction and Conservation Reading-Freeman, Chapter 55 Humans have extensively modified the biosphere The human population passed 6 billion in the year 2000, and is growing at a rate of almost 2% per year. Each human uses so much energy and so many resources that our activities influence virtually every aspect of the biosphere. In temperate areas, nearly all the land area that is suitable for agriculture is plowed or fenced. Worldwide, more than 35% of all land area is used for farms or permanent pastures. Much of the rest is grazed or logged on a regular basis. From 35-45% of Global Net Primary Productivity now goes to serve human needs. In aquatic ecosystems as well, an increasing amount of productivity is harvested by humans. Nearly every major fishery in the Northern Hemisphere has showed strain from overharvesting, and many have collapsed. Major sources of anthropogenic extinction Habitat destruction and habitat fragmentation Habitat Change and Disruption of Ecosystem Processes Introduction of Exotics Overexploitation Habitat destruction and habitat fragmentation Most of the grasslands and forests of the Northern Hemisphere were destroyed by the end of the nineteenth century, the grasslands of the southern hemisphere are now vanishing, and tropical forests are disappearing at a rate of about 2% per year. This type of destruction has become the norm for most biological communities, as the human population expands our economic needs require resources from more and more land. The remaining habitat is often broken into many small fragments, which are separated by large areas of land under cultivation or other human uses, effectively reducing a single "continent" into many "islands". Fragmented Habitats Support Smaller Populations Essentially, every habitat fragment becomes a biological "island" (analogous to continental shelf islands, rather than the oceanic kind). As in the Mac Arthur Wilson model, the smaller the island, the smaller the population of any given species it can support. Small populations are at much greater risk of extinction due to random events, such as weather, disasters, and natural fluctuations in their population and sex ratio. This part of Canada used to be a continuous swath of natural communities. Here is a fragment seen from the air Additionally, smaller populations support less genetic variation, which could lead to the fixation of harmful alleles and the ultimate extinction of the population (for very small fragments), or simply inhibit their ability to evolve in response to changing conditions Fragmented Habitats Frequently Lack Critical Ecosystem Processes Edge effects fundamentally alter habitat. For certain species, this can be critical to their ability to survive. For instance, places where human habitation borders nature preserves frequently have weedy plants, fire is controlled, domestic cats and dogs escape and prey on native wildlife, and human noise and activity disturb the behavior of certain animals....
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This note was uploaded on 04/02/2009 for the course CHEM 112 taught by Professor Jursich during the Spring '08 term at Ill. Chicago.

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16 - Extinction and Conservation Reading-Freeman, Chapter...

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