March 1, March 3 - Ecosystem functioning as a limiting...

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Paul Ehrlich (1968, 199) on ecosystem effects of human population 1. Ehrlich suggests that human impacts on ecosystems can indirectly limit population size - Large human population will cause extinction Based on theories by Charles Elton (founder of ecology) Simple (species - poor) systems are unstable and more likely to collapse Robert May: the theory was not mathematically valid; complex system does not have to be stable Spurred modern day population growth study 1968 (Population Bomb) - "ecosystems. .control the mix of gases in the atmosphere, supply fresh water, control floods, supply food and products, dispose of wastes, recycles essential nutrients, pollinate crops, and control the vast majority of pests that might attack them. If those ecosystems collapse, the human economy will collapse as well, and Homo sapiens will undergo an unprecendented population crash" The population bomb has already gone off Supply food products; controlling atmospheric gases; controlling floods; recycling essential nutrients, etc. If ecosystem collapse, human population will also collapse (with high mortality) Ecosystem do have effect on human population 1990 (Population Explosion) - What is an 'ecosystem collapse' and what would it take to cause it? - "The worst consequence of global warming is likely to be alterations of climate patterns caused by the rising temperatures, changes that will occur at a rate unprecedented in history" (Ehrlich 1990, 118 -19) Expected the loss of species and the suffering of human population Main likely cause for major changes in next decades Greenhouse warming (topic for next week); possibility of major disruptions but plant communities unlikely to have drastically reduced biomass The predicted global damage to forests did not occur "whereas the greenhouse warming represents an impending catastrophe, serious damage from acid rain is already upon us" (p.123) Acid rain greatly reduced since 1980s; damage to forests largely been reversed Acid rain Halted by Montreal protocol Depletion of the ozone layer Does not cause major loss in farmland Desertification Ehrlich's 1990 list - Cohen ends the chapter with example of South Florida as an example of environmental disaster - A classification of effects on ecosystems by human populations 2. A. Due to farming; eventually if erosion > soil regeneration, it will get down to bedrock losing land Food can be produced more by improved technology, hybrids, etc. Irrigation leads to salinization. This is slow process; if continues, it will reduce food production Erosion, salinization of soils - Climate change will change temperatures, water cycle, etc. Climate change effects on food species, hydrology, space - Reduce amount of useable water Industrial use or pollution of water - i.e. copper depletion leads to use of more diffused form of copper (higher energy input and environmental
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This note was uploaded on 06/20/2011 for the course EHJ EHJ351 taught by Professor Peterabrams during the Spring '11 term at University of Toronto- Toronto.

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March 1, March 3 - Ecosystem functioning as a limiting...

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