wk 9 Lec 2sf

wk 9 Lec 2sf - C hapte 18 & 20 rs Ecology and Hum Im an...

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Ecology and Human Impacts
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Ecology and Environmentalism Our current awareness of the biosphere’s limits stems mainly from the 1960s, a time of growing disillusionment with environmental practices of the past. The pesticide DDT , which improved agricultural production, Was developed in the 1950s. Was determined to have harmful side effects. Rachel Carson Was one of the first ecologists to perceive the global dangers of pesticide abuse. Helped initiate our current environmental awareness with her book Silent Spring. The modern environmental movement was catalyzed by Rachel Carson .
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The human population explosion Humans are by far the most abundant large animals. Humans therefore have a disproportionately high impact on the environment. The human species Requires vast amounts of materials and space . Has devastated the environment for many other species.
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Population growth models Two models, the exponential growth model and the logistic growth model, will help us understand population growth. The growth rate is the change in population size per time interval.
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The Exponential Growth Model : The Ideal of an Unlimited Environment The exponential growth model describes the rate of expansion of a population under ideal, unregulated conditions. A key feature of the exponential growth model is that the rate at which a population grows depends on the number of individuals already in the population .
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The Logistic Growth Model : The Reality of a Limited Environment In nature, a population may grow exponentially for a while, but eventually one or more environmental factors will limit its growth . Population-limiting factors restrict population growth. The logistic growth model describes growth of an idealized population that is slowed by limiting factors.
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Carrying capacity is the number of individuals in a population that the environment can just maintain with no net increase or decrease. Comparing growth models
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Regulation of Population Growth Density-Dependent Factors The logistic model is actually a description of intraspecific competition. Describes population growth as density- dependent. Density-dependent factors Are population-limiting factors whose effects intensify as the population increases in size . Increase a population’s death rate and decrease the birth rate.
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Density-independent factors Are population-limiting factors whose intensity is unrelated to population density . Include events such as seasonal freezing. In many natural populations, density- independent factors limit population size before density-dependent factors become important. Over the long term, most populations are
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This note was uploaded on 09/23/2011 for the course BIO 141 taught by Professor Brown during the Fall '08 term at Drexel.

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wk 9 Lec 2sf - C hapte 18 & 20 rs Ecology and Hum Im an...

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