CHAPTER 4 - CHAPTER 4 ECOSYSTEMS: POPULATIONS AND...

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CHAPTER 4 ECOSYSTEMS: POPULATIONS AND SUCCESSION II. Population Dynamics A. Population: "all the members of a given species in a given area" B. Biotic Potential versus Environmental Resistance 1. Biotic Potential - reproductive rate 2. Environmental Resistance - biotic and abiotic factors limiting population size a. Recruitment the ability to survive environment resistance factors and become part of the breeding population. b. Replacement level: when recruitment is just enough to replace the adults. 3. Reproductive Strategies a. High biotic potential and low recruitment bacteria, flies, rabbits b. Low biotic potential and high recruitment humans, elephants, primates C. Growth Curve: how biotic potential and environmental resistance combine to cause a population to grow or decline. 1. J-curve: before environmental resistance factors kick in to reduce population size 2. S- curve: a balance between environmental resistance and biotic potential a. Population equilibrium - deaths equal births
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Fig. 4.2 The J-curve (blue) demonstrates population growth under optimal conditions, with no restraints. The S-curve (green) shows a population at equilibrium. Fig. 4.4 A stable population in nature is the result of the interaction between factors tending to increase population (biotic potential) and factors tending to decrease population (environmental resistance).
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D. Carrying Capacity: "The maximum population of an organism that a given habitat will support without the habitat being degraded over the long term." This is the upper limit on the size of a population. E. Density Dependence and Critical Numbers 1. The density of a population influences how much impact certain environmental factors will have on continued population growth. These factors are called density-dependent factors. a. Food is a density dependent factor; the more individuals competing for the same food source, the more difficult it is to get food. 2. The impact of some environmental factors is not dependent on the density of the population. These factors are called density-independent factors. a. Density-independent factors include an unusual heat wave or hard freeze. If a particular limiting factor moves outside an organism's range of tolerance, then the organism dies irrespective of how many there might be in the population. A spill of pesticides into a river (as happened on the upper Sacramento River in the early 1990s because of a train accident) resulted in the sudden death of the river ecosystem that was not related to the population size of any species. 3. Critical Number -
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This note was uploaded on 10/17/2011 for the course ENVIRONMEN 201 taught by Professor Staff during the Spring '10 term at North South University.

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CHAPTER 4 - CHAPTER 4 ECOSYSTEMS: POPULATIONS AND...

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