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BISC 111/113:Lab 11: Population Growth 2: Difference between revisions
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BISC 111/113:Lab 11: Population Growth 2 (view source)
Revision as of 17:07, 26 February 2015
, 26 February 2015→Population regulation
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'''Density Independent growth''' <BR> | '''Density Independent growth models''' <BR> | ||
When the growth rate does not depend on the number of individuals in the population, growth is density independent. In density independent models birth and death rates remain constant no matter how many individuals are in the population, an unlikely occurrence in natural populations over a long period of time. '''Density-independent factors,''' in particular, environmental factors such as temperature, precipitation, and disturbances (e.g., fire, floods, earthquakes, tsunamis) can alter the rate of population growth. These factors, however, are density independent because they affect a certain proportion of the population independently of population size (and largely independent of individual fitness). | When the growth rate does not depend on the number of individuals in the population, growth is density independent. In density independent models birth and death rates remain constant no matter how many individuals are in the population, an unlikely occurrence in natural populations over a long period of time. '''Density-independent factors,''' in particular, environmental factors such as temperature, precipitation, and disturbances (e.g., fire, floods, earthquakes, tsunamis) can alter the rate of population growth. These factors, however, are density independent because they affect a certain proportion of the population independently of population size (and largely independent of individual fitness). | ||
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Linear growth: <b>N<sub>t</sub> = N<sub>0</sub> + b*t </b> <br> | Linear growth: <b>N<sub>t</sub> = N<sub>0</sub> + b*t </b> <br> | ||
W'''Bold text'''here:<br> | |||
<b>N<sub>0</sub></b> = the initial (starting) population size at time t = 0<br> | <b>N<sub>0</sub></b> = the initial (starting) population size at time t = 0<br> | ||
'''t''' = time elapsed from time = 0 to time = t<br> | '''t''' = time elapsed from time = 0 to time = t<br> | ||
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'''Exponential growth''', if unchecked, could lead to unimaginable numbers of everything from bacteria to elephants. After all, the exponential rate of population increase is proportional to the population size; the bigger the population gets, the faster it grows! Of course, most natural populations never achieve their potential for unlimited size; Darwin was keenly aware of this fact. <BR> | '''Exponential growth''', if unchecked, could lead to unimaginable numbers of everything from bacteria to elephants. After all, the exponential rate of population increase is proportional to the population size; the bigger the population gets, the faster it grows! Of course, most natural populations never achieve their potential for unlimited size; Darwin was keenly aware of this fact. <BR> | ||
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'''Density Dependent Growth Models'''<BR> | |||
'''Density-dependent factors''' such as predators, quality of cover, parasites, diseases, and amount of food determine K, and therefore, may regulate populations by maintaining or restoring them to some equilibrium size.<BR><BR> | '''Density-dependent factors''' such as predators, quality of cover, parasites, diseases, and amount of food determine K, and therefore, may regulate populations by maintaining or restoring them to some equilibrium size.<BR><BR> | ||
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'''Logistic Growth is a model of density dependent population growth that considers carrying capacity as a factor.'''<BR> | '''Logistic Growth is a model of density dependent population growth that considers carrying capacity as a factor.'''<BR> | ||
The '''logistic population growth model''', tends to be more realistic because it takes into account “environmental resistance” (K) or carrying capacity. K is the maximum, or equilibrium, population size that can be sustained theoretically by the environment. When K is reached the population growth rate is zero due to a balance of births and deaths. K is influenced by resource availability, waste accumulation, and other density-dependent factors (see below). | |||
In logistic population growth, '''''d''N/''d''t = r N<sub>t</sub> *[(K- N<sub>t</sub>)/K]'''<br> | In logistic population growth, '''''d''N/''d''t = r N<sub>t</sub> *[(K- N<sub>t</sub>)/K]'''<br> | ||
