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BIO120H1 (305)
Chapter 12

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University of Toronto St. George
James Thomson

Chapter 12Temporal and Spatial Dynamics of Populations 253255 A 257263 A and B remainder CPopulations vary over time Density dependant factors usually encourage population towards its carrying capacity but equally important are environmental conditions which can affect birth and death rates and intrinsic biological systems of a population ie some populations are inherently unstable and tend towards oscillation in their numbers Species can vary in their size fluctuationscycles based on their sensitivity to environmental change generally greater in smaller organisms and their lifespan Species which are resistant o environmental change and have a long lifespan re generally relatively stable intrinsically species which experience a rapid overturn of the population may be less so as their numbers depend on continued reproduction which is sensitive to the environment Periodic cycles when one can observe regular intervals between a populations highs and lows in numbers Temporal variation can have an effect on age structure and affect population growth imagine an illness wipes out all individuals in the human population between the age of 525 Despite irregularity in environmental conditions population cycling seems to be very regular for most populations This is reflective of intrinsic qualities of a population Some populations for example are extremely sensitive to environment fluctuations and can oscillate wildly when such affected Populations have an intrinsic tendency towards periodicity much like a pendulum One can generally observe time delays in a populations increases or decreases due to fluctuations in the environment or other factors These factors impart momentum which may cause a population to either overshoot or undershoot its carrying capacity Populations modeled on the logistic equation can be used to study population cycles Time delays are especially apparent in populations with discrete generations as birth and death are associated with breeding episodes These populations can oscillate between overshoots and undershoots due to the fact that they cant continuously readjust their growth rates One model a populations periodic cycles due to intrinsic growth rate by the equation NtRNtKK Nt where Nt is the change in population size from one time interval to the next where R is the proportional increase or decrease in N per time unit K is the carrying capacityK Nt serves to make R densitydependant by a factor of 1NtK R can be used to predict population oscillations when R is1 the population approaches but does not exceed the carrying capacity when
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