| dc.description.abstract |
Populations are bounded by negative feedbacks operating through fertility ormortality, termedpopulation regulation. If fertility isartificially reduced, the average size of the population is also reduced, butonly under certain conditions. If (i) juvenile survivalor (ii) adult survival improve due to lower fertility,or (iii) territoriality limits populations, the effectsof lower birth rate will not change population size unless such reductionexceeds the effects of these processes.Published data on population trends and birth rates have allowed a comparisonamong species of instantaneous rates of change. The intrinsic rate ofincrease, r<emph type="8">m, and populationvariability are both related to body size, because birth rates andsurvivorship are also related to body size. These rates are trade-offs asadaptations. Populations of species in exotic habitats may fluctuate more thanwhen they are in their indigenous habitats. Fertility control could reducesuch fluctations.Marsupials have lower birth rates than eutherians, and so rely more onsurvivorship, perhaps as an adaptation to unpredictable environments.Compromising survival by either habitat change or increased predation willaffect marsupials more than eutherians. This explains why many marsupialpopulations are declining towards extinction. |
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