6.3 Future approaches

Changes in survival rate leading to decreases in population sizes may be difficult to observe if survival is density-dependent due to the effects of factors such as intra-specific competition, predation or disease. Often, survival rates increase as the size of the population decreases, because there are fewer competitors for scarce resources. Initial decreases in survival rate will therefore lead to a reduction in population density, followed by a subsequent increase in survival rates. The period of time over which survival rates are reduced may therefore be relatively short (Green, 1999b) even though the population declines for a longer period. Understanding the nature of this density depedence, and the factors that affect it, will be important when developing future population models. Incorporating density dependence into population models should enhance both our understanding of changes and accurancy of our predictions concerning the effect of changing land-use (for example) on bird population sizes.

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