The Effect of Climate Change on Birds

by David Leech

4.4 Population size and density dependence

However, the effect that climate-related changes in survival or breeding productivity will have on overall population size will depend on the other factors that act to limit population size. Populations of most bird species are regulated in a density dependent manner; that is, changes in population size
are compensated for by changes in the underlying demographic processes,
survival or productivity. For example, if the size of a population increases, survival rates and/or productivity may decrease due to increased competition for resources, which may counter the tendency for the population to expand in size. Similarly, increases in survival rate, such as those due to warmer winters, may not necessarily result in an increase in population size, as they are likely to be counteracted by a decrease in survival or productivity at another stage in the life cycle. Thus, predicting the effects of climate change on population may not be straightforward, and will require a detailed understanding of the other factors that regulate bird populations. However, changes in climatic factors may alter the number of individuals that can be supported in a specific region, and this is perhaps most obvious where it results in range expansion or contraction.

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