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Population Growth in a Wild Bird Is Buffered Against Phenological Mismatch

Science  26 Apr 2013:
Vol. 340, Issue 6131, pp. 488-491
DOI: 10.1126/science.1232870

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Balancing Act

Life cycles are strongly influenced by seasonal and interannual environmental and climate events. Such phenological timings are likely to shift as our climate changes, but species exist in communities, and not all species can be expected to shift in concert. Reed et al. (p. 488) used long-term data on European great tits to reveal how the negative consequences of phenological mismatch can be buffered: Lower fitness in individuals subject to mismatch-driven reductions of food availability was balanced by reductions in competition. Thus, overall, the population is resilient and has not declined.

Abstract

Broad-scale environmental changes are altering patterns of natural selection in the wild, but few empirical studies have quantified the demographic cost of sustained directional selection in response to these changes. We tested whether population growth in a wild bird is negatively affected by climate change–induced phenological mismatch, using almost four decades of individual-level life-history data from a great tit population. In this population, warmer springs have generated a mismatch between the annual breeding time and the seasonal food peak, intensifying directional selection for earlier laying dates. Interannual variation in population mismatch has not, however, affected population growth. We demonstrated a mechanism contributing to this uncoupling, whereby fitness losses associated with mismatch are counteracted by fitness gains due to relaxed competition. These findings imply that natural populations may be able to tolerate considerable maladaptation driven by shifting climatic conditions without undergoing immediate declines.

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