It’s about time: The temporal dynamics of selection in the wild

Background/Question/Methods

Selection is a pervasive force in nature. Although our understanding of the strength and form of selection has increased, a general understanding of the temporal dynamics of natural selection in the wild is lacking. We assembled a database of temporal replicates of selection from published studies of wild populations to synthesize what we do (and do not) know about the temporal dynamics of selection in nature. We reviewed 1569 studies published in 25 journals. Our final data set included 3310 estimates of selection from 77 studies covering 2-45 years and included broad taxonomic representation.

Results/Conclusions

Morphological traits and studies focused on vertebrates (particularly birds) were well-represented, with other traits and taxonomic groups less well-represented. Overall, four features appear to characterize the temporal dynamics of selection. First, for the traits considered and multiple measures of fitness, strong selection appears to occur relatively infrequently. Second, the strength of selection varies considerably from year to year. Third, reversals in the direction of selection are infrequent. Fourth, changes in the form (directional, quadratic) of selection appear uncommon. Although few studies have identified likely causal mechanisms underlying annual variation in the occurrence, strength, direction, and form of selection, environmental conditions driven by climatic fluctuations appear to be particularly important.