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. 2009 Jan 20;106(3):952-4.
doi: 10.1073/pnas.0809235106. Epub 2009 Jan 12.

Human predators outpace other agents of trait change in the wild

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Human predators outpace other agents of trait change in the wild

Chris T Darimont et al. Proc Natl Acad Sci U S A. .

Abstract

The observable traits of wild populations are continually shaped and reshaped by the environment and numerous agents of natural selection, including predators. In stark contrast with most predators, humans now typically exploit high proportions of prey populations and target large, reproductive-aged adults. Consequently, organisms subject to consistent and strong 'harvest selection' by fishers, hunters, and plant harvesters may be expected to show particularly rapid and dramatic changes in phenotype. However, a comparison of the rate at which phenotypic changes in exploited taxa occurs relative to other systems has never been undertaken. Here, we show that average phenotypic changes in 40 human-harvested systems are much more rapid than changes reported in studies examining not only natural (n = 20 systems) but also other human-driven (n = 25 systems) perturbations in the wild, outpacing them by >300% and 50%, respectively. Accordingly, harvested organisms show some of the most abrupt trait changes ever observed in wild populations, providing a new appreciation for how fast phenotypes are capable of changing. These changes, which include average declines of almost 20% in size-related traits and shifts in life history traits of nearly 25%, are most rapid in commercially exploited systems and, thus, have profound conservation and economic implications. Specifically, the widespread potential for transitively rapid and large effects on size- or life history-mediated ecological dynamics might imperil populations, industries, and ecosystems.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Human predators outpace natural and other human-driven agents of phenotypic change. (A) Mean and (B) maximum phenotypic change (Darwin numerator) in ‘natural’ (n = 20 systems), ‘other anthropogenic’ (n = 25) and ‘human predator’ (n = 40) contexts with respect to the mean interval per study system. Context × Years interactions were not significant (both P > 0.38), so slopes were defined by Years coefficients and intercepts by Context coefficients. Shown are P values for Least Significant Difference Tests comparing marginal means between Contexts. One outlier datum in B (70 years, 2.57 e, other anthropogenic) not shown.

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