Article Critique of:
‘Human predators outpace other agents of trait change in the wild’ by Darimont et al.
In this study by Darimont et al. (2008), the authors’ goal was to understand the impact of human harvesting on wild populations. They tested this by comparing observed changes in exploited systems with those subject to natural or other anthropogenic perturbations in the wild. They also looked into which harvesting characteristics produce the most rapid phenotypic changes. The main findings were that phenotypic changes in human predator systems are much more rapid than both natural and other anthropogenic perturbations, and that these changes were found to be more abrupt in commercially exploited systems than in recreational or scientific harvests. The importance of this study is that it provides insight on the extent of the influence human exploitation can have on the wild populations and thus on ecological dynamics.
The study was conducted by combining data from published studies on phenotypic changes of different species. Using the extracted data, rates of phenotypic change (termed ‘Darwins’) were calculated. Darwins were then plotted against time in millions of years. ANCOVA analysis was used to compare the three different rates of phenotypic changes in human harvesting, natural and other anthropogenic perturbations, and to see if there were any interactions between them. They also used AIC with human predator data to compare models with different variables including years, trait type, capture method, and harvest mode.
One flaw observed in their methodology was that ‘magnitudes’ (proportional changes in traits) that were said to be calculated were not used in any analyses. Showing the calculations for ‘magnitude’ seemed meaningless as only Darwins were used to plot and analyze the results. Nevertheless, their analysis that designates human as the most significant driver of change reflects their findings that showed biggest phenotypic change due to human exploitation.
However, in order to contribute to the accuracy of their findings, a different approach could have been taken by using Haldanes in place of Darwins. The article indicated that they did not calculate Haldanes as the collected data lacked values required for the calculation, but better selection of data could have made this calculation available. With the set of Darwins alone, the results can be arbitrary as it assumes that evolution takes place in million-year time scales. Using Haldanes that uses time interval counted in generations can account for better results as evolution can clearly takes place over shorter period of time.
For the most part I agree with the authors’ findings that describes humans as a