14 Jan 2009. Humans’ prey species evolving dangerously fast. NewScientist.

Hunters and fishermen go after the largest catches they can find, which is driving evolution in a way unlike anything else on Earth, and the rapid changes triggered in wild species risks severe damage to ecosytems.

Rapid changes in size may threaten ecosystems by disrupting size-based interactions such as predation and competition, says Darimont. For example, smaller fish may no longer be big enough to eat species they once preyed on.

Chris Darimont, an evolutionary ecologist at the University of California reviewed 34 papers measuring how fast traits such as body size and growth rate had changed in 29 species that people harvest for food.

The average rate of change was 3 times as fast as comparable changes seen in unhunted populations, they found (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0809235106).

It was well known that hunting and fishing, which often target the largest individuals, can cause species to become smaller and mature more quickly. However, Darimont’s study is the first to show that this effect occurs for species ranging from cod to caribou, and that these species change far more quickly than they otherwise would, says Andrew Hendry, an evolutionary biologist at McGill University in Montreal, Canada.

Here is the abstract of the article being reviewed above:

Darimont, C. 15 Sep 2008. Human predators outpace other agents of trait change in the wild. PNAS.

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.