By harvesting vast numbers and targeting large, reproductively mature individuals, human predation is quickly reshaping the wild populations that remain, leaving smaller individuals to reproduce at ever-earlier ages, said Darimont.
"The public knows we often harvest far too many fish, but the threat goes above and beyond numbers," said Darimont. "We're changing the very essence of what remains, sometimes within the span of only two decades. We are the planet's super-predator."
"The pace of changes we're seeing supercedes by a long shot what we've observed in natural systems, and even in systems that have been rapidly modified by humans in other ways," said Darimont. "As predators, humans are a dominant evolutionary force."
Darimont's findings also dramatically increase scientific understanding of the capacity of organisms to change. "These changes occur well within our lifetimes," said Darimont. "Commercial hunting and fishing has awoken the latent ability of organisms to change rapidly."
Some observed trait changes likely represent underlying genetic changes passed on from one generation to the next. In gill net fisheries, for example, evolution can favor smaller fish that pass through the mesh. Those smaller individuals are more likely to survive, reproduce, and pass on genes for smaller offspring, explained Darimont. By contrast, some trait changes likely do not involve genetic changes, a process called plasticity. For example, shifts to earlier reproduction can occur because of an abundance of food being shared by a much smaller population of fish. Whereas s
|Contact: Jennifer McNulty|
University of California - Santa Cruz