The Hedgehog
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Another one:
Super-Predators: Humans Force Rapid Evolution of Animals
Robert Roy Britt
Editorial Director
LiveScience.com robert Roy Britt
editorial Director
livescience.com
Mon Jan 12, 5:17 pm ET
Acting as super-predators, humans are forcing changes to body size and reproductive abilities in some species 300 percent faster than would occur naturally, a new study finds.
Hunting and fishing by individual sportsmen as well as large-scale commercial fishing are also outpacing other human influences, such as pollution, in effects on the animal kingdom. The changes are dramatic and may put the survival of some species in question.
In a review of 34 studies that tracked 29 species across 40 different geographic systems, harvested and hunted populations are on average 20 percent smaller in body size than previous generations, and the age at which they first reproduce is on average 25 percent earlier.
"Harvested organisms are the fastest-changing organisms of their kind in the wild, likely because we take such high proportions of a population and target the largest," said lead researcher Chris Darimont of the University of California, Santa Cruz. "It's an ideal recipe for rapid trait change."
Darimont told LiveScience that while he considers the changes to be evolutionary, some biologists consider them phenotypic and, without evidence of genetic shifts, would not call them evolution.
The study found dramatic change in several fish species and creatures as small as snails and as large as bighorn sheep and caribou.
Dominant force
The results, published online today in the journal Proceedings of the National Academy of Sciences, are similar to a host of other scientific conclusions dating back nearly two decades.
In 1990, Douglas Chadwick wrote in National Geographic magazine how trophy hunting - the practice of selecting only the largest beasts to kill -"has caused a decline in the average size of Kodiak Bears [in Alaska] over the years."
By harvesting vast numbers and targeting large, reproductively mature individuals, human predation is quickly reshaping wild populations, leaving smaller individuals to reproduce at ever-earlier ages, Darimont explained.
"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," Darimont said. The study found the changes outpace by 50 percent those brought on by pollution and human introduction of alien species.
"As predators, humans are a dominant evolutionary force, he said.
Others agree the problem is serious. Columbia University biologist Don Melnick recently said trophy hunting is akin to selective breeding and is "highly likely to result in the end of a species."
Surprising ability to change
One surprise: The capacity of creatures to change.
"These changes occur well within our lifetimes," Darimont said. "Commercial hunting and fishing has awoken the latent ability of organisms to change rapidly."
Changes occur in two ways. One is sheer genetics:
Evolution can favor smaller fish able to pass through the mesh of gill nets and survive to reproduce, thereby passing on genes for smaller offspring.
Another change process is called plasticity. Shifts to earlier reproduction, for example, can occur because there is a lot of food and fewer fish to dine on it. The fish eat more and reach maturity sooner.
"Whatever the underlying process, shifts to earlier breeding spell trouble for populations," Darimont said. "Earlier breeders often produce far fewer offspring. If we take so much and reduce their ability to reproduce successfully, we reduce their resilience and ability to recover."
One specific example: the overfished Atlantic cod on the eastern coast of Canada. Less than two decades ago, they began mating at age 6. Now they start at age 5.
Government problem
In some cases, as other studies have found, the problem results from decades of big-game hunting and, more recently, poaching. Some populations of African elephants, for example, have unnatural percentages of tusk-free animals among them now, because hunters and poachers favor the ivory.
But some government rules contribute to the problem.
"Fishing regulations often prescribe the taking of larger fish, and the same often applies to hunting regulations," Darimont said. "Hunters are instructed not to take smaller animals or those with smaller horns. This is counter to patterns of natural predation, and now we're seeing the consequences of this management."
Darimont thinks new policies are in order.
"While wolves might prey on 20 animals, humans prey on hundreds of thousands of species," he points out. "We should be mimicking natural predators, which take far less and target smaller individuals."
Policy shifts may or may not save a species, however.
"It's unknown how quickly the traits can change back, or if they will," Darimont said.
Another one:
Trophy Hunting Causing 'Reverse Evolution'By Robert Roy Britt, Editorial Director
In The Water Cooler, Robert Roy Britt takes a daily look at what people are talking about in the world of science and beyond.
The African Elephant (Loxodonta africana) lives in some 37 countries in sub-Saharan Africa. Across the continent, the total population is believed to have declined by about 25 percent between 1979 and 2007. Poaching for ivory and meat is considered the major threat to the species. Credit: Alicia Wirz/IUCN Survival of the smallest is not exactly what Darwin had in mind, but in some animals species, humans may be forcing a smaller-is-better scenario, and the ultimate outcome may be species demise.
Among some species of big game, hunters are limited by lottery systems that allow only a select few to take just one animal each. Another approach is to sell or auction trophy hunting permits for thousands of dollars. The schemes encourage hunters to be picky, passing up smaller males in search of those with the biggest antlers or the largest tusks or the most beautiful manes, so the creature can be stuffed and displayed on a wall.
This unnatural selection, a practice that dates back decades and more to hunters like Teddy Roosevelt who sought trophy animals before there were restrictions, is forcing "reverse evolution," according to a recent article in Newsweek.
Animals shrinking
Biologist Marco Festa-Bianchet of the University of Sherbrooke in Quebec found a 25 percent decline in the size of horns on bighorn sheep over the past 30 years, and both male and female bodies are getting smaller.
The idea is not new. In 1990, Douglas Chadwick wrote in National Geographic magazine how trophy hunting had a similar effect on bears in Alaska: "Continued harvesting of the biggest animals by trophy hunters has caused a decline in the average size of Kodiak Bears over the years," Chadwick wrote.
It's not just about subtracting the biggest beasts from the equation. The populations actually evolve as genes are removed from the pool.
The logic goes like this: Bigger males with bigger horns tend to father bigger offspring, causing the average size of a species to increase over time. With hunters targeting these trophies, smaller males are more successful at mating, so their genes are spread through the population more effectively and the average size shrinks.
Freaks of nature
Trophy hunting of a more dastardly sort has also made freaks common among elephant populations, researchers say.
Tuskless elephants, once a fluke that comprised about 2 percent of the population of African elephants, aren't sought as much by poachers (it's the ivory that's most valuable) so they breed more and are now 38 percent in one Zambian population, Newsweek reports.
Tusks are important for self defense, however, which is one example of why trophy hunting could ultimately harm a species.
Researchers have long known that big beasts are more vulnerable to quick demise. In general, large animal species (think dinosaurs, woolly mammoths) must invest more energy in gestation and weaning precious few young, and they reach sexual maturity slowly.
The sort of selective breeding that humans are carrying out among some animal species, by trophy hunting, is "highly likely to result in the end of a species," said Columbia University biologist Don Melnick.
