Super-Predators: Humans Force Rapid Evolution of Animals
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LiveScience.com robert Roy Britt
editorial Director
livescience.com – Mon Jan 12, 5:17 pm ETActing 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.

Are they for real ??? What and whom did this research. This is a blatent shot at all of us.
Please forward to all posts, forums and anything or anyone you csn think of. Stuff like this hurts us all

"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." "

I don't know about brown bears but I have heard similar comments about the full curl regulation on Dall sheep. By only allowing the shooting of full curl rams, the best of the gene pool is lost. The old rams show the younger ones where the best food, bedding locations and routes for movement are located. I understand there is/has been some discussion about this around the state and I think that I for one would support a lowering of the harvest requirements to 7/8 curl or perhaps, even back to the old 3/4 curl requirement. In addition, for the Brooks Range sheep, they only breed once every 2 years, not annually as is usual in the rest of the state. I have no doubt that the above quote is true regarding the brown bear situation. Just my thoughts.
Bear in Fairbanks

This does not go to Alaska Alone.

What abot game managment practices, especially concerning Whitetail deer. ALL i hear is about bigger and better deer herds and body size. Trophy hunting is a way of life for many of us ans I do not believe this report. I think IMO that this is just another way for the anti's to justify NO HUNTING and to get it out there into the mainstream media. If they can;t take the guns then take away the game and freedom to hunt it.

IMO

quote:

Originally posted by Marabou Slasher:
This does not go to Alaska Alone.

What abot game managment practices, especially concerning Whitetail deer. ALL i hear is about bigger and better deer herds and body size. Trophy hunting is a way of life for many of us ans I do not believe this report. I think IMO that this is just another way for the anti's to justify NO HUNTING and to get it out there into the mainstream media. If they can;t take the guns then take away the game and freedom to hunt it.

IMO

I agree. This is PC BS. It is being discussed on the Africa forum also. The two species mentioned, caribou and bighorn sheep, are not getting smaller, and neither has more than a very small percentage harvested by man. In the case of caribou, many cows and immature bulls are harvested by the Inuit.
We should, as hunters, continue to try to harvest mature males that have reached or passed their prime, and have already left their genetics behind.
If these "scientists" are interested in what best makes for larger members of a species, let them check with "game ranch" Managers anywhere in the world.

This is just one study; we don't know the motives of the researcher. At the same time I would not be so quick to discount it. If multiple studies, by independent, unbiased researchers produce the same results , then we should take heed. We should not ignore these studies just because they do not meet our preconcieved notions. I will await final judgement until I am satisfied with full and complete, unbiased research(further studies). That will probably take some time. FWIW, I think there is too much focus on the tape measure and not enough on the enjoyment of the hunt.

i've always been under the impression your genetics are the same from birth to death, so wouldn't a young sheep with good genetics reproduce the same genetics as he would at a later age??

I haven't ever head that animal numbers are falling due to hunting before either, hard to belive.

Fourtyonesix,

Yup. But how dare you bring biologic reality into the argument of whose dick, er, I mean horns, is/are bigger!

quote:

Originally posted by Fourtyonesix:
i've always been under the impression your genetics are the same from birth to death, so wouldn't a young sheep with good genetics reproduce the same genetics as he would at a later age??

I haven't ever head that animal numbers are falling due to hunting before either, hard to belive.

Point I was trying to make was that it's not the young sheep that reproduce. Nor is it the very old ones.
Bear in Fairbanks

I too would like to see more research before jumping to any conclusions. Too many people are quick to jump on the emotional bandwagon and assume because they received the information in an email or saw it on the news it's got to be true.

Doug Chadwick is a raging greenie who is happy to ignore reality or twist the truth to fit his ideology. The article (hatchet job, more like) he did on the Tongass National Forest and Southeast Alaska in National Geographic is proof of his deep-rooted biases and complete lack of integrity. I wouldn't trust anything he said, period.

Dennis

I'm sure global warming has something to do with it.