Built on Facts

Hunting and Animal Size

This one’s a little of the beaten path for this site, since it’s not physics or even anything I normally follow as a hobby. But along with science and many other things I’m a bit of a firearms enthusiast, and since guns are closely connected with hunting it probably wasn’t unlikely that I’d come across this Livescience piece about the genetic implications of hunting.

The thesis is so simple as to be almost self-evident. Hunters tent to hunt for the largest and most impressive animals, especially when hunting seasons are short and bag limits are small.

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.

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.

And the author goes on to cite some numbers involving other animals. It’s not terribly surprising. Nonetheless, it can be misinterpreted and in fact the author starts off the piece with a misinterpretation:

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.

Neither Darwin nor nature cares in the least about size as such. If it were so, I’d be a huge dinosaur typing this on a huge keyboard designed by dinosaur engineers for use with claws. But in fact I’m a fairly small and puny animal who is part of a species that’s nevertheless managed to do pretty well. All that matter is how well you reproduce. Do it successfully and your species will grow, don’t do it successfully and it won’t. If smaller happens to avoid hunting, than small is what’s going to be around to breed.

However, genetic problems can present themselves. Some locations in Africa have had greatly increased populations of deformed tuskless elephants, since obviously those will have a much smaller chance of being poached. These kinds of features hurt the animals’ chance of natural survival, potentially threatening the entire species.

What can hunters do about it? All of the hunters I know hunt primarily for the meat and the enjoyment of being in nature and part of the food chain in a much more natural way than eating chemically saturated slaughterhouse cows. Some are interested in trophy animals (though the meat is never wasted), but it’s a much less prevalent motivation. Probably a good thing to do would be to set aside genetic preserve locations where smaller animals were deliberately hunted, allowing larger ones to build up. These could be transplanted into regions experiencing diminution. Another possibility could be providing incentives for hunting smaller animals, such as higher bag limits or lower cost licenses. Obviously this could only work for animals which are not threatened, but many game species such as deer are so common as to be nowhere near that point. One more option (sort of the converse of the previous) could be to set inverse size limits – put a comparatively small limit on the number of deer above a certain size that may be taken. I think hunters would likely support all of this if it could be shown to improve the quality of hunted species.

This is for the US and other developed nations which already have a solid and time-tested symbiotic relationship between hunters, prey species, and the cultural and legal rules of the hunt. In places where poaching is a serious problem the top priority will have to be stopping poachers. I suspect the Whale Wars crew would never do something as declasse as buying some rifles and helping guard African wildlife preserves, but it would be a lot more useful than their thus far ineffective petty harassment of one Japanese whaling vessel.

Those are just some ideas from a guy who knows very little about population genetics or hunting. It’s still an interesting thing to think about.

Comments

  1. #1 dominich
    January 8, 2009

    You just have to look at the changes in size distribution and age of maturity for heavily fished stocks (Atlantic Cod etc) to see the truth of the argument.

    I’ve been looking for a citation but will have to leave this as anecdote for now.

  2. #2 Eric Lund
    January 8, 2009

    For many species of fish, and IIRC also for crabs and lobsters, there is a minimum size to what you can legally catch. Ostensibly these rules are to prevent overharvesting of juveniles so that some of them will live long enough to reproduce, but it has the same effect.

    I’ve also noticed a similar effect with dandelions and such on my lawn. The ones that put their flowers up too high lose them to my lawnmower. The ones that put their flowers at a similar height to the neighboring grass survive my lawn mowing and can reproduce. (Using chemical herbicides is not an option for me because the small stream in my back yard puts about half of the property in a coastal protection overlay zone, meaning chemical fertilizers and herbicides are prohibited.)

  3. #3 D. C. Sessions
    January 8, 2009

    We’re not alone. During the last century or so, coyotes moved into the niche formerly occupied by wolves. They hunted large game in packs, and the size range for coyotes increased rapidly.

    Then wolves were reintroduced, and almost overnight (or so seems) coyotes moved down the food chain to “wolf snack.” No more big coyotes (slower, less able to go places wolves can’t.) No more coyote packs, no more hunting large prey.

    Being prey can change the whole picture.

  4. #4 Uncle Al
    January 8, 2009

    The Grand Banks – the largest cod fishery on Earth – were sterilized by Canukistan. When yields declined Ottawa subsidized more and bigger boats. Yield decline was Officially modeled as a linear function. This was oh so cute for two reasons:

    1) Second order kinetics re boy fish and girl fish. If you lose 90% of your reproductive fish the remaining replacement rate is not 10%. It is (0.1/2)^2 or 0.25%.

    2) The line does not go through the origin. Predation takes a swipe – especially through small numbers when it is not saturated.

    Uncle Al suggested planting coelecanths. Lacking swim bladders they are bouyant for a remarkable weight fraction of oil (re biodiesel production). They are armored. The Comoro Islands speak French. The Great Dank North is a bunch of small thinkers.

  5. #5 Greenpa
    January 8, 2009

    Um. If you think North America’s relationship with hunters and prey species has been “time tested” – alas, you are sadly mistaken. It’s only been 100 years or so- and in that time, the rules have changed- oh- constantly. And frequently have been disastrous.

    Look to Europe- which has indeed many places with 400 years of tested rules. One of the systems that works- the prey animals belong to the land owner; NOT the public. The land owner manages the herds- to attract hunters. Do you get to shoot their biggest stag? Not a chance. The landowner is right there when you pull the trigger- and they veto killing the breeding stock.

  6. #6 Morris Hattrick
    January 9, 2009

    Or we could just stop pretending that buffoons running around the woods killing defenseless animals for fun is “sport”.

  7. #7 Karl Withakay
    January 9, 2009

    I’ve read the same thing is happening over in Tibet with the Blue Lotus flower; all the best ones get picked, and the scrawny, pathetic ones are the only ones left to propogate their genes.

  8. #8 Art
    January 11, 2009

    Predators tend to go after the weak. The young, old, diseased or starving animals. Makes sense in that a predator has a lot on the line every time they try for a kill. Even a relatively minor injury can slow a predator so they can’t catch prey or keep up with the pack. A broken bone is usually a death sentence for any predator.

    Hunters tend to go after the biggest, strongest and healthiest animals. Hunters brag about how big or how many pints the deer have. I have never, not even a single time, have I ever heard a hunter brag about how sickly, weak or emaciated the animal they have shot was.

    Which also makes sense. Most hunters at least as much emotional investment in their status as hunter as they have in their prey as food. They get status by bragging about size or points or weight or beauty. That and the simple fact that hunters usually are at no significant risk of being hurt by their prey while hunting. A wolf may risk being felled by a kick by a mule deer. Hunters do the same job from several hundred meters away with a high-powered rifle.

    I would also point out that nature does seem to favor certain size shifts in some conditions even if it is not a firm or very strong shift. Generally animals in cold areas tend to be larger than similar hot climate animals. Also large animals on small islands tend to become smaller over time.

  9. #9 Carl Brannen
    January 11, 2009

    As far as prey animals belonging to the land owner, I believe something similar happens in the US. My family leases land to hunters in east Texas. We may not own the animals but we do own the hunting rights which amounts to the same thing.

    And yes, they do manage the land for animal production. Trees that produce mast are widely planted; they attract deer much better than the pulp plantations. One of the annoying habits the hunters do is they let loose little pigs in the expectation that they will grow to be large pigs. They do this by tearing up the landscape to a degree that has to be navigated on foot to be appreciated. They’re called “piney wood rooters”.

  10. #10 Carl Brannen
    January 11, 2009

    As far as prey animals belonging to the land owner, I believe something similar happens in the US. My family leases land to hunters in east Texas. We may not own the animals but we do own the hunting rights which amounts to the same thing.

    And yes, they do manage the land for animal production. Trees that produce mast are widely planted; they attract deer much better than the pulp plantations. One of the annoying habits the hunters do is they let loose little pigs in the expectation that they will grow to be large pigs. They do this by tearing up the landscape to a degree that has to be navigated on foot to be appreciated. They’re called “piney wood rooters”.

  11. #11 Hamsterpoop
    January 18, 2009

    Although I see the good intention in your ideas, it just can’t happen because phenomena like genetic bottlenecking could threaten the entire species with extinction.

    Stick to physics, man.