Sunday, 6 April 2014

Snowshoe Hare in pencil crayon

This week's Illustration Friday prompt is survival. The problem with it for me is that since I usually go at this from a nature point of view (hazard of the job) it's pretty much all about survival. That's a pretty big range of subjects, and I generally have a lot of trouble narrowing things like that down. Sooo... in the end I finally decided to think about digestion.

Hard to survive without digestion if you're an animal. Hard to survive without digestion for some plants, too.

Plant eaters have a special kind of digestion problem. Large parts of plants aren't terribly digestible, and that creates a bit of an evolutionary conundrum going back to the whole balance of energy thing. If you're a plant eater do you put a little energy into getting the most easily digestible parts of your food out and then eat a lot more, or do you eat less and put a lot of energy into digesting what may, in the end, be low quality food?

There are animals that have gone either way, of course. A good example of the first is the equids, like horses or donkeys. They have reasonably uncomplicated digestive systems that let food pass through quickly (there's a lot of identifiable undigested plant matter in the scat, as anyone who's dealt with horse poop knows). It means that they have to eat a lot and often, but on the other hand their systems don't waste much time on bad food.

The best known example of the other strategy is the ungulates or hoofed mammals. Think cow or deer here. Fancy, complicated four-chambered stomachs that spend a lot of time digesting plants. To aid that, the animals cough up partially digested food known as cud, chew it again, and then send it back to the stomach for further processing. Erm, so to speak. More efficient digestion, but they're hooped if the food isn't good.

So what's the deal with the rabbit?

Well, first of all rabbits and hares aren't the same thing. They might look similar and belong to the same group (the leporids), but there are plenty of differences that I'm going to leave you to look up for yourselves if you're interested. After all, we're supposed to be talking digestion here, and to do that I need to talk feces.

Yep, poop again.

Hares, rabbits, guinea pigs, and things like that need more time to digest than their small systems allow, and they don't have the luxury of those four-chambered stomachs. The solution? Coprophagy. Or, in actual English, eating your own poop. Plenty of animals do it.

Hares and their relatives have two kinds of scat: the familiar hard pellets that we get to see, and a soft, partially digested form that the animal harvests (bad choice of words there? Sorry if I gave any of you interesting visuals) as it comes out, rechews, and sends back through the digestive system. Sounds disgusting, but it's pretty effective.

And, of course, that's what counts for survival.

If anyone's interested in what this all looks like, to be honest it doesn't look like much. There's a video here though, if you've ever wondered how you can tell when your pet rabbit is eating caecotrophs.

And my apologies for all of the poop talk.
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