If you're a certain type of evolutionary biologist you will immediately ask yourself what kind of selective advantage could have led to the fixation of stotting alleles in antelopes? Here's a list of possibilities that Jerry offers ...
Here's another example of animals jumping up and down in a stylized manner. Surely there are specific alleles that make them behave this way? And the alleles must have become fixed in the Maasi population by natural selection. In other words, it has to be an adaptation, right?
- It allows an animal to jump out of high grass to look for predators
- The behavior startles the predator, giving the gazelle more time to escape
- It’s an alarm signal (like bird alarm calls), alerting herd members that a predator is nearby. This would probably evolve only if herd members were closely related, so the behavior could evolve via kin selection (assuming it’s individually maldaptive, which isn’t proven).
- It’s simply play behavior. But not only the young do it: adults pronk too when they’re chased by predators.
- It’s a way, in young gazelles, of letting the mother know the baby has been disturbed. This may be one function, but doesn’t explain stotting in adults.
- It confuses the predator. Presumably a herd of gazelle, all pronking, would puzzle a pursuing cheetah or wild dog, making it hard to pick out a given individual to chase. I don’t believe this for a second; predators aren’t that dumb, and in fact a predator would probably either learn to or evolve to concentrate on the stotting individuals because they might be easier to catch. (This “confusion” explanation was once used to explain zebra stripes: it might be hard to single out one zebra in a mass of fleeing stripey equids. But see my earlier post on another explanation for stripes.)
- It’s a way to attract mates, possibly by showing how fit you are. Sage grouse in the western U.S. form “leks” in which males group together and jump up and down for hours (making loud noises at the same time) while the females watch from nearby. Invariably it is the males who jump the longest that are chosen as mates. Females want a fit father for several reasons. This doesn’t wash for gazelles since both sexes do it, and not in a sexual context.
- This is a favored hypothesis: the “honest signal” theory. This posits that the behavior is saying to potential predators, “Don’t bother trying to catch me as I can bounce really high, so imagine how fast I could run if I wanted to!” In other words, the behavior deters the predator from attacking that individual.
- This is the hypothesis I find most credible: stotting warns the predator that it has been seen, thus discouraging it from pursuing the stotting animal. (Predators like to sneak up on a prey, getting as close as possible before they’re detected.) That is, stotting evolved via individual selection. Remember that predators often don’t go after a whole pack of quadrupeds at once, but single out certain individuals—often young or weak ones—to pursue.
How many just-so stories can you think of?
