Lec17: Anti-predator behavior

Key Takeaways

The following content is provided under a Creative Commons license. Your support will help MIT Open Courseware continue to offer high-quality educational resources for free. To make a donation or view additional materials from hundreds of MIT courses, visit MIT Open Courseware at ocw.mit.edu. We have just this topic to cover before the midterm exam. So, we'll probably have a little bit of it to cover on Friday, but I'm working on a review for you and I won't answer everything on the review. Of course, we won't have time for that, but I will try to go over some of the the points that students have asked me about in the past before the midterm. That seem to points that seem to cause more confusion and I'll give you a few clues to the kind of things I'd put on the exam, but it's basically a short answer exam. There might be some matching. All right. We got started with this last time. I don't want to primary and secondary uh defense mechanisms. Start We talked a little bit about countershading and camouflage. And this is where we left. Many predators develop search images by perceptual learning and then they they learn to search for their prey uh remembering what they've been successful with in the past. And I asked what octopus and squid do. And for that I would like to show a video. Let me see if I'm online here. Just some Some you may not be familiar with this. The mimic octopus, so I want it's only only take couple minutes. This content has been removed due to copyright restrictions. See the readings and viewings page for information about this material. Anyway, there's more you can find a little more online if you want. So, that behavior of the octopus, and there's another example right here on the cover of your book. Another octopus that can change color patterns on its surface. It can mimic predators actually. This This animal can create a thing that looks like two big eyes facing you. It looks like a predator. Most predators have forward facing eyes. It's related to mimicry, and I want to talk here about the different kinds of mimicry. There's two kinds, Mullerian and Batesian. With Mullerian, different different species that are all poisonous um evolve to look similar to each other because then they all benefit like the vespid wasps. So, an animal learns by eating trying to eat one vespid wasp. Um they taste bad, they're poisonous. They The animal, the predator, learns to avoid not just that one species, but other vespids too because they look fairly similar. They all have the bands, uh yellow and black bands on their abdomen. And uh that's the evolution of Mullerian mimicry. With Bayesian mimicry, animals that are not poisonous will evolve to look like a poisonous one. The best known is the monarch butterfly, which is poisonous and bad-tasting. Animals learn to avoid it. Birds will generally not attack monarchs. And this is an example right here, the viceroy butterfly, that's evolved to look very much like the monarch. Here's a a female monarch, here's a a male monarch butterfly. And there's several species that have evolved to look like the monarch. Now, let's talk about way other ways to avoid predation. The ground-nesting birds, why would a Why do some birds nest in the open on the ground? They must have some advantages. And you can see one clear advantage. Advantage, they can see any approaching predator because there's no concealment. But of course, their nest isn't all that well concealed either. So, what do they do to protect their nest from an approaching predator, like a fox or a polecat? And one of the best known examples that's usually cited that is the the way the plovers behave. Here's a couple of uh plovers, black-headed plover and a piping plover. They both nest on the ground, so they have that problem. Uh what to do if there is a predator? They want to protect their eggs. They of course can fly away, but that leaves the eggs unprotected, so uh one of the things they do is reminiscent of what we saw in that very first video we showed in class of the the stickleback. Remember the the male stickleback can have his nest attacked by female sticklebacks and he will he'll behave like he's got a nest some other place. He creates a false nest and he attracts them to that. You know, and so they then are led away from his real nest and that's what these birds do. They'll they'll pretend they're nesting in the wrong place, attract the predator, and of course they fly away and then the predator doesn't get their eggs. Another method is to approach the predator if there's tall grass where he can do it. Uh and then suddenly they'll duck down so they're hidden in the grass and they'll scurry away squeaking like a rodent. And the predator finds that irresistible. He chases after the rodent. And uh and of course that rodent mimic, the plover, is leading the animal away from their nest. And there's another couple of methods they can use. They can especially if the predator's already pretty close, they can run directly at it. They can fly run or fly towards it. They'll call very loudly. They turn away the last second and move away from the nest. That way they attract the predator to attack them. But they're quite able to get away. Another well-known one and a few of you may have occasionally seen this in wild. If you like to observe birds, that's the broken wing display. This animal that's being attacked can flee uh along the ground acting like he can't fly looking exactly like he's got an injured wing. And again, predators can't resist that. You know, an injured bird is their best chance catching a bird. Normally, they can't catch birds, but they can catch them if they're injured. So, that way the plover can again lead the animal away from their nest. So, all of that's kind of secondary defense. Reduces the success of an attack. Uh Reducing the probability of attack, that's the sorry, primary. Now, the secondary defense is when an animal is actually caught by a predator. So, what does he do? Reduce the chance that he's going to be killed. They're not totally helpless even if they're caught. So, Scott describes the behavior of a chick. Chicks, of course, are a lot less able than adult chickens to they can't fly yet. Uh They can't even run very fast. They're much more likely to get caught in the jaws of a predator. And what they What do they do? Well, they they have this physiological change in their body. It's called tonic in immobility. We call it playing dead. But, it's a physiological response. You know, it's an innate it's a fixed action pattern, okay? Uh Other animals, I ask here whether mammals have such response, and many small mammals do. Uh I still remember when I was keeping hamsters in a basement, uh I would kept pet hamsters for a while before I started studying them in the lab. And I remember coming down there and the a female had gotten out of the nest area that cage that I had and But when I turned the light on and made movement, that animal just froze. Became totally immobile. And I thought, you know, as soon as I I walk over here, she's just going to run and get away. I'm going to have to trap her with food or something or water. And if you know these animals well, that's fairly easy to do, but it takes a lot of time. But instead, the animal was totally immobile. I could even touch the animal and move a limb and it would just stay that way. You know, it was a tonic immobility response and they maintain it for quite a few minutes. Hamsters also have that as a response to specific odors of, for example, polecat-like animals and certain species of dog. I had it happen with visitors who had dog. Uh but all dogs didn't elicit that, just certain ones. And I I never have tracked down exactly which ones were more related to the polecat and their odor. But anyway, these chicks are responding to the division of those two predator eyes facing them. That triggers the tonic immobility. And uh And every once in a while, the chick and generally the predator, if he's doesn't struggle and doesn't move, you know, just keeps him in its its area, its nest area, and doesn't immediately kill them. I mean, why why he doesn't need to. Unless he's competing with other animals, in which case he might. It doesn't The method doesn't always work for the chick. But the chick lying there will occasionally peek to find out if the predator's still there. And if it it looks and he still gets that stimulus, he'll continue in that state of tonic immobility. But if he doesn't see the two eyes, the innate releasing mechanism is missing. He will lose the tonic immobility and run away. Now, we know that opossum does something similar. They're the best known. We talk about opossums playing dead. You never don't hear about hamsters, but I can assure you they also would can do that. And many other small mammals with certain kinds of stimulation. Rabbits, for example, can enter that state. Now, we talked about anti-predator benefits of group foraging by birds before and I want you should be able to tell what the major benefits are and the costs. I can count at least three benefits. One is dilution effect. We call it the selfish herd. You know, the more animals are there, the less chance that any one animal's going to be caught and for that reason in the period of reproduction, many animals reproduce in a colony because if the colony's attacked, the chances that it will be their nest and their young that are attacked are reduced. It also, of course, reduces the demands for vigilance on an individual because there's many more eyes to see the predator. So, the chances they're detecting a predator are much greater. And one animal response, it's quickly communicated to all of them either because they fly or they emit alarm calls or both. And of course if they're they all fly up at once it confuses the predator and very often the predator doesn't get any of them. It has costs of course with your you're competing with a lot of other animals for food you're uh other animals they're interfering can interfere with your activities and it's of course a lot worse if you're not a dominant uh individual in the in the flock. We talked about the optimal group size which was not specifically related related to predation but to food gathering ability. So I won't go back over that now. I will mention mobbing here. We've talked about mobbing in in jackdaws and in geese you saw examples of that of the geese in the video you read about it in Lawrence's description of jackdaws. We saw it in the meerkat video as well. Uh Scott discusses the black-headed gulls which uh will show mobbing of predators. And he cites data from a study where they looked at colony nesting gulls uh and how frequently they engaged in mobbing as a function of where their nest was in the colony. Okay, if they were near the center of the colony the rate of mobbing in most animals in most nests was the highest. The rate at which they lost eggs to a predator was the lowest. Okay, and then he went to the edge of the colony further he got from the center Okay. Then they were less likely to engage in the mobbing behavior but they were much more likely to have their nests predated. And they could lose eggs. So mobbing is an effective kind of anti-predator behavior. So what they can they do besides these kinds of behaviors or just running away? Of course that's the main defense an animal has. If he's by himself and he's attacked by a predator, he has to run. And the trick is simply not getting caught. And the But they can do other things, too. For example, some mollusks, they have these uh tentacles that they can Some of these tentacles actually are pretty meaty and animals will often, because they're moving, are more likely to attack that part of the mollusk. But these things can be shed. Similarly, lizards, you know, the tail, they'll move their tail much more than the rest of their body and they will do that purposely. Because if they can attack if the animal attacks them, grabs the tail the lizard just sheds the tail and the tailless lizard will get away. And sometimes the tail will be shed and it keeps wiggling and wiggling and the predator keeps going after it. The movement is irresistible to the predator. Okay, we talked about this a little bit about alarm calls. You should be know that there's both altruistic and selfish aspects uses of alarm calls. We know it can be altruistic, it can help others. But of course the animal doing the calling his position is betrayed to the predator. So that's a cost. And of course you can elicit a the animal can elicit a mass escape and benefit from the dilution and confusion effects. And he can do that, you know, uh He's he's benefiting perhaps more than the others because of the head start he gets. Uh and sometimes he will do that even if there's not a predator just so he gets access to food. So that's another selfish use of of the alarm calls. Cresswell in '94 is reviewed by Scott collected data on that the these animals that wait around shallow water and eat fat worms that they find the bottom of uh ponds. Uh He found that the ones that didn't call Okay? And the ones that flew up the la- the latest were the most likely to be attacked. So those animals that were doing the calling weren't the most likely to be caught even though they did betray their position. You know, the calling might attract the predator to the region, but it doesn't make him select the animal to attack. In fact, if the animal's calling he's probably the one you don't want to attack because he's the vigilant one that saw you first. They want to attack an animal that's less aware and that's exactly what they do. The late fliers and the non-callers were the most likely to be attacked. And of course I mentioned here at the end that alarm calls can also attract predators of the predator. So that's is another occasional benefit of the calling. Redshanks actually have two distinct ways of escaping. Now, some animals even have very distinct calls that gives away which way they're going to escape. And that's because they can be attacked in different ways. And this for the redshanks, they have two major predators, the peregrine falcons, you know, attack from above and in a rapid diving attack. So, they need to crouch low and remain still uh so they're not attracting the vision of that falcon. Whereas the sparrowhawk attacks flying in just above the ground, low. So, their best bet if he's already been detected and that hawk is coming towards him, the best thing he can do is fly up. So, that's why in this there are two very distinct methods of escape. And they each work best for only for one of the one of these predators. And then we come to a really weird one, stotting behavior. It's caused a lot of confusion in studies of animal behavior. Do you know what it is? Now, these little gazelles will be fleeing from a predator and as they flee they're take using extra energy and extra time to leap up high so they can be seen. They make themselves visible to the predator. And this is the way they look like. And when they when you're looking at them as you see in the drawing here, here's a cheetah pursuing one of these Thompson's gazelle, and the cheetah sees him from behind and he's what he sees is this like a white flag. Every time the gazelle leaps up. Now, why would they do that? There's been multiple hypotheses uh the uh the book mentions 11 that there are 11 different hypotheses. Uh he summarizes just three of them and uses data from Caro. This is from 1986. About it, uh he found that attacks by cheetahs uh were appeared to be deterred by the stotting. It does work. And the the interpretation is that it's communicating this. I'm far enough away that I have a high probability of escape, so why waste your time and energy? And of course, if he does if it does deter the attack of the cheetah, then the animal himself will use less energy. He will not have to flee as long. And in fact, they've collected data that is summarized in the book about the frequency of success of these attacks in animals that engage in stotting and those that don't. And those that show the stotting behavior uh are not caught as often. Okay. So, I want to show this video called Great Escapes. It's some of you have seen Marty Stouffer on the TV public television. And these are the thing I will try to I'm not don't know if I'll show all of these things, but these are this is a summary of the number of the things in the earlier part of the the video. So, let Let pull it up here and It'll start out with a a bobcat. The most common big cat in the USA. Not a real huge cat, but a common predator. This content has been removed due to copyright restrictions. See the readings and viewings page for information about this material. Okay, why didn't the bobcat kill it? We've met this before when we talked about predatory behavior and the work of Leyhausen and Lorenz. What's your interpretation? Good exam question. Interpret that what just happened there. Why? Yes. If I'm hearing you right, I think you what you said is great. He had he had exercised his killing bite very recently and killed prey. His motivation for executing the killing bite was reduced below the level where it could be triggered by that very pigeon. But his motivation to stalk and even attack was still high enough that when the stimulus was strong like that ferret taking taking off it elicited the attack. But he wasn't sufficiently motivated to finish that last step. Because the action specific potential, the motivation to do the killing bite does it doesn't build up as fast as the motivation for those earlier parts of predatory behavior. So there's other examples of that in the work of Leyhausen. And that isn't the He wasn't playing with it. But that seems to be what it amounts to. And in fact, these big cats will do that when they themselves have killed and eaten and so forth. They will still actually catch prey without killing and bring it to their young, which then can practice. Now we're going to see a coyote. This content has been removed due to copyright restrictions. See the readings and viewings page for information about this material. I wanted to show you there was only one other thing I could show you. It's just a bobcat attacking a lizard and uh the bobcat ends up chasing a tail. Okay, so I will see you on Friday. And we will just have a little bit more on any predatory behavior and then we'll do a some reviewing.