1 00:00:00,080 --> 00:00:01,800 The following content is provided 2 00:00:01,800 --> 00:00:04,040 under a Creative Commons license. 3 00:00:04,040 --> 00:00:06,880 Your support will help MIT OpenCourseWare continue 4 00:00:06,880 --> 00:00:10,740 to offer high quality educational resources for free. 5 00:00:10,740 --> 00:00:13,350 To make a donation or view additional materials 6 00:00:13,350 --> 00:00:17,237 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,237 --> 00:00:17,862 at ocw.mit.edu. 8 00:00:21,591 --> 00:00:22,350 PROFESSOR: OK. 9 00:00:22,350 --> 00:00:25,130 So I want to talk a little bit about foraging behavior, 10 00:00:25,130 --> 00:00:30,190 and then that will be followed by some things 11 00:00:30,190 --> 00:00:33,190 on antI-predator behavior, and those 12 00:00:33,190 --> 00:00:35,380 will be the last topics before the midterm. 13 00:00:38,500 --> 00:00:42,810 We will finish antI-predator behavior next Friday, 14 00:00:42,810 --> 00:00:45,220 but it should leave time-- because we'll 15 00:00:45,220 --> 00:00:50,870 start that on Wednesday-- we should have time for some 16 00:00:50,870 --> 00:00:57,150 reviewing, since the exam is on Monday, not next Monday 17 00:00:57,150 --> 00:00:58,280 but the following Monday. 18 00:01:02,780 --> 00:01:03,280 OK. 19 00:01:03,280 --> 00:01:05,640 Now this first question you should 20 00:01:05,640 --> 00:01:10,550 be able to answer by now, because it's come up before. 21 00:01:10,550 --> 00:01:13,980 Does the level of foraging or hunting 22 00:01:13,980 --> 00:01:17,180 depend on the amount of hunger? 23 00:01:17,180 --> 00:01:20,030 Is it independent of hunger? 24 00:01:20,030 --> 00:01:23,010 And the reason I raise the question again 25 00:01:23,010 --> 00:01:27,270 is because in the reading by Scott, 26 00:01:27,270 --> 00:01:31,340 he paints a somewhat different picture than the one 27 00:01:31,340 --> 00:01:34,650 we learned about from Konrad Lorenz and Leyhausen's work 28 00:01:34,650 --> 00:01:40,770 with cats and John Flynn's work with cat brain stimulation. 29 00:01:40,770 --> 00:01:42,060 So what's the simple answer? 30 00:01:45,530 --> 00:01:50,180 Is it dependent on hunger? 31 00:01:50,180 --> 00:01:51,650 Or not? 32 00:01:51,650 --> 00:01:55,040 In fact, in some of the videos I show, occasionally 33 00:01:55,040 --> 00:01:57,930 you'll hear mentioned that people just 34 00:01:57,930 --> 00:02:04,410 assume that if they're not hungry they won't hunt. 35 00:02:09,030 --> 00:02:09,820 Well, you'll see. 36 00:02:09,820 --> 00:02:13,000 We're going to see a video next week where you'll 37 00:02:13,000 --> 00:02:16,800 get an example of that that contradicts some 38 00:02:16,800 --> 00:02:21,380 of the ecological studies that we know about. 39 00:02:21,380 --> 00:02:25,970 So Scott doesn't make it clear that some innate foraging 40 00:02:25,970 --> 00:02:27,420 drives are separate from hunger. 41 00:02:27,420 --> 00:02:33,130 But remember we discussed this before. 42 00:02:33,130 --> 00:02:38,870 But Scott does introduce one more thing, this. 43 00:02:38,870 --> 00:02:44,120 On page 120 he talks about the role of social cues 44 00:02:44,120 --> 00:02:46,960 and of learning. 45 00:02:46,960 --> 00:02:49,770 So my question here is, why might an animal 46 00:02:49,770 --> 00:02:58,020 eat more when feeding with a group of his conspecifics 47 00:02:58,020 --> 00:03:02,000 than it would if it was feeding alone? 48 00:03:02,000 --> 00:03:06,270 In fact, sometimes a monkey in a group, 49 00:03:06,270 --> 00:03:09,940 he'll finish feeding alone, but then if suddenly he's 50 00:03:09,940 --> 00:03:13,889 with a group, he will start eating more 51 00:03:13,889 --> 00:03:14,805 if they're all eating. 52 00:03:18,700 --> 00:03:21,110 So why-- what do you think is behind that? 53 00:03:21,110 --> 00:03:22,095 Why would that evolve? 54 00:03:24,620 --> 00:03:28,900 And when I ask you question like that, why it would evolve, 55 00:03:28,900 --> 00:03:30,330 what I want you to think about is 56 00:03:30,330 --> 00:03:35,140 what is the benefit for the individual? 57 00:03:35,140 --> 00:03:38,445 What's the selfish reason why an animal would do that? 58 00:03:41,310 --> 00:03:42,575 He ate to satiation. 59 00:03:42,575 --> 00:03:44,950 He shouldn't be hungry, so why would he now start eating? 60 00:03:48,170 --> 00:03:50,720 Did you read it? 61 00:03:50,720 --> 00:03:54,800 Because Scott does suggest the reason in the reading. 62 00:03:58,470 --> 00:04:00,060 If all the other animals-- there's 63 00:04:00,060 --> 00:04:05,032 a limited amount of food there, and if they're all eating it, 64 00:04:05,032 --> 00:04:06,615 there's not going to be anything left. 65 00:04:10,190 --> 00:04:16,100 And animals need to maximize their food intake to survive, 66 00:04:16,100 --> 00:04:23,280 so an animal will eat more in a social group 67 00:04:23,280 --> 00:04:24,870 for just that selfish reason. 68 00:04:31,180 --> 00:04:35,020 Eat it before it's all gone. 69 00:04:35,020 --> 00:04:37,510 And that's why we think that tendency evolved. 70 00:04:37,510 --> 00:04:43,220 It's also sometimes just called social facilitation 71 00:04:43,220 --> 00:04:45,840 by social psychologists. 72 00:04:45,840 --> 00:04:48,230 But here in animal behavior, you can 73 00:04:48,230 --> 00:04:52,210 call it social facilitation, but there is a specific reason 74 00:04:52,210 --> 00:04:56,580 why that should evolve as innate behavior. 75 00:04:56,580 --> 00:05:01,540 Let's go to the next topic here, on conditioned taste aversion. 76 00:05:01,540 --> 00:05:06,150 It's also called the poison bait effect. 77 00:05:06,150 --> 00:05:10,630 And Scott calls it a form of classical conditioning. 78 00:05:10,630 --> 00:05:15,500 And in fact there's a box in the book 79 00:05:15,500 --> 00:05:19,140 there, on page 122, where he goes through that. 80 00:05:19,140 --> 00:05:25,526 And it was discovered by John Garcia in California. 81 00:05:28,570 --> 00:05:31,160 It has properties that do not fit 82 00:05:31,160 --> 00:05:35,940 the descriptions of classical conditioning, and this is why. 83 00:05:35,940 --> 00:05:40,550 For one thing, it's something the animal learns in one trial. 84 00:05:40,550 --> 00:05:45,240 And there are examples of other one-trial learning. 85 00:05:45,240 --> 00:05:47,820 Like a rat stepping down from a platform 86 00:05:47,820 --> 00:05:49,210 onto an electrified grid. 87 00:05:49,210 --> 00:05:52,060 He will learn in one trial not to step down. 88 00:05:52,060 --> 00:05:54,530 But most things take longer to learn. 89 00:05:54,530 --> 00:05:57,820 At least with positive reinforcement that's true. 90 00:05:57,820 --> 00:06:01,080 In this case it's not only just one-trial learning, 91 00:06:01,080 --> 00:06:05,160 but this so-called unconditioned response 92 00:06:05,160 --> 00:06:10,230 where the animal gets sick and feels 93 00:06:10,230 --> 00:06:12,900 nauseated as a result of eating. 94 00:06:12,900 --> 00:06:17,200 A lot of times that sickness doesn't occur immediately. 95 00:06:17,200 --> 00:06:19,220 It takes a little while, and yet they still 96 00:06:19,220 --> 00:06:22,365 learn to avoid that food. 97 00:06:24,880 --> 00:06:27,540 And the third thing is that the memory 98 00:06:27,540 --> 00:06:29,870 is much more long lasting than you 99 00:06:29,870 --> 00:06:33,920 find in classical conditioning. 100 00:06:33,920 --> 00:06:37,330 Humans that have experienced this, and many of us 101 00:06:37,330 --> 00:06:40,245 have, it can last for years. 102 00:06:42,910 --> 00:06:48,180 For example, when I was a kid, I was probably 103 00:06:48,180 --> 00:06:50,790 on the verge of getting the stomach flu but didn't know it. 104 00:06:50,790 --> 00:06:55,650 But we were roasting marshmallows. 105 00:06:55,650 --> 00:07:00,020 And often we not only browned them, 106 00:07:00,020 --> 00:07:01,240 we burned them a little bit. 107 00:07:01,240 --> 00:07:05,980 And I ate a partially burnt marshmallow, 108 00:07:05,980 --> 00:07:08,680 got sick afterwards or felt terribly sick, 109 00:07:08,680 --> 00:07:12,220 and I couldn't stand the sight of that kind of marshmallow 110 00:07:12,220 --> 00:07:13,335 for 20 years. 111 00:07:16,990 --> 00:07:21,920 A very clear poison bait effect. 112 00:07:21,920 --> 00:07:24,390 It didn't matter whether the illness was really caused 113 00:07:24,390 --> 00:07:26,780 by the marshmallow, because other people didn't get sick 114 00:07:26,780 --> 00:07:28,550 from it. 115 00:07:28,550 --> 00:07:30,280 I think I was getting sick anyway. 116 00:07:30,280 --> 00:07:35,530 How many people here have experienced that kind of effect 117 00:07:35,530 --> 00:07:37,540 in their lives? 118 00:07:37,540 --> 00:07:40,350 About a third of you. 119 00:07:40,350 --> 00:07:42,430 Does anybody want to tell us? 120 00:07:42,430 --> 00:07:43,355 Give us an example? 121 00:07:47,310 --> 00:07:48,860 They might like to hear it. 122 00:07:51,590 --> 00:07:54,160 Come on, one of you tell us what you experienced. 123 00:07:57,149 --> 00:07:57,690 AUDIENCE: Me? 124 00:07:57,690 --> 00:07:59,139 PROFESSOR: Yeah. 125 00:07:59,139 --> 00:08:00,055 AUDIENCE: [INAUDIBLE]. 126 00:08:10,945 --> 00:08:12,420 PROFESSOR: What did you eat? 127 00:08:12,420 --> 00:08:13,336 AUDIENCE: [INAUDIBLE]. 128 00:08:15,619 --> 00:08:17,310 PROFESSOR: Well, that's OK. 129 00:08:22,936 --> 00:08:24,435 AUDIENCE: It was like ground-up meat 130 00:08:24,435 --> 00:08:26,688 and it had, like, fillers in it. 131 00:08:26,688 --> 00:08:29,292 And I just decided it really grossed me out, 132 00:08:29,292 --> 00:08:30,167 and I felt nauseous-- 133 00:08:30,167 --> 00:08:32,770 PROFESSOR: You felt nauseated afterwards. 134 00:08:32,770 --> 00:08:36,159 And it's mainly what causes the effect. 135 00:08:36,159 --> 00:08:40,030 And so you-- how did it affect you later? 136 00:08:44,540 --> 00:08:47,550 You wouldn't eat anything like it. 137 00:08:47,550 --> 00:08:49,530 For how long? 138 00:08:49,530 --> 00:08:51,738 Or is it still there? 139 00:08:51,738 --> 00:08:53,391 AUDIENCE: Oh, I got over it. 140 00:08:53,391 --> 00:08:54,890 PROFESSOR: Well, this happened to me 141 00:08:54,890 --> 00:08:58,060 when I was about, I would say, seven years old. 142 00:08:58,060 --> 00:09:02,810 And I was certainly probably 30 years 143 00:09:02,810 --> 00:09:07,580 old before I could eat a marshmallow like that. 144 00:09:07,580 --> 00:09:09,850 All right, so it's not really-- what is it, 145 00:09:09,850 --> 00:09:12,920 then, if it's not classical conditioning? 146 00:09:12,920 --> 00:09:16,600 Scott has written that conditioned taste aversion is, 147 00:09:16,600 --> 00:09:18,520 of course, a form of classical conditioning. 148 00:09:18,520 --> 00:09:20,680 Why would he say that? 149 00:09:20,680 --> 00:09:23,910 The reason is, first of all, many learning theorists 150 00:09:23,910 --> 00:09:27,190 have lumped all learning into just a few categories. 151 00:09:27,190 --> 00:09:31,020 And many textbooks on learning are organized that way. 152 00:09:31,020 --> 00:09:33,900 The few major sections, classical conditioning, 153 00:09:33,900 --> 00:09:35,000 instrumental conditioning. 154 00:09:35,000 --> 00:09:38,810 And now they usually have a few other types, too. 155 00:09:38,810 --> 00:09:43,350 And also many people, including many scientists, 156 00:09:43,350 --> 00:09:46,080 have believed, as you know from the class 157 00:09:46,080 --> 00:09:49,030 before, that almost every behavior is learned, 158 00:09:49,030 --> 00:09:52,010 especially here in America. 159 00:09:52,010 --> 00:09:56,300 Lawrence calls this form of learning an innate disposition 160 00:09:56,300 --> 00:09:59,320 for learning. 161 00:09:59,320 --> 00:10:05,330 The innate schoolmarm that shows us evidence 162 00:10:05,330 --> 00:10:07,960 for a built-in program for a particular kind 163 00:10:07,960 --> 00:10:11,420 of learning that it's very easy to understand 164 00:10:11,420 --> 00:10:12,680 why that would be adapted. 165 00:10:16,880 --> 00:10:21,720 It's been used to control predation of livestock. 166 00:10:21,720 --> 00:10:29,110 If you are having sheep being killed by wolves, for example-- 167 00:10:29,110 --> 00:10:31,750 it usually has to be a particular wolf pack, 168 00:10:31,750 --> 00:10:40,380 so they're all going to eat some-- you give them a sheep, 169 00:10:40,380 --> 00:10:44,180 a lamb or something that's been tainted, 170 00:10:44,180 --> 00:10:48,560 or calves, or the kind of thing that they're eating. 171 00:10:51,260 --> 00:10:56,260 And they will avoid it for quite some time. 172 00:10:56,260 --> 00:10:59,320 It's somewhat variable in how effective this is, 173 00:10:59,320 --> 00:11:05,050 but of course just how many animals actually eat it and get 174 00:11:05,050 --> 00:11:06,950 sick from it will vary too. 175 00:11:09,510 --> 00:11:12,970 Now it's related to another form of avoiding 176 00:11:12,970 --> 00:11:14,130 food we call neophobia. 177 00:11:17,250 --> 00:11:20,340 Animals tend to avoid new things. 178 00:11:20,340 --> 00:11:27,030 So you set a trap for a mouse or a rat in your house. 179 00:11:27,030 --> 00:11:30,510 If it's not something really familiar to the animal, 180 00:11:30,510 --> 00:11:35,130 they will be very, very cautious. 181 00:11:35,130 --> 00:11:38,080 It needs to be something that they 182 00:11:38,080 --> 00:11:41,220 really love and has a strong odor. 183 00:11:41,220 --> 00:11:44,420 Certain kinds of cheese have that effect and-- 184 00:11:44,420 --> 00:11:45,280 [CELL PHONE RINGS] 185 00:11:45,280 --> 00:11:45,780 Sorry. 186 00:11:58,229 --> 00:12:00,230 Well, I hope that will wait. 187 00:12:03,040 --> 00:12:03,540 OK. 188 00:12:03,540 --> 00:12:07,980 So why would they avoid something novel? 189 00:12:07,980 --> 00:12:10,740 Well, it's not as likely to be safe. 190 00:12:10,740 --> 00:12:12,190 They know what's safe. 191 00:12:12,190 --> 00:12:14,900 They've had experience with it. 192 00:12:14,900 --> 00:12:17,480 How would you expect that effect to vary with those two 193 00:12:17,480 --> 00:12:19,090 factors, hunger level and age? 194 00:12:21,780 --> 00:12:27,410 Would it be greater or less in a young rat or an old rat? 195 00:12:27,410 --> 00:12:29,690 You might say, well, an inexperienced rat, 196 00:12:29,690 --> 00:12:31,725 he's more likely to eat anything. 197 00:12:31,725 --> 00:12:32,975 But in fact, it's the reverse. 198 00:12:35,510 --> 00:12:38,830 You should know with humans, when 199 00:12:38,830 --> 00:12:40,670 you were younger you were probably much more 200 00:12:40,670 --> 00:12:43,072 likely to avoid a lot of things. 201 00:12:43,072 --> 00:12:44,530 And your parents were always trying 202 00:12:44,530 --> 00:12:47,830 to get you to try new things, right? 203 00:12:47,830 --> 00:12:49,610 And you say, I don't like it. 204 00:12:52,250 --> 00:12:56,430 My youngest daughter would say, I don't like that stuff, 205 00:12:56,430 --> 00:12:59,570 and she's never had it in her life. 206 00:12:59,570 --> 00:13:03,190 I knew that because she'd come here from China, 207 00:13:03,190 --> 00:13:07,390 so she had never had many of the American foods we were having. 208 00:13:07,390 --> 00:13:09,840 But her mother, much older, of course, 209 00:13:09,840 --> 00:13:13,490 would try it and like it, and so forth. 210 00:13:13,490 --> 00:13:17,860 But as the daughter grows older, she gradually 211 00:13:17,860 --> 00:13:19,980 will try more and more things. 212 00:13:19,980 --> 00:13:22,520 But if you make them-- as I pointed out before, 213 00:13:22,520 --> 00:13:26,810 if they're hungry enough, neophobia decreases. 214 00:13:26,810 --> 00:13:29,600 And again, of course, that's adaptive, 215 00:13:29,600 --> 00:13:33,940 because an animal doesn't want to starve to death. 216 00:13:33,940 --> 00:13:37,060 So they haven't-- these are innate preferences, though, 217 00:13:37,060 --> 00:13:38,265 that we're talking about. 218 00:13:43,490 --> 00:13:49,000 And then Scott discusses another situation 219 00:13:49,000 --> 00:13:51,580 of social facilitation, in this case 220 00:13:51,580 --> 00:13:56,130 in capuchin monkeys faced with a novel food. 221 00:13:56,130 --> 00:13:59,810 They discovered that the monkey was much more 222 00:13:59,810 --> 00:14:03,450 likely to eat that novel food if other monkeys were 223 00:14:03,450 --> 00:14:04,260 eating near him. 224 00:14:04,260 --> 00:14:06,460 And it didn't even have to be the same food, which 225 00:14:06,460 --> 00:14:09,300 was the surprising part of the study. 226 00:14:09,300 --> 00:14:11,977 It would be understandable if he saw other animals eating it 227 00:14:11,977 --> 00:14:13,060 and it was the same thing. 228 00:14:13,060 --> 00:14:15,570 Oh, that's got to be safe. 229 00:14:15,570 --> 00:14:18,570 They're eating it, it's not going to hurt me. 230 00:14:18,570 --> 00:14:21,080 But they'll do it. 231 00:14:21,080 --> 00:14:24,280 They're more likely to eat the novel food, even 232 00:14:24,280 --> 00:14:26,730 if the monkeys are eating something more familiar. 233 00:14:30,490 --> 00:14:37,191 And I can't really explain that in terms of adaptive behavior. 234 00:14:37,191 --> 00:14:37,690 OK. 235 00:14:37,690 --> 00:14:44,390 Let's talk about another social effect on foraging. 236 00:14:44,390 --> 00:14:53,420 The ospreys, a bird that forages for fish in the ocean. 237 00:14:53,420 --> 00:14:56,390 How can they benefit from hunting, that is, 238 00:14:56,390 --> 00:15:00,680 fishing success of neighbors, even though they don't share? 239 00:15:00,680 --> 00:15:07,750 The osprey that brings a fish back to their communal colony 240 00:15:07,750 --> 00:15:10,360 doesn't share it with the others, 241 00:15:10,360 --> 00:15:13,990 and yet it will affect the others, 242 00:15:13,990 --> 00:15:19,630 because-- and there are some data put in the chapter 243 00:15:19,630 --> 00:15:21,250 there, Scott's chapter. 244 00:15:21,250 --> 00:15:24,220 He presents some data that animals, 245 00:15:24,220 --> 00:15:28,450 the frequency that they fly off in the same direction 246 00:15:28,450 --> 00:15:31,930 greatly increases if a osprey has brought back 247 00:15:31,930 --> 00:15:37,390 certain kinds of fish, but not all kinds of fish. 248 00:15:37,390 --> 00:15:41,160 Why does it depend on the kind of fish? 249 00:15:41,160 --> 00:15:43,020 Even if you've not read it, you should 250 00:15:43,020 --> 00:15:44,569 be able to think of some reason why 251 00:15:44,569 --> 00:15:45,860 it might have evolved that way. 252 00:15:48,850 --> 00:15:50,920 Because fish differ in how likely 253 00:15:50,920 --> 00:15:54,200 they are to be swimming in schools. 254 00:15:54,200 --> 00:15:57,250 If the fish aren't schooling fish-- 255 00:15:57,250 --> 00:16:00,960 like the Aioli, for example, in the oceans out here. 256 00:16:00,960 --> 00:16:04,480 They tend to be schooling fish. 257 00:16:04,480 --> 00:16:11,010 But flounders are not in schools. 258 00:16:11,010 --> 00:16:13,510 So if the osprey comes back with a founder, 259 00:16:13,510 --> 00:16:16,260 the other birds will ignore it. 260 00:16:16,260 --> 00:16:18,550 They'll just consider that bird a lucky bird, 261 00:16:18,550 --> 00:16:20,390 but it's not going to affect them. 262 00:16:20,390 --> 00:16:23,830 But if it was one of these birds-- 263 00:16:23,830 --> 00:16:26,520 he doesn't mention herring, but herring are another schooling 264 00:16:26,520 --> 00:16:28,130 fish. 265 00:16:28,130 --> 00:16:32,320 So if it was a fish like that, then he's 266 00:16:32,320 --> 00:16:34,280 much more likely to fly off in that direction 267 00:16:34,280 --> 00:16:37,670 because he knows there's got to be a school of them out there, 268 00:16:37,670 --> 00:16:41,530 or this bird wouldn't have come back with the fish. 269 00:16:41,530 --> 00:16:46,790 So that gives them some benefit for living in a colony. 270 00:16:46,790 --> 00:16:50,290 So it serves as a kind of center of information transfer. 271 00:16:54,250 --> 00:16:55,820 They've looked for the same thing 272 00:16:55,820 --> 00:17:03,410 with black-headed gulls, which also nest near each other. 273 00:17:03,410 --> 00:17:08,119 And yet they don't respond that way. 274 00:17:08,119 --> 00:17:11,430 Even if a black-headed gull is coming back 275 00:17:11,430 --> 00:17:15,050 from a pile of food, so there's a lot of it available, 276 00:17:15,050 --> 00:17:18,630 the others won't fly off in that direction. 277 00:17:18,630 --> 00:17:20,880 So the question is, why are they different? 278 00:17:20,880 --> 00:17:25,300 I have in the margin of this book, which 279 00:17:25,300 --> 00:17:28,760 I've had for several years, black-headed gulls 280 00:17:28,760 --> 00:17:31,550 are stupid in comparison to ospreys. 281 00:17:31,550 --> 00:17:33,950 But in fact, there is a reason why 282 00:17:33,950 --> 00:17:36,250 they might have evolved that way, 283 00:17:36,250 --> 00:17:37,860 at least earlier in their evolution. 284 00:17:37,860 --> 00:17:41,790 They probably fed mainly on food that was scattered. 285 00:17:41,790 --> 00:17:43,880 OK, so not likely to be found. 286 00:17:43,880 --> 00:17:48,120 So they'd be wasting energy if they constantly flew off 287 00:17:48,120 --> 00:17:52,950 in the direction that an animal had come from just because he 288 00:17:52,950 --> 00:17:57,230 had food, just because of different feeding preferences, 289 00:17:57,230 --> 00:18:01,090 at least for a long period in their evolution. 290 00:18:01,090 --> 00:18:03,760 So they've evolved differently from the ospreys. 291 00:18:06,360 --> 00:18:07,270 OK. 292 00:18:07,270 --> 00:18:09,750 Group foraging. 293 00:18:09,750 --> 00:18:12,245 I want two good reasons why foraging 294 00:18:12,245 --> 00:18:14,800 in a group of herbivores may be better 295 00:18:14,800 --> 00:18:17,840 for an animal like a bird than foraging alone. 296 00:18:20,590 --> 00:18:22,440 And I can give you a hint. 297 00:18:22,440 --> 00:18:25,086 Pay attention to birds right now. 298 00:18:25,086 --> 00:18:26,710 If you've ever looked at birds outside, 299 00:18:26,710 --> 00:18:31,030 you will notice something happening as the fall goes on. 300 00:18:31,030 --> 00:18:32,920 Food is still fairly plentiful, but it 301 00:18:32,920 --> 00:18:37,540 becomes less and less as the winter approaches. 302 00:18:37,540 --> 00:18:41,810 And when snow's on the ground it becomes much harder to find. 303 00:18:41,810 --> 00:18:44,960 So what change do you see in birds? 304 00:18:44,960 --> 00:18:50,610 Birds that you normally never see in groups, in flocks, 305 00:18:50,610 --> 00:18:53,390 start flocking. 306 00:18:53,390 --> 00:18:55,370 It looks like they're all just flocking 307 00:18:55,370 --> 00:18:58,120 because how they're going to fly south together. 308 00:18:58,120 --> 00:19:00,510 But in fact, in many cases that's not the reason. 309 00:19:00,510 --> 00:19:04,690 You'll see sparrows doing this, you'll see juncos doing this. 310 00:19:04,690 --> 00:19:08,930 They all stay around here all winter. 311 00:19:08,930 --> 00:19:10,170 So why would they do that? 312 00:19:10,170 --> 00:19:12,630 What are the benefits? 313 00:19:12,630 --> 00:19:15,610 First of all, protection from predators. 314 00:19:15,610 --> 00:19:18,510 Because when there's a lot more eyes, 315 00:19:18,510 --> 00:19:21,910 the predators have finding less food too. 316 00:19:21,910 --> 00:19:23,700 So they're going to be hunting. 317 00:19:23,700 --> 00:19:26,330 These hawks, the red-tailed hawks around here 318 00:19:26,330 --> 00:19:28,620 certainly catch pigeons. 319 00:19:28,620 --> 00:19:31,080 They prefer those, because they're bigger and fatter, 320 00:19:31,080 --> 00:19:34,380 but they'll catch songbirds too. 321 00:19:36,980 --> 00:19:39,960 So the predator's more likely to be detected 322 00:19:39,960 --> 00:19:43,930 if there's a lot more eyes that could see them. 323 00:19:43,930 --> 00:19:48,380 And also, if they're in a group, and there's a red-tailed hawk 324 00:19:48,380 --> 00:19:51,680 attacking, they're only one a group. 325 00:19:51,680 --> 00:19:55,870 So the chances that they'll be the one the hawk selects 326 00:19:55,870 --> 00:19:57,390 are reduced. 327 00:19:57,390 --> 00:19:59,330 That's a kind of dilution effect that 328 00:19:59,330 --> 00:20:01,540 protects animals in a group. 329 00:20:05,430 --> 00:20:10,610 In addition, we mentioned the-- oh, the second one, of course, 330 00:20:10,610 --> 00:20:13,040 is they're more likely to detect food 331 00:20:13,040 --> 00:20:14,750 sources for the same reason that they're 332 00:20:14,750 --> 00:20:16,250 more likely to detect a predator. 333 00:20:18,780 --> 00:20:21,140 It's very interesting watching a large group 334 00:20:21,140 --> 00:20:22,470 of birds doing this. 335 00:20:22,470 --> 00:20:25,860 All it takes is one seeing the food, 336 00:20:25,860 --> 00:20:28,670 and he flies off separate from the others. 337 00:20:28,670 --> 00:20:33,350 Almost always the entire group almost immediately is with him 338 00:20:33,350 --> 00:20:34,180 and flies down. 339 00:20:37,580 --> 00:20:39,480 And of course social facilitation 340 00:20:39,480 --> 00:20:43,770 does increase their food consumption, in addition. 341 00:20:43,770 --> 00:20:47,300 This is just an example of group foraging. 342 00:20:47,300 --> 00:20:49,730 Here's pelicans foraging in groups. 343 00:20:49,730 --> 00:20:53,320 The groups, they tend to be a little smaller. 344 00:20:53,320 --> 00:20:56,235 Here's the American White Pelican, one foraging group. 345 00:20:58,920 --> 00:21:02,140 Does the same reasoning apply to carnivores 346 00:21:02,140 --> 00:21:04,920 in their hunting behavior? 347 00:21:04,920 --> 00:21:08,780 Well, some of the same reasons apply. 348 00:21:08,780 --> 00:21:11,880 They have increased likelihood of finding prey. 349 00:21:11,880 --> 00:21:14,450 They have increased likelihood of catching them 350 00:21:14,450 --> 00:21:17,650 because of cooperative hunting strategies. 351 00:21:17,650 --> 00:21:21,290 And these are examples I can think of. 352 00:21:21,290 --> 00:21:24,120 All these animals have been studied, 353 00:21:24,120 --> 00:21:26,330 and their hunting behavior has been studied. 354 00:21:26,330 --> 00:21:30,910 We know that lions, or at least lionesses, hunt in groups. 355 00:21:30,910 --> 00:21:36,500 Wolves certainly do, though the groups vary a lot in size. 356 00:21:36,500 --> 00:21:41,980 The wild dogs, the African wild dogs, always hunt in groups. 357 00:21:41,980 --> 00:21:45,540 You find some of that in hyenas as well. 358 00:21:45,540 --> 00:21:48,710 And then in the sea mammals, the killer whales, the orcas, 359 00:21:48,710 --> 00:21:51,870 hunt that way. 360 00:21:51,870 --> 00:21:55,670 And even humpback whales engage in cooperation 361 00:21:55,670 --> 00:21:57,790 in their catching of prey. 362 00:21:57,790 --> 00:21:59,660 Like they trap herring fish. 363 00:21:59,660 --> 00:22:03,770 One of them goes below and emits a string of bubbles, 364 00:22:03,770 --> 00:22:07,380 and the bubbles rise up and form a kind of cylinder 365 00:22:07,380 --> 00:22:09,620 around the herring up above. 366 00:22:09,620 --> 00:22:12,170 And the herring, of course, could swim right through that, 367 00:22:12,170 --> 00:22:13,310 but they don't. 368 00:22:13,310 --> 00:22:14,810 They avoid bubbles. 369 00:22:14,810 --> 00:22:17,480 So they sort of trap them in there. 370 00:22:17,480 --> 00:22:25,970 And the humpback whales up above then can feed on the herring. 371 00:22:25,970 --> 00:22:28,170 So it's a cooperative hunting strategy. 372 00:22:28,170 --> 00:22:29,940 They obviously have to take turns 373 00:22:29,940 --> 00:22:32,690 being the one that creates the bubbles, 374 00:22:32,690 --> 00:22:36,320 because they're getting much less food. 375 00:22:36,320 --> 00:22:37,630 This is just examples. 376 00:22:37,630 --> 00:22:43,840 There you see a bunch of female lions, the lionesses. 377 00:22:43,840 --> 00:22:50,900 And there you see below, a group attack on a buffalo. 378 00:22:50,900 --> 00:22:53,150 And they would have very little chance 379 00:22:53,150 --> 00:22:56,980 of bringing that buffalo down if just one of them were doing it. 380 00:22:56,980 --> 00:22:59,340 It would take at least two, and the more there are, 381 00:22:59,340 --> 00:23:01,110 the more likely they are to bring it down. 382 00:23:03,800 --> 00:23:06,540 I put this in just so I can point out 383 00:23:06,540 --> 00:23:08,740 that just because they're a group 384 00:23:08,740 --> 00:23:10,960 they will not always attack. 385 00:23:10,960 --> 00:23:15,880 I mean, what is the likelihood that even three lionesses could 386 00:23:15,880 --> 00:23:18,680 bring down that rhinoceros? 387 00:23:18,680 --> 00:23:21,670 For one thing, the rhinoceros can run pretty fast. 388 00:23:21,670 --> 00:23:25,840 And the other is, the likelihood that he would gore at least one 389 00:23:25,840 --> 00:23:29,350 of them, and maybe all of them, are very high. 390 00:23:29,350 --> 00:23:33,800 And they can't afford a severe injury. 391 00:23:33,800 --> 00:23:39,650 They don't have lioness doctors. 392 00:23:39,650 --> 00:23:42,390 So they will simply watch animals like this. 393 00:23:42,390 --> 00:23:45,030 They have to make the decision, is it worth it? 394 00:23:45,030 --> 00:23:46,800 What's the cost? 395 00:23:46,800 --> 00:23:48,740 If they're super hungry, yes, they 396 00:23:48,740 --> 00:23:50,850 will attack even animals like this. 397 00:23:53,540 --> 00:23:56,200 Here's a group of wolves. 398 00:23:56,200 --> 00:23:59,960 One will never bring down a buffalo. 399 00:23:59,960 --> 00:24:03,460 The buffalo's too big and strong. 400 00:24:03,460 --> 00:24:06,780 He can kick very hard with those hooves. 401 00:24:06,780 --> 00:24:10,160 But with multiple wolves-- and they 402 00:24:10,160 --> 00:24:14,120 often precede this by running, chasing 403 00:24:14,120 --> 00:24:17,290 the animal for a long distance. 404 00:24:17,290 --> 00:24:20,480 So they tire him out, and that makes 405 00:24:20,480 --> 00:24:24,740 him less able to fight them off when they finally attack. 406 00:24:24,740 --> 00:24:28,020 And so it does take a wolf pack like this-- 407 00:24:28,020 --> 00:24:32,220 this is a fairly large pack-- to bring a buffalo down. 408 00:24:32,220 --> 00:24:33,780 And here's the African wild dogs. 409 00:24:33,780 --> 00:24:35,570 You see how relatively small they 410 00:24:35,570 --> 00:24:37,900 are compared to that zebra. 411 00:24:37,900 --> 00:24:40,870 But again, these dogs are well known 412 00:24:40,870 --> 00:24:45,620 for singling out the weaker ones and then 413 00:24:45,620 --> 00:24:47,830 chasing them for a very long distance. 414 00:24:47,830 --> 00:24:51,650 They have great stamina, and they take turns being the ones 415 00:24:51,650 --> 00:24:57,670 closest to the zebra, which takes a little more energy. 416 00:24:57,670 --> 00:25:00,860 So they take turns doing that until finally they 417 00:25:00,860 --> 00:25:02,710 exhaust the animal. 418 00:25:02,710 --> 00:25:05,560 And then, in spite of their small size, 419 00:25:05,560 --> 00:25:10,640 they can kill an animal like this. 420 00:25:10,640 --> 00:25:13,530 You can see the zebra there. 421 00:25:13,530 --> 00:25:17,510 He will kick out at them if they get too close to him. 422 00:25:17,510 --> 00:25:19,670 The dogs are patient. 423 00:25:19,670 --> 00:25:22,620 They just run him down until he doesn't 424 00:25:22,620 --> 00:25:25,220 have the energy to do this. 425 00:25:25,220 --> 00:25:28,210 And since the year 2000, there's a number 426 00:25:28,210 --> 00:25:31,370 of things you can find on the Web using 427 00:25:31,370 --> 00:25:35,820 Google Scholar, including a number of theoretical models 428 00:25:35,820 --> 00:25:39,880 about group hunting and group foraging. 429 00:25:39,880 --> 00:25:46,000 One article Is about raven scavenging, 430 00:25:46,000 --> 00:25:50,590 which favors group foraging by wolves. 431 00:25:50,590 --> 00:25:52,510 Why would that be true? 432 00:25:52,510 --> 00:25:54,940 This is the article. 433 00:25:54,940 --> 00:25:59,370 And here's what they're talking about. 434 00:25:59,370 --> 00:26:04,660 If a wolf pack-- if there's only two, and sometimes three, 435 00:26:04,660 --> 00:26:11,080 in the wolf pack, they're very, very likely 436 00:26:11,080 --> 00:26:14,900 to be closely related, so they're helping each other. 437 00:26:14,900 --> 00:26:17,620 They're helping the genetic fitness 438 00:26:17,620 --> 00:26:23,150 of their siblings, usually, or their parents. 439 00:26:23,150 --> 00:26:29,530 But the larger wolf packs often include unrelated individuals, 440 00:26:29,530 --> 00:26:33,690 and yet they will still join unrelated individuals, 441 00:26:33,690 --> 00:26:36,820 will join wolf packs and they'll be accepted. 442 00:26:36,820 --> 00:26:38,280 So why would that be? 443 00:26:38,280 --> 00:26:39,620 What would the benefit be? 444 00:26:39,620 --> 00:26:45,560 Because in fact, you find that, on average, they're 445 00:26:45,560 --> 00:26:49,270 going to be able to hunt better and eat more food if they're 446 00:26:49,270 --> 00:26:50,630 not in such a large pack. 447 00:26:50,630 --> 00:26:53,200 Because after all, when they bring down prey, 448 00:26:53,200 --> 00:26:54,305 the whole pack has to eat. 449 00:26:57,900 --> 00:27:01,790 And they found a reason. 450 00:27:01,790 --> 00:27:04,190 Studying these wolves, they found out 451 00:27:04,190 --> 00:27:10,940 that if, let's say there's only two, and they bring down food, 452 00:27:10,940 --> 00:27:13,720 it takes a long time to eat large prey. 453 00:27:13,720 --> 00:27:24,850 And they lose a lot of the meat to scavengers like ravens. 454 00:27:24,850 --> 00:27:29,020 But if they're a larger group, they lose a lot less. 455 00:27:29,020 --> 00:27:32,710 There's a lot more wolves to pay attention to the scavengers 456 00:27:32,710 --> 00:27:35,320 and drive them off. 457 00:27:35,320 --> 00:27:38,780 And they modeled it making assumptions 458 00:27:38,780 --> 00:27:42,400 drawn from their studies, and they 459 00:27:42,400 --> 00:27:45,640 were able to show that this works. 460 00:27:45,640 --> 00:27:49,480 There's a good reason why they would do this, just because 461 00:27:49,480 --> 00:27:51,790 of the ravens scavenging. 462 00:27:51,790 --> 00:27:53,750 So it just points out factors that you 463 00:27:53,750 --> 00:27:54,990 wouldn't think of ordinarily. 464 00:27:57,910 --> 00:28:00,880 But in fact the computer models show 465 00:28:00,880 --> 00:28:03,610 that it's very likely to be true. 466 00:28:03,610 --> 00:28:07,330 Here was another computer model, but it's relevant to something 467 00:28:07,330 --> 00:28:09,950 I'm going to bring up a little later. 468 00:28:09,950 --> 00:28:14,740 So if you're interested in the modeling, 469 00:28:14,740 --> 00:28:17,360 this is a good one on what we call 470 00:28:17,360 --> 00:28:18,930 the ideal free distribution. 471 00:28:18,930 --> 00:28:21,570 How do animals distribute themselves 472 00:28:21,570 --> 00:28:24,370 when they're foraging in groups, but groups 473 00:28:24,370 --> 00:28:26,480 can go to different feeding areas? 474 00:28:26,480 --> 00:28:28,470 Some of those feeding areas are very rich. 475 00:28:28,470 --> 00:28:31,340 Some of them are not so rich. 476 00:28:31,340 --> 00:28:38,810 And yet they distribute themselves in an optimal way. 477 00:28:38,810 --> 00:28:40,650 It's called the ideal free distribution 478 00:28:40,650 --> 00:28:43,650 if you solve it theoretically, where they should be. 479 00:28:43,650 --> 00:28:47,140 So we'll be talking about that. 480 00:28:47,140 --> 00:28:49,450 In this one, I mentioned this briefly. 481 00:28:49,450 --> 00:28:55,050 This was a model dealing with this kind of problem. 482 00:28:55,050 --> 00:28:58,540 When they're foraging in a large group, 483 00:28:58,540 --> 00:29:01,290 they don't actually have a clear leader. 484 00:29:01,290 --> 00:29:06,970 They do not need a clear leader to be able to function well. 485 00:29:06,970 --> 00:29:10,840 Like if they detect food, only one or two birds 486 00:29:10,840 --> 00:29:15,680 has to detect the food, and yet it will very rapidly 487 00:29:15,680 --> 00:29:21,910 be communicated to all of them because of the types of cues 488 00:29:21,910 --> 00:29:23,440 they need to respond to. 489 00:29:23,440 --> 00:29:27,430 Similar things are true of migrating birds. 490 00:29:27,430 --> 00:29:30,220 There often is a leader, but the leader is often temporary. 491 00:29:30,220 --> 00:29:31,990 It can change. 492 00:29:31,990 --> 00:29:35,880 And they keep flying in a concerted way, 493 00:29:35,880 --> 00:29:40,010 even without a clear leader. 494 00:29:40,010 --> 00:29:42,650 And yet they behave in a coordinated way. 495 00:29:42,650 --> 00:29:45,410 If they turn, the whole group turns, and so forth. 496 00:29:45,410 --> 00:29:47,530 So this is about that issue. 497 00:29:47,530 --> 00:29:50,720 And it's been dealt with also in simulation work. 498 00:29:53,350 --> 00:29:58,150 OK What do we mean by the term optimal foraging? 499 00:29:58,150 --> 00:30:02,580 What should a foraging animal be optimizing? 500 00:30:02,580 --> 00:30:05,850 Give me a quantitative expression. 501 00:30:05,850 --> 00:30:11,810 He should be optimizing the amount of food taken in, 502 00:30:11,810 --> 00:30:16,950 the net amount of food, that is, net-- no, that's not fair. 503 00:30:16,950 --> 00:30:21,420 Net energy, which is from the food he's eating, 504 00:30:21,420 --> 00:30:23,420 but that has costs, too. 505 00:30:23,420 --> 00:30:26,050 They're using energy to get it. 506 00:30:26,050 --> 00:30:29,350 So the net energy intake per unit time, 507 00:30:29,350 --> 00:30:32,640 that's what they should be optimizing, OK? 508 00:30:32,640 --> 00:30:35,090 A foraging animal should optimize energy intake 509 00:30:35,090 --> 00:30:39,630 minus costs, and that leads to these kinds of questions. 510 00:30:39,630 --> 00:30:43,290 Why should a feeding animal move to another patch of food 511 00:30:43,290 --> 00:30:45,410 if he's had a rich patch? 512 00:30:45,410 --> 00:30:48,730 Yet we often observe they move to other patches, too. 513 00:30:48,730 --> 00:30:50,150 Why do they do that? 514 00:30:50,150 --> 00:30:52,596 How long should a dive last, if he's 515 00:30:52,596 --> 00:30:57,570 a diving animal, or a diving bird, or a sea mammal? 516 00:30:57,570 --> 00:30:58,690 What determines that? 517 00:30:58,690 --> 00:31:03,520 Why did they evolve the kind of behavior they've evolved? 518 00:31:03,520 --> 00:31:09,420 I picked these examples from the book to discuss a little bit. 519 00:31:09,420 --> 00:31:11,310 The first question is crabs. 520 00:31:11,310 --> 00:31:15,880 Why do crabs choose to feed on intermediate-sized mussels 521 00:31:15,880 --> 00:31:19,630 instead of the bigger, more meaty, larger mussels? 522 00:31:22,430 --> 00:31:24,510 They generally ignore the smallest ones, 523 00:31:24,510 --> 00:31:26,700 but they also will ignore the largest ones 524 00:31:26,700 --> 00:31:28,890 and pick the intermediate-sized ones. 525 00:31:28,890 --> 00:31:30,940 And if they deplete those, then they'll 526 00:31:30,940 --> 00:31:33,090 feed on the smaller ones. 527 00:31:33,090 --> 00:31:35,860 Why don't they feed on those big meaty ones? 528 00:31:35,860 --> 00:31:37,830 Because they're so hard to open. 529 00:31:37,830 --> 00:31:39,295 It takes so much energy. 530 00:31:42,380 --> 00:31:46,210 So it's a very simple matter of, remember, 531 00:31:46,210 --> 00:31:49,410 energy intake minus costs. 532 00:31:49,410 --> 00:31:51,920 So you have to take the costs into account 533 00:31:51,920 --> 00:31:58,420 if you're going to explain the foraging of these animals. 534 00:31:58,420 --> 00:32:01,510 Here we're talking about crabs. 535 00:32:01,510 --> 00:32:06,940 If we deal with marine iguana, we 536 00:32:06,940 --> 00:32:11,650 note that the large ones feed, like this one, 537 00:32:11,650 --> 00:32:14,700 they feed subtidally, that is, at high tide 538 00:32:14,700 --> 00:32:18,610 they will be out in the deeper water catching food. 539 00:32:21,032 --> 00:32:22,240 Here's a whole group of them. 540 00:32:22,240 --> 00:32:27,030 Now the smaller ones, in fact, generally don't do that. 541 00:32:27,030 --> 00:32:29,570 In fact, if you keep track of their size, 542 00:32:29,570 --> 00:32:32,990 you can put them in three groups. 543 00:32:32,990 --> 00:32:37,060 The big ones like this, the intermediate ones, 544 00:32:37,060 --> 00:32:38,690 and the small ones. 545 00:32:38,690 --> 00:32:43,670 The small ones all feed at low tide in the shallow water. 546 00:32:43,670 --> 00:32:47,355 None of them feed subtidally. 547 00:32:47,355 --> 00:32:49,240 And only in the intermediate size 548 00:32:49,240 --> 00:32:52,543 you'll see some of them feeding both situations. 549 00:32:57,240 --> 00:32:59,380 So what is the reason? 550 00:32:59,380 --> 00:33:01,720 Very simple. 551 00:33:01,720 --> 00:33:04,160 They lose body heat. 552 00:33:04,160 --> 00:33:07,560 Remember, these are reptiles, and they lose body heat. 553 00:33:07,560 --> 00:33:12,290 And it's colder there in the deeper water at high tide. 554 00:33:12,290 --> 00:33:18,290 So that is the cost, because they have to make up for it. 555 00:33:18,290 --> 00:33:22,270 They have to eat rapidly enough that they can, by afternoon, 556 00:33:22,270 --> 00:33:26,080 when the sun is out, they can sit on the rocks 557 00:33:26,080 --> 00:33:29,820 and heat their bodies up again. 558 00:33:29,820 --> 00:33:31,930 And if they're smaller and they have to-- 559 00:33:31,930 --> 00:33:35,356 and they're not catching the food as well, especially 560 00:33:35,356 --> 00:33:37,730 because they're slowed down because they're getting cold, 561 00:33:37,730 --> 00:33:39,900 they might not warm up in time. 562 00:33:39,900 --> 00:33:41,980 So it's much more efficient for them 563 00:33:41,980 --> 00:33:45,090 to feed in the less productive shallow water. 564 00:33:50,680 --> 00:33:54,600 Let's talk about, now, the foraging birds again, 565 00:33:54,600 --> 00:33:58,570 in this case dealing with the redshank. 566 00:33:58,570 --> 00:34:03,340 I'm asking here, why do they visit less productive patches 567 00:34:03,340 --> 00:34:06,470 in addition to their focus on the most productive areas 568 00:34:06,470 --> 00:34:09,250 for finding the large worms that they feed on 569 00:34:09,250 --> 00:34:11,170 in the ocean bottom? 570 00:34:11,170 --> 00:34:14,100 And the reason they do it, apparently, 571 00:34:14,100 --> 00:34:17,820 is to get information about food availability. 572 00:34:17,820 --> 00:34:25,239 They find a need to know what's the relative density of food 573 00:34:25,239 --> 00:34:26,989 in all the nearby feeding areas. 574 00:34:29,830 --> 00:34:32,260 And also they need to know how many birds are there 575 00:34:32,260 --> 00:34:33,644 at each one. 576 00:34:33,644 --> 00:34:35,810 Because no matter how rich it is, if there's already 577 00:34:35,810 --> 00:34:39,150 a huge number of birds there, the amount 578 00:34:39,150 --> 00:34:41,629 one animal is going to get is going to be reduced. 579 00:34:44,570 --> 00:34:45,860 These are redshanks. 580 00:34:45,860 --> 00:34:50,130 There's one showing him by himself. 581 00:34:50,130 --> 00:34:51,639 You see the kind of shallow water 582 00:34:51,639 --> 00:34:55,770 that they look for those worms in. 583 00:34:55,770 --> 00:35:00,000 Here he's poking below the water to pull out a worm. 584 00:35:00,000 --> 00:35:01,980 Here's a group of them, and they normally 585 00:35:01,980 --> 00:35:05,750 forage in groups like this. 586 00:35:05,750 --> 00:35:08,750 So we talk about the ideal free distribution 587 00:35:08,750 --> 00:35:13,040 in a description of foraging by groups of animals. 588 00:35:13,040 --> 00:35:16,510 So what do we mean by that? 589 00:35:16,510 --> 00:35:19,460 An animal will tend to go to a less rich food patch 590 00:35:19,460 --> 00:35:22,850 if joining a group of animals at a richer patch 591 00:35:22,850 --> 00:35:26,010 would reduce the amount of food per animal 592 00:35:26,010 --> 00:35:28,010 there to a point below what it could 593 00:35:28,010 --> 00:35:29,860 get at the most rich patch. 594 00:35:29,860 --> 00:35:32,300 You say, well, how could he possibly know that? 595 00:35:32,300 --> 00:35:33,950 They do. 596 00:35:33,950 --> 00:35:36,840 And they do it by this sampling method that I'm talking about. 597 00:35:36,840 --> 00:35:39,920 They're collecting information. 598 00:35:39,920 --> 00:35:43,000 None of them will stay at that rich patch all the time. 599 00:35:43,000 --> 00:35:45,990 They're always flying away a certain percentage 600 00:35:45,990 --> 00:35:47,870 of their time, sampling the other areas. 601 00:35:47,870 --> 00:35:53,990 So they know what the average is for that area. 602 00:35:53,990 --> 00:35:55,060 So they've evolved. 603 00:35:55,060 --> 00:35:57,590 So they distribute themselves in an optimal way 604 00:35:57,590 --> 00:36:01,360 to avoid excessive competition. 605 00:36:01,360 --> 00:36:05,350 And this guy Charnov developed the ideal way 606 00:36:05,350 --> 00:36:07,430 they could do it if they had all the information. 607 00:36:07,430 --> 00:36:12,510 And to make it more practical he modified it. 608 00:36:12,510 --> 00:36:15,850 So they know now that an animal seems to sample food 609 00:36:15,850 --> 00:36:17,880 sources in a region enough to know 610 00:36:17,880 --> 00:36:22,430 the average density of the available food items, 611 00:36:22,430 --> 00:36:25,240 and it changes its foraging location when 612 00:36:25,240 --> 00:36:31,050 food density drops down to or below the average density 613 00:36:31,050 --> 00:36:33,630 of the area. 614 00:36:33,630 --> 00:36:35,250 But there is an additional factor 615 00:36:35,250 --> 00:36:37,910 that needs to be brought up. 616 00:36:37,910 --> 00:36:40,700 And that is that dominant animals often 617 00:36:40,700 --> 00:36:43,280 will exclude the subordinates in the rich patches. 618 00:36:43,280 --> 00:36:47,520 So the animals that are more likely to be 619 00:36:47,520 --> 00:36:52,210 a less rich patch of food early on, 620 00:36:52,210 --> 00:36:54,310 even though there's still a lot of worms left 621 00:36:54,310 --> 00:36:56,985 at the rich patch, are the less dominant animals. 622 00:37:00,310 --> 00:37:05,730 They're each optimizing their feeding success, 623 00:37:05,730 --> 00:37:08,230 because they have to take into account how much time they're 624 00:37:08,230 --> 00:37:12,191 going to be allowed to forage by those dominant animals. 625 00:37:12,191 --> 00:37:12,690 OK 626 00:37:12,690 --> 00:37:18,330 And this is from a figure Scott publishes, 627 00:37:18,330 --> 00:37:21,080 where there's two patches of food. 628 00:37:21,080 --> 00:37:22,980 The profitability is on the ordinate, 629 00:37:22,980 --> 00:37:27,220 so you see one patch is a lot more profitable than others. 630 00:37:27,220 --> 00:37:30,700 But how profitable it is depends on the numbers. 631 00:37:30,700 --> 00:37:34,600 You can see if there's is between one and five animals, 632 00:37:34,600 --> 00:37:39,260 you can see if there's five, it's becoming less profitable. 633 00:37:39,260 --> 00:37:43,340 It drops down to the point that is labeled x there. 634 00:37:43,340 --> 00:37:45,200 And it's just as profitable for him 635 00:37:45,200 --> 00:37:49,950 to be in the other, less rich patch at the point labeled y 636 00:37:49,950 --> 00:37:52,400 there. 637 00:37:52,400 --> 00:37:57,240 And that, of course, depends on numbers of animals there, too. 638 00:37:57,240 --> 00:37:59,600 And that would affect the shape of these curves. 639 00:37:59,600 --> 00:38:02,870 That basically is why animals will move. 640 00:38:02,870 --> 00:38:05,160 They collect enough information to be 641 00:38:05,160 --> 00:38:08,470 able to judge profitability of each of those areas. 642 00:38:08,470 --> 00:38:12,450 And they also seem quite aware of the number of animals 643 00:38:12,450 --> 00:38:14,010 at each place feeding. 644 00:38:14,010 --> 00:38:16,495 They know the rate that the food is being depleted. 645 00:38:21,430 --> 00:38:24,279 So what do they do if there's a predator near? 646 00:38:24,279 --> 00:38:26,320 Just because there are predators around-- there's 647 00:38:26,320 --> 00:38:30,220 often predators around, you can't stop eating. 648 00:38:30,220 --> 00:38:35,790 So when you study that, study the conflict they have, 649 00:38:35,790 --> 00:38:40,595 it's been studied quantitatively in these two types of gobies, 650 00:38:40,595 --> 00:38:44,190 the sand gobies and black gobies. 651 00:38:44,190 --> 00:38:47,800 It's observed that feeding decreases, as you would expect, 652 00:38:47,800 --> 00:38:49,540 if a predator is detected nearby, 653 00:38:49,540 --> 00:38:52,140 because they have to spend more of their time 654 00:38:52,140 --> 00:38:56,700 avoiding that predator or hiding from him. 655 00:38:56,700 --> 00:38:59,840 But that effect is less if the animals are hungrier. 656 00:38:59,840 --> 00:39:03,930 In other words, they will be more risky in their behavior 657 00:39:03,930 --> 00:39:06,460 if they're very hungry. 658 00:39:06,460 --> 00:39:09,305 But it's also less if they're better camouflaged. 659 00:39:09,305 --> 00:39:12,240 And the sand gobies are better camouflaged 660 00:39:12,240 --> 00:39:14,620 than the black gobies, so they were less 661 00:39:14,620 --> 00:39:17,910 affected by the presence of a predator. 662 00:39:17,910 --> 00:39:21,640 They have an innate difference. 663 00:39:21,640 --> 00:39:23,640 It's as if they knew that they're camouflaged 664 00:39:23,640 --> 00:39:26,730 and they're going to be harder for the predator to see. 665 00:39:31,970 --> 00:39:36,380 So I'm asking the question here, is this ideal free distribution 666 00:39:36,380 --> 00:39:38,890 relevant to population control at all? 667 00:39:38,890 --> 00:39:43,480 The answer appears to be no, because the models, anyway, 668 00:39:43,480 --> 00:39:46,380 of it don't attempt to extend overall population 669 00:39:46,380 --> 00:39:49,680 control, but only the small foraging groups. 670 00:39:49,680 --> 00:39:51,790 It would be too much of an extrapolation 671 00:39:51,790 --> 00:39:55,810 to extend it to an entire population. 672 00:39:55,810 --> 00:39:58,200 That has been studied scientifically, 673 00:39:58,200 --> 00:40:01,980 and we know that overcrowding has been studied extensively 674 00:40:01,980 --> 00:40:04,680 in rats, but there are some studies in other species 675 00:40:04,680 --> 00:40:06,020 as well. 676 00:40:06,020 --> 00:40:10,870 We know that fertility goes down, 677 00:40:10,870 --> 00:40:13,170 they end up with impaired immune systems, 678 00:40:13,170 --> 00:40:16,050 so you get more illness, more infections. 679 00:40:16,050 --> 00:40:21,040 They become more irritable, they fight more. 680 00:40:21,040 --> 00:40:22,610 If you look at their adrenal glands, 681 00:40:22,610 --> 00:40:24,905 you see that they're secreting a lot more adrenaline. 682 00:40:24,905 --> 00:40:28,090 They have larger adrenals. 683 00:40:28,090 --> 00:40:32,900 And you also see in these groups really sudden population 684 00:40:32,900 --> 00:40:35,120 declines, not just because they're 685 00:40:35,120 --> 00:40:39,900 being caught by predators, but because of these other factors. 686 00:40:39,900 --> 00:40:45,570 And this has been observed for many small mammals that 687 00:40:45,570 --> 00:40:49,540 tend to reproduce very, very rapidly. 688 00:40:49,540 --> 00:40:55,340 And they tend to move towards an area that's 689 00:40:55,340 --> 00:40:58,935 maximal for what the environment at that time can support. 690 00:41:02,950 --> 00:41:04,910 But if they become overpopulated, 691 00:41:04,910 --> 00:41:08,060 you get population crashes. 692 00:41:08,060 --> 00:41:10,944 It's very well known for some small mammals. 693 00:41:10,944 --> 00:41:12,485 You probably know about the lemmings, 694 00:41:12,485 --> 00:41:17,760 that when they become overcrowded in Scandinavia, 695 00:41:17,760 --> 00:41:19,950 they migrate in large numbers. 696 00:41:19,950 --> 00:41:24,370 And sometimes they seem to get confused 697 00:41:24,370 --> 00:41:28,740 in their navigation, ands they will swim out to sea when 698 00:41:28,740 --> 00:41:31,040 normally they're just swimming across the fjords 699 00:41:31,040 --> 00:41:34,450 to get to another area where there might be fewer lemmings. 700 00:41:34,450 --> 00:41:37,130 But sometimes they just swim out to sea 701 00:41:37,130 --> 00:41:38,570 as if they're committing suicide. 702 00:41:38,570 --> 00:41:41,450 But it appears to be a navigational problem. 703 00:41:41,450 --> 00:41:47,480 And it could be because of malfunctioning nervous systems. 704 00:41:47,480 --> 00:41:48,200 OK. 705 00:41:48,200 --> 00:41:51,350 I don't want to discuss murder right now. 706 00:41:51,350 --> 00:41:56,060 We can do that later when we talk about sociobiology. 707 00:41:56,060 --> 00:41:59,520 But what we'll do is, I want to get started 708 00:41:59,520 --> 00:42:02,930 talking a little bit about anti-predator behavior, which 709 00:42:02,930 --> 00:42:06,740 is the next topic, because I have a couple of nice videos 710 00:42:06,740 --> 00:42:15,300 I want to show, especially one about animals 711 00:42:15,300 --> 00:42:17,770 escaping from predators, so you can see that, 712 00:42:17,770 --> 00:42:20,185 the number of predator-prey relationships. 713 00:42:24,100 --> 00:42:29,140 Scott starts out talking about anti-predator behavior 714 00:42:29,140 --> 00:42:31,710 in his Chapter 7 by distinguishing 715 00:42:31,710 --> 00:42:34,210 between primary and secondary defense 716 00:42:34,210 --> 00:42:36,490 strategies of prey animals. 717 00:42:36,490 --> 00:42:39,100 And these are defined like this. 718 00:42:39,100 --> 00:42:43,010 Primary strategy simply decreases the probability 719 00:42:43,010 --> 00:42:43,850 of being attacked. 720 00:42:43,850 --> 00:42:49,070 So if he's camouflaged or if he has good hiding strategies, 721 00:42:49,070 --> 00:42:52,500 then the probability he'll be attacked is reduced. 722 00:42:52,500 --> 00:42:55,900 He times his foraging. 723 00:42:55,900 --> 00:42:59,600 A hamster comes out only when the shadows are long 724 00:42:59,600 --> 00:43:02,400 in the twilight period. 725 00:43:02,400 --> 00:43:07,330 So he doesn't come out when he's easier to see. 726 00:43:07,330 --> 00:43:09,690 And he comes up when there's still some light, 727 00:43:09,690 --> 00:43:10,810 but the shadows are long. 728 00:43:10,810 --> 00:43:14,150 It's easier for him to hide. 729 00:43:14,150 --> 00:43:18,640 Animals are active at night or day for similar reasons. 730 00:43:18,640 --> 00:43:20,500 Then you have group foraging, again, 731 00:43:20,500 --> 00:43:22,840 that decreases the probability that any one 732 00:43:22,840 --> 00:43:24,950 animal will be attacked. 733 00:43:24,950 --> 00:43:27,780 And then of course you have warning calls. 734 00:43:27,780 --> 00:43:29,800 Sometimes they're responding to warning calls 735 00:43:29,800 --> 00:43:31,700 of another species. 736 00:43:31,700 --> 00:43:37,190 Secondary strategies are when an attack does occur, 737 00:43:37,190 --> 00:43:39,430 they need ways to get away from it. 738 00:43:43,000 --> 00:43:50,260 Fleeing as rapidly as possible, and dodging the predator 739 00:43:50,260 --> 00:43:52,640 chasing them, is extremely important. 740 00:43:52,640 --> 00:43:54,730 And you will see in the video I'll 741 00:43:54,730 --> 00:43:59,940 show next time how successful that can be. 742 00:43:59,940 --> 00:44:04,150 It tires out the predator, greatly 743 00:44:04,150 --> 00:44:06,150 increases the chance of getting away. 744 00:44:09,190 --> 00:44:13,280 Having very high endurance is important. 745 00:44:13,280 --> 00:44:15,690 They have to be able to outrun a predator 746 00:44:15,690 --> 00:44:19,700 and keep running without tiring, so the more endurance they 747 00:44:19,700 --> 00:44:21,040 have the better. 748 00:44:21,040 --> 00:44:24,450 Some of them will just have a play dead strategy. 749 00:44:24,450 --> 00:44:26,230 And the opossum's well known for that, 750 00:44:26,230 --> 00:44:29,060 but there are other animals that do that also. 751 00:44:29,060 --> 00:44:30,900 Why would they do that? 752 00:44:30,900 --> 00:44:33,030 Well, because if they act like they're dead 753 00:44:33,030 --> 00:44:36,990 and they're totally still, it doesn't 754 00:44:36,990 --> 00:44:42,490 evoke predation behavior as much. 755 00:44:42,490 --> 00:44:46,330 The predator is likely to lose interest. 756 00:44:46,330 --> 00:44:49,215 Or he might just say, well, I can come back to this one. 757 00:44:49,215 --> 00:44:50,150 It's dead anyway. 758 00:44:54,310 --> 00:44:55,800 So we will see some of that. 759 00:45:00,550 --> 00:45:01,302 OK. 760 00:45:01,302 --> 00:45:02,260 What is countershading? 761 00:45:04,940 --> 00:45:08,600 And I'm asking another question there besides what it is. 762 00:45:08,600 --> 00:45:13,630 Why would cephalopods need a countershading reflex? 763 00:45:13,630 --> 00:45:17,180 Well, here's an example of countershading. 764 00:45:17,180 --> 00:45:20,910 There's actually two birds here. 765 00:45:20,910 --> 00:45:22,206 How many do you see? 766 00:45:25,044 --> 00:45:29,310 You see this one because he's got countershading 767 00:45:29,310 --> 00:45:32,520 that's opposite to what it would be normally. 768 00:45:32,520 --> 00:45:34,000 It's a model. 769 00:45:34,000 --> 00:45:39,200 Normally birds are lighter on the underside, darker 770 00:45:39,200 --> 00:45:44,040 on the upper side, because when you're above a bird-- 771 00:45:44,040 --> 00:45:45,500 let's say you're an eagle, you're 772 00:45:45,500 --> 00:45:50,090 hunting for small birds flying down below-- if those birds are 773 00:45:50,090 --> 00:45:53,790 dark on top you're less likely to see them 774 00:45:53,790 --> 00:45:57,390 because the ground is generally a lot darker than the sky 775 00:45:57,390 --> 00:45:59,270 above. 776 00:45:59,270 --> 00:46:03,850 But if the bird of prey is below and he looks up, 777 00:46:03,850 --> 00:46:06,700 he's less likely to notice birds if they're 778 00:46:06,700 --> 00:46:10,590 light on the underside. 779 00:46:10,590 --> 00:46:15,010 So with reverse countershading, it makes this bird stand out. 780 00:46:15,010 --> 00:46:20,470 But the other one that's in there is camouflage. 781 00:46:20,470 --> 00:46:22,070 And so it's very hard to make out 782 00:46:22,070 --> 00:46:25,560 exactly where it is, at least in the black-white photos. 783 00:46:25,560 --> 00:46:29,790 So these are a year or two ago. 784 00:46:29,790 --> 00:46:35,020 Jenny Wu was in the class, and she pulled these off the web. 785 00:46:35,020 --> 00:46:37,800 By the time I got to the topic, she was already 786 00:46:37,800 --> 00:46:41,200 doing the reading, and she found these very nice illustrations. 787 00:46:46,520 --> 00:46:48,990 The animals in these pictures don't move. 788 00:46:48,990 --> 00:46:51,450 They're very hard to see. 789 00:46:51,450 --> 00:46:54,330 And I point out what's there. 790 00:46:54,330 --> 00:46:57,680 It's not that easy to tell that that's the body of a spider 791 00:46:57,680 --> 00:46:59,600 right there. 792 00:46:59,600 --> 00:47:01,890 Here the crab is sort of easy to see, 793 00:47:01,890 --> 00:47:03,700 but if you're just glancing around 794 00:47:03,700 --> 00:47:08,760 and there's a lot of unevenness in the gravel bottom 795 00:47:08,760 --> 00:47:13,500 of the water, it's very hard to see that crab. 796 00:47:13,500 --> 00:47:16,260 And here again, if you're glancing around, 797 00:47:16,260 --> 00:47:21,120 you don't notice that frog there that easily. 798 00:47:21,120 --> 00:47:28,870 And here, the dragonfly, it's only because I tell you there's 799 00:47:28,870 --> 00:47:32,060 a dragonfly there that you will probably make out, oh yeah, 800 00:47:32,060 --> 00:47:35,970 those are some legs there, and there's a head there. 801 00:47:35,970 --> 00:47:38,070 And here's some other examples. 802 00:47:38,070 --> 00:47:42,390 There's a bird in this picture, a leaf warbler, 803 00:47:42,390 --> 00:47:46,160 well-camouflaged, he looks just like the leaves. 804 00:47:46,160 --> 00:47:49,940 Here the jaguar, a predator, is pretty well-camouflaged. 805 00:47:49,940 --> 00:47:53,730 Hard for prey animals to see him when he's still. 806 00:47:53,730 --> 00:48:01,380 That's why a predator will spend quite a bit of time still. 807 00:48:01,380 --> 00:48:04,480 And when he does move, he moves rapidly to a new place, 808 00:48:04,480 --> 00:48:06,540 waits again. 809 00:48:06,540 --> 00:48:10,750 And here there's a caterpillar on that leaf. 810 00:48:10,750 --> 00:48:13,280 Almost impossible to see, but that's 811 00:48:13,280 --> 00:48:16,990 the outline of the caterpillar there. 812 00:48:16,990 --> 00:48:18,490 If you don't know he's there I don't 813 00:48:18,490 --> 00:48:20,780 think you'd notice it at all in the picture. 814 00:48:20,780 --> 00:48:26,310 Just like here the grasshopper, taken in Colorado, 815 00:48:26,310 --> 00:48:28,220 very hard to see. 816 00:48:28,220 --> 00:48:29,710 If you look very carefully, you'll 817 00:48:29,710 --> 00:48:33,680 see that there's an eye right there, I think. 818 00:48:36,750 --> 00:48:37,500 That's camouflage. 819 00:48:42,540 --> 00:48:44,240 So we'll start the class next time 820 00:48:44,240 --> 00:48:47,930 about predators who-- because predators develop 821 00:48:47,930 --> 00:48:48,680 search images. 822 00:48:48,680 --> 00:48:51,810 They have an image of the prey they're looking for. 823 00:48:51,810 --> 00:48:56,830 And octopus and squid have developed an incredible ability 824 00:48:56,830 --> 00:49:00,320 to counter that ability by changing their appearance. 825 00:49:00,320 --> 00:49:04,500 And so we'll start with this next time.