1 00:00:00 --> 00:00:04 OK, so the last lecture we were talking about competition, 2 00:00:04 --> 00:00:08 and the result of competition between organisms. 3 00:00:08 --> 00:00:13 And I didn't quite finish, so I just want to finish up on that 4 00:00:13 --> 00:00:17 lecture, and then will move on to predation, an interaction between 5 00:00:17 --> 00:00:22 two species which results in increasing the fitness and one, 6 00:00:22 --> 00:00:26 and decreasing the fitness in the other. But let's just finish up 7 00:00:26 --> 00:00:31 with competition. We were talking about character 8 00:00:31 --> 00:00:36 displacement and beak depths. And we have shown that when you 9 00:00:36 --> 00:00:42 have two closely related birds with the same beak size, 10 00:00:42 --> 00:00:47 if they live on islands separate from one another, 11 00:00:47 --> 00:00:52 they compete for the same food. But if you live on an island 12 00:00:52 --> 00:00:58 together, what happens is that you have this character displacement 13 00:00:58 --> 00:01:03 where the beak of what will get bigger and the beak of the other 14 00:01:03 --> 00:01:12 will get smaller. So they can exploit different food 15 00:01:12 --> 00:01:26 resources. And this character displacement is the beginning of 16 00:01:26 --> 00:01:36 species formation. And this is very common on islands. 17 00:01:36 --> 00:01:43 And these are the famous finches from the Galapagos Islands that 18 00:01:43 --> 00:01:49 Darwin first based his theory of evolution, or it was an important 19 00:01:49 --> 00:01:56 part of his theory of evolution, where he realized that there must 20 00:01:56 --> 00:02:03 have been an ancestor finch, that all of these other finches that 21 00:02:03 --> 00:02:11 had different representation on different islands evolved from 22 00:02:11 --> 00:02:19 through the slow change in traits that is selected as a result of 23 00:02:19 --> 00:02:27 different combination of species being together or alone in different 24 00:02:27 --> 00:02:35 islands. And this is what's called adaptive radiation. 25 00:02:35 --> 00:02:40 And this is really a powerful mechanism for evolution. 26 00:02:40 --> 00:02:46 This is the Galapagos finches, but you also see this in an extreme 27 00:02:46 --> 00:02:51 form in Hawaii among the honey creepers showing this incredible 28 00:02:51 --> 00:02:57 diversity of beak types that have evolved to exploit different 29 00:02:57 --> 00:03:03 kinds of food. OK, so before we go on to predation, 30 00:03:03 --> 00:03:09 I just want to walk you through an evolutionary scenario, 31 00:03:09 --> 00:03:16 so that you can see how this might work on an island, 32 00:03:16 --> 00:03:23 Archipelago. So this is the mainland, and we're going to start 33 00:03:23 --> 00:03:29 with an ancestor species, A, and our Archipelago is going to 34 00:03:29 --> 00:03:37 have three islands. OK, let me draw this. 35 00:03:37 --> 00:03:52 Here's the same three islands. 36 00:03:52 --> 00:04:03 So this is time passing. So as we move, 37 00:04:03 --> 00:04:09 these are the same three islands as a function of time passing, 38 00:04:09 --> 00:04:16 OK? So at the beginning, we're going to have our founder species 39 00:04:16 --> 00:04:23 flying and colonizing the island. OK, so A is on this island. And so, 40 00:04:23 --> 00:04:30 the first thing that happens is that A evolves and becomes B. 41 00:04:30 --> 00:04:35 So each one of these is just the name of the species, 42 00:04:35 --> 00:04:41 OK? This is species A, species B, through what's known as 43 00:04:41 --> 00:04:46 the founder effect. And that is when you have a few 44 00:04:46 --> 00:04:52 members of the species colonizing on this island. You have a tiny gene 45 00:04:52 --> 00:04:58 pool, and the genetic composition of this drifts such that it actually 46 00:04:58 --> 00:05:04 becomes a different species from the one on the mainland. 47 00:05:04 --> 00:05:10 So, A becomes B. So the full arrow means becomes B 48 00:05:10 --> 00:05:17 on the islands through the founder effect. And now, 49 00:05:17 --> 00:05:23 we're going to have B migrate to a new island. So, 50 00:05:23 --> 00:05:30 A is now B on this island, right? 51 00:05:30 --> 00:05:39 And B is going to colonize this island. And through that same 52 00:05:39 --> 00:05:49 founder effect, B becomes C. So let me just write 53 00:05:49 --> 00:05:58 what's happening here. B becomes C. I think you can see 54 00:05:58 --> 00:06:08 what's happening on one island, and then it migrates back. 55 00:06:08 --> 00:06:19 So, let's let C migrate back to where B is, and C also founds a new 56 00:06:19 --> 00:06:31 island. So, we're going to let C migrate here. 57 00:06:31 --> 00:06:38 So we end up with C and B here now able to compete with each other, 58 00:06:38 --> 00:06:46 C here and C here. OK, so we've got a new combination of species, 59 00:06:46 --> 00:06:54 and we are going to let C become D here due to the founder effect, 60 00:06:54 --> 00:07:02 and D is going to migrate over to this island. 61 00:07:02 --> 00:07:32 So, C becomes E when with B because of character displacement. 62 00:07:32 --> 00:07:40 So, C becomes E here when it's with B. So you end up with E and B on 63 00:07:40 --> 00:07:48 this island. D is going to migrate to this island. 64 00:07:48 --> 00:07:56 So, we have C and D here. And, C has evolved to be D here. 65 00:07:56 --> 00:08:04 So, we also have C becomes D when alone. 66 00:08:04 --> 00:08:09 OK, so this is just a scenario we are making up. 67 00:08:09 --> 00:08:15 OK, you can make up any scenario. But it's to give you the idea of 68 00:08:15 --> 00:08:21 how this adaptive radiation comes about. So, starting with one single 69 00:08:21 --> 00:08:26 species on the mainland, if you have an island archipelago 70 00:08:26 --> 00:08:32 where species can be isolated enough from each other to restrict, 71 00:08:32 --> 00:08:38 but not completely eliminate, the gene flow you can have this 72 00:08:38 --> 00:08:45 rapid adaptive radiation. So, evolutionary biologists often 73 00:08:45 --> 00:08:53 study islands in order to study this phenomenon. OK, 74 00:08:53 --> 00:09:02 so just to summarize for competition, interspecific 75 00:09:02 --> 00:09:18 competition results in 76 00:09:18 --> 00:09:32 either competitive coexistence, which can be achieved either through 77 00:09:32 --> 00:09:42 niche differentiation. Do you remember, 78 00:09:42 --> 00:09:50 what was an example of that last time? The barnacles and the inner 79 00:09:50 --> 00:09:58 tidal. One took the high road, and one took the low road. That's 80 00:09:58 --> 00:10:06 called niche differentiation, or character displacement. 81 00:10:06 --> 00:10:10 And this can happen very rapidly. I hesitate to tell you about really 82 00:10:10 --> 00:10:15 interesting things that you don't have to know, but I will anyway. 83 00:10:15 --> 00:10:19 This is really interesting study by a couple at Princeton of the 84 00:10:19 --> 00:10:24 Galapagos finches. And they've shown that you can have 85 00:10:24 --> 00:10:29 character displacement of the islands over a period of one or two 86 00:10:29 --> 00:10:34 years, just depending on the amount of rainfall. 87 00:10:34 --> 00:10:41 So, it can happen very rapidly by just selecting for different 88 00:10:41 --> 00:10:48 character traits, or competitive exclusion, 89 00:10:48 --> 00:10:55 which is the case where the niche overlap is so great that one of the 90 00:10:55 --> 00:11:02 species completely outcompete the other. 91 00:11:02 --> 00:11:07 The example from last time was the zebra mussels and Gause's paramecia 92 00:11:07 --> 00:11:12 in the test tubes excluding the other. So, these are really 93 00:11:12 --> 00:11:17 important ecological and evolutionary forces. 94 00:11:17 --> 00:11:22 The other thing I learned from your comments, which I was very heartened 95 00:11:22 --> 00:11:27 by, is that at least one person really liked the definition of the 96 00:11:27 --> 00:11:32 niche, of the N-dimensional hyper volume, which I have always loved 97 00:11:32 --> 00:11:37 and I think is fundamentally important because people throw 98 00:11:37 --> 00:11:42 around ecological niche in everyday language and think of it as a place 99 00:11:42 --> 00:11:51 in the environment. And I think that a more robust 100 00:11:51 --> 00:12:04 definition is so much more useful. So, let's move onto predation, 101 00:12:04 --> 00:12:15 which is a very strong evolutionary force. It can control population 102 00:12:15 --> 00:12:26 dynamics. It can shape community structure. We're going to talk 103 00:12:26 --> 00:12:39 about each of these. It actually influences competition, 104 00:12:39 --> 00:12:53 which in turn shapes community structure. And it's a powerful 105 00:12:53 --> 00:13:03 evolutionary agent. In other words, 106 00:13:03 --> 00:13:10 it's very important in influencing naturally selection. 107 00:13:10 --> 00:13:17 So, let's start with the classic, here's a classic predator-prey 108 00:13:17 --> 00:13:24 interaction. There is two wolves and a moose being attacked. 109 00:13:24 --> 00:13:32 The wolves are not evil. They're just getting their meal. 110 00:13:32 --> 00:13:37 OK, this is a very famous classic study of the snowshoe hare, 111 00:13:37 --> 00:13:42 and lynx. Lynx is a cat: populations in northern Canada. 112 00:13:42 --> 00:13:48 And these data were collected by the Hudson Bay Company trapping 113 00:13:48 --> 00:13:53 records. So, it's really from the amount of animals that were actually 114 00:13:53 --> 00:13:59 trapped that these abundances come from. And that's where these 115 00:13:59 --> 00:14:04 coupled oscillations, this is the hare, and this is the 116 00:14:04 --> 00:14:10 lynx showing these couples oscillations with a roughly 117 00:14:10 --> 00:14:16 11 year cycle. And people spend a lot of time 118 00:14:16 --> 00:14:23 trying to understand what was driving that oscillation. 119 00:14:23 --> 00:14:30 And mathematicians love these coupled oscillators. 120 00:14:30 --> 00:14:36 And so, the first attempt to model this kind of thing was using a very 121 00:14:36 --> 00:14:42 simple model. Remember we said the dN/dt equals rN? 122 00:14:42 --> 00:14:48 That's our exponential growth equation. And we also said before 123 00:14:48 --> 00:14:54 the dN/dt or that r is equal to the birthrate (b) minus the 124 00:14:54 --> 00:15:01 death rate (d). OK, so grossly oversimplifying the 125 00:15:01 --> 00:15:09 system, the first set of equations that were used to try to describe 126 00:15:09 --> 00:15:16 this, are if you use for the predator, you call the predator 127 00:15:16 --> 00:15:24 dN1/DT equals b1, 1 minus d1,N1. OK, 128 00:15:24 --> 00:15:30 so that's just this equation. And they said, 129 00:15:30 --> 00:15:35 well, how do we modify this equation so that the growth rate of the 130 00:15:35 --> 00:15:41 predator is somehow a function of the density of the prey? 131 00:15:41 --> 00:15:46 Well, the easiest thing to do is just make it proportional, 132 00:15:46 --> 00:15:51 right? So what they do is put N2 in there. So, the prey population is 133 00:15:51 --> 00:15:57 going to be dN2/dt, and we're going to the same thing: 134 00:15:57 --> 00:16:03 b2,N2 minus d2,N2, and the question is how do we modify 135 00:16:03 --> 00:16:10 the prey growth rate equation so that it is somehow a function of the 136 00:16:10 --> 00:16:16 density of the predator? So what would you do? So here, 137 00:16:16 --> 00:16:23 this says the birthrate of the predator is influenced. 138 00:16:23 --> 00:16:30 As prey density increases, the birthrate of the predator 139 00:16:30 --> 00:16:37 increases. How would you modify this equation 140 00:16:37 --> 00:16:43 so that the predator density has an effect on it? It's pretty obvious, 141 00:16:43 --> 00:16:50 but I'm trying to get you with me. Exactly. It would be the death term. 142 00:16:50 --> 00:16:57 As the predator numbers increase, the death term would go up. 143 00:16:57 --> 00:17:08 And it turns out that these are two coupled differential equations that 144 00:17:08 --> 00:17:19 make a beautiful oscillatory system, a couple oscillators, perfect 145 00:17:19 --> 00:17:30 oscillators like that. This is predator density. 146 00:17:30 --> 00:17:35 So that would be N1, N2, and this is time if you chart 147 00:17:35 --> 00:17:41 their density with time. And how many of you have actually 148 00:17:41 --> 00:17:46 had this in the course? Yeah, see? [LAUGHTER] And what 149 00:17:46 --> 00:17:52 courses have you had in it? Differential equations, yeah. 150 00:17:52 --> 00:17:58 Mathematicians love it. But real populations, predator and prey, 151 00:17:58 --> 00:18:03 don't really operate this way. I mean, you see these oscillations, 152 00:18:03 --> 00:18:08 but rarely can it be attributed solely to the interaction between 153 00:18:08 --> 00:18:14 the predator and the prey. There's usually many other factors. 154 00:18:14 --> 00:18:19 So, and I'll just give you one example. So ecologists go ahead and 155 00:18:19 --> 00:18:24 say, OK, so what's really going on? And here's an example. It turns 156 00:18:24 --> 00:18:30 out that in many cases, the food supply of the prey is 157 00:18:30 --> 00:18:35 oscillating. OK, so the availability of food to 158 00:18:35 --> 00:18:39 the prey oscillates, making the prey population oscillate, 159 00:18:39 --> 00:18:43 which then can drive an oscillation in the predator population. 160 00:18:43 --> 00:18:48 So, it's more than just the coupling between the two. 161 00:18:48 --> 00:18:52 There are also an external oscillators driving both of them. 162 00:18:52 --> 00:18:56 And again, I'd like to try to address the role of 163 00:18:56 --> 00:19:02 experimentation. Here is an experiment done with 164 00:19:02 --> 00:19:09 rabbits. And I don't know what the predator was. It might have been, 165 00:19:09 --> 00:19:16 I'm not sure the predator was, but anyway, rabbits, 166 00:19:16 --> 00:19:22 in which through experimentation they increased the food supply to 167 00:19:22 --> 00:19:29 the rabbits through fertilization. And they showed that, so this is 168 00:19:29 --> 00:19:35 the control. And this is the phase of the cycle 169 00:19:35 --> 00:19:41 in the hare population relative to the density in the controls. 170 00:19:41 --> 00:19:46 So, showing that when the food supply was increased, 171 00:19:46 --> 00:19:52 the oscillation was still there. So, it wasn't only relieving the 172 00:19:52 --> 00:19:57 rabbits of food limitation, did not eliminate the oscillation, 173 00:19:57 --> 00:20:03 but if you'd excluded the predators, you still also had the oscillation 174 00:20:03 --> 00:20:09 there. And if you did both of them, 175 00:20:09 --> 00:20:16 it increased the amplitude of the oscillation, relative to the control. 176 00:20:16 --> 00:20:23 So the conclusion from this is that both food supply and the predation 177 00:20:23 --> 00:20:29 affected the oscillation. Another very classic experiment is 178 00:20:29 --> 00:20:36 the experiment by Huffaker back when people began to be enamored of these 179 00:20:36 --> 00:20:43 coupled differential equations. People wanted to test the hypothesis 180 00:20:43 --> 00:20:50 of those equations in the laboratory. And they tried to set up 181 00:20:50 --> 00:20:57 predator-prey systems in the lab, and see if they can get them to go 182 00:20:57 --> 00:21:04 in these coupled oscillations for many cycles. And Huffaker set up a 183 00:21:04 --> 00:21:12 system of a predatory mite and a prey mite. 184 00:21:12 --> 00:21:22 Ecologists like to use insects as experimental systems because they're 185 00:21:22 --> 00:21:32 small and you can do it in the lab. And this one lived on oranges. 186 00:21:32 --> 00:21:38 So it was an herbivorous mite. And the predator obviously lived on 187 00:21:38 --> 00:21:45 mites. And he set up a very simple system in the lab of oranges, 188 00:21:45 --> 00:21:52 and introduced the predator and prey, and inevitably he got this, 189 00:21:52 --> 00:21:59 where prey would increase, and then the predator would increase, 190 00:21:59 --> 00:22:06 and would overshoot, and the prey would die, and the predator 191 00:22:06 --> 00:22:13 would die. So he only got one cycle, 192 00:22:13 --> 00:22:20 with a simple system could not get this to persist, 193 00:22:20 --> 00:22:27 well, that doesn't even qualify as a cycle. So he realized, 194 00:22:27 --> 00:22:33 so this is a simple system. And he had a grid, 195 00:22:33 --> 00:22:39 which is shown up here in which he had oranges. And he had them 196 00:22:39 --> 00:22:44 interspersed with rubber balls to have a little bit of complexity in 197 00:22:44 --> 00:22:50 the system. But he found with that design, he could not get the system 198 00:22:50 --> 00:22:55 to persist. So he hypothesized that the reason it wouldn't persist is 199 00:22:55 --> 00:23:01 that it's much too simple, not close enough to nature. 200 00:23:01 --> 00:23:06 So he introduced all kinds of complexity. He increased the size 201 00:23:06 --> 00:23:11 of his grid relative to the populations, which would give the 202 00:23:11 --> 00:23:16 prey mites more of a chance to get away from the predator. 203 00:23:16 --> 00:23:21 He put barriers of dispersal, like Vaseline moats, and he actually 204 00:23:21 --> 00:23:26 put little launching pads for the prey. I don't know what they look 205 00:23:26 --> 00:23:31 like, diving boards, I don't know what they were, 206 00:23:31 --> 00:23:36 but little launching pads that just increased a lot of complexity so 207 00:23:36 --> 00:23:41 that it gave the prey an ability to move around relative 208 00:23:41 --> 00:23:46 to the predator. And he was actually able to, 209 00:23:46 --> 00:23:52 this shows his results over 200 days. He was actually able to get three 210 00:23:52 --> 00:23:58 full cycles of the predator-prey oscillation. And up here, 211 00:23:58 --> 00:24:04 it just shows you that they're sort of a cat and mouse game going on. 212 00:24:04 --> 00:24:08 It shows you the location of the prey mites relative to the predator 213 00:24:08 --> 00:24:12 mites at these different points in time of this cycle, 214 00:24:12 --> 00:24:16 showing that they're moving around the system, and that the complexity 215 00:24:16 --> 00:24:21 allowed this coupled oscillator to persist. And of course, 216 00:24:21 --> 00:24:25 we present this because it was a classic experiment. 217 00:24:25 --> 00:24:29 It was a pioneering experiment, but I mean, there have been a lot 218 00:24:29 --> 00:24:34 more since then. And of course, 219 00:24:34 --> 00:24:38 it has implications for stability of populations in the natural world. 220 00:24:38 --> 00:24:43 As we make the natural world less and less complex, 221 00:24:43 --> 00:24:48 it reduces the ability of populations that are engaged in 222 00:24:48 --> 00:24:52 these coupled oscillatory systems to persist. It increases the 223 00:24:52 --> 00:24:57 likelihood of extinction. So this was like a tiny little 224 00:24:57 --> 00:25:02 localized extinction in his experimental system. 225 00:25:02 --> 00:25:15 Another classic example that's often cited about the role of predation in 226 00:25:15 --> 00:25:28 regulating population dynamics has to do with rubber plantations over 227 00:25:28 --> 00:25:37 here in Malaysia. Did I spell that right? 228 00:25:37 --> 00:25:42 That looks wrong. Oh well, is that OK? And I don't have any 229 00:25:42 --> 00:25:48 data for you. So this is just a story, but it's very compelling, 230 00:25:48 --> 00:25:53 and there is data somewhere but I don't have a slide. 231 00:25:53 --> 00:25:58 But, in the first half of the century, in its rubber plantations 232 00:25:58 --> 00:26:04 in Malaysia they had a tremendous diversity of insects, 233 00:26:04 --> 00:26:09 but didn't have any real serious problems with insect pests in the 234 00:26:09 --> 00:26:15 rubber plantations. And, in 1950, they had a small 235 00:26:15 --> 00:26:21 outbreak of defoliated caterpillars. And that was right about the time 236 00:26:21 --> 00:26:27 that DDT was invented and synthesized, and became available. 237 00:26:27 --> 00:26:33 And so, entomologists came down and sprayed the plantation with DDT 238 00:26:33 --> 00:26:40 hoping to get rid of this caterpillar. 239 00:26:40 --> 00:26:44 In the next year, the outbreak got bigger. 240 00:26:44 --> 00:26:48 They sprayed more. The next year the outbreak got bigger. 241 00:26:48 --> 00:26:52 They sprayed more, and finally the whole thing was out of control. 242 00:26:52 --> 00:26:56 And they said what's going on here? We are killing these things, and 243 00:26:56 --> 00:27:00 it's getting bigger. To make a long story short, 244 00:27:00 --> 00:27:04 what they were doing, this is a cocoon. 245 00:27:04 --> 00:27:12 Oh boy. How do you spell cocoon? That's not right. Is that right? 246 00:27:12 --> 00:27:21 Anyway, you know what I mean. Caterpillars live in cocoons, 247 00:27:21 --> 00:27:29 and there was a, that's a wasp with a big, long organ that 248 00:27:29 --> 00:27:36 it lays its eggs. It needs some legs, 249 00:27:36 --> 00:27:40 doesn't it? OK, I made some front legs too. There. 250 00:27:40 --> 00:27:44 OK, so that's a wasp that lays its eggs in these caterpillar cocoons, 251 00:27:44 --> 00:27:49 and in doing so, kills caterpillars. And what they were doing with the 252 00:27:49 --> 00:27:53 DDT, is that they were killing the natural predator of the wasp. 253 00:27:53 --> 00:27:57 And the caterpillars themselves, while they were in the cocoon, were 254 00:27:57 --> 00:28:02 actually protected from the DDT. So the more they put on, 255 00:28:02 --> 00:28:07 the more they killed the wasp, and the caterpillars were released 256 00:28:07 --> 00:28:13 from this controlling predation, and they had huge outbreaks. So, 257 00:28:13 --> 00:28:18 it's another example of in nature it's really hard, 258 00:28:18 --> 00:28:23 you can't see what's controlling what until you disrupt it. 259 00:28:23 --> 00:28:28 You have to experiment either inadvertently or on purpose because 260 00:28:28 --> 00:28:34 everything is dynamic and turning over. 261 00:28:34 --> 00:28:40 But it looks relatively stable. And that's why this is so hard. 262 00:28:40 --> 00:28:46 And this is one of my favorite examples of this, 263 00:28:46 --> 00:28:52 because it brings together a lot of concepts that we've been talking 264 00:28:52 --> 00:28:59 about, is predation shapes community structure. 265 00:28:59 --> 00:29:12 And this is another example of 266 00:29:12 --> 00:29:22 introduced species. And this is St. John's Wort, 267 00:29:22 --> 00:29:32 which was introduced at California from Europe. 268 00:29:32 --> 00:29:44 And, it, so I'm going to draw a couple of habitats here. 269 00:29:44 --> 00:29:56 This is a forest, and this is a meadow. So this is grass, 270 00:29:56 --> 00:30:06 OK, this is trees. And these are St. 271 00:30:06 --> 00:30:14 John's Wort. So, it could grow equally well in the meadow and in 272 00:30:14 --> 00:30:23 the forest. And it was getting out of control so they introduced a 273 00:30:23 --> 00:30:31 beetle from Europe that feeds on St. John's Wort to try to bring it in to 274 00:30:31 --> 00:30:41 under control. And what they found was that the 275 00:30:41 --> 00:30:51 beetle, because the beetle's preferred habitat was the meadow 276 00:30:51 --> 00:31:01 that St. John's Wort persisted in the forests but was eliminated 277 00:31:01 --> 00:31:08 from the meadow. Now, because the beetle prefers the 278 00:31:08 --> 00:31:13 sunny habitat of the meadow, so if you were an ecologist and you 279 00:31:13 --> 00:31:19 didn't know that this beetle had been introduced, 280 00:31:19 --> 00:31:24 you just walked into this state, you knew nothing about the history, 281 00:31:24 --> 00:31:29 you wanted to study the ecological niche of St. John's Wort, 282 00:31:29 --> 00:31:35 you would say, well, I only find it in the forest. 283 00:31:35 --> 00:31:40 It must like cooler, wetter environments because you 284 00:31:40 --> 00:31:46 wouldn't really know that it was being controlled by the presence of 285 00:31:46 --> 00:31:52 this beetle. So, this is a perfect example. 286 00:31:52 --> 00:32:03 If we draw the niche or two dimensions of the ecological niche 287 00:32:03 --> 00:32:15 of St. John's Wort, and we say that just on these two 288 00:32:15 --> 00:32:27 dimensions that this is the fundamental niche on the moisture 289 00:32:27 --> 00:32:36 light gradient, in the presence of this beetle, 290 00:32:36 --> 00:32:42 the realized niche is only this low light, high moisture environment 291 00:32:42 --> 00:32:48 that you find in the forest. OK, so in other words, to really 292 00:32:48 --> 00:32:54 understand what's regulating the ecology of a particular organism, 293 00:32:54 --> 00:33:00 you have to understand all of the other organisms that it's 294 00:33:00 --> 00:33:06 interacting with, and what their effect is on this. 295 00:33:06 --> 00:33:11 And again, that's why it's so 296 00:33:11 --> 00:33:16 impossible to do this without some form of experiment, 297 00:33:16 --> 00:33:21 either manipulative experiments like I described, or experiments done in 298 00:33:21 --> 00:33:25 a lab, or inadvertent experiments by introducing species. 299 00:33:25 --> 00:33:30 OK, now let's talk about a couple of other really classic experiments 300 00:33:30 --> 00:33:35 that have been done. And these are experiments that have 301 00:33:35 --> 00:33:40 illustrated the concept of keystone predator. There are some predators 302 00:33:40 --> 00:33:45 and ecosystems that are what are called keystones. 303 00:33:45 --> 00:33:50 And that is if you remove them, the entire structure of the 304 00:33:50 --> 00:33:55 community changes. There are some that if you move 305 00:33:55 --> 00:34:00 them, it doesn't have a dramatic effect, but there are certain ones 306 00:34:00 --> 00:34:06 that are keystone predators that it does. 307 00:34:06 --> 00:34:12 And these, of course, are species that conservation 308 00:34:12 --> 00:34:19 biologists want to first identify, and second conserve above others 309 00:34:19 --> 00:34:26 because there is a cascade of effects if something happens to them. 310 00:34:26 --> 00:34:33 A classic example of this was a study by Robert Payne many years ago 311 00:34:33 --> 00:34:41 in the inner tidal community. I'm not going to go into the details 312 00:34:41 --> 00:34:51 of that, but the rocky inner tidal community is made up of the starfish, 313 00:34:51 --> 00:35:01 which is called pisaster, one of the top predators. 314 00:35:01 --> 00:35:09 And there are also limpets, chitins, if you grew up in 315 00:35:09 --> 00:35:17 California you know probably what these are, mussels. 316 00:35:17 --> 00:35:25 These are invertebrates-like barnacles that stick to the ground, 317 00:35:25 --> 00:35:33 or stick to the rocks, and also algae that stick to the rocks. 318 00:35:33 --> 00:35:38 And Payne hypothesized that the predator was maintaining this 319 00:35:38 --> 00:35:43 diversity. And the way to test that hypothesis was to put a cage over 320 00:35:43 --> 00:35:49 everything and eliminate the predator from certain areas. 321 00:35:49 --> 00:35:54 At what he showed was that that's what that ecosystem looks like if 322 00:35:54 --> 00:36:00 you eliminate the predator. You can see here, here's the algae. 323 00:36:00 --> 00:36:05 Here are some articles. This is a new textbook, 324 00:36:05 --> 00:36:10 see if you get the full story there, but there's a lot of diversity of 325 00:36:10 --> 00:36:15 the small barnacle-like invertebrates. 326 00:36:15 --> 00:36:20 Then you eliminate the predator, and the mussels just completely take 327 00:36:20 --> 00:36:25 over. And this is preemptive competition. They compete with 328 00:36:25 --> 00:36:30 everything else for space and nothing else can survive there. 329 00:36:30 --> 00:36:36 Another example of a keystone predator is the sea otter, 330 00:36:36 --> 00:36:42 which keeps the sea urchins in check in the bottom of the substrate, 331 00:36:42 --> 00:36:49 and if the sea otter is not there the sea urchins takeover and they 332 00:36:49 --> 00:36:55 exclude the kelp, the entire kelp forests and all the 333 00:36:55 --> 00:37:02 fishes that lives in the kelp forests, and all of the diversity of 334 00:37:02 --> 00:37:08 the ecosystem relies on the sea otter's ability to keep the sea 335 00:37:08 --> 00:37:15 urchin population in check. OK, so some of the best evidence for 336 00:37:15 --> 00:37:22 predation as an evolutionary agent, or something that's driving the 337 00:37:22 --> 00:37:30 natural selection of organisms, are these defenses that have evolved 338 00:37:30 --> 00:37:36 to avoid predation. In other words, 339 00:37:36 --> 00:37:41 if you're constantly under attack, your fitness will be increased by 340 00:37:41 --> 00:37:46 features that reduce your susceptibility to predation. 341 00:37:46 --> 00:37:52 So in this case, there are a lot of experiments. I'm going to show you 342 00:37:52 --> 00:37:57 a few, but a picture's worth a thousand words here. 343 00:37:57 --> 00:38:03 I'll show you some examples. Cryptic coloration is when a prey 344 00:38:03 --> 00:38:09 organism has color features that make it blend in to the environment. 345 00:38:09 --> 00:38:15 So here's a very famous example that was actually in another 346 00:38:15 --> 00:38:21 inadvertent experiment. This is a moth that comes in two 347 00:38:21 --> 00:38:27 forms. This is called the melanic form, which is dark black or gray, 348 00:38:27 --> 00:38:33 and this is the other form which is much lighter. 349 00:38:33 --> 00:38:37 And here it is on a birch tree. You can see that this one blends it 350 00:38:37 --> 00:38:42 beautifully, whereas this one, if I were a predator looking for the 351 00:38:42 --> 00:38:47 moth, I would see this but I wouldn't see that. 352 00:38:47 --> 00:38:52 Here's the same two moths on another tree with darker bark 353 00:38:52 --> 00:38:56 showing that in this case, this one would be more fit in that 354 00:38:56 --> 00:39:01 one would be less fit. And there's a very famous study 355 00:39:01 --> 00:39:06 that I don't have time to go into, but it's a textbook, that showed 356 00:39:06 --> 00:39:11 experimentally the relative fitness between these two forms, 357 00:39:11 --> 00:39:16 depending on the color of the tree trunks. 358 00:39:16 --> 00:39:21 And this whole example is called industrial melanism because the 359 00:39:21 --> 00:39:26 reason this was noticed was that in areas of high industrialization the 360 00:39:26 --> 00:39:32 tree trunks are darker colored because of the air pollution. 361 00:39:32 --> 00:39:36 This is back in England back in the days when there is a lot more air 362 00:39:36 --> 00:39:41 pollution. So, they were able to show a shift in 363 00:39:41 --> 00:39:46 the frequency of these two forms as a function of the amount of 364 00:39:46 --> 00:39:51 pollution and environment because their susceptibility to predation 365 00:39:51 --> 00:39:55 was reduced if this form dominated. That study is actually rather 366 00:39:55 --> 00:40:00 controversial now, so I won't teach you the details. 367 00:40:00 --> 00:40:06 But you get the point. But these moths exist in these two 368 00:40:06 --> 00:40:12 forms. Here's another example that's really convoluted that's in 369 00:40:12 --> 00:40:18 your textbook. So I'm not going to write it on the 370 00:40:18 --> 00:40:24 board. You can read about it there. But it's an example of what's 371 00:40:24 --> 00:40:30 called the evolutionary arms race. And it has to do with Cottonwood 372 00:40:30 --> 00:40:36 trees. And Cottonwood trees produce a defense compound that the name of 373 00:40:36 --> 00:40:43 which is on the next slide: salicorten. 374 00:40:43 --> 00:40:50 It doesn't matter what it's called, it's a toxic compound that 375 00:40:50 --> 00:40:57 makes the tree distasteful to predator. You don't think of 376 00:40:57 --> 00:41:05 predators of trees. The beaver is a tree predator. 377 00:41:05 --> 00:41:10 It chops it down. So when a beaver chops it down, 378 00:41:10 --> 00:41:15 a Cottonwood tree, the Cottonwood tree sprouts new sprouts. 379 00:41:15 --> 00:41:21 And the resprouts have much higher concentrations of this toxic 380 00:41:21 --> 00:41:26 compound than the parent tree had. In other words, the tree has a 381 00:41:26 --> 00:41:32 mechanism. And I'm sure we don't understand that yet, 382 00:41:32 --> 00:41:37 but someday we'll understand the genetic underpinnings of this, 383 00:41:37 --> 00:41:43 the molecular biology of beaver defenses. 384 00:41:43 --> 00:41:47 But if it's been felled by a beaver, it increases the production of this 385 00:41:47 --> 00:41:52 toxin in the shoots that come out saying, OK, fool me once, 386 00:41:52 --> 00:41:56 but you're not getting to get me the next time. It means there's beavers 387 00:41:56 --> 00:42:01 around. But the interesting thing is that these shoots are much more 388 00:42:01 --> 00:42:06 susceptible to grazing by a leaf beetle. 389 00:42:06 --> 00:42:10 In other words, this increased toxin, 390 00:42:10 --> 00:42:15 the shoots that have the increased toxin, are actually grazed more than 391 00:42:15 --> 00:42:19 the parent tree by this leaf beetle. So scientists went in and said, you 392 00:42:19 --> 00:42:24 know, what's going on here? This is weird. Why make a defense 393 00:42:24 --> 00:42:29 that makes you more vulnerable to a different predator? 394 00:42:29 --> 00:42:33 And what they showed by experiment was that these leaf beetles were 395 00:42:33 --> 00:42:38 using that toxin as a defense against the ants that 396 00:42:38 --> 00:42:43 want to eat them. So, they were less susceptible to 397 00:42:43 --> 00:42:49 predation by ants because they had taken in the toxin from the shoots. 398 00:42:49 --> 00:42:55 So, it's called the evolutionary arms race between predator and prey. 399 00:42:55 --> 00:43:01 In these systems get very complex. 400 00:43:01 --> 00:43:07 So here's the data that shows that, that the control trees, trees that 401 00:43:07 --> 00:43:13 haven't been felled by a beaver compared to trees that have been 402 00:43:13 --> 00:43:19 felled by a beaver, and resprouted trees have a much 403 00:43:19 --> 00:43:25 higher concentration of this toxin. And this is the larval survival 404 00:43:25 --> 00:43:31 time of these leaf beetles that these are from the control trees 405 00:43:31 --> 00:43:37 versus the browsed trees in the presence of the ants. 406 00:43:37 --> 00:43:43 OK, I'm going to skip that one. That ones in your book, too, which 407 00:43:43 --> 00:43:50 has an experiment showing that anti-predation mechanisms are 408 00:43:50 --> 00:43:57 induced by the presence of a predator. So I would encourage you 409 00:43:57 --> 00:44:04 to look at this in a textbook, this example. 410 00:44:04 --> 00:44:09 And then finally I'm just going to go through a series of pictures that 411 00:44:09 --> 00:44:15 show all of the types of defenses that have been evolved as 412 00:44:15 --> 00:44:20 anti-predation devices. They are the obvious ones like 413 00:44:20 --> 00:44:26 cacti with spikes, or porcupines with spikes, 414 00:44:26 --> 00:44:32 octopi with ink defense. This is a caterpillar that has evolved to look 415 00:44:32 --> 00:44:38 like a snake, at least that's the way it looks to us. 416 00:44:38 --> 00:44:42 I mean that's a hypothesis, that the predation on this would be 417 00:44:42 --> 00:44:46 reduced because it looks like a predator itself. 418 00:44:46 --> 00:44:50 These are two different ones looking like a snake. 419 00:44:50 --> 00:44:54 And often, snakes have a bright colored thing on their tail to draw 420 00:44:54 --> 00:44:58 attention to the tail. If you're going to be attacked by a 421 00:44:58 --> 00:45:02 predator, you'd rather have your tail attacked than your head. 422 00:45:02 --> 00:45:08 So, this is a common motif in nature. And this is an insect. 423 00:45:08 --> 00:45:14 This is its head. And yet, if you're a predator you'd probably 424 00:45:14 --> 00:45:20 think this was its head. And again, whether that's been 425 00:45:20 --> 00:45:26 established by experiments, I don't know. So these are just 426 00:45:26 --> 00:45:32 examples. Moths often have features that look like eyes that what tends 427 00:45:32 --> 00:45:37 to ward off a predator. This is an interesting story that is 428 00:45:37 --> 00:45:43 in your readings that shows that there are just a few genes that 429 00:45:43 --> 00:45:48 control the phenotype of this particular butterfly. 430 00:45:48 --> 00:45:53 I think it's a moth, between having these spots and not having the spots. 431 00:45:53 --> 00:45:59 In the fall, when it's dry and it's more selective advantage to look 432 00:45:59 --> 00:46:04 like a leaf, they look like this. But at other times, 433 00:46:04 --> 00:46:08 they're visible anyway so their selective advantage is to have these 434 00:46:08 --> 00:46:13 eye spots that make them look like they have eyes. 435 00:46:13 --> 00:46:17 OK, I think it's time to quit, so we'll pick this up next time, 436 00:46:17 --> 00:46:22 I promise you. Their wonderful pictures of the creatures in the 437 00:46:22 --> 00:46:26 deep sea that are very evil looking predators that fish with their 438 00:46:26 --> 00:46:29 luminescent light organs.