1 00:00:00 --> 00:00:07 So, today we're going to continue with our series of lectures to come 2 00:00:07 --> 00:00:14 to a conclusion from the section on population and community ecology. 3 00:00:14 --> 00:00:22 At last time, or three lectures ago, we were talking about the regulation 4 00:00:22 --> 00:00:30 of population growth. And this time, 5 00:00:30 --> 00:00:38 we're going to move into, just wanted to make sure the boards 6 00:00:38 --> 00:00:46 are in order, community ecology. And as I said of the first lecture, 7 00:00:46 --> 00:00:54 this is one of the most difficult branches of the ecological sciences 8 00:00:54 --> 00:01:02 to really describe because an ecological community is a bit of an 9 00:01:02 --> 00:01:11 abstract concept. And one definition is that it's a 10 00:01:11 --> 00:01:23 collection of species that are linked together by their 11 00:01:23 --> 00:01:39 feeding relationships. 12 00:01:39 --> 00:01:45 OK, so it's sort of like the ecosystem without the 13 00:01:45 --> 00:01:51 biogeochemistry in a sense. So really what we're looking at 14 00:01:51 --> 00:01:57 here is the interaction between species in a localized area with 15 00:01:57 --> 00:02:04 respect to how they influence each other's fitness, in a sense. 16 00:02:04 --> 00:02:09 And these interrelationships between these species govern all of the 17 00:02:09 --> 00:02:14 things that we talked about in the first half of my lectures set. 18 00:02:14 --> 00:02:19 It's these interactions that shape the biogeochemistry of those systems. 19 00:02:19 --> 00:02:24 So, this is the structure of the system and the biogeochemistry is 20 00:02:24 --> 00:02:30 the function of the system. And it's also these interactions. 21 00:02:30 --> 00:02:40 So, they affect the flow of energy, which we talked about. They affect 22 00:02:40 --> 00:02:50 the cycling of elements. They affect the evolution, 23 00:02:50 --> 00:03:00 the very evolution of species within the community. 24 00:03:00 --> 00:03:06 And these communities self assemble. In other words, if you start with 25 00:03:06 --> 00:03:12 an empty plot of bare land, we talked about this. Remember the 26 00:03:12 --> 00:03:18 example of the glacier retreating and showing the succession of 27 00:03:18 --> 00:03:24 species as the glacier retreated? We started with a bare rock, and 28 00:03:24 --> 00:03:31 you'll start getting lichen growing on the rock. 29 00:03:31 --> 00:03:35 And then that lichen will create a little bit of soil, 30 00:03:35 --> 00:03:39 allowing plants to come in, and that the plants increase 31 00:03:39 --> 00:03:43 productivity. Some of them bring nitrogen and, allowing shrubs and 32 00:03:43 --> 00:03:47 trees and everything. And that's the self-assembly of the 33 00:03:47 --> 00:03:51 community. Once you have plant there, you can have insects there. 34 00:03:51 --> 00:03:55 Once you have insects there, you have birds there. 35 00:03:55 --> 00:03:59 It self assembles. And one of the questions that 36 00:03:59 --> 00:04:03 ecologists ask is, how deterministic is that? 37 00:04:03 --> 00:04:08 I mean, we know there are some random components to it, 38 00:04:08 --> 00:04:13 and we know that there are some things that will happen because we 39 00:04:13 --> 00:04:18 see it happen over, and over, and over. So the big 40 00:04:18 --> 00:04:24 question is what must happen? What could happen? And what might 41 00:04:24 --> 00:04:29 not ever happen? That's really one of the challenges 42 00:04:29 --> 00:04:35 of ecologists is to understand those assembly rules 43 00:04:35 --> 00:04:39 of community if there are any. Now, we're not going to really get 44 00:04:39 --> 00:04:44 into that. We are just going to start looking at the real 45 00:04:44 --> 00:04:49 fundamentals of community [SOUND OFF/THEN ON] which is, 46 00:04:49 --> 00:04:54 what are the possible interactions between species that shape 47 00:04:54 --> 00:05:07 evolution? OK. 48 00:05:07 --> 00:05:13 Species interactions: so, when we talk about species 49 00:05:13 --> 00:05:20 interactions and how they structure communities, we have to first define 50 00:05:20 --> 00:05:27 some terms. One is Darwinian fitness. 51 00:05:27 --> 00:05:43 And the fitness of an individual is 52 00:05:43 --> 00:05:59 the relative ability of an individual in a population to 53 00:05:59 --> 00:06:16 survive and reproduce. 54 00:06:16 --> 00:06:21 So, it's all relative, OK, within a population. 55 00:06:21 --> 00:06:26 And we're going to define also, we'll be talking about adaptations, 56 00:06:26 --> 00:06:31 and I know you know what this is, but let's just make sure that we are 57 00:06:31 --> 00:06:37 all operating with the same assumption. 58 00:06:37 --> 00:06:51 And an adaptation, which is something that affects the 59 00:06:51 --> 00:07:05 fitness, is a heritable trait that increases the fitness of an 60 00:07:05 --> 00:07:20 individual with respect to other individuals in that population. 61 00:07:20 --> 00:07:25 So, these are just some operating assumptions so that when we talk 62 00:07:25 --> 00:07:30 about species interactions, there are several possibilities. 63 00:07:30 --> 00:07:37 If we have organism one and organism two, we can have, 64 00:07:37 --> 00:07:44 and we ask how does the presence of organism two and the presence of 65 00:07:44 --> 00:07:51 organism one affect the fitness of the two organisms? 66 00:07:51 --> 00:07:58 And if the fitness of both organisms is increased by being in 67 00:07:58 --> 00:08:06 the presence of the other, that's called mutualism. 68 00:08:06 --> 00:08:13 Being together increases the fitness of both relative to when they're 69 00:08:13 --> 00:08:20 alone. If being together decreases the fitness of both, 70 00:08:20 --> 00:08:28 that's called competition. And if you have the situation, 71 00:08:28 --> 00:08:36 what we recall that? It could be parasitism, 72 00:08:36 --> 00:08:44 yeah, parasitism. What else? Was the ultimate form of reduced 73 00:08:44 --> 00:08:52 fitness? Predation, yeah, being dead is the ultimate 74 00:08:52 --> 00:09:00 reduced fitness. So, parasitism and predation. 75 00:09:00 --> 00:09:06 And then there are some other sort of rather vague interactions where 76 00:09:06 --> 00:09:12 when you put two individuals together, the fitness of one is not 77 00:09:12 --> 00:09:18 influenced but the fitness of the other is either influenced 78 00:09:18 --> 00:09:24 positively or negatively, and we're not going to talk about 79 00:09:24 --> 00:09:30 those. But this one's called commencalism. And this one's 80 00:09:30 --> 00:09:37 called amensalism. And obviously there are gradients. 81 00:09:37 --> 00:09:44 Actually, an example of commencalism is something that we've 82 00:09:44 --> 00:09:51 talked about. Can anybody think about what that is when we talked 83 00:09:51 --> 00:09:58 about food webs? It's kind of a stretch, 84 00:09:58 --> 00:10:04 but detritivory. An organism eating detritus, 85 00:10:04 --> 00:10:09 in a sense, is commencalism because it doesn't affect the fitness of the 86 00:10:09 --> 00:10:13 dead individual because it's already dead. So, that gets to not having 87 00:10:13 --> 00:10:18 that much meaning. So anyway, these we are not going 88 00:10:18 --> 00:10:23 to spend time on, but they are forms of interaction 89 00:10:23 --> 00:10:28 that do exist. And there are gradients between 90 00:10:28 --> 00:10:33 these. Obviously, it's not all black and white. 91 00:10:33 --> 00:10:46 So, we're going to start by talking about competition. 92 00:10:46 --> 00:10:59 And just to remind you, competition comes in two forms. 93 00:10:59 --> 00:11:12 There is intraspecific competition, which means within a species, OK? 94 00:11:12 --> 00:11:19 And that's not what we're going to be talking about today, 95 00:11:19 --> 00:11:27 but we've already talked about this without explicitly, 96 00:11:27 --> 00:11:34 remember our logistic equation and the density dependent feedback 97 00:11:34 --> 00:11:40 mechanisms in that population that caused the population to deviate 98 00:11:40 --> 00:11:47 from exponential growth was due to intraspecific competition: 99 00:11:47 --> 00:11:54 individuals within a species competing with each other for 100 00:11:54 --> 00:12:01 resources. We are going to talking about now is more interspecific -- 101 00:12:01 --> 00:12:20 -- which is competition 102 00:12:20 --> 00:12:31 between species, OK? So, I want to show you some slides 103 00:12:31 --> 00:12:35 that are just from your textbook, but just to get you in the mood for 104 00:12:35 --> 00:12:40 competition. So, it comes in all different forms, 105 00:12:40 --> 00:12:45 and I don't care whether you know the names of these. 106 00:12:45 --> 00:12:49 It doesn't matter. This is just to give you an idea of the different 107 00:12:49 --> 00:12:54 types of competition that we see in nature. This is what's called 108 00:12:54 --> 00:12:59 consumptive competition, and this is just showing the roots 109 00:12:59 --> 00:13:03 of the trees competing for nutrients in the soil. Preemptive competition 110 00:13:03 --> 00:13:08 shows these are barnacles. We're going to talk a little bit 111 00:13:08 --> 00:13:12 more about that later, just totally taking over the 112 00:13:12 --> 00:13:16 substrate. So no other organism could possibly settle there. 113 00:13:16 --> 00:13:21 Overgrowth competition in plants where this plant would be shading, 114 00:13:21 --> 00:13:25 so other plants that require a lot of light could not grow underneath. 115 00:13:25 --> 00:13:30 Chemical competition also occurs where one plant will actually 116 00:13:30 --> 00:13:34 excrete certain chemicals that create these corridors of no growth 117 00:13:34 --> 00:13:38 around them so other plants can't get near to compete 118 00:13:38 --> 00:13:43 for the nutrients. The classic form of competition, 119 00:13:43 --> 00:13:48 say, in birds and a lot of higher organisms is competition for 120 00:13:48 --> 00:13:52 territory. So these are displays so that an individual can keep a 121 00:13:52 --> 00:13:57 certain territory, and therefore make that food 122 00:13:57 --> 00:14:02 available to itself, therefore increasing its fitness 123 00:14:02 --> 00:14:07 because it's able to feed its young. 124 00:14:07 --> 00:14:13 And then this is sort of the classic, really tooth and claw competition 125 00:14:13 --> 00:14:19 where encounter competition where all these species are competing over 126 00:14:19 --> 00:14:25 this zebra carcass, hyena, vultures, etc. 127 00:14:25 --> 00:14:31 OK, now before we can talk more and more in detail about competition, 128 00:14:31 --> 00:14:37 we need to define the ecological niche. 129 00:14:37 --> 00:14:41 And this is an interesting concept in ecology that has been around for 130 00:14:41 --> 00:14:45 quite some time, and it kind of went out of 131 00:14:45 --> 00:14:50 popularity for a while. And I was gratified to see that 132 00:14:50 --> 00:14:54 it's made it back into the introductory biology textbooks 133 00:14:54 --> 00:14:59 because I think it's a very profound concept. 134 00:14:59 --> 00:15:04 In this particular competition, the fundamental ecological niche 135 00:15:04 --> 00:15:09 comes from G. Evelyn Hutchinson, who is one of the founders of modern 136 00:15:09 --> 00:15:14 ecology. He defined as the fundamental niche of an organism as 137 00:15:14 --> 00:15:20 an N-dimensional hypervolume, every point on which a species can 138 00:15:20 --> 00:15:25 survive and reproduce indefinitely in the absence of other 139 00:15:25 --> 00:15:30 species, OK? So, this is an abstract concept, 140 00:15:30 --> 00:15:35 because those species are rarely in the absence of other species, 141 00:15:35 --> 00:15:40 except maybe in a test tube. But it defines the, and also we can't even 142 00:15:40 --> 00:15:45 think about N-dimensions, right? We're able to think about, 143 00:15:45 --> 00:15:50 we can envision three dimensions. But what he's talking about here, 144 00:15:50 --> 00:15:55 is every single dimension in the environment that would have any 145 00:15:55 --> 00:16:01 effect on the fitness of an organism. 146 00:16:01 --> 00:16:05 So here, just to wrap our brains around this, we're looking at three 147 00:16:05 --> 00:16:09 dimensions. Our organisms here is a ladybug, and this would be food size. 148 00:16:09 --> 00:16:14 These guys eat little aphids and things. I don't know if you've ever 149 00:16:14 --> 00:16:18 used them under house plants, but it's a good way to keep aphids 150 00:16:18 --> 00:16:23 off your house plants if you want to introduce ladybugs to your dorm room, 151 00:16:23 --> 00:16:27 which maybe you don't. But there's a certain range of size, 152 00:16:27 --> 00:16:33 food size, that they can eat. And so, that's three dimensions. 153 00:16:33 --> 00:16:39 There are undoubtedly many other dimensions that we don't even know 154 00:16:39 --> 00:16:45 about, elements that they require, etc. So, this would be everywhere, 155 00:16:45 --> 00:16:51 in this space is a space where this organism could survive and reproduce 156 00:16:51 --> 00:16:57 indefinitely. And the reason this concept lost favor is its something 157 00:16:57 --> 00:17:03 you could never ever measure this because we can't know 158 00:17:03 --> 00:17:09 the N-dimensions. Well, you can never say you can't 159 00:17:09 --> 00:17:13 know anything, but it's very difficult to say you 160 00:17:13 --> 00:17:17 could know all the dimensions that influence the fitness of an organism. 161 00:17:17 --> 00:17:21 But it's still a very important concept for thinking about it. 162 00:17:21 --> 00:17:25 And the niche is not a physical place, OK? The niche of an organism 163 00:17:25 --> 00:17:30 is not a physical place. In an N-dimensional hypervolume. 164 00:17:30 --> 00:17:35 It's an abstract concept. So this is the fundamental niche, 165 00:17:35 --> 00:17:39 and here's another closely related species whose niche has some overlap 166 00:17:39 --> 00:17:44 with this one, but has different ranges for 167 00:17:44 --> 00:17:49 temperature, humidity, and food size. And when you have 168 00:17:49 --> 00:17:54 overlapping niches is when you have the possibility, 169 00:17:54 --> 00:17:59 the potential, for competition. And two things can happen. 170 00:17:59 --> 00:18:04 If they overlap a lot, than those two species cannot 171 00:18:04 --> 00:18:09 coexist in the same environment. One will outcompete the other, and 172 00:18:09 --> 00:18:14 it will move on to some other place where it doesn't have a strong 173 00:18:14 --> 00:18:19 competitor. But if they overlap a little, you can actually have 174 00:18:19 --> 00:18:24 competitive coexistence. And we're going to talk about the 175 00:18:24 --> 00:18:29 results of these degrees of niche overlap as we go on in the lecture. 176 00:18:29 --> 00:18:33 So, if the species can makes it realized, so this is its fundamental 177 00:18:33 --> 00:18:38 niche, this one's fundamental niche, and what happens if it can make its 178 00:18:38 --> 00:18:43 realized niche small enough so that there's no niche overlap, 179 00:18:43 --> 00:18:48 then you can have coexistence of those two species, 180 00:18:48 --> 00:18:53 or very little niche overlap in the same environment. 181 00:18:53 --> 00:18:58 So that's the difference between the fundamental and the 182 00:18:58 --> 00:19:04 realized niche. I think this is from your textbook. 183 00:19:04 --> 00:19:10 This is just one dimension, seed sized, for, say, 184 00:19:10 --> 00:19:16 a bird eating seeds of this size range. We'll be talking about birds 185 00:19:16 --> 00:19:22 a lot in this. And here's partial niche overlap, 186 00:19:22 --> 00:19:28 species to where they eat some seeds of the same size, 187 00:19:28 --> 00:19:34 but by and large the mode is different. 188 00:19:34 --> 00:19:39 You can have species coexisting. Partial niche overlap can lead to 189 00:19:39 --> 00:19:45 competitive coexistence. And here's the complete overlap in 190 00:19:45 --> 00:19:51 just this one dimension, which would lead to competitive 191 00:19:51 --> 00:19:57 exclusion. But obviously it matters what's happening on all the 192 00:19:57 --> 00:20:03 dimensions. This is just an oversimplification, to 193 00:20:03 --> 00:20:11 give you the idea. OK, so before we go to that, 194 00:20:11 --> 00:20:23 I want to talk about the classic experiment that led to this, 195 00:20:23 --> 00:20:35 they're going to put this screen up. Screen, screen, screen, screen. 196 00:20:35 --> 00:20:56 Can you see, or do I need to turn 197 00:20:56 --> 00:21:01 the lights on? Thank you. I'm sorry, 198 00:21:01 --> 00:21:04 I always ask my questions that way, where there's no possible answer. 199 00:21:04 --> 00:21:19 200 00:21:19 --> 00:21:25 There were some classic competition experiments that's carried out by 201 00:21:25 --> 00:21:32 Gause way back in 1934 -- -- that I'm just going to use to 202 00:21:32 --> 00:21:38 illustrate the concept of competitive exclusion, 203 00:21:38 --> 00:21:44 because these were done with very simple protozoa in a test tube, 204 00:21:44 --> 00:21:50 paramecia, and actually this was back in the days when they were 205 00:21:50 --> 00:21:56 developing these theories for population growth. 206 00:21:56 --> 00:22:03 And these organisms were growing according to the logistic equation. 207 00:22:03 --> 00:22:07 So here we are with, and this is the classic experiment 208 00:22:07 --> 00:22:12 actually in your textbook that they talk about in the context of the 209 00:22:12 --> 00:22:17 ecological niche. So this is Paramecia caudatum. 210 00:22:17 --> 00:22:22 These names aren't important. Don't worry about it, 211 00:22:22 --> 00:22:27 but we have to call them something. P. aurelia, which, when grown alone 212 00:22:27 --> 00:22:32 in a test tube grow according to the logistic equation, 213 00:22:32 --> 00:22:37 they grow up and then they level off at a certain level. 214 00:22:37 --> 00:22:46 And what Gause did is that he wanted to see, look at this phenomenon of 215 00:22:46 --> 00:22:55 competition and he grew them together, and he found that, 216 00:22:55 --> 00:23:04 actually that no matter what combination he put in, 217 00:23:04 --> 00:23:13 aurelia would always win out in competitive exclusion. 218 00:23:13 --> 00:23:23 And he learned through a series of 219 00:23:23 --> 00:23:27 experiments, we don't have time to go into the details, 220 00:23:27 --> 00:23:32 but this would always occur if you made two species compete in a very 221 00:23:32 --> 00:23:37 simple environment. In the test tube where he was 222 00:23:37 --> 00:23:41 feeding these guys exactly the same food, some form of bacteria, 223 00:23:41 --> 00:23:46 in a test tube this one would always outcompete the other, 224 00:23:46 --> 00:23:50 and there would be competitive exclusion. If he made the 225 00:23:50 --> 00:23:55 environment more complex, where there were layers in it, 226 00:23:55 --> 00:23:59 or there was sediment in the bottom of the test tube, 227 00:23:59 --> 00:24:04 that allowed more niche dimensions. There were conditions under which 228 00:24:04 --> 00:24:10 the competitive coexistence would be allowed. And he actually developed 229 00:24:10 --> 00:24:15 a set of equations to describe his competition that I'm going to write 230 00:24:15 --> 00:24:20 for you. We're not going to use them; we're not going to analyze 231 00:24:20 --> 00:24:26 them in detail, but I'm just going to show them to 232 00:24:26 --> 00:24:31 you so that you have an appreciation for how population ecologists and 233 00:24:31 --> 00:24:37 community ecologists start to think about these systems. 234 00:24:37 --> 00:24:43 So, he said we can model this interaction using our logistic 235 00:24:43 --> 00:24:50 equation. So he said dN/dt would be the growth rate of, 236 00:24:50 --> 00:24:57 let's call, the top one, one. It doesn't matter what you 237 00:24:57 --> 00:25:04 call which. The dN/dt equals r1, N1. Now here's our logistic, K1 238 00:25:04 --> 00:25:11 minus N1 over K. But he said I'm going to modify this 239 00:25:11 --> 00:25:18 equation so that the actual growth of the organism is reduced to some 240 00:25:18 --> 00:25:25 amount that's proportional to the number of the other organisms that 241 00:25:25 --> 00:25:32 are there. So, he called that alpha-N2. 242 00:25:32 --> 00:25:41 OK, so some amount that's proportional to amount the other 243 00:25:41 --> 00:25:50 species that's here. And then, he said dN2/DT is equal 244 00:25:50 --> 00:26:00 to r2, N2, K2 minus N2 minus beta-N1 over, this should be K1, over K2. 245 00:26:00 --> 00:26:05 So, the growth rate of species to in the presence of species one is 246 00:26:05 --> 00:26:10 reduced by some amount that's proportional to the abundance of 247 00:26:10 --> 00:26:15 species one. And these, the values of these, these are 248 00:26:15 --> 00:26:20 called competition coefficients. You can actually do experiments and 249 00:26:20 --> 00:26:26 put values on these, and they are a measure of how strong 250 00:26:26 --> 00:26:31 a competitor each of these species are with respect to 251 00:26:31 --> 00:26:36 the other one. So, you're not going to have to deal 252 00:26:36 --> 00:26:41 with these, but I just wanted you to see them, and see how population 253 00:26:41 --> 00:26:46 ecologists began to model these systems. And so, 254 00:26:46 --> 00:26:52 it's the relative values of these relative to the carrying capacities 255 00:26:52 --> 00:26:57 that will ultimately determine whether species will coexist or not 256 00:26:57 --> 00:27:02 when they are competing. OK, so that's more of a theoretical 257 00:27:02 --> 00:27:07 analysis. Now let's look at the real world. Competitive exclusion, 258 00:27:07 --> 00:27:12 that is, the exclusion of one species from an environment because 259 00:27:12 --> 00:27:16 of strong competition in another, is very difficult to study, because 260 00:27:16 --> 00:27:21 if it's not there, you don't know it was excluded, 261 00:27:21 --> 00:27:26 right? I mean, you don't go to some place and say I don't see 262 00:27:26 --> 00:27:31 the species here. It must have been eliminated by 263 00:27:31 --> 00:27:36 competitive exclusion. It might never have been there. 264 00:27:36 --> 00:27:40 So, the way we learn about this phenomenon is either through 265 00:27:40 --> 00:27:45 inadvertent experiments, and that is the introduction of 266 00:27:45 --> 00:27:50 species to new environments and then see what happens, 267 00:27:50 --> 00:27:55 or actual intentional ecological experiments. So, 268 00:27:55 --> 00:28:00 we're going to talk about both of those. 269 00:28:00 --> 00:28:11 And the first one -- 270 00:28:11 --> 00:28:26 -- we'll talk about invasions -- 271 00:28:26 --> 00:28:33 -- and competitive exclusion. And one of the classic examples of 272 00:28:33 --> 00:28:41 this is the zebra mussel. I don't know what happened. 273 00:28:41 --> 00:28:49 Oh, there it is. I didn't realize this was animated. 274 00:28:49 --> 00:28:57 That's why there was nothing there. So, the zebra mussel is a tiny 275 00:28:57 --> 00:29:05 mussel that was introduced to the United States back in, 276 00:29:05 --> 00:29:10 I guess, 1988. And up here, introduced into the 277 00:29:10 --> 00:29:14 Great Lakes by ships just being attached to ships, 278 00:29:14 --> 00:29:18 or it's possible it might have been the larvae in ships' ballasts. 279 00:29:18 --> 00:29:22 Ships go into port, they take on water into their ballasts to 280 00:29:22 --> 00:29:26 stabilize, and then they go to another port and let it out. 281 00:29:26 --> 00:29:30 And they're filled with larvae and species. 282 00:29:30 --> 00:29:37 So, the entire world oceans are now filled with introduced species from 283 00:29:37 --> 00:29:44 ships ballasts. So here's 1988. 284 00:29:44 --> 00:29:51 The zebra mussel is there. 1990: here. 92: here. 94, 285 00:29:51 --> 00:29:58 90 whatever, oh, 2001. It spread amazingly fast. 286 00:29:58 --> 00:30:04 And it is this tiny little mussel that seems to thrive everywhere: 287 00:30:04 --> 00:30:10 clogs, all kinds of pipes, settles on top of other native 288 00:30:10 --> 00:30:16 shellfish and kills them, and has led to extensive competitive 289 00:30:16 --> 00:30:22 exclusion of native shellfish in a number of ecosystems. 290 00:30:22 --> 00:30:28 Some of the effects of these: in some ecosystems they cleared 291 00:30:28 --> 00:30:34 up the water. They are able to filter just an 292 00:30:34 --> 00:30:39 amazing amount of water when they're feeding. So they actually have 293 00:30:39 --> 00:30:43 increased the clarity of the water in many ecosystems, 294 00:30:43 --> 00:30:48 filtering out plankton, which allows the light to penetrate 295 00:30:48 --> 00:30:53 deeper in those systems, allowing aquatic plants to grow from 296 00:30:53 --> 00:30:58 the bottom. So the introduction of this one species can completely 297 00:30:58 --> 00:31:03 change the structure of the entire ecosystem. 298 00:31:03 --> 00:31:06 I just heard a lecture. I was just visiting the Institute 299 00:31:06 --> 00:31:10 for Ecosystem Studies which is out in Millbrook, NY. 300 00:31:10 --> 00:31:14 By the way, if any of you are looking for summer internships and 301 00:31:14 --> 00:31:17 are interested in ecology, they have a fabulous summer 302 00:31:17 --> 00:31:21 internship program. I've had several students go there 303 00:31:21 --> 00:31:25 that have had great experiences. But there's somebody there studying 304 00:31:25 --> 00:31:29 the zebra mussel invasion in the Hudson River. 305 00:31:29 --> 00:31:33 And he showed this incredibly depressing graph of over the last 306 00:31:33 --> 00:31:37 ten years of the native mussels in that river going down to basically 307 00:31:37 --> 00:31:42 extinction. And then, this is the weird thing about 308 00:31:42 --> 00:31:46 ecosystems, just last year it started to turn around. 309 00:31:46 --> 00:31:50 And they haven't done anything to eradicate the zebra mussels, 310 00:31:50 --> 00:31:55 but the native mussels are starting to have a comeback. 311 00:31:55 --> 00:31:59 And nobody knows why, and nobody knows whether it's a real 312 00:31:59 --> 00:32:04 comeback because it could come back for a couple of years. 313 00:32:04 --> 00:32:10 So, it's really interesting how unpredictable these complex systems 314 00:32:10 --> 00:32:17 are. But these mussels can cause millions and millions of dollars of 315 00:32:17 --> 00:32:23 damage. And I also learned on that trip that ecologists are trying to 316 00:32:23 --> 00:32:30 get in place policies that if an industry for whatever reasons wants 317 00:32:30 --> 00:32:36 to intentionally introduce, Here's an example of an application 318 00:32:36 --> 00:32:40 of fundamental ecological knowledge. The reason people study the ecology 319 00:32:40 --> 00:32:45 of invasive species, understanding this competitive 320 00:32:45 --> 00:32:49 exclusion and all that, is that you want to use that 321 00:32:49 --> 00:32:54 understanding to be able to predict, if you introduce a new species to a 322 00:32:54 --> 00:32:58 new habitat, whether it will be invasive or not, 323 00:32:58 --> 00:33:03 there are some species you can introduce and they will fit right in 324 00:33:03 --> 00:33:08 and not exclude every other species. 325 00:33:08 --> 00:33:13 And so, what they're trying to put in place is insurance that a company 326 00:33:13 --> 00:33:18 would have to buy that was either intentionally introducing a species, 327 00:33:18 --> 00:33:23 or whatever practice that they were doing was likely to introduce a 328 00:33:23 --> 00:33:28 species, and the cost of that insurance would be a function of the 329 00:33:28 --> 00:33:34 probability of that species actually causing competitive exclusion. 330 00:33:34 --> 00:33:39 And this is something that people are trying to put into place in to 331 00:33:39 --> 00:33:45 the economic system basically. So, it puts a new meaning to 332 00:33:45 --> 00:33:50 limited liability company, LLC. So, you have to insure your 333 00:33:50 --> 00:33:56 liability, which I think would go a long way to reduce some of these 334 00:33:56 --> 00:34:01 ecological crises. OK, so that's an inadvertent 335 00:34:01 --> 00:34:06 experiment. Now there are many, many examples of this. There's 336 00:34:06 --> 00:34:11 books written on invasive species. And if I can get this thing to work, 337 00:34:11 --> 00:34:16 I'll show you some clips of invasive species, snakes. 338 00:34:16 --> 00:34:20 And the biggest impact is on islands because islands have been 339 00:34:20 --> 00:34:25 isolated ecosystems for so long that if you introduce a species, 340 00:34:25 --> 00:34:30 you have dramatic changes. In Australia, a big example was a 341 00:34:30 --> 00:34:35 prickly pear cactus which was introduced many years ago to create 342 00:34:35 --> 00:34:40 living fences for livestock. They completely took over not all of 343 00:34:40 --> 00:34:46 the grasslands, but a lot of the grasslands and turn 344 00:34:46 --> 00:34:51 them into thickets. OK, so invasive species are 345 00:34:51 --> 00:34:57 inadvertent ecological experiments. Let's talk about intentional 346 00:34:57 --> 00:35:02 experiments. And this is also very classic textbook experiment that was 347 00:35:02 --> 00:35:08 one of the first ecological experiments to be done. 348 00:35:08 --> 00:35:12 And it was done with barnacles. This was Joseph Connell was a 349 00:35:12 --> 00:35:17 professor at the University of California, Santa Barbara. 350 00:35:17 --> 00:35:21 Barnacles have a larval stage that floats around in the plankton, 351 00:35:21 --> 00:35:26 and then they settle on rocks. So this was a classic barnacle 352 00:35:26 --> 00:35:31 ecosystem in Scotland, actually, in which the upper inner 353 00:35:31 --> 00:35:36 tidal there is a species called Chthamalus. 354 00:35:36 --> 00:35:40 And then the lower was dominated by a species of mussel called Balanus. 355 00:35:40 --> 00:35:45 So, he asked the question, is this distribution where the two are 356 00:35:45 --> 00:35:49 exclusive of one another, is it due to competition between 357 00:35:49 --> 00:35:54 them, or is it just that this one tolerates desiccation longer than 358 00:35:54 --> 00:35:58 this one? The inner tidal zone, the tide goes up and down, so this 359 00:35:58 --> 00:36:03 one's going to be exposed to dryness a lot longer. 360 00:36:03 --> 00:36:07 So, how do you answer that question? Well, you do an experiment and so 361 00:36:07 --> 00:36:12 what he did was he took rocks from the upper, inner tidal that had the 362 00:36:12 --> 00:36:17 Chthamalus on them, and he moved them to the lower one. 363 00:36:17 --> 00:36:22 And he let the Balanus, the species that dominates down here colonize on 364 00:36:22 --> 00:36:27 those rocks. But then he divided them in half, and removed the 365 00:36:27 --> 00:36:32 Balanus from half of the rock. And then he monitored the 366 00:36:32 --> 00:36:37 survivorship of the Chthamalus. And remember the survivorship 367 00:36:37 --> 00:36:41 curves that we talked about when we created those life tables, 368 00:36:41 --> 00:36:46 he actually measured survivorship curves on these. 369 00:36:46 --> 00:36:51 If you go to the original paper, you see LX is a function of time. 370 00:36:51 --> 00:36:56 So that's a tool that we use, to ask the question, is the 371 00:36:56 --> 00:37:01 survivorship of Chthamalus increased in the absence of Balanus? 372 00:37:01 --> 00:37:05 And this is all from your textbook, showing that the percent of 373 00:37:05 --> 00:37:09 mortality, when a competitor is present is much higher than the 374 00:37:09 --> 00:37:14 competitor is absent. So, he's able to show directly that 375 00:37:14 --> 00:37:18 there was competition between the two. And in fact, 376 00:37:18 --> 00:37:23 this was that kind of aggressive kind of competition where one just 377 00:37:23 --> 00:37:27 plucks the other one off the rock. I mean it's direct: you're on my 378 00:37:27 --> 00:37:32 rock; get out of here, and it pops it off. 379 00:37:32 --> 00:37:37 He also was able to show that tolerance to desiccation is also a 380 00:37:37 --> 00:37:42 factor in this system. It's not like it's totally 381 00:37:42 --> 00:37:47 competition. But competition was playing a role, 382 00:37:47 --> 00:37:52 and so I've summarized that in this slide using our terminology. 383 00:37:52 --> 00:37:57 He was able to show that the fundamental niche of Chthamalus, 384 00:37:57 --> 00:38:05 in other words -- -- the region in the inner tidal, 385 00:38:05 --> 00:38:15 where the larvae could actually settle and live in the absence of 386 00:38:15 --> 00:38:25 competitors was much broader than the realized niche. 387 00:38:25 --> 00:38:36 All right, so let's get this over. This is from your textbook. 388 00:38:36 --> 00:38:50 And we're going to just use, I'm going to use an example of that. 389 00:38:50 --> 00:39:04 So, competition can also lead to character displacement -- 390 00:39:04 --> 00:39:18 -- which in turn can lead to actual 391 00:39:18 --> 00:39:27 competitive coexistence. And an example of this, we're going 392 00:39:27 --> 00:39:37 to talk about Darwin's finches in the Galapagos Islands. 393 00:39:37 --> 00:39:46 And one of the ways that ecologists actually measure, 394 00:39:46 --> 00:39:56 that's a bird, in case you didn't notice it. And this 395 00:39:56 --> 00:40:04 is beak depth. The shape and size of a beak tells 396 00:40:04 --> 00:40:11 you what kinds of seeds a bird can eat, and so they measured beak depth 397 00:40:11 --> 00:40:18 as a niche dimension, basically, because it tells you what 398 00:40:18 --> 00:40:26 size seeds the bird can eat. And a study was done; we're going 399 00:40:26 --> 00:40:33 to make the islands here. What is going to call them A, 400 00:40:33 --> 00:40:41 B, C, D; these are islands. And there are two species of finches, 401 00:40:41 --> 00:40:49 which we are just going to call F. Well, they're fuliginosa. Again, 402 00:40:49 --> 00:40:57 the name's not important, and the other one is called fortis. 403 00:40:57 --> 00:41:05 So, we'll just call them, 404 00:41:05 --> 00:41:12 on islands that have both of them, and there are some islands that have 405 00:41:12 --> 00:41:18 only one. So, what was done is they measure the 406 00:41:18 --> 00:41:25 beak depth of the different finches on the islands where they were found 407 00:41:25 --> 00:41:32 together versus islands where they were found alone in the 408 00:41:32 --> 00:41:40 Galapagos Islands. And what they found, 409 00:41:40 --> 00:41:48 and this has been shown for many, many different studies. You look at 410 00:41:48 --> 00:42:07 the beak depth distribution. 411 00:42:07 --> 00:42:23 This is percent in size class. And this is island C, D, and A, 412 00:42:23 --> 00:42:34 and B. And they found that when the species 413 00:42:34 --> 00:42:42 were on islands where they lived alone, they had almost complete 414 00:42:42 --> 00:42:49 niche, oh this is beak depth. They had exactly the same size beak 415 00:42:49 --> 00:42:57 distributions. In other words, 416 00:42:57 --> 00:43:05 they were feeding on the same food. And on the islands where they were 417 00:43:05 --> 00:43:13 together, A and B, I'm just making sure this actually 418 00:43:13 --> 00:43:21 holds together, they found what is called character 419 00:43:21 --> 00:43:29 displacement, and that is that the birds that had longer beaks and 420 00:43:29 --> 00:43:37 smaller beaks, were preferentially selected for 421 00:43:37 --> 00:43:45 such that reducing the amount of niche overlap. 422 00:43:45 --> 00:44:03 So, and this leads to competitive coexistence. 423 00:44:03 --> 00:44:07 OK, and that's what we're looking at here. This is from your textbooks. 424 00:44:07 --> 00:44:12 This is from African seed crackers showing that birds with smaller 425 00:44:12 --> 00:44:16 bills consume soft seeds more efficiently. Birds with larger 426 00:44:16 --> 00:44:21 bills crack hard seeds, and you can see that the width of 427 00:44:21 --> 00:44:24 the bill here is different.