WEBVTT 00:02.230 --> 00:06.570 Prof: Last time I discussed the planet as a 00:06.565 --> 00:10.365 basically physical and chemical machine, 00:10.370 --> 00:13.600 and how climate affects temperature and water and 00:13.604 --> 00:16.304 nutrient relationships on the planet, 00:16.300 --> 00:20.660 both on the continents and in the ocean. 00:20.660 --> 00:26.050 And what that does is it creates a mosaic of ecological 00:26.046 --> 00:28.536 problems for organisms. 00:28.540 --> 00:32.240 And the part of ecology that looks at how organisms 00:32.237 --> 00:35.707 individually deal with the problems posed by the 00:35.712 --> 00:38.962 environment, things like temperature and pH 00:38.958 --> 00:41.938 and water availability and stuff like that, 00:41.940 --> 00:45.360 is called physiological ecology. 00:45.360 --> 00:49.410 And I'm going to give you a brief description of that today, 00:49.406 --> 00:53.376 using a historical framework, which is up here on the first 00:53.384 --> 00:54.074 slide. 00:54.070 --> 00:58.610 Now the purpose of this historical framework is to show 00:58.611 --> 01:03.911 you that between about 1860 and about 1960 people conceptualized 01:03.908 --> 01:08.698 both the way the organisms deal with these problems in the 01:08.701 --> 01:12.421 environment, and then how to integrate that 01:12.417 --> 01:16.507 into a comprehensive vision of where organisms can live, 01:16.510 --> 01:18.980 and why that is the case. 01:18.980 --> 01:21.930 And that vision of where organisms can live and 01:21.927 --> 01:24.387 reproduce, survive and reproduce, 01:24.388 --> 01:28.298 the ecological niche idea, is something that turned into 01:28.302 --> 01:32.182 an intellectual tool that became very useful in many different 01:32.179 --> 01:33.449 parts of ecology. 01:33.450 --> 01:36.950 So what we're doing here is starting off with Claude 01:36.953 --> 01:39.273 Bernard, the great French physiologist 01:39.268 --> 01:42.598 who came up with the idea that one of the basic things going on 01:42.599 --> 01:45.549 in organisms is that they're trying to keep their inside 01:45.554 --> 01:48.794 constant, while the outside changes; 01:48.790 --> 01:52.390 the idea of homeostasis, la constance du milieu 01:54.080 --> 01:58.990 And well then I'll briefly mention L.J. Henderson, 01:58.992 --> 02:04.302 who said, "You know, it's extremely interesting that 02:04.301 --> 02:08.461 the properties of important things in the environment, 02:08.460 --> 02:11.750 like water and air and the molecules out of which organisms 02:11.752 --> 02:14.182 are built, and things like that, 02:14.182 --> 02:18.622 are in some cases extremely convenient for life." 02:18.620 --> 02:21.050 He called that the fitness of the environment. 02:21.050 --> 02:23.890 So he kind of turned the whole idea of evolutionary fitness 02:23.889 --> 02:25.289 around, and he said, 02:25.289 --> 02:29.309 "The environment appears to be peculiarly fit, 02:29.310 --> 02:32.080 as a place for organisms, like the ones that we know, 02:32.078 --> 02:33.088 to live in." 02:33.090 --> 02:35.310 And, of course, that's not too surprising, 02:35.312 --> 02:38.242 given that this is the planet on which life evolved. 02:38.240 --> 02:41.270 Nevertheless, it's worth considering the fact 02:41.268 --> 02:45.258 that water has some completely extraordinary properties. 02:45.259 --> 02:47.629 It has very high heat capacity. 02:47.628 --> 02:52.638 It transfers heat very rapidly, and water can put into solution 02:52.644 --> 02:57.744 probably more different kinds of atoms and molecules than almost 02:57.740 --> 02:59.520 any other solvent. 02:59.520 --> 03:03.820 So on a planetary scale, water serves very effectively 03:03.816 --> 03:08.996 as a heat transfer mechanism; what we saw in the lecture last 03:09.002 --> 03:09.522 time. 03:09.520 --> 03:14.270 It serves very effectively as a medium in which a huge diversity 03:14.270 --> 03:18.490 of chemical reactions can occur, out of which life has selected 03:18.490 --> 03:20.960 some of them, and so forth. 03:20.960 --> 03:24.320 And you can carry this kind of thinking on, into other parts of 03:24.318 --> 03:24.858 biology. 03:24.860 --> 03:28.270 For example, why is it that phosphorus was 03:28.265 --> 03:33.165 the element that was selected to be the medium of biological 03:33.169 --> 03:36.409 energy transfer in the form of ATP? 03:36.410 --> 03:40.430 And if you look into the shell structure of the phosphorous 03:40.434 --> 03:42.684 atom, you will find that it actually 03:42.684 --> 03:44.834 has some options for storing energy, 03:44.830 --> 03:49.360 and then forming bonds with oxygen, 03:49.360 --> 03:54.490 that help us to understand why it was phosphorous that was the 03:54.488 --> 03:59.198 one that life selected for the generalized unit of energy 03:59.197 --> 04:00.287 currency. 04:00.288 --> 04:02.878 So L.J. Henderson's ideas actually are kind of provocative 04:02.883 --> 04:04.513 and interesting, and the book, 04:04.507 --> 04:06.557 The Fitness of the Environment, 04:06.560 --> 04:07.970 is well written and a pleasure to read. 04:07.968 --> 04:10.648 So if you get interested in that--and by the way, 04:10.647 --> 04:13.327 Claude Bernard's book, A Study of Experimental 04:13.325 --> 04:16.055 Medicine, is easily available in English. 04:16.060 --> 04:19.760 These people are very bright people who wrote some classics, 04:19.759 --> 04:22.579 and it's nice to be able, as a scholar, 04:22.579 --> 04:26.409 to tap into that history of the development of ideas. 04:26.410 --> 04:30.650 Now the culmination of this, at least for today's purposes, 04:30.649 --> 04:34.549 was Evelyn Hutchinson's concluding remarks at the Cold 04:34.547 --> 04:38.147 Spring Harbor Symposium on Long Island in 1959. 04:38.149 --> 04:41.189 That was the output of his graduate seminar here in this 04:41.194 --> 04:45.794 department where he had-- in his graduate seminar at that 04:45.791 --> 04:51.801 time he had people like Larry Slobodkin and Bob MacArthur and 04:51.798 --> 04:53.098 Alan Kohn. 04:53.100 --> 04:56.880 So there was kind of a dynamic group of grad students in the 04:56.879 --> 05:00.229 Yale Biology Department, studying ecology at that time, 05:00.233 --> 05:02.873 and they had come up, together with Hutchinson, 05:02.867 --> 05:06.307 with this idea of the niche as an N-dimensional hyper-volume. 05:06.310 --> 05:10.040 And that was a very powerful tool for condensing all of these 05:10.043 --> 05:13.473 ideas about how individual organisms and populations are 05:13.466 --> 05:17.136 dealing with their physical and chemical environments, 05:17.139 --> 05:21.189 and representing it as an object that then could be used 05:21.189 --> 05:22.809 further in analysis. 05:22.810 --> 05:24.720 So that's the framework. 05:24.720 --> 05:27.850 These are the guys, Bernard, Henderson and 05:27.848 --> 05:28.838 Hutchinson. 05:28.839 --> 05:30.869 There's a portrait of Hutchinson in the Saybrook 05:30.874 --> 05:31.484 Dining Hall. 05:31.480 --> 05:33.120 I actually think the photo's a little bit better. 05:33.120 --> 05:37.380 This is a bush baby; that's a Galago. 05:37.379 --> 05:39.689 I wouldn't mind having one of those. 05:39.690 --> 05:42.650 And the outline of the lecture is going to be a bit about 05:42.654 --> 05:44.934 temperature and about thermal regulation. 05:44.930 --> 05:48.170 So the basic idea here is that ectotherms and endotherms have 05:48.165 --> 05:50.965 really quite different problems with temperature, 05:50.970 --> 05:53.310 and they deal with it in quite different ways. 05:53.310 --> 05:55.850 In homeotherms, we're going to look at 05:55.851 --> 06:00.181 metabolic rate and brown fat and hibernation, and why it is that 06:00.180 --> 06:02.930 intermediate sized things hibernate. 06:02.930 --> 06:06.640 The really little ones can't and the really big ones can't, 06:06.644 --> 06:08.764 but the ones in the middle can. 06:08.759 --> 06:11.799 We'll take a bit of a look at temperature and evaporative 06:11.800 --> 06:13.980 water loss, and then I want to talk a bit 06:13.978 --> 06:16.568 about how plants deal with drought and with too little 06:16.572 --> 06:19.042 water and oxygen, and then we'll end up with the 06:19.043 --> 06:19.913 ecological niche. 06:19.910 --> 06:23.240 This is a very, very quick and kind of spotty 06:23.235 --> 06:27.465 summary of some major themes in physiological ecology. 06:27.470 --> 06:30.780 It's a big field, and it contains a lot of neat 06:30.783 --> 06:35.113 experiments, and I'm only able to touch on it quickly in this 06:35.107 --> 06:35.897 course. 06:35.899 --> 06:38.339 One of the themes that I want to bring up now-- 06:38.339 --> 06:42.719 and I hope I remember to come back and mention it again later 06:42.716 --> 06:46.306 in the lecture-- is that we will see that 06:46.314 --> 06:51.454 organisms have lots of adaptations for dealing with the 06:51.454 --> 06:53.744 external environment. 06:53.740 --> 06:56.430 We'll see it in the nose and the brain of the oryx, 06:56.432 --> 06:59.662 and we'll see it in the special organs of plants to deal with 06:59.663 --> 07:01.443 oxygen problems and so forth. 07:01.439 --> 07:05.729 And one way to think about that is that evolution has designed 07:05.733 --> 07:10.103 organisms to extend the range of environments in which they can 07:10.098 --> 07:13.268 survive and reproduce, and therefore that the 07:13.271 --> 07:16.571 definition of what is critical in the environment has been 07:16.567 --> 07:18.647 continually changed by evolution. 07:18.649 --> 07:19.789 It's been a moving target. 07:19.790 --> 07:23.270 You cannot think of an ecological niche as being 07:23.266 --> 07:27.696 something that pre-existed on the planet, before life started 07:27.704 --> 07:28.744 to evolve. 07:28.740 --> 07:32.550 But we now use, as a tool in ecology, 07:32.550 --> 07:36.410 the concept of the ecological nice as an artificial construct, 07:36.410 --> 07:39.770 invented by human minds, as an intellectual tool to try 07:39.766 --> 07:42.746 to make sense out of the complexity of nature. 07:42.750 --> 07:45.870 And our definition of it actually is the product of 07:45.867 --> 07:48.547 evolution, and it's been a moving target. 07:48.550 --> 07:51.780 So don't think of the environment as consisting of a 07:51.781 --> 07:55.581 pre-existing chessboard on one of which- each square of which 07:55.584 --> 07:58.034 is a niche, and into which you can put an 07:58.028 --> 08:00.368 organism, and then it will all get filled 08:00.367 --> 08:00.597 up. 08:00.600 --> 08:03.880 Because the organisms themselves have been defining 08:03.882 --> 08:06.512 what these things are, as they evolve. 08:06.509 --> 08:10.159 Okay, a little bit about ectotherms and endotherms. 08:10.160 --> 08:12.470 Here's, on the X-axis, we've got environmental 08:12.466 --> 08:15.026 temperature, outside temperature, in Centigrade; 08:15.028 --> 08:17.288 and here we have body temperature. 08:17.290 --> 08:21.240 And a mouse is maintaining its temperature at a nice 37, 08:21.242 --> 08:25.482 and the lizard is letting its temperature fluctuate with the 08:25.483 --> 08:27.283 external environment. 08:27.278 --> 08:29.508 We'll see that actually lizards can control this, 08:29.509 --> 08:31.009 to some extent, behaviorally, 08:31.007 --> 08:33.687 and that things like mice, of course, do have daily 08:33.692 --> 08:35.252 temperature cycles and so forth. 08:35.250 --> 08:37.920 But just at this level--and it's a very rough 08:37.921 --> 08:41.441 contrast--endotherms maintain constant internal temperature 08:41.442 --> 08:43.632 and ectotherms let it fluctuate. 08:43.629 --> 08:47.699 Now lizards have a preferred temperature, and actually their 08:47.697 --> 08:51.487 preferred temperature is a bit hotter than the mouse. 08:51.490 --> 08:57.130 They like it to be oh about 30--well maybe not quite as hot 08:57.130 --> 09:00.630 as the mouse, but they like it in the 09:00.631 --> 09:05.791 mid-30s; so say around somewhere between 09:05.793 --> 09:10.563 90 and 95 Fahrenheit, say 88 and 95. 09:10.558 --> 09:13.808 And their surroundings have a huge temperature range, 09:13.812 --> 09:17.252 and the actual temperature range--this is what you would 09:17.250 --> 09:18.690 measure in the lab. 09:18.690 --> 09:19.840 If you made a temperature gradient, 09:19.840 --> 09:22.890 and you put your lizard in and you let it just settle down in 09:22.886 --> 09:25.336 the temperature gradient, it would wander back and forth 09:25.341 --> 09:28.401 until it found what it liked, and it would settle down right 09:28.403 --> 09:28.873 there. 09:28.870 --> 09:32.950 Its actual temperature in nature is much narrower than the 09:32.947 --> 09:36.737 range of temperatures out there in the environment. 09:36.740 --> 09:40.190 And, for example, it can do things like having 09:40.191 --> 09:44.721 its back facing east or its back facing west, depending upon 09:44.715 --> 09:47.625 whether it's morning or afternoon. 09:47.629 --> 09:50.419 Right at noon, when the sun's directly 09:50.422 --> 09:53.292 overhead, it won't orient like that. 09:53.288 --> 09:57.718 So if the lizards are basking, they bask in such a way that 09:57.720 --> 10:02.300 helps them to maintain their actual temperature above that of 10:02.302 --> 10:04.902 the environment, in this case. 10:04.899 --> 10:08.759 They manage to be warm when they need to run fast, 10:08.758 --> 10:11.748 and they manage to be cool at night. 10:11.750 --> 10:14.870 If you're a herpetologist and you like to catch lizards, 10:14.870 --> 10:18.120 you know that a lizard that's been sitting on a nice warm rock 10:18.120 --> 10:21.270 is going to run away from you really quickly when you try to 10:21.267 --> 10:22.437 go up and grab it. 10:22.440 --> 10:24.980 And, of course, they have developed this 10:24.979 --> 10:28.039 because they need to get away from predators. 10:28.038 --> 10:30.898 So they will bask in the morning, to get their 10:30.897 --> 10:33.447 temperature up, and then they will move back 10:33.453 --> 10:35.933 and forth between sun and shade during the day, 10:35.928 --> 10:38.188 to maintain their body temperature, 10:38.190 --> 10:41.090 in the high 30s, and then they go back into 10:41.085 --> 10:42.735 their burrow at night. 10:42.740 --> 10:46.800 So there is a kind of behavioral thermoregulation in 10:46.797 --> 10:49.737 this ectotherm, which is not doing its 10:49.740 --> 10:53.400 thermoregulation with internal physiology; 10:53.399 --> 10:58.679 it's doing it by moving in and out of sun and shade. 10:58.678 --> 11:02.838 Another very important idea for ectotherms, 11:02.840 --> 11:07.140 and particularly for small ones--the smaller you are, 11:07.139 --> 11:10.889 because of the surface area volume ratio, 11:10.889 --> 11:12.859 the more rapidly you take up or lose heat. 11:12.860 --> 11:16.300 11:16.299 --> 11:18.419 This idea is physiological time. 11:18.418 --> 11:18.698 Okay? 11:18.696 --> 11:21.396 So physiological time is something which is really 11:21.400 --> 11:23.610 directly proportional to temperature; 11:23.610 --> 11:26.800 and you can see an illustration of it over here. 11:26.798 --> 11:30.638 This is the percentage of development that's going on in 11:30.635 --> 11:32.305 the course of one day. 11:32.308 --> 11:36.178 So in 24 hours this is how much development is occurring in 11:36.176 --> 11:39.506 standardized stages, depending upon temperature. 11:39.509 --> 11:42.679 And if you transform that into a rate per day and plot it 11:42.678 --> 11:46.248 against temperature, you get this nice straight 11:46.250 --> 11:51.840 line, which basically means that time is directly proportional to 11:51.840 --> 11:53.150 temperature. 11:53.149 --> 11:55.889 So the hotter it is, the faster they'll develop. 11:55.889 --> 11:59.039 And what that means is kind of interesting for ecology, 11:59.038 --> 12:01.168 because on the one hand you've got a lot of predators who are 12:01.168 --> 12:03.948 homeotherms, and who don't have this kind of 12:03.952 --> 12:05.192 reaction at all. 12:05.190 --> 12:06.690 So they're running around rapidly. 12:06.690 --> 12:10.510 Shrews, mice, birds; lots of things that will eat 12:10.505 --> 12:14.225 insects are fairly insensitive to the external temperature, 12:14.227 --> 12:17.177 and they can be active at all temperatures. 12:17.178 --> 12:19.358 Whereas the insects are actually forced, 12:19.360 --> 12:24.080 by their small size and their ectotherm status, 12:24.080 --> 12:25.930 to grow more slowly when it's cold, 12:25.928 --> 12:28.408 and they're forced to grow more rapidly when it's hot. 12:28.408 --> 12:31.628 And that has cascading effects on their population dynamics and 12:31.630 --> 12:33.450 on their predator/prey relations. 12:33.450 --> 12:37.310 12:37.308 --> 12:41.518 Now what about endotherms, how do they deal with the 12:41.524 --> 12:43.844 environmental temperature? 12:43.840 --> 12:47.620 Well this is the body temperature of a model 12:47.616 --> 12:52.006 endotherm, and this is its heat production here. 12:52.009 --> 12:55.939 Now what's going on is that there is an upper critical 12:55.937 --> 12:58.867 temperature, and if the environmental 12:58.868 --> 13:01.078 temperature, in the long-term, 13:01.081 --> 13:04.131 goes above this upper critical temperature, 13:04.129 --> 13:07.899 the endotherm can no longer thermoregulate, 13:07.899 --> 13:09.859 and its body temperature will rise. 13:09.860 --> 13:12.930 If I take you out into the Sahara, 13:12.928 --> 13:14.798 on a hot day, and I sit you down, 13:14.799 --> 13:17.489 you're going to thermoregulate pretty well, 13:17.490 --> 13:21.410 until the external temperature gets above about a steady 110, 13:21.408 --> 13:22.818 or something like that, Fahrenheit, 13:22.820 --> 13:26.010 and at that point your sweating and so forth isn't going to 13:26.009 --> 13:28.889 function anymore, and your body temperature will 13:28.893 --> 13:31.333 rise, and if that goes on very long 13:31.332 --> 13:32.452 you'll be dead. 13:32.450 --> 13:34.800 So that's what this critical temperature means. 13:34.799 --> 13:37.549 Lower critical temperature. 13:37.548 --> 13:42.598 Basically if the environmental temperature drops below the 13:42.599 --> 13:47.559 lower critical temperature, then internal heat production 13:47.559 --> 13:49.509 starts to ramp up. 13:49.509 --> 13:52.299 That would be both direct burning of fat, 13:52.298 --> 13:55.998 down at the cellular level, and it would be shivering, 13:55.995 --> 13:57.735 and things like that. 13:57.740 --> 14:02.210 And that would allow you to maintain a nice steady internal 14:02.205 --> 14:06.045 temperature, until you got down to your 14:06.046 --> 14:10.486 maximum heat output, by all physiological mechanisms 14:10.490 --> 14:12.890 combined, and if the external temperature 14:12.889 --> 14:16.159 drops even further than that, and you're no longer able to 14:16.163 --> 14:19.133 keep up, you will freeze and die down at 14:19.130 --> 14:19.900 that end. 14:19.899 --> 14:20.609 Okay? 14:20.610 --> 14:24.290 So you can see that there is a range of environmental values 14:24.293 --> 14:27.663 that can be dealt with, and then outside that range you 14:27.663 --> 14:29.603 can't deal with it anymore. 14:29.600 --> 14:34.200 And this is something that's evolved, where these points are. 14:34.200 --> 14:38.250 So what's going on here is variations among different kinds 14:38.254 --> 14:41.614 of endotherms in their insulation blood flow, 14:41.610 --> 14:45.210 how they select microclimates, shivering and huddling. 14:45.210 --> 14:46.920 Insulation. 14:46.918 --> 14:51.068 Take a Weddell seal or a Leopard seal or something like 14:51.065 --> 14:54.665 that, freeze it, cut it in half with a band saw, 14:54.673 --> 14:57.133 look at it in cross-section. 14:57.129 --> 15:00.209 It's about one-third fat, on the outside. 15:00.210 --> 15:01.830 It's extremely well insulated. 15:01.830 --> 15:04.660 Same thing for a humpback whale or a blue whale. 15:04.658 --> 15:07.128 So insulation can be very important. 15:07.129 --> 15:08.429 Bears do it. 15:08.429 --> 15:12.799 We do it; we have subcutaneous fat that 15:12.801 --> 15:15.021 serves as an insulator. 15:15.019 --> 15:17.389 Shivering and huddling; well you know all about 15:17.394 --> 15:18.014 shivering. 15:18.009 --> 15:20.979 Huddling is something, for example, 15:20.975 --> 15:23.675 that the emperor penguins do. 15:23.678 --> 15:27.428 Emperor penguins have this totally bizarre lifestyle where 15:27.432 --> 15:31.252 they have chosen to lay their eggs on part of the Antarctic 15:31.251 --> 15:34.241 continent, which is exposed during the 15:34.241 --> 15:36.601 summer, but their lifecycle is such 15:36.596 --> 15:40.346 that it takes them about six months for the eggs to hatch and 15:40.345 --> 15:42.215 then to start to feed baby. 15:42.220 --> 15:47.300 And so at the time when they have these little chicks that 15:47.299 --> 15:50.859 need lots of warmth, and they are shuttling back and 15:50.856 --> 15:53.766 forth to try to go way out to the edge of the pack ice to get 15:53.773 --> 15:56.293 squid-- because now it's winter and the 15:56.287 --> 16:00.267 pack ice is frozen-they huddle and get into a big circle where 16:00.274 --> 16:03.484 you'll have hundreds of these giant penguins-- 16:03.480 --> 16:06.060 they're about this big--that are all packed together. 16:06.058 --> 16:11.178 And the Antarctic hurricanes are blowing over them with -40, 16:11.178 --> 16:14.848 -50 Fahrenheit temperatures, and the birds are basically 16:14.846 --> 16:18.706 forming a continually moving clump in which the ones on the 16:18.712 --> 16:22.652 outside are getting desperate and pushing their way into the 16:22.645 --> 16:24.515 inside, and the ones on the inside, 16:24.524 --> 16:26.524 they're a little bit warmer and not quite so desperate, 16:26.519 --> 16:28.699 and are getting pushed out to the outside. 16:28.700 --> 16:29.780 So that's huddling. 16:29.779 --> 16:33.489 16:33.490 --> 16:37.250 Okay, now let's go inside some organisms and look at some of 16:37.246 --> 16:41.126 the adaptations that evolution has produced that allow them to 16:41.131 --> 16:43.681 regulate their internal environment. 16:43.678 --> 16:47.798 So this is a classic example of something that would cause the 16:47.798 --> 16:50.768 internal environment to be held constant, 16:50.769 --> 16:53.999 despite great variation in the external environment: 16:54.000 --> 16:56.090 countercurrent heat exchangers. 16:56.090 --> 17:06.500 And the way these things work basically is that if you have 17:06.499 --> 17:11.439 concurrent flow-- this is the countercurrent 17:11.442 --> 17:14.572 case, and it's being explained here by contrast to the 17:14.568 --> 17:15.688 concurrent case. 17:15.690 --> 17:18.400 In concurrent flow you would have say venous blood going in 17:18.395 --> 17:20.525 this direction; and then running right next to 17:20.528 --> 17:23.028 the vein you've got an artery, going in this direction. 17:23.028 --> 17:28.078 So the artery perhaps is nice and warm, 17:28.078 --> 17:30.938 but it's running next to the vein, and there's an exchange 17:30.943 --> 17:33.313 gradient along it, and as these two things 17:33.307 --> 17:36.087 exchange heat they end up at the same temperature, 17:36.093 --> 17:36.893 coming out. 17:36.890 --> 17:40.950 That's what happens if the flow is going in the same direction. 17:40.950 --> 17:43.630 But if you arrange it physiologically, 17:43.630 --> 17:46.660 and morphologically, so that the flow in the artery 17:46.655 --> 17:49.795 is going in the opposite direction to the flow in the 17:49.804 --> 17:51.854 vein-- so this is going into the organ 17:51.852 --> 17:53.622 and this is coming out of the organ, 17:53.618 --> 17:56.598 going back to the heart--then what goes on is that the blood 17:56.598 --> 17:58.488 that's coming in, in the artery, 17:58.486 --> 18:02.116 is getting heated by the blood that's going back out in the 18:02.115 --> 18:04.885 vein, and that's going to maintain 18:04.894 --> 18:07.274 the temperature on this side. 18:07.269 --> 18:10.699 Now which way you would want to set this up would depend upon 18:10.703 --> 18:14.373 whether you wanted the warmth to be in the core of the body or in 18:14.366 --> 18:15.966 the outside of the body. 18:15.970 --> 18:18.550 In most cases, this is in the core of the 18:18.548 --> 18:18.998 body. 18:19.000 --> 18:22.060 You guys have got this, right here. 18:22.058 --> 18:24.658 You can walk in water, and a countercurrent heat 18:24.660 --> 18:28.200 exchanger in your legs will make sure that your body core doesn't 18:28.200 --> 18:29.860 drop temperature too much. 18:29.858 --> 18:32.068 Yours is okay, but it's not really nearly as 18:32.067 --> 18:35.197 impressive as the ones that are in the feet of ducks and geese 18:35.202 --> 18:39.942 and moose and things like that; that can stand around in water, 18:39.942 --> 18:45.262 which is right at the freezing point, and their core body 18:45.260 --> 18:48.870 temperature stays a nice stable 98. 18:48.869 --> 18:49.249 Okay? 18:49.250 --> 18:52.710 18:52.710 --> 18:55.890 Let me just mention, before I go into the oryx, 18:55.890 --> 18:59.120 that there are countercurrent exchangers that deal with ion 18:59.115 --> 19:01.335 concentrations in vertebrate kidneys-- 19:01.338 --> 19:04.208 so the vertebrate kidney is actually designed using this 19:04.210 --> 19:06.950 same principle-- and with oxygen concentration 19:06.949 --> 19:07.879 in fish gills. 19:07.880 --> 19:11.390 So countercurrent exchangers are something that is obviously 19:11.385 --> 19:14.645 such a good engineering idea that it has been arrived at 19:14.653 --> 19:18.283 convergently by evolution to deal with similar problems, 19:18.278 --> 19:22.728 but completely independently solved. 19:22.730 --> 19:23.630 Let's take a look at one. 19:23.630 --> 19:27.290 This is the desert oryx--really a beautiful animal, 19:27.290 --> 19:31.680 I've seen them in Namibia--and we're going to look inside its 19:31.683 --> 19:32.713 head here. 19:32.710 --> 19:38.500 So the problem that the oryx has is that it needs to regulate 19:38.501 --> 19:42.751 both its temperature and its water supply. 19:42.750 --> 19:44.700 It's living in the desert. 19:44.700 --> 19:52.570 And if you look into its head, it's got a lot of exposure of 19:52.567 --> 19:58.567 its blood supply to external air coming in. 19:58.568 --> 20:04.128 It doesn't want to lose too much water by sweating. 20:04.130 --> 20:07.970 So what it's done is it's allowed its body temperature to 20:07.973 --> 20:10.243 go up to 44 degrees Centigrade. 20:10.240 --> 20:13.110 So it won't regulate its body temperature until it hits 44 20:13.111 --> 20:14.171 degrees Centigrade. 20:14.170 --> 20:16.910 And it's a big animal, so overnight it can cool down, 20:16.910 --> 20:19.810 and it'll take a long time to hit 44, during the day. 20:19.808 --> 20:24.838 But its brain would die if it ever got to 44 Centigrade. 20:24.838 --> 20:28.968 So it has to figure out a way, how to hold its brain at a nice 20:28.971 --> 20:31.571 39 degrees, while its body temperature, 20:31.574 --> 20:34.024 which has most of its blood supply in it, 20:34.023 --> 20:34.763 is at 44. 20:34.759 --> 20:37.659 So it's got to drop that body temperature by about 5 degrees 20:37.664 --> 20:39.344 Centigrade going into the brain. 20:39.338 --> 20:44.898 And the way it does it is it first takes the blood and it 20:44.900 --> 20:46.290 gets cooled. 20:46.288 --> 20:47.928 So there's blood that's being pumped out, 20:47.930 --> 20:51.680 into its nose--it has a great big nose-- 20:51.680 --> 20:54.640 blood is getting pumped out into its nose and coming back 20:54.644 --> 20:55.814 through these veins. 20:55.808 --> 20:58.938 And this is cold because--colder--because of the 20:58.936 --> 21:02.526 evaporative processes that are going on in the nose. 21:02.528 --> 21:05.448 It gets passed through what is called a rete mirabile, 21:05.450 --> 21:09.040 right here, and the oxygenated blood, 21:09.038 --> 21:10.588 which is going to go into the brain, 21:10.588 --> 21:13.068 passes through this, and the cold blood coming out 21:13.067 --> 21:16.147 of the nose cools the oxygenated blood off before it gets into 21:16.152 --> 21:16.862 the brain. 21:16.858 --> 21:21.248 It's really a beautiful adaptation, and it's something 21:21.251 --> 21:25.641 that gets repeated in other organisms to solve similar 21:25.644 --> 21:28.384 problems in other situations. 21:28.380 --> 21:30.460 For example, tuna. 21:30.460 --> 21:34.940 Here are some yellowfin tuna, and they have a countercurrent 21:34.942 --> 21:38.062 heat exchanger, and they use it to keep cold 21:38.057 --> 21:41.797 sea water from chilling their warm venous blood that's coming 21:41.803 --> 21:44.553 out of their hot high performance muscle. 21:44.548 --> 21:51.358 So they cannot really retain very much heat overall, 21:51.358 --> 21:53.418 because in order to get oxygen out of the water, 21:53.420 --> 21:56.280 they're pumping--and they're very high energy animals, 21:56.279 --> 21:58.719 so they're pumping a lot of oxygen through their gills. 21:58.720 --> 22:00.510 And that is a big surface. 22:00.509 --> 22:03.189 The water has, as I mentioned with Henderson, 22:03.186 --> 22:06.836 very high heat capacity and a great ability to strip heat off 22:06.837 --> 22:09.087 of the blood supply in the gills. 22:09.088 --> 22:13.698 But down the core of their body they've got some dark muscle 22:13.700 --> 22:17.920 that they want to keep up at 37 degrees Centigrade, 22:17.920 --> 22:22.120 so that they can do things like swim from San Francisco to Tokyo 22:22.116 --> 22:25.646 in seven days, at speeds of up to 50 22:25.652 --> 22:27.942 kilometers an hour. 22:27.940 --> 22:31.070 These fish are amazing. 22:31.068 --> 22:35.578 Well what they've done--this is sort of a perch or a largemouth 22:35.579 --> 22:36.089 bass. 22:36.088 --> 22:40.638 And you might think of that as the ancestral condition, 22:40.640 --> 22:42.440 and they've taken this ancestral condition, 22:42.440 --> 22:47.670 where the vein, coming back into the heart, 22:47.670 --> 22:50.020 looks like that, and the dorsal aorta going out 22:50.017 --> 22:54.177 of the heart looks like that, and that kind of circulation 22:54.179 --> 22:59.239 has been altered so that you have a rete mirabile between 22:59.238 --> 23:05.018 arteries that are running out under the surface of the skin, 23:05.019 --> 23:07.749 and veins that are running out under the surface of the skin. 23:07.750 --> 23:12.160 And when these arteries are then pumping through the rete 23:12.163 --> 23:14.503 mirabile, into the core of the animal, 23:14.496 --> 23:17.516 they are picking up heat that's being generated by that muscle 23:17.515 --> 23:19.525 tissue, and then in the countercurrent 23:19.528 --> 23:21.778 heat exchanger, or the rete mirabile, 23:21.778 --> 23:24.958 that heat is exchanged, going back into the veins. 23:24.960 --> 23:27.790 So on the external part of the body the blood's right at 23:27.788 --> 23:30.768 environmental temperature, and in the core of the body, 23:30.772 --> 23:33.872 it is probably maintained at anywhere from 10 to 20 degrees 23:33.865 --> 23:36.635 Centigrade above the environmental temperatures, 23:36.640 --> 23:38.690 so that these very efficient muscles can work. 23:38.690 --> 23:43.550 23:43.548 --> 23:47.398 Mammals maintain their internal temperature, particularly small 23:47.400 --> 23:51.070 mammals, maintain their internal temperature using something 23:51.065 --> 23:52.365 called brown fat. 23:52.368 --> 23:57.278 So this is now not a morphological adaptation, 23:57.279 --> 24:01.369 at the level of an organ--which is what the rete mirabile or the 24:01.367 --> 24:03.767 countercurrent heat exchanger are-- 24:03.769 --> 24:07.589 this is a cellular adaptation. 24:07.588 --> 24:11.948 So if you take a cute little eastern chipmunk and you look 24:11.953 --> 24:14.793 into its body, you find that there are 24:14.788 --> 24:18.998 specific places where it has deposits of brown fat. 24:19.000 --> 24:21.870 And this is what brown fat looks like under a microscope. 24:21.869 --> 24:23.039 This is white fat. 24:23.039 --> 24:24.009 Okay? 24:24.009 --> 24:27.359 This is what I've got hanging on my belly. 24:27.358 --> 24:30.988 And in a brown squirrel, they have, 24:30.990 --> 24:33.890 above the kidney and in the back of the neck and so forth, 24:33.890 --> 24:37.110 brown fat, and the reason it's brown is that it's loaded with 24:37.114 --> 24:37.924 mitochondria. 24:37.920 --> 24:42.530 And so if they get a signal that the temperature's dropping, 24:42.529 --> 24:45.269 and that comes into their brain, into their hypothalamus, 24:45.269 --> 24:48.149 they will put out a hormone that carries a hormonal signal 24:48.154 --> 24:51.224 out to their brown fat, and the mitochondria in the 24:51.223 --> 24:55.133 brown fat receiving that signal will start to simply generate 24:55.125 --> 24:57.485 energy, and that generates heat. 24:57.490 --> 25:00.050 Okay? 25:00.048 --> 25:03.568 This is actually the mechanism that allows hibernation, 25:03.568 --> 25:07.478 because they can regulate that heat generation up or down. 25:07.480 --> 25:11.440 And hibernation is something which is done in mammals, 25:11.442 --> 25:14.662 of course, to avoid dying, in the winter. 25:14.660 --> 25:17.340 I have, I think, three or four eastern chipmunks 25:17.339 --> 25:20.739 that live in my yard in Hamden, and they tend to disappear 25:20.743 --> 25:24.353 towards the end of September, and I'll probably first see 25:24.353 --> 25:27.323 them again sometime during the next month. 25:27.318 --> 25:29.408 They've been down for several months. 25:29.410 --> 25:30.180 Okay? 25:30.180 --> 25:32.810 They're all wrapped up in a ball underground, 25:32.805 --> 25:33.755 sleeping away. 25:33.759 --> 25:39.259 And you can only do that if you're kind of an intermediate 25:39.255 --> 25:39.925 size. 25:39.930 --> 25:46.270 So when it's preparing for hibernation, it's regulating its 25:46.272 --> 25:48.682 temperature near 37. 25:48.680 --> 25:51.510 Then when it's down in the ground, it will drop it, 25:51.510 --> 25:53.040 down to about 10 degrees. 25:53.038 --> 25:55.978 And it's got a temperature sensor, in its brain, 25:55.980 --> 25:57.920 which keeps it from freezing. 25:57.920 --> 26:00.670 In other words, the temperature will go down to 26:00.666 --> 26:04.006 about 10, or maybe a little bit below in some other small 26:04.011 --> 26:06.761 mammals, but it will never go to freezing. 26:06.759 --> 26:09.459 So it can tell if it's getting dangerously cold, 26:09.461 --> 26:12.971 and it will regulate its lower temperature with the brown fat, 26:12.970 --> 26:15.040 so it doesn't completely freeze. 26:15.038 --> 26:18.688 And they do wake up a little bit sometimes during the winter, 26:18.691 --> 26:20.701 but they don't really come out. 26:20.700 --> 26:24.010 They'll wake up and roll over, and if they have stored seed 26:24.009 --> 26:27.319 underground, they will go eat their seed stores so they can 26:27.317 --> 26:28.457 keep doing this. 26:28.460 --> 26:32.550 And then right about now they'll come out again. 26:32.548 --> 26:37.188 So what's going on in one bout of hibernation here-- 26:37.190 --> 26:40.080 so if we just take one little bout here-- 26:40.078 --> 26:43.378 they drop their metabolic rate, they drop their body 26:43.378 --> 26:46.738 temperature, and for about a week they have 26:46.739 --> 26:51.039 a very low metabolic rate and a low body temperature; 26:51.038 --> 26:57.118 it's down, in Centigrade, it can get down to maybe 3 or 4 26:57.115 --> 26:58.195 degrees. 26:58.200 --> 27:03.100 And then they will arouse, eat and then do it again. 27:03.098 --> 27:07.028 So this is regulated actually both by physiology and by 27:07.028 --> 27:08.968 behavior; and by morphology. 27:08.970 --> 27:11.060 They have pouches in their cheeks where they can store the 27:11.058 --> 27:13.098 seeds, and they have a seed deposit in 27:13.095 --> 27:15.735 their burrow, and when they wake up and they 27:15.743 --> 27:17.843 need to recharge, that's what they use, 27:17.836 --> 27:19.526 and then their physiology takes over; 27:19.528 --> 27:21.218 and that's what gets them through the winter. 27:21.220 --> 27:25.460 Now you can imagine that this has greatly extended the 27:25.463 --> 27:29.953 geographical range in which something like a chipmunk can 27:29.949 --> 27:30.669 live. 27:30.670 --> 27:33.560 Now I want you to think about the surface area to volume 27:33.561 --> 27:34.721 ratios for a minute. 27:34.720 --> 27:38.680 I think you all know that the surface area is proportional to 27:38.676 --> 27:42.986 the square of a body dimension, and the volume of an organism 27:42.986 --> 27:46.546 is proportional to the cube of a body dimension, 27:46.548 --> 27:49.768 so that when things get big, they have proportionally less 27:49.773 --> 27:52.103 surface area, and when they get small they 27:52.099 --> 27:54.079 have proportionally more surface area. 27:54.078 --> 27:56.958 And I want you just to take a minute and explain to your 27:56.961 --> 28:00.211 partner why it is that really small things can't hibernate, 28:00.210 --> 28:03.070 and really big things can't hibernate. 28:03.068 --> 28:06.798 And let's see how you do, and I'll give you the answer in 28:06.798 --> 28:08.128 about two minutes. 28:08.130 --> 29:06.790 <> 29:06.788 --> 29:08.228 Student: How do bears hibernate? 29:08.230 --> 29:09.140 Prof: They don't. 29:09.140 --> 29:10.090 Student: They don't? 29:10.089 --> 29:11.209 Prof: They sleep. 29:11.210 --> 29:19.240 29:19.240 --> 29:26.330 Yes Myra? 29:26.328 --> 29:28.378 Student: We learned that bears hibernate-- 29:28.380 --> 29:31.380 Prof: Bears don't hibernate, they sleep. 29:31.380 --> 29:33.690 A very bad idea to try to take the body temperature of a 29:33.686 --> 29:34.606 sleeping brown bear. 29:34.609 --> 29:35.959 It can wake up in a hurry. 29:35.960 --> 29:37.860 A chipmunk can't wake up. 29:37.859 --> 29:38.529 Student: Oh. 29:38.529 --> 29:41.159 Prof: You can pick a chipmunk up and toss it in your 29:41.163 --> 29:42.303 hand, it won't wake up. 29:42.298 --> 29:46.138 You go in and try to take the rectal temperature of a brown 29:46.143 --> 29:49.393 bear and you better be ready to run in a hurry. 29:49.390 --> 29:51.720 Student: What is the difference between hibernating 29:51.724 --> 29:52.334 and sleeping? 29:52.328 --> 29:56.878 Prof: How far the body temperature will drop. 29:56.880 --> 29:59.440 A bear--your body temperature drops when you sleep; 29:59.440 --> 30:03.290 it goes from about 98.6 down to about 96 or 95, 30:03.286 --> 30:07.046 and then it warms back up when you wake up. 30:07.048 --> 30:10.568 A bear might drop down to about 90. 30:10.569 --> 30:12.109 A chipmunk will drop to 40. 30:12.109 --> 30:19.209 30:19.210 --> 30:24.110 Okay, who can tell me why really small things can't 30:24.105 --> 30:25.275 hibernate? 30:25.278 --> 30:27.488 Like shrews, which I have in my garage, 30:27.487 --> 30:29.227 in the middle of the winter. 30:29.230 --> 30:31.130 Okay, why do really small things not hibernate? 30:31.130 --> 30:34.440 30:34.440 --> 30:38.910 What's their problem with surface area and volume? 30:38.910 --> 30:40.880 Student: Their surface area is really big compared to 30:40.876 --> 30:41.366 their volume. 30:41.368 --> 30:43.608 So there's a lot of surface to-- 30:43.609 --> 30:44.499 Prof: Right. 30:44.500 --> 30:47.470 So even though evolution has done a great job of developing 30:47.473 --> 30:49.683 these temperature regulating mechanisms, 30:49.680 --> 30:53.760 there comes a point at which they can no longer do it, 30:53.759 --> 30:57.569 and if you get really small, there's just no way that you 30:57.570 --> 31:01.520 can build say a 20 gram shrew that will be able to regulate 31:01.518 --> 31:02.878 its temperature. 31:02.880 --> 31:04.840 It just has too much surface area. 31:04.839 --> 31:05.879 Okay? 31:05.880 --> 31:08.420 What about something that's big? 31:08.420 --> 31:10.510 I've heard a couple of comments about bears; 31:10.509 --> 31:11.829 bears are big. 31:11.828 --> 31:12.078 Okay? 31:12.075 --> 31:13.785 Bears don't hibernate, they sleep. 31:13.789 --> 31:18.129 Why can the bear not hibernate? 31:18.130 --> 31:22.050 Remember, hibernation is a condition where you really drop 31:22.047 --> 31:24.107 your body temperature a lot. 31:24.109 --> 31:24.959 Yes? 31:24.960 --> 31:28.190 Student: Maybe its volume to surface ratio is 31:28.188 --> 31:31.228 larger, and so it has > 31:31.230 --> 31:33.350 Prof: Yes, it can't get rid of the heat 31:33.346 --> 31:35.366 fast enough to drop its body temperature. 31:35.368 --> 31:39.468 So just a bunch of kind of torpid bear fat, 31:39.467 --> 31:42.977 if it's alive, is still making enough 31:42.979 --> 31:44.539 temperature. 31:44.538 --> 31:47.988 So it can't radiate it off fast enough. 31:47.990 --> 31:51.400 So that's basically why you get these rough limits. 31:51.400 --> 31:55.830 Even in something which is as ectothermic as my compost heap 31:55.832 --> 31:58.802 in the backyard, whose temperature is being 31:58.801 --> 32:02.281 regulated by bacteria and fungi, I can go out there when it's 20 32:02.280 --> 32:04.390 degrees below 0, take the snow off, 32:04.394 --> 32:07.494 and steam will come out of my compost heap. 32:07.490 --> 32:08.280 Okay? 32:08.278 --> 32:12.678 Which is a pretty big area and it has not too much surface area 32:12.684 --> 32:15.534 for a large volume, and it maintains high 32:15.526 --> 32:18.436 temperature right through the winter. 32:18.440 --> 32:24.390 Okay, now what about evaporative water loss? 32:24.390 --> 32:29.560 Here is a real physiological tradeoff. 32:29.558 --> 32:34.758 If you want to maintain your internal temperature by cooling 32:34.759 --> 32:39.519 yourself through evaporation, you need a good supply of 32:39.518 --> 32:41.588 water; it can take a tremendous amount 32:41.586 --> 32:41.966 of water. 32:41.970 --> 32:45.500 As you all know, when you get really thirsty, 32:45.497 --> 32:49.267 running or working, to just maintain your proper 32:49.265 --> 32:51.585 balance of bodily fluids. 32:51.588 --> 32:58.088 And there comes a point where the resting metabolic rate and 32:58.092 --> 33:02.172 the resting water loss really get-- 33:02.170 --> 33:04.420 there's an attempt here, with the metabolic rate 33:04.415 --> 33:07.525 starting to go up, that's because the water loss 33:07.529 --> 33:10.949 is no longer able to cool the organism enough. 33:10.950 --> 33:14.170 So it gets up to about 42,43 Centigrade, 33:14.170 --> 33:17.220 and this little bird is getting into serious difficulty because 33:17.218 --> 33:20.068 it can't evaporate enough to hold its temperature down, 33:20.068 --> 33:23.268 and it's starting to get up into dangerous territory. 33:23.269 --> 33:23.759 Okay? 33:23.759 --> 33:27.649 33:27.650 --> 33:31.110 Really dangerous territory. 33:31.108 --> 33:35.898 So that's another illustration of physiological ecology. 33:35.900 --> 33:40.110 Let's now go to plants, and think about water in the 33:40.111 --> 33:40.691 soil. 33:40.690 --> 33:44.210 Because, of course, for plants what do they need? 33:44.210 --> 33:46.980 Plants need sunlight, they need water, 33:46.979 --> 33:50.139 they need carbon dioxide; of course they need more than 33:50.136 --> 33:52.446 that, but if they're going to make food, if they're going to 33:52.451 --> 33:54.571 feed, they need sunlight, water and carbon dioxide. 33:54.568 --> 33:57.468 They're going to get their water out of the soil, 33:57.465 --> 33:59.875 and they're going to do it with roots. 33:59.880 --> 34:05.510 And if we look into the soil, what we find basically is that 34:05.506 --> 34:09.126 at a certain pore size in the soil-- 34:09.130 --> 34:12.750 34:12.750 --> 34:19.490 the low for certain levels of water, 34:19.489 --> 34:22.229 right about here, in terms of bars. 34:22.230 --> 34:25.860 By the way, the bars would mean how much pressure do I have to 34:25.860 --> 34:29.490 exert on the soil in order to see the water come out of it? 34:29.489 --> 34:33.899 So this would mean that I'd have to exert a pressure of 1000 34:33.902 --> 34:38.092 atmospheres here to squeeze any water out of the soil. 34:38.090 --> 34:40.390 So this would be really dry. 34:40.389 --> 34:42.989 This would be 10 atmospheres here. 34:42.989 --> 34:47.719 And up here the water is draining away freely. 34:47.719 --> 34:52.099 So this basically is the water which is available to the 34:52.101 --> 34:52.821 plants. 34:52.820 --> 34:56.030 It's between about 10 atmospheres of pressure and 34:56.027 --> 34:59.967 about 1/10^(th) of an atmosphere of pressure, right here. 34:59.969 --> 35:03.179 And that's associated with whether you're dealing with 35:03.177 --> 35:05.717 soils which are very fine and claylike-- 35:05.719 --> 35:09.339 so they have fine particles and small pores-- 35:09.340 --> 35:14.880 or whether you are dealing with soils that are gravely or sandy 35:14.882 --> 35:16.852 or things like that. 35:16.849 --> 35:22.539 So what the plant does is it puts its roots down into the 35:22.538 --> 35:28.428 soil, and it's going to suck that water out of the soil. 35:28.429 --> 35:32.069 Now I don't know if any of you have ever stood on the edge of a 35:32.072 --> 35:35.722 pool and tried to suck the water from a swimming pool up a tube 35:35.717 --> 35:38.007 which is only as tall as your body; 35:38.010 --> 35:39.670 okay, less than 2 meters. 35:39.670 --> 35:40.990 It's hard. 35:40.989 --> 35:42.759 Your cheeks really hurt. 35:42.760 --> 35:44.540 And, in fact, you can't do it very well. 35:44.539 --> 35:50.299 Most of us can deal all right with the level of the latte or 35:50.300 --> 35:54.890 the milkshake, but the swimming pool is hard. 35:54.889 --> 35:58.759 I now want you to think about a Redwood or a Doug fir that is 35:58.759 --> 36:02.819 going to put its roots down into the soil and suck that water up 36:02.822 --> 36:03.792 100 meters. 36:03.789 --> 36:06.809 > 36:06.809 --> 36:08.569 It's not easy. 36:08.570 --> 36:14.350 There has to be tremendous negative pressure maintained, 36:14.349 --> 36:19.149 continuously over that 100 meters, to pull that water up to 36:19.146 --> 36:23.216 where a leaf can use it, to combine with carbon dioxide, 36:23.224 --> 36:27.194 using the energy from the sun, to photosynthesize 100 meters 36:27.192 --> 36:28.332 off the ground. 36:28.329 --> 36:29.639 Okay? Not simple. 36:29.639 --> 36:32.339 So how do they do it? 36:32.340 --> 36:37.710 Well here's a leaf, and here's the business end of 36:37.706 --> 36:41.426 the leaf, right here, the stoma. 36:41.429 --> 36:45.059 There are some guard cells here that are regulating the diameter 36:45.056 --> 36:45.916 of the stoma. 36:45.920 --> 36:50.360 There's carbon dioxide coming in, and the oxygen is coming 36:50.362 --> 36:50.832 out. 36:50.829 --> 36:53.499 Here's the delivery system over here. 36:53.500 --> 36:55.100 We've got the xylem and the phloem. 36:55.099 --> 36:57.229 This is the vascular bundle. 36:57.230 --> 36:59.830 And the question is, how do they do it? 36:59.829 --> 37:04.109 Well the transpirational pull is being caused by the water 37:04.114 --> 37:06.824 that evaporates inside the leaves. 37:06.820 --> 37:07.880 Okay? 37:07.880 --> 37:11.630 So if we go back to this, you should think of water that 37:11.634 --> 37:14.984 is going to evaporate and go out of the stoma-- 37:14.980 --> 37:19.640 and it's coming off of these cells right here, 37:19.639 --> 37:25.699 next to the xylem and the phloem--and it will cause, 37:25.699 --> 37:27.499 as the water is evaporating from the stoma, 37:27.500 --> 37:31.170 it will cause the water surface in the stoma to pull back into 37:31.172 --> 37:34.032 pores in the cell walls-- well it's not from the stoma, 37:34.027 --> 37:37.697 it's actually from the cell, inside the leaf--and there it 37:37.697 --> 37:40.837 will form kind of a concave meniscus. 37:40.840 --> 37:44.000 But it's got very high surface tension--and this is back to 37:43.996 --> 37:46.336 L.J. Henderson; water has these amazing 37:46.336 --> 37:47.016 properties. 37:47.018 --> 37:48.978 Water has amazing surface tension. 37:48.980 --> 37:53.000 Water can climb up the edge of a glass. 37:53.000 --> 37:54.840 Okay? 37:54.840 --> 37:57.570 And that's caused by the hydrogen bonds between the water 37:57.565 --> 37:58.145 molecules. 37:58.150 --> 38:00.980 They have this beautiful little, kind of Y-shaped 38:00.976 --> 38:03.916 structure, and they readily form hydrogen bonds. 38:03.920 --> 38:08.920 And actually liquid water is this beautiful set of sheets of 38:08.918 --> 38:13.748 these layers of molecules that have formed these bonds. 38:13.750 --> 38:17.290 So that surface tension pulls the concavity back out. 38:17.289 --> 38:19.019 Okay? 38:19.018 --> 38:22.628 So the combined force that's generated by billions of these 38:22.628 --> 38:26.318 things is strong enough-- this should be 'lift' not 38:26.322 --> 38:30.512 'life'--to lift water from the roots up 100 meters. 38:30.510 --> 38:35.270 Now if you're going to do that, boy do you have to build a heck 38:35.271 --> 38:37.671 of a straw; and that's what xylem is. 38:37.670 --> 38:37.930 Okay? 38:37.932 --> 38:41.042 The xylem vessels that will transport the water have to have 38:41.036 --> 38:42.296 very small diameters. 38:42.300 --> 38:44.800 They have to be built very strongly, 38:44.800 --> 38:47.070 because otherwise the water cone is going to be broken by 38:47.072 --> 38:48.812 cavitation, and as soon as it's broken by 38:48.813 --> 38:52.313 cavitation, the leaves on the top dry out 38:52.307 --> 38:53.227 and die. 38:53.230 --> 38:56.400 So cavitation is a big problem; that's the formation of a 38:56.396 --> 38:57.806 bubble, inside the xylem. 38:57.809 --> 39:01.859 39:01.860 --> 39:05.150 Okay, that was a little bit about the physiology of how 39:05.153 --> 39:06.073 plants drink. 39:06.070 --> 39:09.170 It's more complicated than that, but I think that I have 39:09.170 --> 39:12.270 been able at least to illustrate the problem to you, 39:12.268 --> 39:16.148 and I think I have shown you that the physiological problem 39:16.148 --> 39:20.088 posed by the environment has been solved by the evolution of 39:20.094 --> 39:24.124 xylem and phloem; which happened about 3 to 400 39:24.119 --> 39:28.539 million years ago, and has since been perfected to 39:28.543 --> 39:30.173 a great degree. 39:30.170 --> 39:34.590 If you go out now and you're doing work in the short-grass 39:34.594 --> 39:36.534 prairie, or in the long-grass prairie, 39:36.529 --> 39:39.179 for that matter-- Mindy Smith works in the Kanza 39:39.179 --> 39:42.429 Prairie in Kansas, and in South Africa--and you do 39:42.427 --> 39:45.757 a section through the soil, you can see that a lot of the 39:45.755 --> 39:48.375 life of plants, and a lot of both their 39:48.375 --> 39:52.715 individual ecology and their competitive relationships with 39:52.724 --> 39:55.734 other plants, is actually being mediated by 39:55.731 --> 39:58.241 where their roots are foraging for water. 39:58.239 --> 40:01.249 Some of them can go deep, some of them stay shallow, 40:01.251 --> 40:04.801 and they partition that soil environment into different areas 40:04.795 --> 40:06.975 that they are sucking water from. 40:06.980 --> 40:08.820 By the way, the earthworms are also partitioning it. 40:08.820 --> 40:12.200 There are some that up here and some that are down there, 40:12.197 --> 40:14.367 and some that move back and forth. 40:14.369 --> 40:17.389 So there are some organisms, some plants, 40:17.385 --> 40:20.245 that are really extreme competitors. 40:20.250 --> 40:22.620 Eucalyptus trees from Australia, and Casuarina trees, 40:22.619 --> 40:23.869 which come from Northern Australia, 40:23.869 --> 40:26.279 New Guinea and the Solomon Islands, 40:26.280 --> 40:28.130 have been introduced around the world. 40:28.130 --> 40:31.240 So I have been in a field station in Corsica, 40:31.237 --> 40:33.567 surrounded by Eucalyptus trees. 40:33.570 --> 40:36.100 I've been on the Berkeley Campus surrounded by Eucalyptus 40:36.097 --> 40:36.457 trees. 40:36.460 --> 40:39.240 I have been in Central Uganda, surrounded by Eucalyptus trees. 40:39.239 --> 40:41.889 People have just planted these things all over the world, 40:41.885 --> 40:44.575 and boy are they good at sucking water out of the soil. 40:44.579 --> 40:46.569 And, in fact, what they'll do is they'll suck 40:46.570 --> 40:48.880 the water table down to where they will kill off any 40:48.880 --> 40:51.670 competitors, because they've just made a 40:51.666 --> 40:54.576 desert out of the upper layer of soil. 40:54.579 --> 40:56.469 Casuarina does much the same thing; 40:56.469 --> 40:58.709 and Casuarina also has the advantage that it can fix 40:58.711 --> 41:01.221 nitrogen in its root nodules, and so it can grow in places 41:01.217 --> 41:02.667 that many other things can't. 41:02.670 --> 41:06.320 So these things spread quite well. 41:06.320 --> 41:08.580 If you were to do this kind of section, 41:08.579 --> 41:12.009 not in a short-grass prairie, but if you were to go into the 41:12.012 --> 41:15.682 Kalahari Desert and look at how far down an Acacia tree can send 41:15.677 --> 41:18.567 its roots, it'll go down 46 meters. 41:18.570 --> 41:19.500 Okay? 41:19.500 --> 41:24.820 Well 46 meters is over 150 feet deep, down, and it's going to 41:24.815 --> 41:27.735 suck that water up into a tree. 41:27.739 --> 41:31.809 which is probably 20 meters high, and in the process it's 41:31.811 --> 41:36.251 going to drive the water table down to where many other things 41:36.246 --> 41:38.206 can't reach it anymore. 41:38.210 --> 41:41.560 So these physiological adaptations are things that not 41:41.561 --> 41:45.481 only have consequences for the survival and the reproduction of 41:45.481 --> 41:49.161 the individual organisms, they also have consequences for 41:49.157 --> 41:51.507 everything which is living around them, 41:51.510 --> 41:56.140 and the ones that can do it better hurt the ones that can't 41:56.141 --> 41:57.421 do it so well. 41:57.420 --> 41:59.280 If we go into the environment of estuaries, 41:59.280 --> 42:02.440 42:02.440 --> 42:04.020 the plants that are growing in estuaries, 42:04.018 --> 42:07.148 like these mangroves, have the problem that is 42:07.150 --> 42:11.120 basically caused by the fact that estuaries are one of the 42:11.115 --> 42:13.895 most productive ecosystems on earth. 42:13.900 --> 42:16.590 And there's just a tremendous amount of leaf litter, 42:16.590 --> 42:19.690 and there are algae living in the water, 42:19.690 --> 42:22.500 and the leaves and the dead algae and whatnot fall down to 42:22.498 --> 42:24.568 the bottom and they start to decompose, 42:24.570 --> 42:27.280 and the bacteria that are decomposing them use up the 42:27.280 --> 42:27.750 oxygen. 42:27.750 --> 42:31.730 And so if you take a sample down, through the mud, 42:31.730 --> 42:36.150 the soil, at the bottom of one of these mangrove estuaries, 42:36.150 --> 42:40.140 you will hit a layer that is just black. 42:40.139 --> 42:42.359 It is a very reducing environment. 42:42.360 --> 42:45.310 It's got hydrogen sulfide, stinks like rotten eggs, 42:45.306 --> 42:48.246 and if you're a root of a plant, living down there, 42:48.253 --> 42:51.203 you've got a problem, because you need oxygen. 42:51.199 --> 42:55.129 You are a multi-cellular plant, and all of your cells have 42:55.125 --> 42:57.875 evolved in an oxygenated environment, 42:57.880 --> 43:01.040 at least in your ancestors, but now your ecology is asking 43:01.041 --> 43:04.371 you to grow in a place where in order to feed your plant, 43:04.369 --> 43:07.859 you have to probe into what is an extremely dangerous 43:07.860 --> 43:10.530 environment; it doesn't have any oxygen in 43:10.530 --> 43:10.770 it. 43:10.768 --> 43:16.178 And so mangroves have these morphological adaptations. 43:16.179 --> 43:20.159 Their roots stick up little siphons-- 43:20.159 --> 43:25.899 okay, they have snorkels--so that the roots can suck oxygen 43:25.898 --> 43:28.838 down, from above, and get a flow of 43:28.835 --> 43:32.085 oxygen coming down that will help them out. 43:32.090 --> 43:33.970 Remember, the roots don't have chloroplasts. 43:33.969 --> 43:35.429 They're down in a dark environment. 43:35.429 --> 43:37.339 They can't make their oxygen endogenously, 43:37.342 --> 43:39.492 they've got to get it out of the atmosphere. 43:39.489 --> 43:41.509 So this is what happens. 43:41.510 --> 43:45.030 43:45.030 --> 43:47.810 Okay, so I've done this fairly quickly. 43:47.809 --> 43:51.049 But the point of it is that both in plants and animals, 43:51.050 --> 43:54.790 and endotherms and ectotherms, anything you look at, 43:54.789 --> 43:58.889 any organism, from a virus and a bacterium, 43:58.889 --> 44:00.799 on up to a blue whale and a redwood, 44:00.800 --> 44:02.050 that you look at on the face of the earth, 44:02.050 --> 44:05.140 is going to be loaded with physiological and morphological 44:05.144 --> 44:07.194 adaptations, and these things are 44:07.188 --> 44:10.498 determining the range of conditions and resources under 44:10.503 --> 44:12.963 which they can survive and reproduce. 44:12.960 --> 44:16.040 So if we look at that, just as a general conceptual 44:16.036 --> 44:20.096 problem, we can summarize it in the form of an ecological niche. 44:20.099 --> 44:21.359 Okay? 44:21.360 --> 44:24.900 So if you look at the performance of that species, 44:24.900 --> 44:27.930 with respect to some environmental variable-- 44:27.929 --> 44:31.469 this could be temperature or oxygen concentration or pH-- 44:31.469 --> 44:36.609 there will be a range of that environmental variable within 44:36.614 --> 44:39.814 which the organism can reproduce, 44:39.809 --> 44:43.959 there'll be a slightly broader range within which it can grow, 44:43.960 --> 44:48.080 and there will be an even broader range within which it 44:48.081 --> 44:49.151 can survive. 44:49.150 --> 44:53.570 So it can explore parts of the environment within which it 44:53.572 --> 44:58.382 cannot grow, and it can grow in parts of the environment within 44:58.382 --> 45:00.712 which it cannot reproduce. 45:00.710 --> 45:05.980 But there will be a core where life is easy and it can carry 45:05.981 --> 45:07.771 out its lifecycle. 45:07.768 --> 45:11.048 For example, here's a two-dimensional niche. 45:11.050 --> 45:12.670 This one is just measuring survival. 45:12.670 --> 45:14.480 So these are actually experimental data. 45:14.480 --> 45:18.660 This is salinity down here and temperature over here. 45:18.659 --> 45:21.859 And it's for a sand shrimp, Crangon. 45:21.860 --> 45:27.040 And basically what this is telling you is that it has zero 45:27.041 --> 45:32.771 mortality in a salinity range of about two-thirds sea water, 45:32.768 --> 45:34.788 up to slightly over full sea water. 45:34.789 --> 45:38.199 This is full sea water right here, about 35 parts per 45:38.197 --> 45:38.917 thousand. 45:38.920 --> 45:44.800 And up here it's showing you that it will start hitting some 45:44.804 --> 45:50.394 mortality at about 25, and some mortality at about 10. 45:50.389 --> 45:51.619 Okay? 45:51.619 --> 45:54.379 So you could imagine carrying this process further, 45:54.380 --> 45:56.190 putting a third dimension on, putting a fourth dimension on, 45:56.190 --> 46:00.670 and having the organism tell you in what part of the 46:00.666 --> 46:05.756 potential range of conditions on the planet can it live. 46:05.760 --> 46:08.830 And there are interactions--I mean, an interaction will be any 46:08.833 --> 46:10.903 time there's a curve in the slope here. 46:10.900 --> 46:12.190 Okay? 46:12.190 --> 46:18.550 So the range of salinities at which it has no mortality is 46:18.550 --> 46:20.540 affected, to a certain, 46:20.543 --> 46:22.563 and in this case fairly slight degree, 46:22.559 --> 46:23.689 by the range of temperatures. 46:23.690 --> 46:27.100 46:27.099 --> 46:32.229 So the niche is an N-dimensional hyper-volume. 46:32.230 --> 46:36.030 We just saw a two-dimensional one here, and I told you that 46:36.029 --> 46:38.839 could be extended to three, four, five, ten, 46:38.844 --> 46:41.404 however many you wanted to pack on. 46:41.400 --> 46:45.760 That is a mental tool, and it was invented by humans, 46:45.760 --> 46:49.140 actually in this building, to understand how organisms 46:49.144 --> 46:52.024 evolve to deal with environmental problems. 46:52.018 --> 46:52.518 Okay? 46:52.521 --> 46:56.931 So it's an attempt to extract key features. 46:56.929 --> 46:59.679 You can think of those dimensions both as abiotic and 46:59.684 --> 47:00.324 as biotic. 47:00.320 --> 47:03.280 So the abiotic ones usually are things like temperature, 47:03.275 --> 47:05.525 salinity, humidity, oxygen, carbon dioxide, 47:05.532 --> 47:05.912 pH. 47:05.909 --> 47:09.249 The biotic ones are predators, competitors, 47:09.250 --> 47:13.540 pathogens, mutualists; and the biotic ones co-evolve. 47:13.539 --> 47:13.799 Okay? 47:13.800 --> 47:17.040 So the niche of one species is going to be co-evolving with the 47:17.038 --> 47:18.498 niche of another species. 47:18.500 --> 47:22.970 So you should think of these things as changing through 47:22.972 --> 47:24.632 evolutionary time. 47:24.630 --> 47:27.390 All the biological evolution in the world isn't going to do very 47:27.393 --> 47:29.853 much to the distribution of temperature on the planet. 47:29.849 --> 47:32.679 So it's not as though the biotic variables are going to be 47:32.679 --> 47:35.509 causing a co-evolutionary response in the abiotic ones; 47:35.510 --> 47:36.200 they won't. 47:36.199 --> 47:39.779 Those things are just things that are imposed on the process. 47:39.780 --> 47:42.250 But if you have a predator/prey interaction, 47:42.250 --> 47:46.090 or a parasite/host interaction, or two competitors dealing with 47:46.092 --> 47:48.922 each other, the area of the niche 47:48.920 --> 47:52.170 hyper-volume, within which each of them can 47:52.173 --> 47:54.983 reproduce and survive, is going to be changed by their 47:54.976 --> 47:55.546 co-evolution. 47:55.550 --> 47:58.660 47:58.659 --> 48:02.929 So what that means is that niches aren't pre-existing 48:02.929 --> 48:06.299 molds, out there, into which organisms are 48:06.295 --> 48:07.195 poured. 48:07.199 --> 48:11.069 They are the products of an evolutionary play that is 48:11.070 --> 48:14.940 creating the theater while it's writing the roles. 48:14.940 --> 48:19.020 And while the play is running, evolution is rewriting the 48:19.021 --> 48:21.101 script, it's remodeling the actors, 48:21.103 --> 48:24.673 it's putting in new actors, it's redesigning the sets, 48:24.670 --> 48:27.350 and it's renovating the theater. 48:27.349 --> 48:30.299 It's a very long running play, it's got a lot of characters. 48:30.300 --> 48:33.640 48:33.639 --> 48:37.349 So if you think of a niche as static, essentially what you're 48:37.347 --> 48:40.617 doing is you're just taking a snapshot out of a video, 48:40.621 --> 48:42.601 or a snapshot out of a film. 48:42.599 --> 48:43.399 Okay? 48:43.400 --> 48:46.380 They're really dynamic things. 48:46.380 --> 48:50.410 Okay next week, next time, we will start with 48:50.409 --> 48:55.359 population growth and the issue of what density does to 48:55.355 --> 48:57.365 population growth. 48:57.369 --> 49:01.999