The Rules that Govern Life on Earth - with Sean B Carroll

Wow if if I could just sort of summon the ghosts of the people who stood here it's a spine-tingling place for a scientist especially a scientist with a keen interest in history so thanks to the Royal Institution for having me and thanks to all of you folks for coming out on a Wednesday night to hear about science and kids we're gonna see some animals and I might even ask you a couple of questions so be on your toes okay all right so I am going to talk about the Serengeti rules we're gonna get out on the Serengeti in a couple of minutes but I want to give you some context it was the summer of 2014 I had just finished work on a film for the Smithsonian channel in the US on mass extinction and in addition to getting to know some of the geologists that had studied major events in the past I got to know several ecologists and went around parts of the world with them and I began to appreciate that even some highly protected places like say Yellowstone National Park in the United States we're starting to show some issues and if I thought I was began to worry if some of the most protected places were having problems what was that going to say about the rest of the world and like you I saw headlines like this one talking about what had happened to the world's wildlife over the last 40 to 50 years and other headlines about for example paving a highway right through the middle of the Serengeti the world heritage site in Panza Nia and I thought well two things I'd never been to the Serengeti despite a lifelong dream of going there so I thought it was probably better be time to go and I thought if I was gonna go I should take my family so I did six of us shared a vehicle for a couple of weeks and when I went I really went with a combination of excitement that is going to go to a place I always dreamed dreamt of going but a little bit of anxiety from those headlines what would I find when I got there so I spent just a few minutes to show you what we found when we got there this is we're just posing outside the Serengeti entrance gate I think the first thing that surprised me was that was the entrance gate yes one of the great wildernesses of the world welcome from looking over sort of the rooftop of the vehicle you can see it's a gravel road going into this grassland the grass is maybe at this stay this is late June not quite maybe knee-high but you can see it's fairly brown and as we drove in I started getting a little bit worried because we're looking left and we're looking around we're looking on the horizon and we do spot you know hopefully you can see our there we see a lioness but you know all we can see is the you know her back against that grass and I'm thinking you know we're in trouble here I'm the only biologist in my clan and they're not gonna want to do this for days on end if that's what we're gonna see of wildlife but we drove further in and we started to see little streaks of green and a few acacia trees and came up over a bend and then this is what we encountered just little footage these are home movies we wound up being just surrounded by zebra a couple thousand stripes in all directions couple thousand zebra there was a waterhole there that they had come down to swim in and and to drink from and then on the horizon a troop of elephants coming down to that same waterhole and so here we were just this magnificent 360 degree view and from that moment on I had no worries about the Serengeti because it offered up an unending canvass of animals of all sizes and shapes and colors from sturdy warthogs to lounging hippos which they're particularly good at sleek impala majestic giraffes i my wife and I were so enchanted with giraffes I made them stop the vehicle every time we came upon a giraffe which was probably a couple hundred stops over over a week never got tired of looking at them and then on one of our last days this beauty shared in a private evening and morning with us while she dined on a gazelle that she had stuffed up in a tree so it was more than I expected I thought I had really been prepared from everything I had read or TV shows I had seen but it was it really topped my expectations and as I sort of gazed out over this landscape and all this wildlife over the first few days a bit of an unsettling thought occurred to me which which was and I was awestruck but I didn't understand what I was looking at I'm a professional biologist I didn't understand why or how the Serengeti was the way it was and that's you know a bit embarrassing for me because I've actually spent my entire career as clive mentioned studying animals and actually studying how they form even studying how they get stripes in spots but i've been doing that mostly through a microscope and seeing sort of the invisible things that happen inside animals that build their bodies and build their body parts and build different kinds of animals mostly small creatures like butterflies and things like that so what really had me stumped were the numbers of animals i've been fortunate to be really nice interesting places in the world on many continents but i was just floored by the number of animals that i was looking at on the serengeti i I didn't I didn't know why there would be different numbers of animals no whatsoever well I did because I've studied biology a long time I know a few things about what at least goes on inside animal bodies and one thing I did know is that you know they're inside animal bodies there's lots of reactions going on lots of processes going on so I began to think about well what do we know about the internal world of animals and what can we could that possibly explain what we know about so the external world of animals so I didn't know why there were so many wildebeest on the Serengeti I didn't know why they were so few topi that are virtually about the same size well what I did know was that all the substances in animal bodies and in our bodies are regulated the amount of everything fats like cholesterol salts like calcium hormones like estrogen enzymes that digest our food all maintain in particular ranges and in different ranges over many many many different order of magnitude and that generally even the number of cells in our body are maintained red cells white cells kidney cells gut cells etc they're maintained in a particular range and that one of the major quests of biology over the last 50 60 years particularly the tribe I belong to so called molecular biologists has been to look at these processes and understand well I'll call the rules of regulation to really understand how life works how we are the way we are we need to understand the rules that for example regulate our bodies now how have scientists been doing this so we've generally been doing it by trying to find to use some sports terms so the key players in any particular process in this case molecules that regulate a process and once we have identified those key players we sort of see how do they play with other things how do they play with other molecules for example and figure out those rules that govern their play and that knowledge has been tremendous power because by understanding precisely what regulates processes in our human body that has guided all sorts of advances in medicine and I think it's not an exaggeration to say a revolution in medicine because that knowledge allows us when these things fall out of whack when regulation is somehow awry and really most diseases that I could think of or that you can think of are really problems with regulation where too much or too little of something is being produced give you a couple familiar examples and we use drugs to restore things that are missing or reduced or to fix sort of broken links in these regulatory processes we give insulin to diabetics shown up here in the upper left a component that's missing that we or reduce that we need to replace in other cases we exploit the logic for example how cholesterol is regulated in our bodies and that's what the whole class of drugs known as statins do all the lipitor is meth occurs etc that have reached the market in the last thirty years and have had a dramatic effect on cardiac medicine vastly reduce the incidence of heart attacks and strokes and the death rate due to cardiac events so we've learned an awful lot about how regulation works and in the new book I tell the stories of some of the pioneers who figured out these rules of regulation in the human body but the central question that I want to focus on in my talk tonight is about life on a larger scale not about the number of molecules or cells but really the number of animal bodies and the question I want to ask is how are the numbers of animals and plants regulated out there in nature I want to even ask the question are there rules that govern life at larger scales well it turns out if there weren't we wouldn't be here I wouldn't have a book and you'd have the night off ok so this is what we're going to explore so for most of the talk I'm going to talk about some of the pioneers who've gone out into the world and asked this question I think largely stories that are unknown people that are unknown but they're enormous ly important figures in in biology and then in the last part of my talk in the same way that we've used this knowledge of the rules of regulation in the body to improve medicine how can use the rules we learn about how nature works on a larger scale to preserve or even cure ailing ecosystems so to start this adventure I want to give you a little history of the Serengeti I thought you might enjoy the put in perspective the Serengeti was it went through various stages in the development as a National Park but it really what tourism was not a big deal through the first half of the 20th century and some of the first people that go into the Serengeti and really take a serious look around were biologists and one of the first things they wanted to do and confront it you can imagine with all that wildlife you know scientists count things right how many things are here so what did they do well I'm going to show you clips from a film about the first aerial survey of wildlife in the Serengeti so you can see how this was done in 1958 by two German zoologist Bernard and Michael jimick and this is a clip that's going to show a little bit of their methodology so here's there's bernard on the left and his son Michael on the right and they're plotting their course in their fancy airplane pretty cool looking plane and they and two other spotters are going to climb into this plane generally with the doors open so they have a nice clear view and take off and fly low and slow over the Serengeti and here's complex computer graphics in films of the 1950's showing you their paths back and forth back and forth okay so what's that look like let's go counting with the gym --ax ready 1 2 3 4 5 6 7 8 that's exactly what they're doing at about 120 miles an hour they're counting all the wildebeest in this picture okay and as you can see the wildebeest are not standing still so they did this day after day in this grid pattern but they're not just counting wildebeest they're counting all the large mammals they can see and count by eye from from whatever altitude that they feel safe to fly it which is pretty low so what did they come up with this is the results of their survey January 1958 they came up with ninety nine thousand four hundred and eighty-one wildebeest okay not four eighty two not four eighty fifty-seven thousand one hundred ninety-nine zebra okay and with further sort of Teutonic precision 5,000 or so topi eighteen hundred buffalo just sixty elephants so elephants were pretty scarce in those days still sort of a leftover a hangover effect of the ivory trade in earlier decades but in total three hundred and sixty six thousand large mammals now they admitted they said they might have missed oh maybe ten thousand out of the edges but they thought this was a pretty accurate survey they tried really hard to get the numbers right they wrote a book of the same name as their movies Serengeti shall not die and they wondered aloud you know were there enough plains and mountains and river valleys and Bush areas to maintain these last giant herds still in existence they were worried that the number of wildlife was so astonishing to them did the Serengeti really have enough space enough food enough water for all of these animals oh really in a within a few years an answer to that question would start to materialize and it wasn't the answer that the jimick see the expected or you might think feared okay and those answers started to materialize when a young student from Oxford University named Tony Sinclair went as an undergraduate still in his undergraduate years to the Serengeti now he went with Oxford faculty the purpose was primarily to study birds but they quickly drafted him into the aerial survey going on that year and in the course of that aerial survey Tony and the others conducting the survey turned up a mystery and the mystery concerned the number of Buffalo in 1961 several years earlier they've counted 16,000 Buffalo in the Serengeti but that number it somehow jumped in 1965 to 37,000 what's going on with the Buffalo so scientists said to Tony who is now interested that maybe he could do his doctoral work on the Serengeti would you like the study of the Buffalo and he's sure he was enchanted with the Serengeti he thought it would be a great question to pursue so over the next dozen years or so first triggered by the Buffalo Tony focused all of his research on the Serengeti and he addressed a few general questions and here's Tony by the way with with a buffalo kids I think that's a tranquilized Buffalo or else that's really not the way to study Buffalo on the Serengeti that's a little too close he looks like he's being a little cautious but that's way too close okay so what he wanted to ask was why were the Buffalo increasing if indeed they were increasing and then really what explained the great differences in the number of different kinds of animals why were there so many of one kind and fewer of another why were there so many of any kind and really what was in in Tony's heart was was to wanting to know why is the Serengeti the way it is because it was such a amazing spectacle of this great diversity of Wildlife these giant herds the only place like it left on the planet so he tackled this Buffalo mystery first by continuing the aerial surveys to see how many Buffalo were in the Serengeti and he confirmed that the Buffalo population was growing in fact it kept growing from 16,000 and 1961 37,000 first save survey he participated in then into the 50,000th over in the next few years so the population was was growing so that was a mystery why if you might think sort of all of a sudden were there more buffalo in the Serengeti so right so I see some some youngsters probably taking science classes right now so I'm gonna give you a shot at this why might there be more Buffalo in the Serengeti give me one idea fire away you think the Buffalo might have might have killed off other animals well they certainly did reproduce more so that's a really important thought that's one possibility and what about another great maybe they weren't being hunted maybe they were maybe they were better protected another good idea any other ideas okay so this is what go get far away right here in front sorry missed you might have come in from somewhere else yep great look at that four hypotheses right there oh sorry kids I'm blinded by the light so thank you for that help I can I can barely see past the fruit rows there you go where's another hand Center and the gallery just just shout it down I can't see you another idea right right great so logical possibilities that's what you all gave me right there logical possibilities something could be going on so let me tell you let me show you the logic that Tony Sinclair worked through he thought he had to answer a really basic question which was maybe there were more Buffalo because there was more food all right wouldn't that give you more Buffalo - there was just more food but looking through the Serengeti he had been flying over it year after year it seemed like you know the Buffalo like these sort of woodland grassland sort of areas it seemed like the grass was growing there seemed to be as much food as any time before so he thought no that's probably not the answer now he did think of what a couple of you folks brought up he thought maybe there's fewer predators for whichever reason either a natural cause or maybe because humans were taking them out but as it turns out two things that Tony observed first of all most Buffalo didn't die from predators okay so that wasn't very common that Buffalo would be taking down most Buffalo when they died they died of something else and secondly counts were going on of predators and for example lions are the only things big enough to take down Buffalo and lions were not only fewer they were actually increasing in this time so we had to eliminate that possibility and this is exactly the way scientists work think of all the possibilities and start to work your way through them and we neither rule them in or rule them out see what you can do to exclude them so he then thought there was another possibility which none of you brought up and I didn't think of either when I first read this story and that is the possibility of disease then another thing that affects wild populations just like us is our diseases that can either reduce the ability to have babies or obviously cause death and Tony knew that wildlife got a lot of diseases Buffalo got a lot of diseases but there was one disease in particular that he was suspicious of and that was a disease called cattle plague or the German named render pass and it was well known in East Africa and well-known in the Serengeti because many times in the previous 70 or 80 years it had swept through the Serengeti now here's an important thing to think about it hit three different kinds of animals in the cattle that were being grazed by humans you know especially by the pastoral people Buffalo and wildebeest but not other animals and it was thought that the Buffalo and the wildebeest the wild animals were the reservoir for the virus meaning the virus was hiding out in the wild population and that the humans livestock human cows were getting sick from the wildlife well a vaccine became available in the early 1960s and a vaccination program was launched in East Africa and Tony thought maybe that vaccination program has had even though it's just cattle being vaccinated maybe that's had some spillover benefit to the Buffalo now how would he how do we check this out well if an animal or your IR is exposed to a virus our immune systems make something caused antibodies that can be measured in our bloodstream so Tony got blood samples from Buffalo age-matched them to the Buffalo populations and said ok is something going on with the exposure of Buffalo to virus in the Serengeti and the answer is his first Eureka moment something really big was going on that while older Buffalo had almost a hundred percent exposure rate to this virus Buffalo born after 1964 showed no exposure to the virus whatsoever so now he had a good suspect that this virus which could cause massive mortality massive death on the Serengeti a buffalo was disappearing from the Serengeti we also learned something else which was that was because of vaccination of cows so actually people had it upside down the virus wasn't in the wildlife the virus was in the cow so when you vaccinated the cows the Buffalo didn't get sick okay now he knew that the other animal that got sick from this virus was wildebeest and he started paying attention to the wildebeest so if the Buffalo were booming because this virus had been eradicated well then wouldn't the same thing be true of wildebeest right it's the Buffalo were benefiting from getting rid of this virus wouldn't the wildebeest be benefiting well here are the numbers the Tony got four wildebeest over the years that's a lot of wildebeest he almost couldn't believe it himself in the 1977 survey they calculated 1.4 million wildebeest okay a huge number over the 1960's so before we get into the explanation of why that is just imagine the reaction of the Jim exceed that maybe the Serengeti didn't have enough food and space for all those animals there's now a million more million plus more wildebeest alone in the Serengeti by 1977 there was plenty of capacity in the Serengeti what was happening was that virus must have been keeping that population down now to confirm his suspicions he still did the right experiments which was to get blood samples from those wildebeest of various ages and see about the exposure to rinderpest saw the very similar pattern to the Buffalo in fact no wildebeest born after 1963 had exposure to the virus so we had his explanation why were the Buffalo and the wildebeest booming in the Serengeti it's because a virus had been keeping them down now since he was studying the Serengeti so intensively as were several other scientists they were noticing other changes taking place in the Serengeti over this time so I'm going to give you three observations we're going to see whether that we can kind of connect the dots and figure out what's going on on the Serengeti so we know we've got more Buffalo we know we got more wildebeest well one other thing that was noticed was that there was less fire in the Serengeti if you looked compared to the early 1960s versus the early 1970s a lot less of the park was burning and those fires were less intense so those are percentage of burn areas and you can see easily cut in half across the park and more dramatically so in certain regions of the park so the Serengeti burns every year it's a natural phenomenon but the fires were covering less area and they were and they were less in intensity okay so less fire what else was going on well in certain parts of the park the census revealed there were more giraffes okay twice as many giraffes in 1976 in 1971 okay keep that in mind what else could they see going on in the Serengeti well it took a little longer to see the pattern but I'm going to show you photograph taken from the same point in the Serengeti over 30 years and what it reveals is more trees first photographs taken on a shady day so you have to sort of pick out the acacia trees they're in the foreground but as you move to 1986 there are more trees 1991 more and then this is all filled in by 2011 now early on in the early 1980s they could tell there were more young trees you're looking at really mature trees here in the picture here on the lower right so for some reason more trees were growing in the Serengeti so let's see whether or not we can figure out that reason and connect it with the other observations I gave you so what's happened on the Serengeti well first we got rid of this virus that led to more wildebeest what a wildebeest do they eat grass and when they eat that grass they actually mow it down from about 30 centimeters to about 10 centimeters high and so that means there's going to be less and shorter grass left over when the Serengeti are done grazing that grass is the fuel for the fires in the Serengeti so with less fuel you're gonna have less frequent and less intense fires you know what does fire do on the Serengeti well one thing that fire does in the Serengeti is it burns up young trees so with less fire they're now more trees well what's the effect of more trees well if you happen to like grazing the tops of acacia trees like giraffes you've got more food so this change in the Serengeti this elimination of this virus set in motion this whole sequence of events where more wildebeest mowed down the grass reduced the number of fires there was now more tree cover more giraffes for feeding and a lot more effects because for example that greater tree cover meat there's more places for birds to nest there's actually also more cover for the Predators so these changes have many effects on other kinds of creatures so what Tony became to appreciate is that and this may be contrary to what you've seen on TV I sort of imagine if you see if you see a film about the African savannah within the first two minutes you're gonna see a cat chasing a gazelle or a zebra am i right okay is that what makes the Serengeti the way it is no but Tony Sinclair would say what makes this Serengeti the way it is is a million lawnmowers it's 1 million wildebeest just chewing grass and they move in a 600 mile circuit around the Serengeti in the course of a year and by chewing that grass down they have changed the habitat for so many other creatures shorter grass not only is means there's less fire but that shorter grass creates better habitat as it turns out for butterflies the more trees as I told you needs is better for the bird life greater diversity of birds more cover for predators it's the sarin it's the wildebeest mowing the Serengeti that make the Serengeti the way it is and a little later we'll ask you whether you think they should put a paved highway through the migration route so scientists ecologists have a term for an animal that has such an important influence on the whole community to which it belongs and that's my first Serengeti rule of the night I'm gonna give you four and the first rule borrows a little bit from from George Orwell but for a long time biologists sort of looked at a at a community and sort of thought that well everybody was a component and sort of everything was equal well some animals are equal but some animals are more equal than others ok and we call these keystone species keystone species they regulate community diversity they have a disproportionate effect on the diversity of creatures that live in a given place the name comes from not from the Serengeti this was discovered somewhere else not by Tony Sinclair in fact in a really different system it was discovered by Bob Paine an ecologist working off the coast of Washington in the USA looking at starfish and the communities they belong to and what Bob Paine found that the starfish were Keystone's in that community the idea he came up with in this little kind of manic diagram on the right is that if this species removed and he did the experiment of removing starfish the whole community collapsed just like if you remove the key stone from a Roman arch the arch collapses so he said so some species are much more important than others at holding together a community at the diversity of the community and he even did the experiments of removing other things in the community and showing that they didn't have any major effect so wildebeest are keystone species and Bob pain the same ecologist so again working off in tide pools on the Pacific Ocean coined another word to describe the phenomenon I just I described for you where one species has this sort of chain reaction effect through the whole ecosystem now if you think about food chains we describe a lot of the way the world works and is a is a series of food chains where plants provide the food for animals that graze on plants and then those animals provide the food for predators like lions and things like this and that when we describe each level of the food chain we call it a trophic level and what Paine described this sort of chain reaction as a trophic cascade a series of indirect effects rippling out from one particular species having a big impact on the rest of the community and that quickly gets this to our Serengeti rule number two so you're almost halfway home alright and that is that some species have really strong indirect effects on other species through trophic cascades this was incredibly surprising to scientists that wildebeest would affect the number of giraffes right who would suspect such a thing and there's some other examples I'll give you before I finished tonight okay so we've learned a little bit about what makes the Serengeti the way it is but you might be wondering what about what controls the wildebeest did they just keep right on growing without that virus around well the answer is no if they kept right on growing then basically East Africa would be a carpet of wildebeest and they'd probably be spilling out into the ocean so wildebeest are regulated - and what actually happened was that 1977 that 1.4 mil wildebeest was the peak year for wildebeest they leveled off at about a million a lower number okay and here's a curve so what's plotted on the left is how many wildebeest there are in different years and you'll notice a really steep growth of the wildebeest as I've telling you about up through about nineteen seventy seven and then they kind of declined a bit kind of overshot the mark really now I want to explain this pattern to you but in general as they asked the question about what regulates the wildebeest again kids now that what you've heard about Buffalo you could come up with these possibilities the world abuse can be regulated by the amount of food that's around or they could be regulated by who's eating them right and we call that bottom up from food or top down from predators regulation so think of a food chain like a pyramid here the wildebeest are in the middle of the pyramid they're eating plants they're eating grass but they are to some degree taken by predators so what controls the number of wildebeests are they kept in check by predators are they limited by food and before I tell you the answer to the wildebeest I thought it'd be interesting for you to know in general what's going on the Serengeti with other animals because I think I'll help you as it helped me understand the Serengeti as I looked at it so you've got this possibility of top-down and bottom-up regulation so which Serengeti Memo mammals are regulated in which way think of those storybook creatures that live on the Serengeti what do we know about how they're regulated well what we know comes from work by Tony Sinclair Simon M Duma Justin brashears and collaborators over a long period of time of observing what Serengeti animals die from okay so here's a graph you know you might be thinking okay but just study it because I it's one of the most informative little graphs I I've enjoyed in a long time so on the Left they're mapping the percent of animals that died from predation as a cause of mortality and on the right and the body size of the animals and look at the relationship these are the smaller Serengeti mammals the order B being the smallest look at that death rate from predation 100 percent okay.i times imagine you know what is an order be parent tell their young lar be about their future okay kind of kind of fill that in alright but look at the other end of the spectrum here elephants hippopotamus rhinoceros generally giraffes essentially zero predation it happens but it's so occasional makes no dent in the population and look at the relationship to body size these big animals are so big they've escaped the power of predators so now for everyone I think you probably may have to be under fifty to sort of get this comparison but I would describe this this is the James Dean live fast die young lifestyle okay and this is the more Marlon Brando eat all you can kind of lifestyle out here on the right and and what's going on here is that of course these animals yes they suffer a lot of predation but generally they do reproduce rapidly okay so they're keeping their numbers up by reproducing rapidly their small body size so they have lower requirements for food and they can reproduce more rapidly these animals really large they reproduce slowly takes a long time to get to sexual maturity gestation time as you know in the elephants the longest of any land mammal so this is a different lifestyle that says okay I'm going to escape predation but I'm really dependent upon food supply I need massive amounts of food every day okay and there's some animal sort of in the middle so where does the wildebeest land and careful observation shows that in fact the wildebeest are regulated by food it's the food supply that has the greatest effect yes some die from predation but that's not the major effect the major effect has to do the amount of food that's around okay and this is our third Serengeti rule many animals show this food regulated pattern this density regulated pattern okay so the regulation of a good number of species depends upon their density if your food regulated and that's true of Buffalo which don't turn generally die a bunch of predation it's true of elephants okay they're limited by their density by the amount of food that's available in this sort of way in fact elephants you know if there's a bad season a dry season there's not a lot of food there's even a feedback in the elephants hormonal e that suppresses reproduction so the don't have babies born in under bad conditions okay all right so why have I told you this all about the Serengeti all of these rules keystone species trophic cascades density regulation all of these rules were discovered somewhere else first I just thought it would be most enlightening easiest to grasp if I told you in terms of what's going on in the Serengeti in terms of these storybook animals but I've also told you these rules and dubbed them sort of the Serengeti rules because really almost every habitat in the world is the Serengeti from the tiniest little plant to the greatest forests to the deep ocean okay and because every place is a Serengeti with predators with things that eat plants we think with the plants themselves then these rules matter in each place and if we're going to intervene in ecosystems intervene in places we really need to know the rules of regulation just as we need to know the rules of regulation in the human body we need to know the key players in any community those species that regulate community structure we need to understand the rules that govern their play who eats whom are there trophic cascades operating and then if there's a problem we need to figure out what it might take to either replace what is missing or fix broken links in that ecosystem so let me in the last part of my talk illustrate for you in a three examples sort of putting these rules into practice so I told you even a tiny blade of rice could be a Serengeti let me explain you what I mean by that so here's a rice plant with a little insect called a plant hopper on it and I'm only going to show you this part of sort of the food chain which is these plant hoppers feed on these rice plants now you can imagine if you're a rice farmer and your livelihood or your family's food security depends upon having rice plants this presence of this bug might concern you and over the years you know the habit might have developed that if you see these bugs you might want to hit them with pesticide but in the early to mid 1970s some farmers particularly in Indonesia noticed a strange phenomenon when they hit their fields with pesticide the plant hoppers could go up 800 fold that's not a good thing okay they devastate the rice plants they caused this phenomenon called hopper burn so you see a lot more plant hoppers in the rice and you see this sort of brown out in the field where the essentially the plants have been sucked dry by the plant hoppers now how could this happen you give a pesticide and the number of bugs goes up now you'd think if the bugs were resistant to the pesticide they would just shrug it off and in fact that's what happened the bugs evolved resistance to the pesticide so it didn't affect them but why would the numbers go up well it took a little deeper investigation think about whether they may go up if anybody wants to take a guess why they might go up and shout it out go ahead you go bring your numbers because they'd be they'd be scared of the pesticide yeah so they're devoid they'd avoid things they try to get out of the way so you think they're clever clever plant hoppers avoid the pesticide I like that yeah that's right they got plenty of food look at that field right all the rice you can eat okay restaurants open all day long you're right go ahead I don't know if you give high-fives over here but we're gonna get me right there we're gonna go right to that even if there's an answer other people were holding this that's right on the nose again different possibilities what's happening well it turns out spiders prey on plant hoppers and a few other things do as well and what happens is the pesticide kills the spiders which are not resistant and without those spiders the plant hoppers go crazy and if you change your habits and don't spray the moment you see some plant hoppers it turns out the fields do much better so the practice of pest management has changed completely in these rice fields away from bombarding with pesticides and mortars trying to have natural enemies around and that means planning your fields differently planting some other plants around the give a hideout for things like spiders or planning some of those plants amongst your your rice so there's some population of spiders and other things around to control the plant hoppers so here's an example a little miniature Serengeti where the predator was missing because of something we were doing and the absence of that predator was causing problems I'll give you another example a lot bigger scale so I said every place is a Serengeti let's go back to a place I've been a number of times Yellowstone National Park in the American West the sort of iconic plant in the American West is the aspen tree here it is in the fall showing its fall colors but biologists started to notice there was something really strange about the aspen in Yellowstone and what was strange was that this is in the mid 1990s or so they're all pretty much very old if you looked at how old the different Aspirin were it turns out that sort of younger Aspen were just plain missing from the park they were pretty scarce so that meant that most of the Aspen were pretty old that meant that they were more vulnerable to disease more vulnerable to being blown over in storms and things like this so Yellowstone was losing its Aspen as were other parts of the American West now why might this be happening well I'll give you a picture that might be a hint okay so here's a biologist Bob ripple who worked on this standing in a field in front of some Aspen and you can see that that arc is queued up to perhaps ten feet or more high on all of those trees and the only creature that can chew that high on bark is elk so the suspected culprit of what was causing the aspen problem was that the elk were really chewing down the aspen why would that be happening why would that be happening you know for decades in Yellowstone well now that you know something about the Serengeti rules if the elk are grazing on these plants and being allowed to do that freely maybe that's the problem why would that be happening maybe there's a predator missing oh sorry I'm gonna give it to you well that's right and they like this they like this bark it's something they really like to eat but why would there be so many elk and the suspicion was that something was missing and what was missing from Yellowstone well we got to go to historical records and you remote you can always shout these out or mumble them it doesn't it's fine with me you can this is a this is an audience participation yeah here we go wolves exactly okay the wolves were exterminated from Yellowstone in the 1920 something that happened across most of North America so maybe the problem was just like on those rice plants we were missing the big predator in Yellowstone that controlled the number of elk well if that was right I wonder what would happen if you put Wolves back in the Yellowstone now there's a pretty big experiment it took 20 years of debate before it happened but it happened in 1995 here's the first wolf coming back into Yellowstone imported from Canada there's a lot of dignitaries carrying that for wolf okay so what happened what happened so I'm going to show you a little data about what we know and this is really an ongoing experiment so what do we know well the wolves a good number of wolves were introduced and they sort of established themselves and sort of bounced around a number in Yellowstone but there's been a pretty steady pattern of decrease in the elk in Yellowstone they reduced by more than half okay so maybe that would be a good prediction more if you got wolves in there a predator in there they're gonna they're gonna eat their favorite food and they're gonna eat elk okay what happened what else happened in the park well let's look what happened to browsing on Aspen drops dramatically what happens to Aspen height increases dramatically so yeah this is what's happening you put a predator in and the trees are now growing okay that's the insight of a trophic cascade that's what still shocks people that a presence of a predator influences what plants grow in a place and not just as it turns out Aspen as people looked around the park look at willow so this is a picture taken from the same vantage point in Yellowstone before the wolves were reintroduced and now after this is all willow growing in a foreground and willow is not only a favorite food for things like beavers it's what they make their dams out of so when Eva's see this will these willows they start making more beaver dams and there's a lot more beaver colonies in Yellowstone now than we're there before wolves are introduced so who would think that if you put more wolves for wolves back into Yellowstone you'd have more beavers crazy right welcome to biology welcome to the Serengeti rules okay so willows rebound and cottonwood rebound along the stream beds so reintroducing wolves has had a dramatic effect on the trees and vegetation in Yellowstone and then with things Weavers building dams with willows their bird life is changing the coyote patterns are changing all sorts of other animals are changing due to the presence of this keystone predator the wolf's okay now the other thing that I'd like you to take home tonight partly shown by this Yellowstone story is Nature rebounding this was measurable on a scale of a decade or less we're now two decades into the experiment well it's not the only time we've seen a dramatic effect and the effect that's really stunning and it's the last Serengeti rule the night is that nature is incredibly resilient and what I mean by that is it given a chance that might mean provided a proper habitat some protection from us time populations can rebound dramatically let me give you a handful of other examples that we know from other protected species here's that here's a handful from across say the last century in the late not 1800s we got down to as few as 20 elephant seals in the world there's 200,000 northern elephant seals today sea otters were almost exterminated by the fur trade by 1911 down to about a thousand animals there are over a hundred thousand today by the way sea otters are keystone species in that coastal communities of the Pacific Ocean they're responsible for the growth of kelp forests in the same way that Will's influence Aspen you can see northern huh Pacific humpback whales come back about twelve fold bald eagles back about twenty fold from low numbers in the late 1960s and wolf populations not just by introduced to Yellowstone but as they've spread across northern America are thriving in many areas but look at that a thousandfold recovery 10,000 fold recovery on the scale of perhaps a century but even dramatic discovery on the on the course of just a few decades nature is resilient but these are individual species that were protected because of for example Endangered Species Act Yellowstone took a lot of work to put just a small number of wolves into Yellowstone that's my that's manipulating single species what happens when a system is in really bad shape and you're not just missing one predator or one species and I want to finish tonight by telling you about a really important story going on in the world and it involves a park in central mozambique in southern southeastern Africa called Gorongosa National Park now Gorongosa in the 1960s was a tourist destination especially for so the jet setters kind of the Hollywood types because it had a massive concentration of Lion and elephants and Buffalo and hippos the things that tourists like to see kind of concentrated especially along this lake that's right in the center of the park the little map I'm showing you here on the right is showing you this Lake is sort of the central feature of the park and here's a little footage from those days I don't have the 1963 soundtrack which i think would have been pretty snazzy but you can see tourists riding around in VW buses Lions just kind of lounging near the wildebeest and playing around there were about 500 lions in Gorongosa National Park and here comes the terrible side of the story after Gorongosa sinned after mozambique's independence from Portugal a civil war broke out in Mozambique lasted almost two decades killed a million people displaced five million more and unfortunately Gorongosa was about the geographic center of that civil war and in addition to being shot for food a lot of the wildlife was shot for example poached and sold for four body parts like ivory and things like that and all of the buildings in the park were destroyed this is what Goren goes to look like at the end of the Civil War in the late 1990s that's what the tourist bus looked like shot full of holes all the buildings bombed out as for the wildlife it's a little complicated graph to look like look at because the effects were so dramatic so if you look up here before the war in 1972 there 14,000 buffalo were counted in Gorongosa that was reduced to fewer than 50 at the end of the war elephant again from 2,500 down to perhaps 100 hippo from 3,000 or so down to 50 you can see the same sort of pattern all sorts of animals lion completely disappeared pretty bad story pretty bad situation until the early 2000s when an American philanthropist named Greg Carr learned about Mozambique learned about Gorongosa and thought you know every other country in southern Africa has a tourist industry but Mozambique has lost theirs that could be an important economic development engine for Mozambique to make its way back after three decades of horror and so Greg Carr signed a joint management agreement with the Mozambique government to help to try to restore Gorongosa National Park starting in 2004 he committed his own personal funds he invited in scientists from around the world and he really started from scratch building the first building or restoring buildings and reestablishing the park and I was fortunate enough to go there in the summer of 2015 so here's the last home movie of the night so you'll forgive me the the jitteriness but I was hanging out of a helicopter with a handycam which I don't do as a profession so here's a here's a flight over the lake you can see that central feature of the lake now the habitat is there in Gorongosa and what that what happens is during the wet season the rains come down sort of the lake expands enormous Li an area a lot of nutritious silk comes down and really fertilizes this valley it's like a salad bowl and the animals come out to graze on it and the animals kids that you can see running around there are called water buck you can see some birds taking flight as well and you can see little little sort of rivulet sand creeks that connect some of the waterways out in this massive plane in the center of Gorongosa now we're going to fly on a little bit more where the water widens a little bit and see who can pick out and identify these little black dots that are there in there in the river there you go you want to count those hippos you got about ten seconds okay that's a lot of hippo in fact what do you think how many 50 60 okay it's a lot of hippo and I'm glad I'm in a helicopter because if you're ever that really close to sixty hippo you can smell them a good distance away but this is all course good news for Gorongosa there's a big pot of hippos you can see some other single hippo swimming here through the river in just a minute I'm gonna be down on the ground in a second and near another waterhole in Gorongosa we're gonna look at another species in Gorongosa here we go alright you can let that all out as loud as you like I kind of live for that it's the same feeling I had so not only is this group of elephants you know enjoying that waterhole sorry I just disappeared quickly but if you look quickly there are a lot of youngsters in that group maybe half the elephants were juveniles so what's going on with wildlife in Gorongosa eleven years into the restoration project okay how the large animal populations changed in 2000 when you added up all the animals I talked about elephants hippos antelope buffalo etc there were fewer than a thousand animals combined fewer than a thousand large animals combined today 71,000 nature is resilient Greg Carr imported maybe about 300 animals couple hundred Buffalo some zebra some elephants and hippos this is largely the rebound of animals that were already there and animals that once the fighting disappeared migrated in from other parts of Mozambique so now as I showed you from the helicopter you can see animals all over Gorongosa in fact this is working so well in Gorongosa the division has changed the question ten years ago was is it possible for Gorongosa to come back at all and Greg Carr was told he was wasting his time and his money Gorongosa was dead well that was wrong now the vision has changed - hmmm maybe this will work elsewhere in the country maybe we can make an even bigger reserve for these animals and so the future of Gorongosa is actually to get a lot bigger it's a plan that's unfolding right now to expand the whole area about eight fold so the the boundaries of the park but the future plan is to expand the conservation area all the way to the Zambezi River and to the Indian Ocean picking up some already existing reserves and some hunting concessions there'll be people living here just as they live in the Serengeti conservation area but forestry will be controlled farming will be controlled and monitored to be done in a way where humans and animals can share the land that Eightfold expansion by the way wouldn't make Gorongosa essentially the same size of the Serengeti which includes parts of Kenya parts of northern kanzen iya nor the un'goro crater a vast area okay this is not the direction that most parks are going in the world expanding back out from what they used to be and they think that an expanding Gorongosa could carry about 10,000 elephants and about 500 lions so guess is this is perhaps gonna take the next 25 or 30 years and if you ask greg carr he'd say that is exactly how he's going to spend the rest of his life he's on the ground in Gorongosa about six months out of the year directing the and managing the project so the future Gorongosa looks a lot more promising what about the Serengeti itself well I am a happier report from home video I lied that I have one more for you that the only roads through the Serengeti remain unpaved and let's let's keep them that way thank you for listening why do we not have any really big mammalian predators you know I've read to the size of a of a wildebeest for example

Channel: The Royal Institution

Views: 193,416

Rating: 4.751503 out of 5

Keywords: Ri, Royal Institution, biology, sean b carroll, sean carroll, serengeti, rules of life, ecosystems, evolutionary, evolution

Id: yzDISuJdfZk

Length: 54min 36sec (3276 seconds)

Published: Wed May 18 2016

Reddit Comments

[u/walktwomoons]

Great lecture, thanks.

I was wondering where I had heard about the trophic cascade involving wolves in Yellowstone recently, and it was the How Wolves Change Rivers video.