Sean B. Carroll is an award-winning scientist, writer, educator, and executive producer. He is vice president for science education at the Howard Hughes Medical Institute and the Allan Wilson Professor of Molecular Biology and Genetics at the University of Wisconsin–Madison. His books include Endless Forms Most Beautiful, Brave Genius, and Remarkable Creatures, which was a finalist for the National Book Award for nonfiction. He lives in Chevy Chase, Maryland.


Biologist Sean B Carroll talks to Craig Barfoot about his latest book, The Serengeti Rules. We find out how wolves can change the physical shape of rivers and why, on the plains of the Serengeti, 150kg is the number which determines whether you will likely get eaten or not. A thoughtful and at times humorous conversation about the state of our worlds wildlife areas and the rules which determine how nature operates. How does life work? How does nature produce the right numbers of zebras and lions on the African savanna, or fish in the ocean?


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00:00:00you're listening to ideas books my name's Craig buffet ideas books is a weekly show interviewing authors about books that help change the way we think about our world in today's conversation with biologist shown be Carol we find out how wolves can change the physical flow of a river
00:00:26these sort of connections we just didn't imagine them very many decades ago and we also discover why if you're an animal on the African serin getting one hundred fifty kilograms is the number which determines if you're going to get or not that it makes me think you know
00:00:45what is what order be parents tell their youngsters as they're growing up you know some day some days someday junior you're going to be eaten alive and to fill your purpose in nature professor Schorr be Carol has written a book that travels the globe in search of the
00:00:58logical rules that govern old of life from tiny molecules to entire ecosystems and seek some answers to the question how does life work soon thanks so much for taking time out to have a chat with me my pleasure to start off with could you maybe give us a
00:01:17bit of an overview as to how wildlife pox and and nature protection areas around the world going out are they working thriving struggling well %HESITATION it's Apache picture of the the overall the organizations that closely monitor wildlife would report that about half of the world's wildlife is disappeared
00:01:42in last forty years so populations have overall decreased and that's most attributable to the fact that we use more of the land now than we did fifty years ago and when humans are using land that's going to be %HESITATION less wildlife now parks are a significant force in
00:02:05preserving what's %HESITATION around what wildlife is around and it's in the low %HESITATION teens percentage perhaps of land that set aside for %HESITATION for wildlife in and you know for for us not explaining it in other ways so N. and how well those parks are doing is again
00:02:24is Apache picture around the world some parks are just really parks on paper if there's not protection and enforcement going on then those parks maybe being emptied of their wildlife in other places there well patrolled %HESITATION there's been a good guidelines around lots of visitors healthy tourism industry
00:02:44and those parks %HESITATION maybe thriving when you say that %HESITATION it's in the low teens is is there a sort of a a rough percentage of the earth's surface I scientists say would be optimal in order to maintain and stop the disappearance of species I don't know that
00:03:01there's a consensus number yet %HESITATION I think we understand in the reset it's tricky on land in the reason why stricken land is it has to do with how connected those areas are because as you wall off populations and they can't move in flow between places we do
00:03:18understand critically from but the last forty years work that %HESITATION as you as you him in populations you were sort of restricting %HESITATION their resilience to other things that could happen you're restricting %HESITATION genetic diversity between populations so as we get to sort of islands of parks in
00:03:39a otherwise in a world of humans that is %HESITATION that's good that's going to be a difficult situation to sustain over the long term %HESITATION because the smaller a place is the dramatically less that it can %HESITATION support so the land bill the land %HESITATION it's a it's
00:03:59a store it's it's an issue of connectedness in the ocean everything is much more connected also species in the ocean are incredibly productive they produce you know lots of eggs or lots of offspring and the ocean can rebound from %HESITATION over exploitation fairly quickly and on a broad
00:04:20G. A. graphic scale because of the the the connectedness of of the seas so it's a different situation in the in the two so if we if we had %HESITATION you know a relatively modest but part of the land set aside but the these were large interconnected areas
00:04:37that would work if we have an even larger man of the world set aside but soon in tiny little patches that's not gonna work so it's %HESITATION it's a different answer for the land in for the ocean so let's %HESITATION let's get a background because you your miraculous
00:04:51biologist yet you'll research arguments in this book about the lives of really large animals on the Serengeti and you and you draw strong comparisons between the rules that govern molecules in our bodies and the rules that govern these large animals Sir can you walk to explain this and
00:05:13and I guess tell us how did this all come about %HESITATION this all started with a visit to the Serengeti in twenty fourteen first time had been there and it's you know it's a biologist dream as a little kid I grew up in a in a biodiversity cold
00:05:28spot in the upper Midwest of the United States and %HESITATION you know I just read about these places are saw them on television and I you know I hope that might someday get a chance to go there and when I went there I was still not prepared for
00:05:42what greeted me and that was the overwhelming numbers of animals thousands and thousands of zebras and wildebeest into cells and troops of elephants and large numbers of giraffes and so forth and I realized I didn't understand what I was looking at I really had no idea why there
00:06:01were so many wildebeest and really so few non topi which is an animal of about a similar size and I don't know whether anybody knew these things and as a professional biologist uses you know made his living understanding about how the world works at the more molecular scale
00:06:16that's unsettling feeling to have reached one of your goals and to stare out across the landscape and go I have no clue what I'm looking at so that's what prompted this investigation of of on my part of of you know what do we know when and how do
00:06:31we know it now who's figured this out in a lot of the stories in the book are about the pioneers who figured out how life works at various scales and for me these were new stories new heroes for me to discover in terms of folks in the done
00:06:45long term work on the Syrian Getty or some the painting work and that of creatures in the Pacific Ocean that it taught us some basic in a first principles about what controls the numbers of things in what what started to resonate with me was that I thought they
00:07:00were asking it least in scope sort of the same sort of questions we ask them at the molecular level which is what controls the numbers of these things I've worked on this aspect of regulation for my entire career and I've worried about well how do you make this
00:07:16many molecules of that and that many molecules of that you know how does the machine re work and it turns out they were just asking that question about you know wildebeest and starfish %HESITATION and I saw some analogies there and I'll give you one of them %HESITATION so
00:07:30a general phenomenon you see at all skills in biology is feedback feedback regulation and there's a there's a logic to it so if you know how does the body no %HESITATION what it needs and how much to make of what it needs well it it works on a
00:07:48lot of feedback principles where if you don't have enough of something you make it and as you start to have enough of that or too much you don't make it and have to be mechanisms of the body to sort of sense the amount of a particular substance and
00:08:00feedback on its production either to ramp up production up or shut it down and you see the same sort of feedback logic out on the Syrian Getty which is when certain animal populations are scarce perhaps after a disease outbreak they rebound the boom in this was witnessed in
00:08:17the nineteen sixties and seventies with wildebeest in buffalo they roar back then they sort of fill the place and as the amount of food per individual starts to go down the growth rate goes down and actually can can tip over negative and such if you plot that curves
00:08:32that the making of will to be some this hearing Getty in the making of say cholesterol in your body really follow a similar logic and so I I realize I said Hey I've seen this logic before that what controls the number of things that this large scale is
00:08:46at least a logical level very similar to what controls the numbers of things at at the molecular in and sailor scale and I thought that seems to be something you know worth writing about worth talking about because I think it it ties a bow around a lot of
00:09:01biology that no matter what skill you're working at this principle of regulation what controls you know the number of anything %HESITATION is a really important process you know no matter what it brings pieces of biology together that generally have spent a long time either you know conceptually or
00:09:21physically or in a text book you know geographically a long a long distance apart and and the ability to sort of talk about the human body and the numbers of bodies on the Savannah or the number of fish in the ocean in the same breath is %HESITATION something
00:09:36that %HESITATION and has not not gone on before yeah let's talk a little closer about some of these rules that do you argue regulate the number of animals in nature Sir %HESITATION first of all could you talk to us about what a keystone species is and why they
00:09:54are so important the discovery keystone species was was really surprising to a colleges if if you just sort of gaze out upon nature in and we sort of been raised with this idea that well you know every creature has its place in nature and so we sort of
00:10:08think you know they're all important and the it and you know maybe in some sense they are but I'll just have to do experiments and it turns out if you remove these creatures individual creatures from their place and you ask what does that do to the whole system
00:10:21they're not equal and those first experiments done that we were done by as while just at the university of Washington named Bob Payne working in the %HESITATION coastal system of the Pacific and little intertitle regions that had starfish and mussels and barnacles and kelp and as he removed
00:10:40the starfish the top predators in the system he saw dramatic effects and perhaps not what you'd expect which as you might imagine remove a predator from the system will then all of its prey will will %HESITATION you know increase in numbers and you actually have greater diversity perhaps
00:10:56but as it turns out the whole community collapses down to essentially one species which is muscles to take away the predator and in this case this the prey this superior really competitive pray muscles outcompete everything else on the rock and roll all the rest is appears except for
00:11:13the muscles so this predator the starfish was necessary for maintaining the diversity of the whole community and and pain calling the word a keystone after the architectural termina Roman arch where the keystone is in the last stone inserted it supports the the two columns and without that keystone
00:11:32of the Collins collapse and without the keystone species the community collapses and been doing here we have we gone through I mean do we experimented on all the way from starfish up to lodge predators Wuxi well he how we by accident we have %HESITATION here wasn't wasn't done
00:11:48in a in a in a scientifically rigorous way it's it's done in hindsight really so what we now understand is that predators often play a keystone role so in places like Yellowstone it's clear because we've had situations where wells were present and then we took them all away
00:12:04and now we've put them back that wolves play this keystone role and have this dramatic impact on the diversity of the whole system not just what happens with its prey but what happens all the way down to the tree life to the plant life in a place like
00:12:18Yellowstone %HESITATION we know that it's it's just often the case that %HESITATION predators top predators play this keystone role they don't always play the key soon role in some keystone aren't predators wildebeest on the Savannah %HESITATION keystones because they sent to groom the whole landscape of the Serengeti
00:12:36bees are keystones because the politics so many plant species %HESITATION so it's sort of a mixture of sort of ecosystem engineers and and top predators that play these keystone role to amazing like the Yellowstone example which is quite a well known one because it it didn't the course
00:12:53of the river changed yeah any got understand Sir due to connect all those dots so that without the wolves what happened was that elk at just had for you know for that complete freedom to roam the park wherever they wanted and and grew in numbers exploded in numbers
00:13:11%HESITATION such that they were browsing down the Aspin the cotton would the willow and some of those species are grow long stream banks and they sort of hold the soil in on the stream banks and without the walls and walls and and cutting down all those %HESITATION they
00:13:27%HESITATION cutting down all those cotton wood and all that willow's you're getting a lot of erosion of the stream banks in Yellowstone and that's changing the course of the river now twenty years after the reintroduction of the wolves the willow have grown back willow is a favorite food
00:13:43and building material for beavers you have more beaver colonies in Yellowstone that changes the course of of water in Yellowstone you have cottonwood growing back now along the stream banks holding the soil in place so you know the sort of connections we just didn't imagine them very many
00:14:00decades ago so you know we're still learning about how nature works but we're learning that you know things are connected in ways that we just didn't appreciate and so we didn't understand the things that we were undoing when we for example have a radic heated predators from from
00:14:16lots of habitats is it is it Ole species in a community that have this kind of strong relationship %HESITATION not at all so strong interactions are are the rare ones and that's really %HESITATION the ecologists working in this area will tell you that the really important questions to
00:14:32figure out the strong interactives that's really important to the management of things like our fisheries is to understand when a what are the consequences you know the top predators in the ocean a some of them are incredibly tasty like tuna and cod and so what happens when we
00:14:47move remove those top predators %HESITATION that's really important even on our croplands of predators that you know you and I might not appreciate spiders can play a huge role in the natural regulation of crop pests and some of our practices annihilate %HESITATION some of these natural controls on
00:15:07past like like spiders and we need to understand you know how things are working even at that you know a a blade of grass can be as complex %HESITATION a food chain a no as the Serengeti and we need to understand what's going on there just in terms
00:15:21of his understanding and looking at the system of a of a of a wildlife pock where are we at with the understanding in terms of how much life that specific area can maintain like for example at the sites a one square kilometer wildlife pock so we do we
00:15:38know it could be like three monkeys for buffalo a lion and a flock of geese he had a great question lesson there's a there's a concept in ecology call carrying capacity and and really %HESITATION if you know what an area can produce in terms of say food so
00:15:57basically the bottom of the food chain are the plants they use the energy from the sun and of course %HESITATION nutrients from the soil and rainfall %HESITATION to make food for the next level of the food chain which of the things that eat plants if you basically understand
00:16:13the productivity of a given area you can take a stab at how much of that plant eater life can be sustained by that by that area now that's just give you sort of a gross number so that you might say if if you make this much plant food
00:16:30per acre you can support say in just mass of this many plant eaters the proportion of those plant eaters in %HESITATION that could be all grasshoppers right it could be a field of grass and it could be in the form of all grasshoppers it could be in the
00:16:45field of all cows it could be in the form of all wildebeest so we can't predict how the a diverse population what kind of diversity could exist there we just basically no can support probably you know a given amount of full of forage can support a given weight
00:17:03of forage eaters and then that given mass of grazers if you like %HESITATION can support %HESITATION a fraction in the form of predators so we can kind of do those numbers of of sort of the food chain but the actual composition at each of those levels is gonna
00:17:21very around the world and we're really not I think in command of the rules that might say why would there be you know one major dominant grazer in one place but maybe ten in another place I think we we need to study %HESITATION how that works %HESITATION one
00:17:38thing we know is that the more diverse the food supplies to say lots of different kinds of grasses may tend IT support %HESITATION a greater diversity of wildlife and so the closer you get to a mono culture the closer you make to %HESITATION in may have a sort
00:17:54of less meals to be support less diversity than that then they'll greater array of of of plant life we now know the roof the ideas about how animals of regulated and this is the the fascinating I dear of a hundred and fifty kilograms hold that the animals the
00:18:13way less than a hundred fifty kilograms eaten by predators and animals larger than a hundred and fifty kilograms escape that but then regulated by food and disease I love that story it's amazing a couple cents first of all I think that the punch line is I think it
00:18:31really helps us understand a place like the searing Getty what astounded me was that we even had this data and again this is the reward of people working for a long time on the Syrian Getty making careful observations over a long period of time and Tony Sinclair from
00:18:45the university of British Columbia has been out on the sand Getty for fifty years any release want to understand how does this place work and he and his colleagues Simon M. Duma and and Justin Bashir's monitor the causes of mortality for some of the large mammals on the
00:19:00Serengeti and when you plop these yes sort of at this is this kind of a real simple sort of %HESITATION too big bins here %HESITATION you've got a lifestyle of the smaller mammals things like or be an impala and Toby where they essentially die hundred percent from predation
00:19:19that it makes me think a you know what is what order be parents tell their youngsters as they're growing up you know some day some days someday junior you're going to be eaten alive and to fill your purpose in nature %HESITATION at the other end of the curve
00:19:32elephants hippopotamus I Nasserists giraffes a large animals essentially zero predation I mean occasionally happens but it's it's insignificant relative to the population so you really got to lifestyles these animals that need to sort of they live fast die young kind of the James Dean lifestyle and then at
00:19:53the other end you've you've got you know the eat as much as you can and get so big that you escape predation and I call that the Marlon Brando lifestyle is just is get really big and and when you see that when you realize that animals are using
00:20:06two strategies you know elephants as we all know they live a long time they have a long jazz station they have a long period of parental care they need a lot of food so they've escape predation yes but they need a lot of food in two thousand sixteen
00:20:23%HESITATION up at the moment we've kind of been given the keys to the cop like is humanities humanities is B. C.'s we're win now running the shower and I'm interested in your opinion do we have the scientific understanding to effectively manage nature and the environment that's scientific understand
00:20:44as a continual process I mean sciences is is never done at what we do know is we know a lot of things now that we didn't know thirty to fifty years ago but they but that knowledge has not yet become policy we know better ways of managing our
00:20:59fresh water system in lakes and ponds so that we could have more fish cleaner water better drinking water you know more fun boating more fun swimming things like this %HESITATION we know that areas need to be connected on land for wildlife to do well and %HESITATION so people
00:21:17are working to try to find quarters that will connect %HESITATION wildlife we know that you know putting roads right through the middle of things and sort of creating edges and and isolating areas one from another %HESITATION have really disproportionate negative effects on what how much %HESITATION wildlife how
00:21:37much nature can be supported in NYC in a given place so we have to learn all these sorts of things whether we're implementing that knowledge is a is a very packed patchy picture across the globe you have to have agencies you have to have infrastructure you have to
00:21:52have an expert work force you have to have policy got have rules and regulations to do this sort of thing and you know lots of parts of the world %HESITATION just you know haven't been in the mode of field of managing their natural resources you know for as
00:22:06long as some others and so on the on the challenge before us is to share that knowledge here that expertise and especially the fine policies that go across national borders because some of this %HESITATION %HESITATION a lot of this is of in a joint concern for certain areas
00:22:22if not you know widespread international concern such as such as the oceans so I wouldn't say I know we know enough to do better we need to know more in lots and lots of situations owner page nine of fuel book you give could the graph that says talking
00:22:39about earth's production capacity can you explain why you well you spend what it is and why you included that well the picture site is a man trying to estimate essentially how much of the earth's production does humanity use and the estimates were for you know fifty or sixty
00:22:55years ago it was less than what the earth produced in a given year but now we've way over shot that a some of that overshoot comes from using fossil fuels so there's a lot of energy buried in the ground from previous hundreds of millions of years that we're
00:23:09in a we're tapping but none the less you know whether you eat when you can think about this on a planetary scale you can think about you know the ability of an acre to support you know any given my life there's a certain carrying capacity of any given
00:23:21area there's only so much food and water that it that it contains an only so much food they can produce year after year they can support the population that's there and the the concern is that seven point four billion people are ex our demands are exceeding what nature
00:23:39can supply with the planet can supply and we you know so we have we have a lot of demands for that that much larger population that was a hundred years ago has a lot of demands and so we need to figure out how we can meet those demands
00:23:53how are we going to manage you know land and water in in such a way that we can we can meet our needs so really I what one thing I hope people take away from the book is it's not about just about you know making places pretty like
00:24:05the Serengeti or Yellowstone or going closer but it's really about making places functional that when you see you know a giant lake that's just choked with algae that's an enormous waste of resources that's a that's a place that could be far more productive with this from a human
00:24:21point of view %HESITATION than it is and when we see crop plants that have been %HESITATION exhausted or in a soil that's been spoiled again that's a wasted opportunity and we have to be mindful that there's only so much the earth can produce and if we don't manage
00:24:39these places %HESITATION forests lakes oceans %HESITATION you know well we're gonna reach crises in terms of food supply water supply to two large populations I'd like to end today shown talking about the resilience of animal populations to come back after they've been decimated because you write in your
00:25:03book about the particular examples of of %HESITATION of wildlife pock %HESITATION Goring goes %HESITATION in Africa but overall if we reducing the species to dangerously low numbers what is the chance of them actually coming back in two thousand the year two thousand survey if all you added up
00:25:25all the large animals the antelope the buffalo the elephants zebra etcetera there are fewer than a thousand Goring goes today ten years into the restoration seventy one thousand so the herds are rebounding you know eat in an amazingly and and this is really largely in a sense of
00:25:46just protecting them that the the what your what you the limit is the excess mortality due to humans and you're simply refilling this park the habitats there the land is there the plant life is there the water is there %HESITATION the spaces there it just had all been
00:26:03emptied and that's storing gringos illustrated a principal at large and I think it's just too little appreciated which is how resilient nature is on a scale of a decade this park is roaring back and if we look at other cases of protected species elephant seals bald eagles sea
00:26:22otters humpback whales wolves they can come roaring back just in the recently %HESITATION manatees of Florida they've they've quintupled since they were protected about forty years ago grizzly bears have about quintupled in Yellowstone so nature's incredibly resilient given a chance and that chance is generally habitat and some
00:26:43protection in some time and we see the oceans with fisheries when fishery stocks get depleted so long as they're not exhausted %HESITATION we can see pretty dramatic rebounds if we relieve the pressure upon them and this is I think really that the source of hope %HESITATION you know
00:26:59going forward is to understand that given a chance nature will rebound so we've got to manage these places that that give nature chance shown it was a pleasure going through your book and it was really great to be able to have a check to you thanks so much
00:27:11for taking time out today thanks for having me you have been listening to shown Carol talk about the ideas in his latest book the serin Kitty bulls Sean's %HESITATION professor of molecular biology and genetics at the university of Wisconsin and you can check out his and many other
00:27:30interesting interviews at our website ideas books dot all my name is Craig box forty thanks so much for listening

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