What is ecology? Big-picture summary of history and traditions

♪ Music ♪ In this short introduction to the discipline of ecology, Dr. Brian McGill lays out the history of ecology in terms of key theories and research areas. He describes the different scales at which, ecologists study populations of species, relationships among species in a specific ecological community, and the dynamics among population’s communities and the abiotic environment. He then discusses the contemporary shift in ecology towards modeling and notes that the use of models are limited in terms of how realistic, precise or generalizable they are depending on the assumptions and approaches used. He summarizes the field by noting that the core sub-disciplines of ecology are physiological, behavioral, population, community, and ecosystem ecology, and discusses the newly emerging sub-disciplines of evolutionary, macro, landscape, and global ecology. So I’ve been given the challenge of overviewing the field of ecology and the core questions of ecology and the role of theory in 45 minutes. We’ll see how this goes. You may know, just to be sort of be enatic here, root of ecology is the word oikos, right, which is actually an interesting word, it’s a Greek word for household. It was this very expansive word that included the family, but it included the building, it included the land, it included the slaves, it included the livestock, so it’s this very comprehensive word and of course we we spun two disciplines off of this: economics comes from the same word and ecology comes from the same word. I think it’s kind of interesting to think that those two fields are starting from the same concept. It’s basically the environment in which we live and the interaction with the environment in which we live. I’m going to kind of give you a quick history of ecology and the roots it, roots it starts from and kind of the key questions. So, you can of course trace ecology all the way back to the the Greeks, the Apyrases, and plenty of Aristotle all wrote about ecology and of course ecology’s one of those topics that every person who was alive thought about, right, if you can’t live on this planet and not think about ecology, but as, as a self-referential discipline, I think we, probably we would start in the 1800’s with the Victorians and the naturalists and the exploration of the world. For some reason, when you live on a farm in England or in France, or wherever it may be, you don’t tend to think about it as a bunch of questions coming up, but when all of a sudden you have ships going all over the world and bringing back butterflies this big, right, and observing thousands and thousands of species, all of a sudden these questions start popping into your mind, so ecology has a lot of its roots in the Victorian naturalists and the 1800’s. Ecology was maimed as a discipline by Haeckel in 1880 or 1878, somewhere around there. I didn’t know this before, but apparently the word biology really meant ecology and Haeckel said ‘no, we need a word that covers everything that’s living’ and so ecology was invented to free up biology to actually cover a bigger area. So a lot of ecologists like to trace their roots back to Darwin, it’s kind of a little parlor game; can you take your question and find it in Darwin, and the answer is always yes you can. Darwin was an amazing broad thinker. He thought about everything, but I’m going to briefly, if we kind of take the core questions of reporting, who, or at least several of them, who, where, when, how many, two questions, how many species and how many individuals. If we think of these as the core questions and I’m just going to kind of divide things up into a couple of eras, so we have the very early foundational days of ecology 1880 to 1900. We have 1900 to about 1940. We’ll take 1940 to about 1960. 1960 through the 1980s. One of the first papers that people identify as an actual academic paper in ecology, apart from Darwin’s publications, was by Forbes, who basically looked at a lake and talked about all the amazing, complicated interactions that are happening in a lake and the connections between a lake, so the core, who didn’t use the word food web I don’t believe that the who I’m going to choose is who interacts with who. So the core idea of food webs, this is, I would argue, one of the central organizing themes in ecology. The interconnections between different species has been a dominant theme in ecology all the way from the beginning. The big question, I mentioned the ships going all over the world and people started realizing things look different in different places. You’d go somewhere and you’d see a grassland, you’d see a forest, you go somewhere else you’d see a rainforest with all the lianas and the taller trees. So the climate, climate physiognomy, which is just a fancy word for the shape of the plants. Physiognomy. You can’t read that and I probably didn’t spell it right anyway, but, right, the connection between climate and the structure of vegetation was a big thing. Werner, this was very, Germans were really into this. Werner and Schimper, started organizing this in the late 1890s. Another big question that came up right in the beginning was succession. Cowles had a paper in 1898 that was looking at changes over time, alright, so you all are familiar with the basic idea of succession, you started with a crafts field, whether you start with a farm field that turns into a grass field. It’s got perennials and shrubs and then trees and then different trees, so this process of changes through time. These are all core questions, I would argue these might be the three core questions and are dominant themes in ecology and they all were established in the late 1800s. In this next period, the professional societies were established around 1913. BES. The British Ecological Society just celebrated their hundredth anniversary in late 2013, the Ecological Society of America just celebrated its hundredth anniversary in 2015, two weeks ago. So this is really the forming as an academic discipline. These ideas continue. Elton was a British ecologist, spent a lot of time looking at food webs and also came up looking at predator/prey. Also, came up with the definition niche, that’s certainly been a core concept in ecology. If you have a species, it has a niche and ecologists have had a surprisingly hard time really defining that and making it operational, but it certainly has never gone away as a central organizing concept. What’s the niche? Elton kind of focused on what the species was doing to the world around it, what do they eat and the impacts it had. The idea of elevational gradients was noticed that there’s a similarity between latitudinal and elevational gradients. Merriam and Shelfer made a big emphasis of that. That was especially as Americans moved into the west and had these large elevational gradients at their hands. Grinnell defined a niche, came up with a somewhat different version, which is the requirements of the individual. What’s the habitat? What’s the climate? What’s the food that an individual needs? So already we had two separate versions of niche. The question of how many individuals in a population started to become a big question. The 1920s saw the rise of, or if you want the import, of differential equations as a key tool for describing populations. So n is the state variable, the variable of interest, that you’re trying to describe and you write a differential equation about how n changes over time as a function of various things, and that has been a dominant approach in ecology, I would argue, one of the dominant approaches ever since, but that got its rise in the 1920s. Somewhat related to that, Elton wasn’t quantitative, but he looked at population cycles, famous links hair, where the predator and the prey are cycling up and down, and up and down, and that’s been a question that’s driven ecologists, I would say crazy ever since. We’re fascinated with it and we’ve had some very hard questions to get traction on. The 1940s and the 1960s, Lindeman came up with the idea of trophic levels and more generally started to put the idea of focusing on energy and energy flow and energy as a key constraint. In this time period also, I’m trying to focus on ideas, not names. Hutchinson came up with a niche as an n-dimensional hyper-volume. This has been a dominant idea. You can argue that it maybe hasn’t actually worked out or been implemented very well, but this idea that if you think of the requirements of an organism, there’s a requirement for temperature, there’s a requirement for humidity, there’s a requirement for possibly food, right, and, so there’s many different axis of requirement for any organism and then what you’re looking at is the location of that n-dimensional space that that species can exist. Interestingly, succession started to fade. Oh I missed a big one. Huge debate in ecology was Clements versus Gleason. Clements very much emphasized the interactions between organisms and succession as a process, where organisms, in Clements view, often cooperated to reach some peak or N point in a succession process. Gleason very much focused on individuals and their interaction with abiotic environment and came up with the idea of individualism, that every species just interacts with the environment and doesn’t really care what the other species are doing. So two very contrasting points of view and this, this has been a major theme and debate in ecology. Lotka’s focus on how many species, so Hutchinson wrote the famous paperHomage to Santa Rosalia, which is why are there so many species. He was looking at plankton, actually zooplankton, little daphnia, little crustaceans in the water and in one pond where the water was pretty well mixed, and so it had the same nitrogen and food and everything, you could find a dozen different species of, of these zooplankton, and he was asking why do we need so many species? Why are there so many species? That’s been a very defining question. Why so many species? Dejanski really put the latitudinal gradient on the map, which is why are there more species in the tropics? And that’s been a dominant question in ecology. Certainly, I think, you know, even Darwin asked that question, but Dejanski was one of the first to come up with ideas why that might be true. In this period from 1940 to 1960, was a massive debate, I’m going to come back and talk about the debates in a little bit more detail later. Density dependence, that sounds like a technical concept. If you look at a population and you look at the growth rate of a population, not the growth rate of an individual, you know, physically growing, but the number of individuals in a population changing over time, density dependence says as the population gets bigger the rate has to get, of growth, has to get smaller and eventually it has to go negative and the effect of that is to create an equilibrium. The population grows up to an equilibrium population size and then, stops growing because if it goes over it has a negative growth rate, then it gets pushed back down. And this has been a central concept in all the differential equation models, you almost have to have them in order to make these models work, but there was a huge ferocious debate about whether density dependence really mattered in the real-world or not, and their opposing view, there were some Australian ecologists, in particular, who really said yeah, you know, you can’t grow until you’re knee deep on the whole planet, there are limits to growth, but real populations never actually experience those limits. They’re hitting other constraints, they’re getting knocked back by climate, they’re getting knocked back by predation, they’re getting knocked back by other factors, so density dependence doesn’t matter. This led to a massive, arguably one of the first working groups called Spring Harbor. They got all these people from both sides together and they had a big discussion about density dependence and then they published a book, which was individual chapters and fifty years later, we’re still debating the importance of density dependence. And I would argue that this is another, this is a core debate and this is a core debate that highlights some of the tensions in ecology which we’ll come back to. Just to finish things off, so in the 60s and 70s we had Robert Paine’s keystone species concept. He did the famous experiments where he removed starfish and noticed that the whole system changed just a single species on intertidal, rocky intertidal in Washington. MacArthur really elevated competition between species, the idea of limiting similarity, so that niches could have only limited overlap, so this is another dominant theme that led to huge debates throughout the 1970s and 80s. A somewhat different take on when, Margaret Davis started looking at pollen and looked at the last 20,000 years since the glacial retreats and noticed a lot of things that surprised ecologists once that timescale got expanded out a bit. On the how many species, Dan Janson suggested several questions talking about the role of predators and also talking about the role of seasonal variations, so starting to get into some mechanisms on how many species there are. So this is my 15-minute summary of the history of ecology, but you’ll notice that some of these core questions, the connections between species and the interactions between species has been a dominant theme and we’ve, you know, added to it and varied it, but its been a dominant theme. The idea of niche and where a species can live and what requirements a species has, has been a dominant theme all the way through the history of ecology. Succession has come in and out. I would actually say succession became kind of passé for the last half of the 20th century, not to say that there wasn’t a lot of good research being done on it, but it was a central question that occupied people’s minds; it wasn’t necessarily there, but as global change and human impacts, and land use change, and all these things have, have come up again. In the more recent decades, this has come back in about in a, I would argue, in a guise response to human impacts. Some of these really big questions about why we have so many species, remain a fundamental question, which we, in my opinion have gotten almost no traction on, but its still, you know, a fascinating question. And this idea of modeling populations, this of course is another question that has had management implications from day 1. Whether you’re managing a deer population or a fish population, you would really like to know how many individuals are going to be next year if I don’t hunt or fish and how many individuals will be there next year if I do hunt or fish. So this has been an implied question from the beginning. I have a colleague at the University of Maine who likes to go on at great length about how badly this has turned out as well, in particular in the fisheries cause,you know, we’ve decimated the fisheries on a very scientific basis the entire way through. Science has been involved in fisheries since the 1950s and yet somehow we’ve still completely decimated those populations. A couple of themes that are more recent that I wanted to highlight – space has become a big actor up through the 1970s or 80s and by this I mean spatial structure. The actors were basically the critters and the physical environment, things like climate or maybe nutrients, but the role of actually putting things structured in space has become a dominant theme in the last 40 years. How things are arrayed, the idea of meta-populations and patchy landscapes and fragmented landscapes, just the idea that you can have populations in different places doing different things and moving back and forth corridors, all these kinds of ideas, again, lots of applied implications. We finally got around to talking about positive interactions between species. We focused on competition and predation for a long time and we finally got around to looking at mutualism, facilitation, things like that, you know, there are papers in the 20s that talk about mutualism, even have models of mutualism, but as a core emphasis, this is a more last 40 years kind of focus. The idea of optimality and evolutionary ecology, you know, why do we have two sexes, well why do individuals of different species walk together in a mixed species herd, these kinds of questions, why are some species social and some species not social, have all become big questions. And the last one is, we’ve gotten very interested in biogeochemical cycles. So this is my quick overview of kind of the core concepts that have driven ecology for a long time. I want to turn to the lenses and the tools and I also want to turn to models, but before I do that, anybody feel like I have something big that’s missing here? Yes, go for it. Can I borrow your pen? Yes. Okay, so if you come back here, biogeochemistry’s over there, but actually ecosystem ecology’s also a really big component of ecology and it’s not all organism-centric, so we might say why and how Yep. And we could put Vernadsky and, and Tansley who thought of systems. Yep. So, and we’ll talk a lot more about that. We will. But I think it’s really important that you just kind of put in systems with organisms plus. I would argue niche is the most troublesome concept in ecology. Its been central almost from the beginning. The idea that each species is different. I mean otherwise if every species is the same, we’re just kind of slapping labels on different colors of critters and there’s, there’s no importance to the fact that they’re different species, yet actually measuring a niche, or to use a phrase I like a lot, operationalizing niche, we have not figured out how to do that. You know, everybody thought Hutchinson’s n-dimensional hyper-volume was this great idea, but nobody’s ever mentioned measured n-dimensional hyper-volume or if they do its only got two dimensions, we know that twenty three actually matter. So its been this, I was on campus, we actually had a reading group on niche. It was mostly faculty cause we’re all fascinated as this central concept and yet ecologists have never gotten our arms around it really defined niche. So I did want to focus on tools and lenses that we have through this, so these are sort of the questions. Just to make the point that through much of this period, the primary tool was observation. Occasionally starting to merge into experiment, field experiments at the end, but all of this stuff you know, Werner and Schimper going around, it was just traveling around on boats looking at different places making observations. Population cycles were initially about observations, so observation was the dominant paradigm through about here. So I said in the 1920s, differential equations became a very dominant paradigm that’s through the present day. It’s not very hard to find a prominent scientist who will stand up and say if you don’t have differential equations, you’re not doing science. I don’t agree with that, but you can find a lot of people in the field who say that. You can find a lot of people today who will say if you’re not doing experiments, you’re not doing science as well. That’s another disciplinary divide. And then, this was already brought up, but starting really with Lindeman the idea of pools and flows, stocks and flows. So we have this much nitrogen in the plants, this much nitrogen in the soil, this much nitrogen in the atmosphere and there’s flows back and forth between these compartments, became a very major paradigm. And I would say starting in the 90s or 2000s, just big data sets and correlation have become a very dominant as we move to larger scale questions, they become a very dominant paradigm as well. I blanch a little bit using the phrase big data because I don’t think that’s a constructive phrase, but, but now that we have computers, they have changed the way we do science, so we tend to gather these big data sets and then look at correlations. I’m gonna talk. Yeah, let me start very quickly with the lenses and this could become a conversation we spend a long time on, so I’m just going to quickly put it up and I want to switch to modeling for a minute and then we can come back. I mentioned that there are a number of debates or tensions running through these questions. The big one is complexity versus simplicity. Alright. A lot of ecologists say well, we should be like physicists and we shouldn’t be reductionists and we should break things down into their pieces and put them back together, and others are looking for big overarching principles that will cut across things. And a lot of people say, MacArthur has a famous quote that says ‘to do science is to look for general patterns’. It was the introduction to his deathbed books, so that was clearly an important point to him. So looking for these big sweeping general patterns and other people including Dan in one of the papers you read have really emphasized those general patterns may be so general and so vague, they’re not very useless, pretty useful, we might be better off to really just dive into the details that are going to be context dependent, we should just embrace the context dependence and dive into the details. A very closely related contest throughout all of ecology has been theory versus field. And in particular mathematical models versus empirical work in the field. Sharon Kingsland, who, is she at Maryland? John Hopkins Yeah, she’s at John’s Hopkins, so not too far away, wrote a book on history of ecology and she identifies that as the core tension through the entire history of ecology. She wrote this book in the 1980s, but she identifies that it’s the mathematical models versus empirical field, and that very closely align with people seeking general principles versus people seeking details and complexity as the central tension in ecology. There’s a debate between competition and predation. Mutualism is a late-comer, but that’s been an ongoing debate. What’s the most important force in ecology? Is it competition or predation? Similarly, there’s been a debate between biotic and abiotic, alright. Is it climate and all these things like these people were saying that are driving everything or is it who eats who and who competes with who that’s driving everything? These are some major lenses or views that have driven through all of ecology. So I wanted to briefly talk about modeling. That was also in my mandate. So I’m going to give you my version of what a model does. In my version, you have reality and you have some domain of abstraction. And you start with some known reality, it could be many, many things, but this critter weighs 10 grams might be a known reality and you turn those into assumptions, and move over to the domain of abstraction, and the domain of abstraction we are able to apply a sense of in-domain of abstraction, we’re able to apply principles of logic. We come up with, how did I phrase it, with predictions. Alright. We suggest things are going to happen based on applying the rules of logic and then we take that back to what is hopefully unknown reality, new knowledge. Right, and I like to call this process, people ignore this process, but it’s often a very non-trivial process going from a model back to reality and call that unpacking. So to me this is the essence, mathematicians do this all the time, they call it lifting and they go from one domain like ellipses to another domain like polynomials that they can work in better and then they go back. The problem is mathematicians have one-to-one mappings back and forth between these things, but of course in the messy real world these are anything but one-to-one mappings. These are very complex mappings back and forth. So this is, I would, another phrase would be new knowledge. Right, so it, it hopefully takes us someplace that we didn’t know before through using a model and the model’s hopefully are making some sorts of predictions, which when turned back into the real world become new information. So this is what I would say is the essence of a model, it’s a very general definition To me, it’s about taking things into this domain of abstraction where we can apply abstract reasoning, which is something that adult humans, right, that comes late in human development, that’s something that adult humans are quite good at, and then using that to tell us new things about reality. Now just to say, this process could take a lot of different forms. It can be a verbal model, right, it could be a graphical model, it could be a mathematical model, and if it’s a mathematical model it could be differential equations, computer simulation, it could be a statistical relationship. So this, you know, this is not, I’m not going to claim, I think it’s a mistake to claim that a model is a mathematical statement. The central feature of a model is to take things into the domain of logic. There are a lot of different goals for modeling and there are trade-offs; you can’t achieve all possible goals. Levins had a triangle where there are three goals. He had precision, so this is quantitatively precise, 10 and not 12. He had generality, which is this model applies to lots of different places and times and organisms. And he had reality, we’re capturing what’s really happening in the real world. And he argued that you could achieve two, but not three of these trade-offs, so he heard that most models exist on this edge or this edge or this edge. So for example, he said many of the simulations for example used in fisheries and wildlife or lots of other applied domains have high precision, they’re quantitative predictions, and they have high reality, they take the numbers from the local deer population and the local fisheries population about birth rates and body sizes, and so they’re very good on this, but by definition they’re not very general at that point. They don’t inform us about all of life or even all mammals or all vertebrates or anything. May was in that reading that I put, that little 3-page excerpt from May’s book on modeling, was mostly in this domain. He was trying to come up with very simple mathematical models that were highly general, and hence these differential equations that say assume there’s two species and that they have some effect on each other, and just put in a big whopping coefficient that has no explanation of exactly what it is of impact of species A on species B and impact of species B on species A, right. So he was in this domain. Levins suggested things like optimality models often are over in this domain, but the, the key, I don’t think, I think this is a nice framework, I don’t think it’s important to memorize it or something, but the key point is models have trade-offs, models can’t do everything, models have limits, and depending on your goals, different kinds of models are appropriate. Another trade off that I tend to think about more and May, this is what May talks about too, is tactical versus strategic models. And I think that would map onto Levins triangle like this. So a tactical model is for a very specific situation, right, it’s parameterized by the local conditions and context and it’s designed to solve one specific goal. Strategic model’s a very big picture, very broad, they’re going to be highly general, and they’re going to be highly inaccurate, so that I, that’s, that’s a trade-off that I tend to think about a lot is tactical versus strategic models. So coming back, how am I doing for time, we’ve got some time. So coming back, you know, modeling is, as I suggested Sharon Kingsland said, and I think, I don’t know if it’s the dominant or primary theme, but it’s a major theme, is this tension between, in particular mathematical models, in the school for generality versus field work and the specificity in embracing all the complexity and details of a system. So that I think has been a central disciplinary tension within ecology. We had a request for listing disciplines in ecology and this is going to be a landline, and I’m sure I’m going to immediately get different opinions, but physiological ecology, right, so this is the physics of interacting with the environment around me – temperature, water, things like that; behavioral, right, so this applies, there is increasing push to have behavioral ecology of plants, but it applies more obviously to animals. Back in the late 90s, it was trendy to call this functional ecology and merge those two disciplines. Population ecology focuses on one species and it often times is tightly tied to the question of how many individuals, how the population goes up and down. I don’t know if this is also the point at which evolution comes in, so evolutionary questions are often framed as population questions. Community ecology is explicitly embracing all the species living together in one place at one time, so community ecology is the many species version and this is the focusing in on one species. It’s an open question, how much community ecology embraces the abiotic environment. It’s traditionally the physical environment, its traditionally been very focused on species interacting with each other. Ecosystem ecology has been another major discipline and it’s been focused on things like nutrient flux, energy flow, and the whole systems perspective, right, put a box around a place and you’ve got the physical environment and the biotic environment and looking at what’s happening. Is that a fair characterization? Yeah, we’ll get into that a lot more. Yeah, good. These have probably been the dominant disciplines. Some emerging disciplines have been evolutionary ecology, which get a lot at the why questions of, like I said, why do we have sociality or something like that. There’s been a big push to larger scales. This is my discipline, so I can go on for a long time about what to call it. I actually call it large scale ecology, but probably the most commonly recognized phrase is macroecology. Landscape ecology. Okay, yep. Global ecology. Yep, global ecology and I would argue for global change ecology and this is where I get into my opinions, but I would call all this large scale ecology. Anything else I’m missing? I mean they’re all sorts of applied, right, so you can get into invasion biology or climate change ecology, so we’re increasingly looking at things through that, those lenses, but the traditional disciplines have been largely, you’ll notice, this is very much organism, population, community ecosystem. This is the very classic hieroglyphic breakup of biological systems, is how we’ve been traditionally arranged. So human beings as part of the systems start from the macroecology group? A lot of people would say they start here. I certainly think they’re involved here as well. That’s, I mean I didn’t say that, but I think that’s been a central tension through the whole history of ecology. Is ecology not include human beings or does it include human beings? Yeah And what about kind of the emergence of human ecology? Do people even consider that within this spectrum or how and when that kind of emerged in this trajectory? Yeah, so I think when a lot of fields have adopted the paradigm of ecology and the language of ecology and the vocabulary of ecology to describe, so discipline, so a lot of what used to be called home economics departments are now called human ecology departments on campuses. Ecology is a very trendy framing in education these days. We’ll talk about the ecology of a classroom. So this notion that you’re embracing the oikos the whole system is increasingly being applied to a lot of other areas, so it depends on what you mean by human ecology. And then, there’s also just the idea that ecological tools should be applied to humans and ecologists are increasingly doing that. Urban ecology is a rapidly growing field these days. We all woke up and realized that all ecologists were going out to the wildlands, which are five-percent of the earth’s surface, and that we better start studying other systems that are agricultural ecology, restoration ecology, landscape ecology, so those are places where we’re looking at human impacts, but there’s increasingly start, you know, evolutionary ecology applied to humans. That’s traditionally evolutionary psychology. Yeah, I mean this is one of those things you ask an ecologist, you’ll get ten answers on where humans fit into ecology. ♪ Music ♪

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