 Good morning. Welcome back to another week. The lecture today is a continuation of last lecture on community ecology. So we're going to continue our discussion of ecological succession and then move into a few other topics in community ecology and we'll further build on these topics as we move into ecosystem ecology on Wednesday. So we'll start by discussing succession and then we will introduce a very important topic, albeit briefly, related to our selection and K selection and that will reflect back to our models of population growth. Then we will have a foray into biogeography island biogeography specifically. That's not the case. That's just not updated. We've done that. Excuse that erroneous bullet. I don't think I forgot to include something there. No, I think from biogeography we're going straight into food chains, food webs, and trophic dynamics. A very exciting subject in ecology. One of my favorite parts of ecology. Recall we were looking at an example of succession from Glacier Bay, Alaska discussing this unique situation in Glacier Bay where the glaciers have retreated from 1760. They've been steadily retreating and so the vegetation in this area is of different ages at these different spatial locations in relation to that glacial retreat. You can study succession in this one area, one fairly large area, a scale of 15 kilometers here, and essentially have a temporal axis for studying succession in this single spatial context. That's not something that we always have the luxury of. In many cases, successional studies require decades and decades of research. This is an opportunity to study succession over hundreds of years in one area. I did introduce this a bit so I'll just highlight the things I did not discuss. We talked about how there's a pioneer stage in the earliest phase of succession. That's a technical term in successional studies, the pioneers. They're the organisms that arrive at the site rapidly, often reproduce quickly, and become established in the area where other species may not be able to because of different physiological requirements. Perhaps species such as this tolerate an abundance of sunlight or a lack of nutrients if the soil is not well developed or if it doesn't exist at all. Perhaps they can fix elements that are important to growth that other organisms cannot. And then succession is often seen to move through relatively discrete stages. But this is the subject of great debate in ecology, the nature of succession, the degree to which these stages are discreet, the directionality, the inevitability of these later stages. All of these things were actively discussed in the history of ecology. In this case you have this driest stage, a stage after the pioneers have arrived and settled where these shrubby plants come in and come to dominate, become most numerically abundant in the area. These are pretty good nitrogen fixers. They rely on a mutualism with bacteria in their roots to fix nitrogen from the atmosphere. And they start to build up a bank of nitrogen in the soil with the alder stage that really takes off because these are exceptionally good nitrogen fixers. And so the existence of that element in the soils increases much more rapidly. It's required for plant growth and some plants which can fix nitrogen now are able to occupy this area. So you might think of this as a sort of facilitation mechanism for the later arriving species. Remember we had these categories of inhibition, tolerance, and facilitation in our study of succession. The effect that an earlier arriving species would have on a later arriving species. We certainly can't think of this as any well certainly not any conscious facilitation of the later species. But we don't in a natural selection context of course we're not thinking of these alders as wanting the other species to come in and replace them. So when we speak of facilitation we're just speaking in terms more of the later arriving species relative to the earlier one. Its existence, these later arriving species such as spruce and some of the conifers as having been facilitated there by the existence of a strong nitrogen base. Now one of the other things that's happening in these soils during the successional process is the acidification of the soils. And that can be inimical to much plant growth. If the soils are too acid many plants will struggle to grow in those soils. And particularly the needles as they drop in this spruce conifer phase will further acidify the soil and make it difficult for other certainly for those earlier successional plants to even exist here. Our book gives you a nice figure of soil nitrogen levels quantified in grams per meter squared with each of these stages of succession. Note that in these later stages you could have inputs of nitrogen as a result of animal activity. Migratory birds or bats or big mammals walking around insects coming in and out that would bring in nitrogen even in the absence of nitrogen fixing plants. So this is a you can't just think of the plants in the successional process. Think of all the other organisms, the microbes. And very often you see a trend in increasing species richness in the successional process. That's a characteristic arrow in the directionality of succession. But it doesn't stop with I had a slide of it doesn't stop with the spruce conifer phase because in the hollows in the poorly drained basins the mosses will come in. Particularly the sphagnum moss. And it'll even further acidify the soils and it'll hold water. You may have heard of sphagnum bogs. Those mosses will hold the moisture and cause the water to pool in these basins that basically inhibits the growth of any of these trees. So once the mosses get in and really get anchored they hold the water and prevent the growth of other trees. And then it's theirs in those little basins until something happens to disturb that condition. And you can see that that's related to the physical contours of the environment. That would just be in the more poorly drained areas. We don't want to just focus on succession in terrestrial environments necessarily. Here's a beautiful, flourishing reef coral reef. These are some of the most productive and diverse habitats on earth. These shallow water coral reefs. And they're some of the most threatened ecosystems on earth as well. But a mature reef, a late successional reef will be characterized by these branching corals. Corals with stag horn and elk horn corals and corals that have these you can see how these are relatively fragile construction of relatively fragile construction. Imagine if a massive storm came through what might happen to this structure. And it's partly as a result of this great physical structure, the complexity of this physical structure that you have such a diverse ecosystem. It creates so many spatial areas of potential occupancy for all these organisms to shelter to reproduce and to make their living. When a strong storm comes through it can simply level all of that three-dimensional spatial complexity and restart a successional process here. If this did occur and this does occur, Caribbean coral reef systems, the ones really that I'm familiar with it's probably happened elsewhere. But over the last decades they've suffered various insults from anthropogenic activity, from human activity. But some of the hurricanes that have passed through the Caribbean in the past decades have really have really hit those reefs hard. And what would happen here if the hurricane comes through and the reef is leveled like this? Would this be a primary successional context or a secondary successional context? First of all secondary. Remember that your book focuses on I think soil. Is there soil Well no, there's no soil here. I don't think anyone speaks of soil on a coral reef but there are plenty of living organisms. Even some of these even many of these corals are surviving. They're just set back and they'll take a long time to grow back that three-dimensional complexity but given time and some stability they typically will grow back. Let me just I've used the term disturbance and so as not to be disturbed by that strange term. Let me give you a definition of it. It's a very important concept in ecology. The concept of disturbance. There's a whole sub-discipline of disturbance ecology. So let's define it as any relatively discreet event that eliminates organisms and creates space. Creating opportunities for new organisms to become established. It's a long definition but I want you to make sure you have a good handle on that term disturbance. Any relatively discreet event that eliminates organisms and creates space. Creating opportunities for new organisms to become established. It clears the substrate very often a disturbance does. So it creates physical space where none existed previously and removes organisms, removes potential competitors and creates opportunities for new organisms to become established. The pioneers are the ones that are going to come in first. What makes a plant or another organism a good pioneer we can, I'm going to continue to talk here. We can talk about in a second when we talk about our selection. But let me note another important aspect of disturbance. A disturbance like we just saw on the coral reef that was really a cataclysmic disturbance where it leveled the whole reef. But one of the fantastic things about disturbances is that for many ecosystems absolutely critical to their proper functioning to their functioning in a healthy manner. So let's set up a couple of axes and just look at diversity or species richness. We'll call it diversity on this axis from low to high. Increasing diversity on the y-axis and disturbance frequency, how often a disturbance of a particular type occurs in that area from low to high. What you often see is that areas where disturbance is very low species diversity is relatively low. And that with time you see a sort of curve like this. With increasing frequencies you see increasing diversities of species in the system. But in areas with disturbances of extremely high frequency diversities are also low. Don't take this too seriously whether diversity is higher with these extremely high frequencies than it is at low frequencies. Continue that down if we want. Magnitude of disturbance or size of disturbance could also be on this axis. So the size of the disturbance from small to large. So you can think in terms of how often this disturbance occurs or its magnitude. And it's a similar phenomenon, similar effect. And this has implications for the way we manage ecosystems. And I'll discuss that. But let's look at a couple of examples of real world data on disturbance. Is there something I should do up here? No, I don't think it's the computer. My computer's working. So the computer button is highlighted up on the console. Brilliant. Thank you. That's the cue to me to go to the board case. Thank you. Such a smart bunch. Okay. Here's a real world example from New Zealand from your text. And you can read about it. You can read about the details in the book. I should have put the figure number here on it for you. But basically they went to various streams that had experienced different intensities of disturbance and measured the number of taxa, counted the number of taxa in those systems. Taxa just, you can replace that with species here for simplicity. It's the plural of taxon. And please look it up if that's not a familiar term for you. But basically you can think of that as number of species or diversity on the y-axis. But specifically that's something more akin to species richness, right? But there's your familiar sort of curve with intensity of disturbance at low levels related to relatively low species richness or number of taxa and at high intensities. The same. And the highest levels of richness at those intermediate intensities of disturbance. I don't know where these data came from. But it can be fun to think about it at least. But don't. I don't think someone empirically derived these from experiments on the ground or anything like that. I mean that a meteor strike or acid rain requires a longer period of recovery. It probably does relatively speaking. And occurs over a greater spatial scale than something like a landslide or slash and burn agriculture. Or a lightning strike. But I put these in for you to think about these different types of disturbance and the magnitude of their effects on spatiotemporal axes. Because all of these are fairly considered types of disturbance. According to our definition I suppose maybe something like modern agriculture is less a relatively discrete event as I define the term than something like a landslide. But these are important disturbance phenomena. A tree fall is a disturbance phenomenon of critical importance in the functioning of forests. A forest ecosystem with all these canopy trees shading the lower levels. When one of those big emergent giant trees falls in the forest it creates a gap in the canopy. And all of a sudden a flood of light comes in and an opening of space sometimes great spaces. If those trees are festooned with vines and they're connected even to other trees by vines and lianas they can tear down other trees and as they fall they knock down still other trees. And they can create a huge gap in the forest for occupation by new organisms. And it's the pioneers that will come in those systems. Fire is a major force of disturbance and one that's particularly familiar to us here in California and to us right now given what's happening in Colorado near Boulder. Fire occurs naturally of course and is often sparked by lightning and it occurs cyclically in many ecosystems and it has occurred cyclically in many ecosystems over such long periods of time that the organisms in those systems have evolved to have become adapted to fire and in some cases even require fire to complete their life cycles. Some plants for example their seeds will not open. The casing of their seed will not open unless the resins are melted not temperatures of a fire to disperse the seeds for example. This is a and think about this in relation to our graph of disturbance in relation to species richness and species diversity. An old smoky bear who was so instrumental in our preventing forest fires for so long. Think about that in relation to fundamental ecological principles and we don't have time to get into it but it's a great controversy. The role that that attitude toward fire, the stamping out of fire over so many years without exception that attitude, the role that that attitude had in the shaping of ecosystems that we see now. I'd love to get into that more but I just don't think we have time. One thing that fires can also do in some systems in coming through not only creating space but pathogen loads parasite loads can build up over time in a forest or in an ecosystem and the fire coming through can kill the pathogens where the trees might survive or resprout from the stumps even if the above ground portions of the plants are killed off they might still have a fully functioning root system. They can produce new shoots pathogen free and so preventing fire can have that sort of unsuspecting effect of increasing pathogen loads. So let's introduce this concept of our selection and case selection in the context of succession. There are various ways to discuss these life history strategies are selected and case selected strategies but we will look at it just in terms of in the context of succession. So here's an example of old field succession or something like that where let's say that there was agriculture here it was the land was cleared for some crop and then the farm was abandoned for some reason and gradually first the annual plants came in the small flowering plants and then some perennial plants some plants that lived across seasons across years and grasses then the shrubs then some softwoods, pines and conifers and finally in this sequence these larger hardwood trees with some of the shrubs maintained below them but little trace of the original pioneer annual plants in this more quote unquote mature ecosystem. You see the axis here from R selected to K selected what do we mean that plants in this portion of the successional sequence are R selected and these in the later successional sequence K selected. Think back to our population models and the definitions of R and K R refers to the per capita growth rate so in these early successional stages on R selected species is one that is going to be reproducing rapidly have a high R value that's where we get the term there it also will have many other traits that might be successful in this early stage can somebody think of one that might make a plant successful as a pioneer here in the early stage please. Light tolerance yes or the ability to capture light and efficiently process high light levels something else from the distance perhaps. I always sat in the back and didn't say much too so sorry to bug you back there but I'd love to hear from you many offspring yeah so an abundance of offspring what about those offspring if they're going to if they're going to get there what is important about those offspring sorry mobility yes that they're highly mobile mobile so that often means small or easily dispersed. Features such as that yes and then in this later successional phase you gotta please think about the competitive aspects of life in this in these conditions it's very different from the need to grow rapidly to come to occupy and hold the canopy in these early stages to grow fast and to put your leaves forward to create a catchment for the for solar energy in order to you know succeed in photosynthesis to dedicate that to growth and reproduction in these later stages the competitive factors that might exist are much different and we speak of case selected forms here selection referring to natural selection something you haven't been fully introduced to yet but these case selected species are existing in environments closer to carrying capacity where the system is you know closer to its carrying capacity in numbers of individuals or if you want to think about it loosely in terms of the biomass held in that ecosystem loosely speaking so I just made a table of some of these features that would be typical you'll get this on your PDF so no need to scribble it all if you don't want to but the number of offspring compared for an R selected case selected form many versus few the size of the offspring small versus large the large offspring in the case selected context you're dedicating a lot to fewer offspring so that to better ensure their survival and potentially their need to survive for a longer period of time before being given the opportunity to germinate and grow that large offspring might need to sit and wait for an opening a gap a tree gap for example for light to even come through the forest canopy these organisms may take a long time to develop to reproductive maturity whereas the R selected species they're living short and fast right it's that strategy live fast die young kind of thing they reproduce early and these much later they die at a more rapid rate and at a lower rate partly as a result of that the larger amount of energy given to the offspring in the early phases and then in an animal behavior context it's interesting perhaps you'll look at that in the evolution section parental care if you're thinking about animals it's often the case selected forms where the parents will dedicate time to nurturing the young and better ensuring their survival so in that case selected context they'd have few offspring but they're big they take a long time to mature they're older at the age of first reproduction mortality rates are relatively low so think of that in relation to your species survival curves in type 2 and type 3 curves please reflect on that later and with long life spans with extensive parental care so it's the you know all these traits you can see how powerful this idea was of R selection and K selection it came about in the late 60s I guess this notion and it had a powerful effect in uniting many different areas of biology one of these great synthetic conceptual advances we're going to detour into biogeography before finishing with some food chain investigations Alexander von Humboldt from the very early 1800s when he was at the height of his travels and the height of his powers this was an extremely influential individual a German who was widely read around the world there are said to be more places in the world named after Humboldt than after anyone else and we have several examples in California of course he was all over the place but he spent a lot of time in the Americas he was interested in politics but all forms of science you know one of these renaissance people and took with him great instruments for studying nature and mapped and revealed much about the world that he knew to Europe that he brought home to Europe and he was very much celebrated and a huge influence on Darwin so Humboldt also was one of the first biogeographers which is why he's coming in here one of the things he was first to notice is a very empirically solid relationship that it's the number of species to an area of space so in relation to an area of space the number of species is often seen to follow a fairly strict curve of this nature on an arithmetic scale the curve looks like that if you put it on a logarithmic scale a log log scale where you take the logarithm of both axes it forms a straight line and this holds in with so many different organisms in so many different areas it's usually focused on a particular type of organism and I'll give you some examples tree species in Japan and Japanese forests on an arithmetic scale you can see how that familiar shape of those curves have different forest sites in Japan those curves have different slopes and that's of interest mathematically but it's also of interest biologically why would these things have different slopes even though they do all follow a similar shape ants on New Guinea and on islands adjacent to New Guinea on the big island of New Guinea it has a different why intercept this line on a log log scale of course here then it does in relation to these isolated islands why should this very very large island an almost continental scale island have a different why intercept from the one seen with the isolated islands and yet both have fairly similar slopes but that's often of interest too any difference is in slope in these relationships so things I want you to consider and we can talk about further or you can talk about in your discussion sections birds the breeding birds of North America this is a huge area and again we're focused on a particular group and again we did ants in New Guinea and adjacent areas these are birds in North America but for all of them you see these characteristic relationships these are species area curves another major focus in biogeography island biogeography launched by two of the most influential ecologists from the end of the 20th century they were very much active today writes popular books and you may have bumped into him and his works and Robert MacArthur their early work in island biogeography these were a couple of the guys behind the ideas of our selection and case selection as well but what they did their work was partly so influential because of the it was a great empirical study in the islands off the southern tip of Florida you have these mangrove islets these mangroves of this type of tree they grow in the open water they put down their roots and they start to form a stable substrate on which they can grow and these islets can grow fairly large they can be right on the beaches or they can be somewhat offshore and they can be various sizes distances from the land and of various sizes themselves as islands or islets there's one and you can see how they come to be occupied by different forms of life maybe an osprey there and some cormorants there and you can imagine the insects in the canopy that certainly could not be there where they're not a tree growing out of the marine water so they create space and opportunities for these other organisms by their existence what's the relationship between the size of these islands and islets their distance from the mainland and the community of animals and other organisms that live on them there's a very big one one of the things these guys could do this was late 60s early 70s and have other ecologists not really blink is they could fumigate these islands they could put a cover over the whole island or islet and introduce a gas and kill everything on it to study the arrival process of organisms back on to that island or islet we probably couldn't get the permits to do that today but it was a good idea but just those few decades ago certainly you could and I mean measured against the information gleaned from such a study it would hard to be in retrospect hard to argue against doing it again how much we've learned for conservation biology about a study like that from studies like this really we've learned a lot so this is sort of the apparatus there are little boats and then cover the island and then nuke it doesn't kill the tree just kills everything pretty much everything else on it doesn't kill the mangroves so these islets are not unlike other archipelagos of islands here are the Galapagos the Galapagos islands take the names away and you have all these different land masses of different shapes and sizes and different distances to the mainland so think about it that way think about those mangrove systems in that sense when you're thinking about it theoretically and they what these biologists did they were great integrative biologists they knew a huge range of organisms and they could follow the recolonization of these islets over time over days these richness on the different islets and they looked at it in relation to the size of the islands and islets and their distance from the mainland and then they started to develop the theory behind this behind the empirical observations so let's think about it a little bit these figures are often hard to interpret students find a hard time interpreting these in the book so I'm just going to try to help with that a little bit number of species on this axis how many species are present in the space it's a function of the rate of immigration and the rate of extinction immigration in red extinction in black where those two curves cross where those two rates cross you have your equilibrium number of species okay let's think about that first of all that it's a the number of species on the island is related to rates of immigration and extinction now these are species not individuals right we're talking about species here let's look at the effect of island size on the process again immigration in red and extinction in black in terms of immigration how is a small island going to differ from a large island well a bigger island is a bigger target for immigrants coming from the mainland so the rate of immigration is going to be higher on a large island than it is on a small island you haven't had this in evolution yet but I can just tell you extinction the rates are going to be higher on a small island because population numbers are lower a population with a lower number of individuals is more likely to go extinct just as a result of chance but other factors as well than it is in a large population on a large island so you can see how the number of species predicted to exist would be different depending on the size of the island distance from the mainland something similar where the immigration is going to be immigration rate is going to be higher on islands nearby they're just more likely to be landed upon by dispersing organisms than islands far away and you can follow that with the in relation to their equilibrium numbers so these empirically derived theoretical constructions have greatly influenced our understanding of ecosystems and what influences the number of taxa, number of species present in ecosystems and I said it had a big influence on conservation biology and it continues to because islands really we can think of a lake as an island a lake is an island of water in a sea of land or a pond is an island in a sea of forest you need to think with that kind of conception when you're thinking about islands a Tilden park up in the hills above us is an island of an island ecosystem really in a surrounding area of urbanized ecosystems so parks and preserves are often islands in developed spaces so some of these models of island biogeography can be mapped onto those other ecosystems ecosystem types aquatic ecosystems or terrestrial preserves and thus the generality and importance of of the ideas finally let's do some food web dynamics and we'll pick it up tomorrow but we've got five great minutes here so please if you need to go feel free to do so quietly now but then we'll try to hang together right till the five minutes are up the idea of a food chain is familiar to you I think where big fish eat smaller fish and smaller fish eat smaller fish you often hear it in just common language right the idea of a food chain it has a really rich and long history and you can go back and look at a bunch of neat examples from ancient times Darwin spoke of a food chain in his writings that became very familiar to people he this is one from his backyard he was basing it on research of another scientist but it was something that he could observe as well he observed that bumble bees or humble bees as they called them maybe they still do in Britain I don't know bumble bees pollinate clover little clover flowers that grow in the lawn and that the bees and their larvae are eaten by field mice field mice in turn are eaten by cats so what would happen if you took away the cats well if you took away the cats then the field mice would go crazy and they would devour all the bees and if all the bees were devoured the clover couldn't be pollinated and you would lose one of the basic components of the community so not only did was Darwin articulating a food chain here but he was suggesting some of the dynamics in the process of the food chain and then others built on this and noted that it was mostly old maids who were keeping cats and that the clover itself was feeding the cattle that were supplying the meat to the British Navy so if it weren't for the old maids the Navy would probably go hungry and the whole British Empire would collapse which highlights much about ecology really and the way ecologists think in terms of the interrelationship of these causes and effects that changes in one component of the ecosystem can have rippling effects unsuspected effects sometimes that are out of proportion to the original cause and food webs as they exist in reality are extraordinarily complex here's one marine system based on cod probably developed on the east coast of the United States where cod was a major fishery for so many years it's the basis and source for so many other organisms the intricacy of these connections is very real and someone asked me about one of my slides in the last lecture I had arrows pointing from the starfish to other organisms those arrows represent the trophic relationship the arrow from one component to the other represents energy and mass in the form of food going to that other component a couple more minutes you guys so here's an example of a food web from the Antarctic with krill at the base krill are crustaceans they're shrimp like crustaceans and your biggest animals on earth your baleen whales are primarily eating krill they're opening their big mouths and really whatever goes in will be eaten whether it's a turtle or a jellyfish but they're primarily after in these waters krill these krill sustain in a real way this massive upper ecosystem including six baleen whale species 20 squid 7 seals it's not only krill that are part of this and krill themselves are eating other microorganisms but from that base from that extremely productive base in these nutrient rich waters you have this upper ecosystem sustain we'll talk more about it tomorrow or Wednesday