We've been talking about biodiversity conservation throughout the past several modules, and we've talked about types of biodiversity, we've talked about setting priorities in biodiversity conservation, but one of the things that we haven't talked about in terms of setting priorities is understanding where all of the biodiversity is so that we can actually do conservation. And that's what I want to talk about in this video. So again, we've talked about species diversity, we've talked about genetic diversity, we've talked about ecological diversity, and we've talked about this kind of ideal combined approach to doing conservation and to setting priorities in biodiversity conservation.
So the first step that we talked about in our ideal conservation planning is to identify areas, regions, zones, biotic communities for protection before moving on and focusing on individual species to set clear goals and, of course, trying to maintain genetic diversity of those species. But one thing that we haven't talked about is how to identify those priority areas. So first thing...
we have to do is we have to determine what are the criteria or what is the criterion that we want to use to set priorities, to find the zones, the regions, the biotic communities that we want to focus on. So do we want to focus on high species richness, number of species? Do we want to focus on some other measure of species diversity?
So evenness or turnover or something else? Do we want to focus on a certain... kind of sub-segment of species diversity. So do we want to focus on the, or sorry, of species richness?
So do we want to focus on the richness in terms of endemics? So the endemism of a place? Do we want to focus on the general threat, the kind of number of species that are threatened or endangered in a particular area?
Whichever one of these things becomes the goal, we still then have to go and identify where those places are. So where are the places that have high species richness? Where are the places with lots of endemics? Where are the places with lots of threatened or endangered species?
And so how do we determine where all of this diversity is located? And one thing that we know is that species are not evenly distributed. across the planet.
And so we don't have this nice, even species richness across the globe. Instead, we have concentrated areas where we have high species richness in some places, low species richness in others. And so before I tell you about some of the widely documented patterns of species distribution on the planet and about why we think we see that, I first want to remind you that you actually know something about this already. So you know something about what determines whether or not a particular species will be in a place. And that's kind of the first step, determining whether or not a species could exist in a place, is the first step in understanding where it could exist potentially across the planet and then, of course, determining its actual species distribution.
And so what I mean is that you already know about limiting factors influencing the distribution of species. You already know about the role of environmental criteria, which are these abiotic critical resources or critical factors. Things like temperature and precipitation and soil moisture and all of these critical abiotic factors that can determine whether or not a species can be somewhere.
Thank you. And so recall that we learned about range of tolerance and how we have to assess the range of tolerance or understand the range of tolerance for each species, for each of its critical environmental factors. So we know about environmental criteria.
We also know that there are certain regulating factors, ecological criteria, the biotic factors, things like predators and competitors and disease and symbiotic relationships that... interact with the environmental criteria to eventually determine the distribution of any given species. Okay.
And all of... All of these factors interacting for each species then are what ultimately determine these patterns of species distribution. So where do we find species across the planet? And I'm going to tell you about these three patterns that are listed here one at a time. So first we're going to start with the latitudinal gradient.
The latitudinal gradient, or it's actually called the latitudinal biodiversity gradient, refers to the... different numbers of species, the differences in species richness at different latitudes on the planet. And so right here in this chart, you're seeing that at high latitudes, we have really low species richness, or I should say relatively low species richness. But then at low latitudes, we have much higher species richness.
And we see this for birds and trees and mammals right here. But this also exists for... for other taxonomic groups as well. And so a way to remember this, the mnemonic that you can use to remember this is that species richness is greater near the equator. Okay.
So at the equator, we have the highest biodiversity richness. And then as you move away from the equator in either direction towards either pole, we have a loss of species richness as we move to higher latitudes. All right. So the latitudinal biodiversity gradient, again, is this increase in the number of species and species richness as we go from high latitudes to low latitudes.
And we see this gradient not just for species, but also at the genus level and at other higher taxonomic levels, families, classes, things like that. But the question I want to talk about right now is why? Why do we see low species richness in environments that look like this?
and very high species richness in environments that look like this, and a gradient between the two. Well, there are, there's a collection of hypotheses that probably together explain the latitudinal biodiversity gradient. And the first of these is that the tropics have greater geographic area.
So whenever you have a place with more physical space, that tends to support greater numbers of species, as well as higher population sizes. But right now we're interested in greater numbers of species. So greater area, greater species diversity. Tropical regions near the equator also receive more sunlight.
And what that means is that more sunlight coming in, more energy entering the ecosystem, more potential photosynthesis. And as we have more photosynthesis happening by primary producers, we end up with more... primary productivity, more net primary productivity.
And we know that net primary productivity, NPP, is the resource base for the entire ecosystem. And so the more NPP that we have, the more productivity that we have, the more species can be supported throughout the entire system. So more sunlight eventually leads to more species overall. All right, our third hypothesis is that the tropics have had longer stable periods.
So right here in this image right here, you're seeing the ice advance during the Wisconsin glaciation about 10,000 years ago in North America. And what I mean by longer stable periods in the tropics is that the tropics were not covered in an ice sheet, right? So their climate remained very stable and the species there... There wasn't a lot of species turnover there.
Species were able to continue doing what they were doing. Whereas the species that existed up here, where the ice sheet advanced, either disappeared or had to retreat away from the glaciers, the glaciation event. And so you lose a lot of species.
Not as many species are able to make it through those unstable periods. Okay. The fourth hypothesis is that, well, we know that it is difficult to evolve tolerance to cold environments.
And so the hypothesis is that we tend to have fewer species in areas that are colder. And so higher latitudes tend to be colder, well, they are colder overall. And so we tend to have fewer species that can specialize and live in those places.
So we have greater species richness in warmer environments. And then finally, tropical climates are more predictable, and this is kind of a related to the stable periods piece but on a smaller scale. And what I mean here is that the climate doesn't vary all that often from day to day, month to month in the tropical areas relative to other places where we see a lot of seasonal variation.
And so species in these more predictable zones can evolve to be very specialized on narrow ranges of tolerance. So they can have a very narrow range of tolerance for temperature or for precipitation or whatever it is, because, for want of a better way to say it, they know that they're going to have that. They can count on that predictability of the climate. So those are the five main hypotheses for why we see this latitudinal biodiversity gradient. And now I want to return back to the first hypothesis here about the tropics having greater geographic area.
because that actually leads us to our next pattern of species distribution. So our next pattern of species distribution is called the species-area relationship. And this says exactly what we were just looking at, that larger geographic area, with all other factors held constant, a larger geographic area will support a greater number of species. And this right here... This figure that you're looking at is the first species area curve, species area relationship, that was ever mapped, as far as we know.
So this is from 1859, and this shows geographic area on the x-axis, and the number of species of plants on the y-axis, and then you see that as the area gets larger, so as you go from left to right here, as the area gets larger, greater, then we have a larger number of species represented. So we start out here at one county in the UK, in Britain, and then we go up to a larger area, to an even larger region, to all of southern England, and then finally to all of Great Britain. And so we're just kind of increasing the area that was surveyed, and as you increase the area, you get...
larger number of species. One thing I'll mention here, because this is called a species area curve, and that's kind of confusing because it's a straight line, so notice that both axes here are log transformed, and so when you log transform the curve, you get a straight line. So that's why you're looking at a straight line. Okay, so that last example was just this one area of this, you know, area of Great Britain looking at plants. Here we're looking at another survey of plants, but these data that you're looking at right here show plant species in 86 countries.
And so here again we have all of these different dots represent a place, so a different area that was surveyed, and the number of species that that were found there. So again we have a geographic area on the x-axis and species on the y-axis. And we see this same relationship, positive correlation between the geographic area, the size of the area, and the number of species found.
You do see a little bit of variation in different environments, and that's partially because you just have less diversity in certain environments than you do in others. But overall, we see the same trend of more species, the greater the area that you survey. So, so far we've only looked at plants, and so I just wanted to show you a couple of examples here.
This is amphibians and reptiles, and this is birds from the West Indies and here from Malaysia. And so this is showing that we find the same relationship of the greater the geographic area, the larger the number, the greater the number of species. We see this with all different taxonomic groups, not just plants. So plants, amphibians, reptiles, birds, and we've seen it with other groups as well.
Alright, the last pattern of species distribution I want to talk about is this relationship between what we call environmental heterogeneity and then species richness. And so environmental heterogeneity can refer to really a whole host of variations that we have in the environment. And so one example that we're looking at here in this figure is elevation.
So as you change... As you have a wider range of elevation, so you have like low areas and going up much, much, much higher in elevation, as you increase the range of elevation that you have, have in an area, you get a greater number of species. We could also look at other factors like soil moisture or plant structure or other types of heterogeneity, other types of variability in the physical environment in the habitat.
But we'll use range and elevation as our example right now. Okay. So, um, I'm going to show you in a second just an example of how we might see increased species richness with greater elevation.
But I wanted to mention again, because we have it up on this slide, that some of the factors that could be considered environmental heterogeneity is a wide range of soil properties. A lot of different microclimates represented. a lot of topography represented.
So lots of like hills and valleys and things like that. So whenever you have lots, a lot of variation of one of these kind of habitat factors or environmental factors, that can be considered heterogeneity. If you had only one kind, so if you had only a lowland area like we see here, that's considered more homogeneous, right? Less heterogeneity.
And we would expect to see lower species richness here. than we would when you have all of this topography and lots of elevation. So one of the reasons that we would expect this is kind of similar to if you think back to our kelp forest example and our coral reef example, we talked about how the kelp and the coral reef, part of what they do as foundation species is they create all of this kind of partitioning of the environment and all of these different niches for different species to specialize on and different species to occupy. And we would expect the same thing in a more heterogeneous environment, that there are lots of different species that can kind of specialize and find their niche in the different kind of micro areas that are represented in a more variable heterogeneous environment.
Okay, so we have our examples here, right, of our less heterogeneous and our more heterogeneous spaces. And so an example with birds. is that if you only have this lowland forest area, which is maybe characterized by being warmer in temperature, kind of moister soils, lower wind, then maybe you have a low species diversity of birds, right? But as you expand, not the area, not the space, but the heterogeneity in elevation, right? So as we, let's say we cut down, the amount of forest here to like half of this amount of forest right in this foreground.
But then the other half of our space is made up of this mountain. Right. And so what this mountain represents is a gradient that goes from warm, moist, low winds from down here in the lowland up to much colder, wetter, windier habitats up at the top of the mountain.
Right. And then there's a gradient all the way up. And different species can occupy those different environments.
They can thrive in those different environments. And so we would expect to see that as we increase the variability of the environment, the heterogeneity of the environment, that we would have more species represented. Okay, so we just identified these three.
Species distribution patterns talked about why they might occur. We have latitudinal biodiversity gradient, species area relationship, and this relationship between environmental heterogeneity and species richness. So we know kind of how species are distributed.
We know maybe where to find higher species richness. But ultimately, we have to return to this question, which is which of these species is the most important species? kind of aggregations, these clusters of species, will drive the selection of our conservation areas, of the places that we want to protect.
So is it going to be, returning to these questions we asked earlier, is it going to be just high species richness in general, which these help us out with a lot? Is it going to be high endemic richness? Is it going to be high number of threatened or endangered species?
What criteria are we going to use to select our conservation areas? And this brings us to the topic of biodiversity hotspots. So you've read a little bit about biodiversity hotspots.
This is one example of a type of area that is is used, that is prioritized in conservation sometimes. And so the term biodiversity hotspot, or hotspot I should say, has been kind of appropriated and used in lots of different ways, but the original idea of biodiversity hotspots is very specific, and it focuses on a couple of key features of the environment. I'm hoping that you're remembering now, recalling your reading, what type of biodiversity does a biodiversity hotspot value or what does it kind of emphasize? Well, the first thing that is probably coming to your mind is endemics, right? So it's not just high species richness, but it's high endemic species richness is really prioritized.
So high number of species, high number of endemic species, but also a high level of threat is prioritized with biodiversity hotspots. So actually, let me back up a second. So originally, when biodiversity hotspots was first established as a concept, this was it was established using plant species as the kind of the model. And The criteria were that there had to be a certain number, I can't remember what it is now, it's like over a thousand, endemic species of plants in this region. And the other criterion was that 70% of the native plant species had to already have been lost, had to already have been destroyed.
And that was supposed to be a measure of threat, a really high level of threat. was represented by 70% or more of the plant community was lost. So you have this high level of endemics and a high level of threat.
So now I want to talk, and so a lot of people think, oh, that's really good because we want to protect threatened areas and we want to protect endemic species, right? Because they're only found in certain places. But there's a lot that can be lost by focusing only on those criteria. First of all, I would ask, do you think that plants are the best model or that we can only look at plants to establish biodiversity hotspots?
Because originally when the 25 biodiversity hotspots were established, they were established based on plant species. And so we're not taking into account a lot of the other species. Some people would say... that plants are a great model because, again, plants are the photosynthesizers. They're the ones that create the net primary productivity.
They're generally one of the major factors in an environment that creates structure in the environment and habitat and food resources for the other species. So from that perspective, yeah, it makes sense. But you have to ask...
Specifically, there are a lot of things we could pick at with the biodiversity hotspot approach, but one of them that is particularly kind of frustrating is that the level of threat is determined by how the percentage of the plant species that are already missing in the environment, right? So at least 70% of the plants are missing in the environment. So my question is, is that really a good measure of current threat?
You know, are we identifying places that are already potentially too far gone? Should we be looking at maybe the rate of loss of plant species or the rate of loss of species richness in general, not just the total percentage of loss? Because if all that loss happened, let's say, 50 years ago, and there isn't a current threat to a place, then maybe we shouldn't be focusing our attention on that area.
So this is just one example of... why those criteria that we use to establish biodiversity hotspots might not be so great. Of course, biodiversity hotspots also overlook unique biotic communities that don't have as many species in them, but that perform really important functions, right? That maybe provide very important ecosystem services, but they're not necessarily these... high species richness, high number of endemics areas.
And so we have to ask ourselves, do we want all of that to be lost? And then another thing that's overlooked that I haven't mentioned yet, but you can kind of see it if you look at this map right here of biodiversity hotspots, is that all of these hotspots are on land. And so we're not taking into account any of the coastal and marine species on the planet when we're focusing on only biodiversity hotspots.
And so we have to ask ourselves, should these be a conservation priority? Okay, so I said that Biodiversity hotspots are only on land. A kind of an answer to that was this idea of hope spots that was proposed by Sylvia Earle.
And her idea was that we need to also protect marine areas that are critical to the health of the ocean, which incidentally is connected to the land. And so not protecting, not conserving marine species and coastal species. is really overlooking the needs of the terrestrial species as well. And so Sylvia Earle, in her 2009 TED Prize, all of these TED Prize winners get to make a wish, a TED wish, where they ask people to get on board with something.
They ask people to do something. And her wish... was that we essentially start to establish and protect these hope spots. And hope spots are not a technical, how do I say this, they're not recognized in a way where they receive protection under the law.
This is more of a symbolic, ethical movement to get people thinking about protecting the marine environment as much as we think about protecting the terrestrial environment. So Sylvia Earle put this on the map for us. All right, so we've talked a little bit about biodiversity hotspots.
I mentioned biodiversity hope spots, which bring us some focus on the ocean. And then I want to briefly tell you guys about a concept called cold spots. So Peter Kariva and his co-author... I can't remember her first name, but her last name is Marvie.
So Kariva and Marvie wrote a paper about biodiversity cold spots. And it was kind of a critical paper about biodiversity hot spots that was talking about some of the things, some of the many things that are missed when we only protect areas based on these criteria used for biodiversity hot spots. And one of the arguments that was made was that if you look at the country of Ecuador, which is one of the most biodiverse countries in the world, if not the most biodiverse country in the world, it's approximately the same size.
The country of Ecuador is approximately the same size as the state of Montana in the United States. And so we look at these two places. They're about the same size.
Ecuador meets the biodiversity hotspot criteria. Montana doesn't. It's also not a nation. But if we lost all of the species and the unique biotic communities that exist in Montana, that would be a huge loss, not only to our country, but to the world.
There are unique biotic communities like ones that we've learned about in Yellowstone. You watched a video about wolves in Yellowstone. That entire, imagine that entire ecosystem being lost.
because we didn't prioritize it because it's not a biodiversity hotspot. And so really the idea of cold spots is, again, it's kind of like the hope spot idea. It's not an actual, it doesn't have criteria.
It's not an actual designation, but it's just an idea to get us thinking beyond the biodiversity hotspot concept. So I am not trying to totally tear down the idea of biodiversity hotspots. They're important.
They've helped do a lot of protection. But I think that we need to broaden our scope when we're doing conservation planning and think beyond the biodiversity hotspot. And so that's I really wanted to put all of these and there are more, but all of these on our radar, that it's not just about protecting these high endemic, high threat areas, but it's also about protecting some of these less speciose areas, the lower diversity areas that are unique, that protect ecological diversity.
Right.