'Biodiversity' (adapted from 'Biodiversity of Australia and North Queensland' lecture series)
Defining the term 'biodiversity'
The word 'biodiversity' itself is probably pretty self-explanatory. And I guess most of you have an idea of what that means. 'Biodiversity' is simply the diversity of life. But it's probably a little more layered than most people think, as it's the diversity of life in add it's forms. It's the diversity of environments, diversity of species, diversity within species. So it really has three different levels of diversity.
From the widest possible view it means diversity of environments. Now environments themselves can be classified in different ways according to your perspective and the size of frame. So now we're looking at levels within levels. First, we can speak generally, and talk of 'biomes'; these are the classic (and a little bit old fashioned) very general physical descriptions of natural environments, such as temperate grasslands, or tropical rainforest. You've probably heard of these back at school. Then we can focus in a little more on that, and start to talk about ecosystems specific to different regions, such as Australian tropical rainforests. And then we can go even further and look at vegetation communities. These are, if you like, ecosystems within those last ecosystems. For example, within an Australian tropical rainforest, we might have a 'complex mesophyll vine forest', a type of Australian tropical rainforest. So, in the end we have a complex mesophyll vine forest, as part of Australian tropical rainforest, as part of tropical rain forest globally. There's no real consistent, international system you can use to subdivide this, and you can look closer and closer and go in further and further; and in fact that's what happens in well studied environments. And, that's just one aspect of biodiversity.
But when most people think of biodiversity, they're probably thinking of diversity of species. This then is the second level of biodiversity. It's simply the amount of species in any given area. And that leads onto the next level down of biodiversity.
This is the level is of genetic variation within the species. That is, it's the different races or forms or varieties of that one species that exist. One of the best examples I like to use is that of dogs. The species name, the scientific name is Canis lupus is their scientific name. And that name covers a huge range of forms that we know by different names, from Marmaduke the great Dane, to the chiachau out of the Taco commercial, and even to the Australian Dingo, to the common Grey Wolf of much of Europe and North America. These are all the same species, Canis lupus forms are so varied and so different, your average non-scientist may be absolutely convinced they are different species. But they are biologically the same species. And these differences represent biodiversity in the form of genetic diversity.
Exploring the world for biodiversity
Now the term 'biodiversity' is new. It's a new word, because in many ways it's a new concept. It relates to the expansion of western science and discovery across the planet, and the shrinking of the world as we travel. If we look on a map of the world at the middle east and the Mediterranean, where Europe, Asia and Africa intersect, we are at the beginnings of western civilization, and the observation and testing of the world which we now call science. Here, the first observers of the natural world like Aristotle started off with a few species. The fig, the pigeon, the rabbit, often just one or two of each type of animal or plant.
Then there was the age of exploration. The nations of Europe; France, Holland, Spain, Portugal and England, began to competitively explore the seas. This resulted in both of our countries being colonized (or invaded, if you look from the perspective of the people already there) by our ancestors. It was at this time that western science really began to expand it's horizons. Wealthy naturalists such as Charles Darwin, scientists such as Carl von Linne (Carolus linneaus), and collectors such as Alfred Wallace began to increase the species list. These guys were the first eco-tourists, and what an amazing world that must have seemed. From a temperate, quiet European background, these guys were consistently awed and dumbfounded by the luxuriance of plants and animals brought back from, or found in, the tropics. And so it became obvious that the real biodiversity of life was not back home, but in the exotic tropics...
But to appreciate the tropics, it's size and diversity, we have to look at a more accurate map, for the standard Mercator projection map is not accurate at all. But it's a typical map of the world from a typical atlas, being available in any bookstore or library. We've been brought up with this map, this view of the world, for some practical reasons, but also for some biased reasons. It's developed historically because of that flow of discovery that I just replayed. But with our modern world view and scientific reasoning_ this seems awfully old fashioned and outdated representation of the world.
The most obvious factor is of course the position of the equator. Of course the equator is the middle divide of our planet, but it's not exactly middle here. It can be fully two thirds of the way down the globe. Some of the other major distortions of the map are a result of this. The Southern Hemisphere continents such as South America and Australia are shrunk. Also, being transferred from a globe to flat paper means that the equatorial countries, even though they cover more area, are shrunk, and the polar countries, even though they are smaller, are expanded. So Greenland, Europe and North America look much larger than they are, while Africa, India, the Amazon region, and the amazing Indonesian archipelago are shrunk.
Compare this to an 'equal area projection' or 'Peters projection' map. And it gives us not only a more accurate view of the planet in regards to the size and relations of the countries and continents, but it helps us make some sense of the biodiversity of the world. Suddenly it becomes clear that the tropics are by far the biggest area of the world. And places like Africa, South America, India and south-east Asia are suddenly symbolically represented as important as they biologically really are, because it's here where the diversity of life was found.
But a real appreciation of the diversity of the tropics, the real number crunching didn't occur until much later. In fact, the real scientific exploration of the tropics, didn't start into halfway through last century. Now, with such huge areas and such grand diversity, and such a bewildering array of unidentified species, they couldn't just run off through the jungle counting species. So scientists sampled in quite small plots of a particular group of life forms. For example, scientists measured the species of trees found in a hectare. (A hectare is a square plot of area that is 100 meters by 100 meters. It's roughly 2 and a half times the size of an acre.) In this size plot, they were finding an average of between 60 to 150 species of trees in a lowland tropical rain forest. This didn't include bushes, shrubs, epiphytes, vines; it's just the trees. In very rich rain forest regions, such as western South America, or south east Asia, they might find over 200 or even over 300 species of tree per hectare (Richards 1996).
But then we really started to look even closer. And they started to identify and count the life that was even more numerous in the forest than the trees, the invertebrates that lived amongst those trees. Again, it wasn't feasible to count everything, so they had to sample in small plots. But, instead of sampling a hectare, they'd sample a single tree. In 1982, that's only 20 years ago, a scientist named Erwin, sampled 19 trees of one particular species over three seasons, and he found almost a thousand different beetle species alone. From these sample numbers, they extrapolated the figures. And Erwin himself did calculations from his own studies. And that's exactly what that guy Erwin did with his beetle count. Some people say the results have been exaggerated, some people say the results are too conservative. Estimates vary from 2 or 3 million species in the world, to Erwin's 30 million (Whitmore 199) to other estimates that run into hundreds of millions. And, we'll never really now for sure.
And this was the pattern that began to emerge in studies of the distribution of organisms in the tropics. The graph below displays this popularity of the tropics with organisms. It is a classic pattern well known to biologists. This particular example is for swallowtail butterflies, but it is a trend that has been found in many organisms. For the larger animal, such as mammal and birds, there is roughly twice as many species in the tropics as in the temperate regions (Whitmore 1998). With the smaller critters, such as these guys, it seems its probably even more. In one tree in Peru, scientists found 43 ant species; so in a single tree in the rain forest, there is more ant species than live in all of Canada (Whitmore 1998).
So there are various ways scientists actually can measure biodiversity. They're based on graphs and statistics and they're all designed to be incredibly boring. But there is one measurement that I'm going to force upon you. But before you all run off or fall asleep, just remember this a simple and fun measurement that you can do in the safety of our own head, and in fact I keep it in the back of my mind when I'm on tour. You kind of do it sub-consciously anyway. It's based on something called the 'species/ area curve', but it's a little bit different, and it's a good sampling technique. In Figure 4 the vertical line represents the numbers of new species that you find, that horizontal line represents the amount of times that you sample the same area. You go out and you see say, 10 species. Of course, in your first sample, they are all new species. Then you go out again and see 10 more species, but say eight of them you haven't seen before. You go out and see another 10 species, but half of them you haven't seen before.
Eventually of course, you'll end up seeing less and less new species and the curve flattens out. But in a really rich ecosystem, it takes a while to curve flatten out and you're constantly finding new and exciting different species. Applying this to my work is an interesting case example. My curve hasn't flattened out yet after years of exploring the area. 3 weeks ago I saw a new species, on a tour I've done forty times over the last three years. To me it proves how diverse the area is. And rarely does a tour go by where I don't see something new. Not only does that keep me interested, but it's inspiring to see so many species, such a range in the tropics.
But why is there so much in the tropics? Well the simple answer is, why not? Look. I'm not going to go into the reasons of biodiversity, because they are complicated and unresolved. Moisture, light and good temperatures, and all these factors in consistent amounts. These are the things that life in general likes. Moisture is one of those, and the graph below demonstrates this. This plot is from South America and shows a direct and obvious correlation between the higher rainfall, the more species found (Richards 1996). Light is another factor. It obviously promotes growth of plants. And the more consistent it is, the better. High temperature is often a by product of all this light, but most importantly it's presence is going to mean the lack of low temperature. So life here in the tropics life is very good. It's wet, it's sunny, it's warm. I mean who wouldn't want to live here? I live here. Everyone wants to live here. So there are more organisms living in the tropics because the conditions are ideal for life. And really, the question of 'why is there so much life in the tropics?, should be turned around and we should really be asking 'why are the temperate areas so poor?' And this is a question that is much easier to answer. And there's two basic answers. First, the temperate areas are so much smaller than the tropics. The tropics is simply a bigger area. And second, there are harmful limiting factors such as a water stress caused by limited rainfall, or temperature stress caused by cold parts of the year, known in temperate areas as 'winter'.
The relationship between higher rainfall and higher species richness
So really, the tropics of the world, the larger part of the globe, is rich with life. If this is the larger part of the world, then, being rich and teeming with life is normal. Life simply is diverse, and it's meant to be. Now going back to the map, the tropics are located between the tropics of Cancer in the north and the tropics of Capricorn in the south. As you can see, it cuts right through Australia, and fully a third of the continent is thus in the tropics. And this determines much of it's biodiversity.