How does biodiversity vary spatially across the globe? Where is biodiversity highest and lowest?
Read first: Gaston, K.J. 2000, Global patterns in biodiversity, Nature, 405, 220-227
The paper by Gaston (2000) is an excellent place to start researching the spatial patterns of biodiversity, and some of the theories proposed to explain these patterns. The first two and a half pages are particularly good; after this the discussion become a little technical, but you should still be able to draw some useful understanding from it – just don’t worry too much if you don’t understand all of it! Concentrate on the latitudinal gradient of biodiversity – the most obvious and important spatial pattern of biodiversity.
HINT: In these scientific journal papers, you will sometimes come across terms that you may not be familiar with (“endemic species”, for example). It is important that you look these terms up. A geography-specific dictionary is particularly useful for this. Another excellent resource is the Encyclopaedia of Life Sciences.
Most of the discussion in the Gaston (2000) paper is based on terrestrial patterns of biodiversity. But what about spatial patterns in the oceans?
Why are there more species at the equator than the poles?
Gaston includes discussion of lots of theories that have been proposed by biogeographers and ecologists to explain the latitudinal gradient of biodiversity.
When confronted with many possible explanations, it can be tempting to try to decide which of the theories is best (and therefore perhaps the correct theory). However, many of these explanations are complementary, and some are strongly related. They also apply differently to different groups of species. For example, birds are very mobile, and therefore have the potential to colonise new areas very quickly. Therefore, the theory that the high latitudes have low biodiversity because they are still recovering from local extinction during the last Ice Age is unlikely to be relevant to the pattern of diversity in birds. However, for other less mobile groups of species, this slow colonisation may be more important in explaining their low diversity in the high latitudes.
A good way to consider the different theories is to think about a particular example or case study – as you will see in the activity on Madagascar.