The speciation-latitude relationship in ferns

The latitudinal gradient of diversity (LGD), the pattern that shows that the highest numbers of species in major taxa are at low latitudes and that they decrease towards high latitudes, is the most conspicuous trend on the relationship between geography, environment, and biodiversity. But there is not a concrete answer of why it exists. Three hypotheses have been proposed so far: 1) tropics contain more species because communities have been climatically stable for longer time than the temperate areas; 2) the tropics receives more energy, which allows groups to diversify at higher rates; 3) the tropics provide a higher diversity of ecological opportunities for new species to specialize. By analyzing the fern community from the American continent, I tested the three hypotheses, and found that the first hypothesis is the most likely. The tropics contain more species not because they produce more species than the temperate areas, but because extinction has been lower historically. These results suggest that the climatic instability (cycles of interglaciation-glaciation) at high latitudes have shaped this curious pattern. I am using this seminar to show you some of my research progress, and to briefly mention some of the problems that I have encounter while trying to test my hypotheses. Maybe we can make some ideas to improve the methodological aspects of this kind of macro-ecological research