Speciation

Why is biodiversity higher in the tropics than at higher latitudes and where do most species arise? Weir & Schluter examine this in the paper "The Latitudinal Gradient in Recent Speciation and Extinction Rates of Birds and Mammals". It is always intriguing when scientists find evidence that things might be totally the opposite of what is generally thought. Here is a review by John Simpson. And here, the author comments on the findings. What would I need to perform an analysis like this for lichenised fungi? Perhaps this paper gives clues to it?