Sister species range overlap across latitudes in the New World
Species diversity patterns across latitudinal gradients have been studied for decades. Several hypothesis have been put forward to explain the high diversity in the tropics, one of which is the role of biotic interactions, suggested that biotic interactions are higher at low latitudes than at high latitudes. It has been demonstrated that biotic interactions, such as competition, could set the species range limits. Potentially then, if there is a strong competition, species ranges overlap less. Here, we investigate whether the range overlap ratio of passerine sister pairs in the tropics is different from those in the temperate regions. We found that about half of the tropical sister pairs do not have overlapping ranges, when they do, they overlap in a small proportion of their ranges. On the contrary, most of the temperate pairs have overlapping ranges, that with high overlap ratios. But of course, the range overlap ratio pattern that we observed may be due to the range sizes of species since the range sizes of the tropical species are smaller than the temperate species. Our analyses showed that the pattern that we observed is not due to range sizes, the size of the regions, or the age of sister taxa. However, the main reason for the pattern observed remains unresolved.
