Phylogenetic data has revealed, among other things, that recent speciation rates appear to be faster in the temperate regions than in the more biodiverse tropics, but that tropical species harbor more population substructure and within-species genetic diversity. These findings have upended conventional explanations for the existence of the latitudinal diversity gradient.
These inferences are, however, critically dependent on species’ being defined in a consistent way across latitudes. Evidence from case studies suggests that this assumption is not met. Instead, many good tropical species are not (yet) recognized, creating a taxonomic debt in the tropics.
Understanding the ecological and evolutionary processes that generate the latitudinal diversity gradient will require engaging seriously with taxonomic practice and developing strategies to mitigate the biases that it may create.