According to phylogenetic niche conservatism (PNC), closely related taxa share similar distributions along major environmental gradients, e.g. temperature. The probability of a species evolving within the range of its ancestor is therefore high.
Using a novel approach to testing the PNC theory, authors compared disjunct genera on separate continents with a shared ancestor, but few common species. By compiling GBIF-mediated occurrence data of eight woody phanerophyte genera in two regions differing in extent and complexity–the Nepalese Himalayas and the Peruvian Andes–they analyzed 997 species along a temperature gradient.
All Himalayan genera showed a unimodal response with more species in the center of the temperature range. In the Andes, three genera were most speciose towards the warm end of the gradient. By statistical ranking, the authors were able to successfully predict the order of Andean genera based on Himalayan genera–and vice versa.
The study shows that temperature tolerances within a clade are conserved over time and space, and supports the notion that the highest number of species are found around the center of a temperature range of a genus.