An intercontinental comparison of niche conservatism along a temperature gradient

AIMS: Phylogenetic niche conservatism (PNC) predicts that closely related species will have similar distributions along major environmental gradients, e.g. temperature. We test this theory by comparing the central tendencies of temperature for selected woody genera, and investigating whether these genera have a similar rank order (sequence) across continents and hemispheres. A strong correlation may indicate niche conservatism, as inherited temperature tolerance would best explain a positive correlation. LOCATION: Peru (Andes) and Nepal (Himalaya). METHODS: Elevation and temperature ranges for all species belonging to eight disjunct genera of woody plants were compiled. Central tendencies of congeneric species along the temperature gradient were established by means of reciprocal averaging and weighted average temperature. We correlated the rank order of genera from the Himalaya and Andes, and tested if the order in the Himalaya could predict the order in the Andes, using permutation procedure. RESULTS: Most genera exhibit a bell‐shaped or curvilinear pattern with the maximum number of congeneric species in the centre of the temperature range, but some curvilinear responses and monotonic increases are found in Andes. The order of generic optima along the temperature gradient in each region is highly correlated (ρ > 0.81), as well as the size of the temperature range and minimum temperature limit (ρ > 0.90). CONCLUSION: The analyses verify the conjecture that the maximum number of congeneric species is found towards the centre of the temperature range of the genus. This may be caused by newly evolving species not dispersing very far from their ancestors and inherent temperature tolerances. Inherent temperature tolerance and covariates such as primary production and soil conditions are the main factors that may explain consistency of the rank order of disjunct genera along temperature gradients between continents and hemispheres. Hence temperature tolerances within a clade are conserved over time and space.