Aims The tropical conservatism hypothesis (TCH) links environmental tolerance, diversification, dispersal and evolutionary history in explaining why warm, wet tropical regions harbor more species than colder, drier regions. The TCH is considered as a dominant explanation for broad-scale patterns of species richness across the globe, such as the latitudinal diversity gradient. At its core, the TCH predicts a positive relationship between clade age and temperature. Here, I test this prediction using a data set of angiosperm tree assemblages from Malesia.
Methods I assembled an altitudinal gradient of 15 communities of angiosperm trees. I calculated the mean family age (MFA) of tree species for each community. I used ordinary regression analysis and spatial autoregression analysis to determine the relationships of species richness and MFA with elevation, temperature and precipitation. I used correlation analysis to assess relationships between paired variables.
Important findings MFA is negatively correlated with tree species richness, and increases with elevation and decreases with temperature for the altitudinal gradient. MFA remains significantly increasing with decreasing temperature along the altitudinal gradient after accounting for spatial autocorrelation in a species-ordination space. The negative relationship between clade age and temperature along the altitudinal gradient in Malesia is contrary to the TCH.