The Latitudinal Gradient in Dalodesmidae Cook, 1896a Species Richness

The Tropical Conservativism Hypothesis suggests processes of speciation, extinction, and dispersal resulted in higher species richness in the tropics and declined away from the equator. Biogeographical Conservativism Hypothesis suggests that the processes invoked are not intrinsic to the tropics but were dependent on historical biogeography to determine the distribution of species richness. 117 valid species were identified as belonging to the family Dalodesmidae with the objective to test the two hypotheses. There was a significant correlation between the number of species and latitudinal degrees away from the equator (R=-0.79, R2=0.62, n=116, p<0.01). An evolutionary preference for temperate environments appearing to have led to climatic constraints on dispersal based on precipitation/temperature seasonality gradients and predation was suggested.