Assessing the importance of reproductive modes for the evaluation of altitudinal distribution patterns in tropical frogs

Altitudinal patterns in species richness vary among taxa and are shaped by
the intrinsic traits of different organisms and their response to
environmental variables. We evaluated the relationship between anuran
richness and elevation along local and regional altitudinal gradients
within the Brazilian Atlantic Forest based on data from fieldwork (local
dataset; 100-1,900 m a.s.l.) and on compiled secondary information
(regional dataset; 0-2,300 m a.s.l.). We also tested whether frog
distribution patterns were consistent with the predictions of the
mid-domain (MDE) and Rapoport effects. In each analysis, we also
considered the impact of reproductive mode, classified here as either
water-dependent or water-independent, on species richness patterns.
Considering the local dataset, species richness decreased with increasing
altitude for all species pooled and (more strongly) for the species with
water-dependent reproductive mode, whereas the water-independent species
presented increased richness at intermediate altitudes. For the regional
dataset, richness peaked at intermediate altitudes in all three cases. At
the local scale, the observed patterns (except for the water-dependent
species) fit the MDE model, whereas at the regional scale, there was no
fit in any case. Neither local nor regional data were consistent with the
predictions of the Rapoport rule. Our findings indicate a strong influence
of reproductive mode on the altitudinal distribution of tropical frogs,
and that distribution patterns may vary according to the spatial scale
considered. This highlights the importance of taking life-history traits
into consideration when assessing the distribution patterns of tropical
frog species along environmental gradients.