Influência do gradiente climático na riqueza de espécies e número de modos reprodutivos de anuros amazônicos

Abstract

Analyze how the relationships between species richness and traits of organisms’ biology vary according to environmental gradients is fundamental in the understanding of patterns and mechanisms associated with biogeographical variation. These evaluations are particularly interesting when considered as different components of the life history of these organisms. Here, we evaluate the relationship between species richness and the number of reproductive modes of anuran amphibians in a longitudinal gradient in the Amazon. In addition, we also access this relationship among groups of species with different reproductive modes, and we test the effect of climatic variables on these relationships. For this, we used literature records and unpublished data from 18 sampling sites located between the north of the state of Pará and the west of the state of Amazonas, Brazil, comprising a gradient of just over 1,800 km. In all, we analyzed 186 species, with a total of 17 reproductive modes. These species were separated into three categories according to the reproductive modes: aquatic, semi-terrestrial and terrestrial. We used Non-Generalized Linear Models to evaluate the degree of slope of Linear Regression lines for the relationship between species richness and the number of reproductive modes as a function of the longitudinal gradient. Likewise, the relationship under the effect of total annual precipitation and mean temperature was also evaluated. The comparisons were made jointly and individually among the three groups of reproductive modes. We found no concordant relationship between species richness and number of reproductive modes along the longitudinal gradient, as well as considering the different groups of reproductive modes. In both cases, the increment of species was not accompanied by the number of modes. Annual precipitation was related to variation in species richness together, and between groups of reproductive modes. The mean temperature was only (negatively) related to the relation between the species with semiterrestrial reproductive modes. Although we did not find a concordant relationship between species richness and number of reproductive modes, our results reinforce the longitudinal variation of the local anuran assemblages in the Amazon. We sustain here the tendency in the increase of the wealth of anurans species towards the West portion of the Amazon. In addition, we highlight the importance of rainfall in the structure of the anuran assemblages in the Amazonian plains, and an assumed higher sensitivity of species with semiterrestrial modes to temperature variation. New approaches that consider greater longitudinal spatialization in the Amazon are fundamental for future understanding of this relationship, as well as differential approaches that consider and minimize the effects on design difference and sampling.