Determinants of butterfly distribution in the Amazonian Forest

Abstract

Species distribution is driven by historical, ecological and evolutionary processes, being determined by dispersion, environmental and biotic filters. These filters act at different spatial scales to select local species composition. The aims of this work were: (i) to assess how historical changes in the distribution of Antirrhea ulei – a rare butterfly endemics to the Pantepui – were influenced by climatic fluctuations since the last glacial maximum (LGM; ~21,000 years ago); (ii) test whether the abundance, richness and composition of butterfly species differ between várzea and terra firme forests in Central Amazonia, evaluating the role of forest flooding in assemblage structure at local scales; and (iii) evaluate the influence of dispersion limitation and environmental filtering as determinants of species spatial distribution at large scales in the Amazon. The distribution of A. ulei was strongly influenced by environmental gradients. Historical projections of its distribution suggest that the species likely had a wider area of occupancy during the LGM, migrating upwards to the present-day tepuis as its suitable habitat were being lost during Holocene warming. These results are in accordance with the Vicariance-Migration Hypothesis and help to understand the evolution of the Pantepui biota. The várzea forests showed greater abundance and density of species, probably due to the high primary productivity of these forests. Also, a pronounced difference in species composition was found between várzea and terra firme, and species turnover was strongly associated to environmental and biotic changes between these forest types. These findings reinforce the role of the flooding as an important environmental filter acting at local scales in the Amazonian floodplain forests. At larger scales, the strong species turnover along environmental gradients, especially climatic, suggests that species are specialized in different parts of the environmental gradients, partitioning their niches to allow for coexistence. The effects of distance, position and geographic barriers tended to be less important, suggesting that butterflies are less likely to be limited by dispersal filters. Thus, these results suggest that environmental constraints are more important than dispersion limitation (isolation by distance or geographic barriers) to explain the distribution of Amazonian butterflies at large scales.