Uma abordagem experimental para avaliar a importância de árvores isoladas para populações de anuros em poças artificiais

Abstract

Isolated trees in the matrix occur in a wide range of fragmented landscapes around the world and the few studies about them have suggested that isolated trees can function as "key elements" to maintaining biodiversity, by having a special importance in comparison with the reduced area that they occupy. In this context, using an experimental approach - building artificial ponds - and amphibians as model organisms, the present study evaluated the importance of isolated trees for the maintenance of amphibian diversity. Thirty artificial ponds were built, 10 located at the edge of a continuous forest, 10 associated with isolated trees and 10 on the open pasture. Sampling of all ponds occurred simultaneously during 3 consecutive days and every 3 months, from May 2017 to May 2018. To identify which factors influenced the richness and abundance of the anurans, two local variables were measured, hydroperiod and the average height of pasture vegetation. To determine the relative importance of treatment and local variables on amphibian communities, five complementary dependent variables were used: (i) total abundance of species, (ii) total species richness, (iii and iv) abundance of the two numerically dominant species in the ponds, and (v) community composition. In general, our results showed that isolated trees have an important role in maintaining communities of amphibians in fragmented landscapes. Ponds located beneath isolated trees had a greater total abundance of amphibians than the ponds located in open pasture, corroborating the hypothesis that isolated trees are biodiversity foci. In addition, the composition of amphibian species was similar in ponds located beneath isolated trees and at the edge of the continuous forest, confirming the hypothesis that isolated trees are key-elements in landscapes. These results reinforce the importance of isolated trees in the pasture matrix, not only because they increase the abundance of anuran species in ponds, but also because they favor the maintenance of communities more similar to the communities of pools near the continuous forests. The combination of a local environmental variable (hydroperiod), essential for the survival of the anurans, with the presence of these isolated trees in the pasture, was fundamental for the composition of species in the ponds. However, despite the increasing number of studies on the importance of isolated trees in landscapes, they are still neglected in management and conservation plans, a circumstance that accentuates the socioenvironmental relevance of this research. Therefore, as a practical suggestion to guide future conservation actions, we recommended to protect and plant isolated trees in pasture areas, especially those associated with natural ponds. We also suggest the creation or maintenance of permanent artificial ponds, with a long hydroperiod, near isolated trees. These actions have low cost and can contribute substantially for the maintenance of the communities of anurans and other species.