Caldas, F. L. S., B. D. Silva, C. B. De-Carvalho, D. O. Santana, F. F. A. Gomes, L. B. Q. Cavalcanti, R. A. Santos & R. G. Faria

Factors determining the spatial and temporal variation in the abundance of Pithecopus nordestinus tadpoles (Anura: Phyllomedusidae) in a semi-arid Brazilian environment. pp. 253-263.

Abstract. Microhabitat choice by tadpoles is related to several physical or biological characteristics, and variations in these factors have a direct influence on their distribution and abundance at different scales (e.g. time, space). Our work sought to investigate how Pithecopus nordestinus tadpoles use water bodies at a Caatinga site and quantify how biotic and abiotic variables affects the occurrence of this tadpole species. We developed the study in the Protected Area Monumento Natural Grota do Angico/Sergipe, from December 2009 to November 2010 and collected samples (408 plots) using a “throw trap”. In addition to the tadpoles collected in the plots, we quantified five variables (competitors, percentage of emergent and aquatic vegetation, predators and depth) and acquired variation of some data throughout the year (size, maximum depth and hydroperiod) for each water bodies. Tadpoles were found in lentic water bodies that fit their habits and that were also suitable for mating by their adult relates. Most of the studied environments maintained water throughout the period of the study, with P. nordestinus tadpoles being present from April to October, with abundance peak both in July and May. The absence of P. nordestinus tadpoles from February to March may allow the establishment of other species during this period, minimizing the competition between them. The larvae of P. nordestinus showed an aggregate distribution (Id > 1) in most of the water bodies throughout the year, which may reduce the predation. This could explain the positive relation that was found between the tadpole abundance and the predator’s presence. The aggregations were not intensified by the reduction of water bodies as the drought progressed. Among the ecological variables, the presence of competitors (other tadpoles) and the percentage of emergent and aquatic vegetation did not favor tadpole abundance. Interspecific competition can drastically reduce the amount of resources and damage metamorphosis in periods when there is still water regularity in the environments. Branching and abundant vegetation can damage the habit of P. nordestinus tadpoles, which are nektonic suspension-raspers, requiring that this portion of the space is unoccupied.

Key words. Amphibia, anurans, larvae, aggregations, spatial resources, temporal resources, Caatinga, predation, competition, throw trap.