Aspectos da ecologia de Ischnocnema Parva (Girard, 1853) (Brachycephalidae) em uma área de Mata Atlântica da Serra da Concórdia, RJ.

Abstract

The genus Ischnocnema (Brachycephalidae) includes many species which are important members of the anuran community of forest floor litter of Atlantic Rainforest in Brazil. Ischnocnema parva is endemic of Atlantic Rainforest biome and has geographic distribution restrict to the forests of southeastern Brazil. Actually, available information about ecology of I. parva are scarce. We studied the diet, the habitat use, reproduction and density of Ischnocnema parva in an area of Atlantic Rainforest at the Santuário de Vida Silvestre da Fazenda Santo Antônio da Aliança, Serra da Concórdia, RJ. Individuals of I. parva were captured in April 2005 utilizing different sampling methods: time constrained search (transects), plots of 5 x 5 m (25m2) in the litter and pitfall traps with drift fences. We found 240 frogs; 35 females and 205 males. Females (mean SVL = 19.1mm) were significantly larger (F1.238 = 143.016; R2 = 0.375; p < 0.001) than males (13.2 mm). The diet of I. parva was mainly composed of arthropods. Ants and isopods were the most important items, with values of index of importance higher than 6 (Ix = 50 and 26.7, respectively), differently of the remaining itens ingested by this anuran. There was no significant relationship between body size and the number of preys consumed by individuals, however jaw width significantly influenced (F1.218 = 72.336; R2 = 0.249; p < 0.001; N = 220) the mean volume of items consumed. Ischnocnema parva is a terrestrial species whose preferential microhabitat in Serra da Concórdia was the litter of forest floor (78.7%). The activity was predominantly crepuscular-nocturnal and the estimated density of I. parva in the locality was 25 ind/100m2 of forest floor. For the eight ovigerous females captured, the mean number of mature ovocites was 25 per female (range: 22-30) and the mean diameter of ovocites was 1.07 mm (N = 40 ovocites). The mean reproductive effort of ovigerous females was 3% in relation to female body mass. The number (F1,6 = 6.107; R2 = 0.504; p < 0.05; N = 8) of ovocites increased with the increase of female body size indicating that as females increase in size they produce larger clutches. We conclude that Ischnocnema parva from Serra da Concórdia, Rio de Janeiro State, has a carnivorous diet, composed mainly by arthropds, predominantly Formicidae and Isopoda. The main microhabitat used by the species is the leaf litter of the floor of the Atlantic forest where active individuals are found, mainly during the crepuscular-nocturnal period. Mean density of Serra da Concórdia population (25 ind/100m2offorest floor) is the highest presently known among areas of occurrence of the species. Females are larger than males in body size, probably as result of the intrasexual selection acting within females to produce larger clutches. The mean number of ovocites produced by ovigerous females is 25 and the fecundity increase with the increase of body size.