Ecology of Ischnocnema parva (Anura: Brachycephalidae) at the Atlantic Rainforest of Serra da Concórdia, state of Rio de Janeiro, Brazil

Abstract

Ischnocnema (Brachycephalidae) includes many species that are important members of the leaf litter frog communities in the Atlantic Rainforest of Brazil. Ischnocnema parva (Girard, 1853) is endemic to the Atlantic Rainforest biome and is restricted to the forests of southeastern Brazil. Currently, the available information about the ecology of I. parva is scarce. We studied the diet, the habitat use, reproduction and density of I. parva in an area of Atlantic Rainforest at the Concórdia mountain range, Rio de Janeiro. Individuals of I. parva were captured in April 2005 using different sampling methods: time constrained search (transects), plots of 5 x 5 m (25 m²) on the litter, and pitfall traps with drift fences. We found 240 frogs; 35 females and 205 males. Females (mean SVL = 19.1 mm) were significantly larger (F1,238 = 143.016, R² = 0.375, p < 0.001) than males (13.2 mm). The species preyed mainly on arthropods, with ants and isopods being the most important items, both showing high values of importance index (Ix = 50.0 and 26.7, respectively). Ischnocnema parva is a terrestrial species whose preferential microhabitat at the Serra da Concórdia was the litter of the forest floor (78.7%). The activity was predominantly crepuscular-nocturnal and the estimated density of I. parva was 24.9 ind/100 m². For the eight ovigerous females captured, the mean number of mature oocytes per female was 25 (range: 22-30) and the oocyte mean diameter was 1.11 mm (N = 40 oocytes). Oocyte number increased with female body size (R² = 0.504, F1,6 = 6.107, p < 0.05, N = 8), indicating that as females increase in size they produce larger clutches. Some ecological aspects such as diet and microhabitat use were similar to that observed for an insular population of I. parva, whereas reproductive traits differed. Thus, long term studies are necessary to understand the extent to which these differences are explained by environmental factors.