Synchrony in small mammal populations of montane forest patches in southern India

Abstract

1. Small mammal populations were studied in montane evergreen forests in the Nilgiris, southern India, using live-trapping from January 1994 to September 1996. Two sites were selected, one with a single large forest patch and adjoining plantations, and the other with several small forest patches separated by grassland. 2. Nine species were recorded, of which eight were trapped in the forest patches, two in the grasslands and five in plantations. Rattus rattus was the most abundant species (2-36 individuals ha⁻¹) followed by Suncus montanus (0-11 individuals ha⁻¹). Densities of seven other species recorded were very low. 3. Synchrony in various population variables-density, biomass, mean weight, density of adults and adult females, and proportion of adults, adult females and sub-adults-was examined for Rattus rattus populations in the forest patches and plantations. Density and biomass were studied in seven other species recorded at these sites. Spearman's rank order correlation was used as a measure of synchrony between the population variables. 4. Within-site synchrony was higher than between-site synchrony in population characters. Synchrony was also higher between plots within the unfragmented site than they were between plots in the fragmented site. Relatively high synchrony in proportions of adults, adult females and juveniles in the forest patches implied that breeding is probably influenced by climate and food availability, which are seasonal in this habitat. 5. Given the small patch sizes (≈1-10 ha) and low population sizes, asynchrony is likely to be an outcome of demographic and environmental stochasticity, and low dispersal rates may impede establishment of synchrony.