Edge effects on small mammal assemblages in Sri Lankan rainforests

This project was carried out with the objective of investigating edge effects on species richness and abundance of small mammals in rainforests of Sri Lanka. Core and edge habitats of twelve rainforests were live-trapped for five consecutive nights each, during 2006 and 2007. Habitat assessments were also carried out to ascertain differences in microhabitat features between core and edge habitats. A total of nine species (seven rodents and two shrews) were captured during the survey (two species were from additional trapping sessions). Species richness was marginally higher in core areas (six species) than at forest edges (five species). No marked differ ences were also evident in total abundance with 91 individuals being captured from core habitats and 89 from forest edges. With regard to habitat utilization patterns of the small mammals, of the four endemics, Mus mayori and Crocidura miya used both core and edge habitats whilst Funambulus layardi and Suncus zeylanicus were confined to core areas of the forest. Of the non-endemics, F. sublineatus was confined to the forest, Vandeleuria oleracea and M. booduga used only edge habitats and F. palmarum and Rattus ratttus were found in both core and edge habitats. Interestingly, a remarkable disparity was evident between the abundance of the endemics and non-endemics. The number of endemics was much higher in core areas (55 individuals) than in forest edges (34 individuals). A reverse trend was noted for the non-endemics. The microhabitat conditions within the forest were different to that in forest edges. Core areas were generally characterized by greater numbers of large trees and seedlings, higher humidity and cooler temperatures. These findings indicate that although rain forest fragmenta tion and the resultant changes at forest edges do not have a great impact on the overall diversity of small mammals and the endemics would suffer greater adverse consequences than the non-endemics.

M R Wijesinghe
Department of Zoology, University of Colombo