Distribution, diversity and population status of herpetofauna in Lower Tana river forests, Kenya

Abstract

A study of the herpetofauna of lower Tana River forests was conducted between September 2007 and May 2008, to determine the community structure and threats of the protected and unprotected forest patches, with a view to improving habitat conservation and management. Standardized methods (a time-limited search, traps with drift fences and night transects) as well as opportunistic visual encounter survey were used for herpetofauna survey. A questionnaire was also used to assess the cultural significance and threats to the herpetofauna. Species richness (S) and Shannon- Wiener's diversity index (Hi) were used for comparisons amongst forest fragments. One-way ANOV A test was used to test for differences in the mean values of habitat characteristics within sites, among forests and herpetofaunal species richness, abundance and diversity among the three forests. Two sample t-test was used for differences in the mean values of herpetofaunal species richness, abundance and diversity between the wet season and dry season. Regression analysis was used to assess relationship between habitat characteristics and herpetofaunal species richness, abundance and diversity. A total of 56 species were recorded of which 7 amphibian and 17 reptile species were recorded for the first time in this region. Habitat characteristics (leaf litter cover, percent canopy cover, soil pH, tree density, ambient temperature, percent vegetation cover) differed significantly (p < 0.05) within sites in the forests. However, the same habitat characteristics did not differ significantly (p> 0.05) across the forests. Herpetofaunal species abundance and diversity did not differ significantly (p > 0.05) between the dry and wet season Similarly, amphibian and lizard species abundance and diversity did not differ significantly (p > 0.05) across the forests, except for snakes (p < 0.05). There was no significant relationship between habitat characteristics and herpetofaunal species abundance and diversity (p > 0.05). The study confirmed that the lower Tana River forests surveyed supported a moderately rich herpetofauna which is characteristic of coastal forests. It also confirmed that the major threats to herpetofauna were forest destruction through burning and clearing for agriculture. It also detected seasonal variability in the abundance and diversity of herpetofauna in these forests. Species found within the forests were generally similar, reflecting similarity in forest habitat structure. Amphibian species abundance, richness and diversity were lower in disturbed than in protected forest fragments. This study provided crucial information in establishing the conservation status of herpetofauna of the lower Tana River forests. A study of the offtake of crocodiles and the cost-benefit analysis of their utilization by the local communities is recommended.