LAND MOLLUSC DIVERSITY IN THE OKOMU FOREST RESERVE, EDO STATE, NIGERIA.

ABSTRACT

This study on the species diversity and individual abundance of land mollusc fauna in an ecosystem of Okomu forest reserve, was done by surveying and sampling six plots each of 20m², employing a combination of direct search and collection of leaf litter and top soils which were searched for snail shells. A total of 1873 specimens was found representing 11 families and 53 species. Thedetritivorous Subulinidae family, dominated the fauna in regard to individual abundance constituting 47.50% of the total specimen collected with 891 individuals. The carnivorous Streptaxidae family, dominated the faunal composition with regards to species diversity with 17 species representing 32.07% of the total species collected. The Urocyclidae family also showed richness with 7 species and 148 individuals and the family Achatinidae followed with 5 species and 37 individuals. The remaining 7 families showed low species richness with 2 families having 2 species and the remaining 5 families with 1 species each. Chao and jack knife estimates of 52.58 and 55.21 species respectively representing an inventory completeness of over 90% of the area sampled. Whittaker index calculated 1.493 indicating a moderately high degree of beta diversity among the sampled plots. The reserve showed an increase in species diversity as well as increased individual abundance of most species when comparatively analyzed alongside a major survey in the Okomu forest reserve by Oke and Alohan in 2006. The presence of 8 species with 1 individual representative suggests low vagility and high endemism in such families. Hence there is need for urgent conservation measures to be put in effect which could determine both the conservation and diversification of these species or their extinction from the Okomu forest reserve.