DIVERSITY OF SPECIES ASSEMBLAGES OF ISLANDS - PREDICTIONS AND THEIR TEST USING TREE SPECIES COMPOSITION OF SHOLA FRAGMENTS

Based on all possible combinations of species that can theoretically e xist on islands of different sizes, we estimated similarities among is lands of equal size in their species compositions. We found that simil arity coefficients among islands of equal sizes increases and the coef ficients of variation for similarities decreases with increase in the size of islands. Accordingly, it can be predicted that the species com positions of small fragments shall be more diverse compared to large f ragments. We tested this prediction using the tree species composition of the shola fragments at BR Hills, Western Ghats. Similarities among sholas were measured as coefficients of correlation between the frequ encies of species in them and also as proportions of species shared am ong sholas. Small sholas were less similar and shared fewer species am ong themselves, compared to medium and large sholas. Also, small shola s showed higher coefficient of variation for the correlation coefficie nts and for proportion of species shared than medium or large sholas. In other words, species assemblage diversity among sholas was found to decrease with their size and large islands appeared to converge towar ds a common assemblage of species. Based on our results, we argue that small fragments add structural and functional heterogeneity to the ec osystem and hence are as important as are the large fragments in conse rving biodiversity.