Impact of tropical forest degradation on nymphalid butterflies: A case study in Chandubi tropical forest, Assam, India

Abstract

Study examines the hypothesis, whether the diversity of Nymphalid butterflies in tropical primary forest of Chandubi is associated with vegetation structure and canopy openness and that this relationship differs between butterfly taxa in relation to phylogenetic differences in light and shade preferences. Study has emphasized whether the increasing diversity of butterflies in degraded tropical forest is associated with the loss of species with restricted geographical distribution. Study considered altogether eight habitat variables and the t-test using equal variance, Spearman rank correlation and multiple regressions were also used for statistical analyses. Species diversity was analyzed using Margalef’s D indices that indicate both the species richness and abundance. Bootstrap method was used to compare the diversity among samples. PCA was done to examine the relationship between vegetation structure and species diversity in primary and degraded forest. The relationship between vegetation factor scores and species diversity in each sampling station in primary and degraded forest was analyzed using stepwise multiple regression. Results indicates that the butterflies species sampled in closed canopy forest had more restricted geographical distribution than those being sampled in disturbed forest. The species with greater light preference had significantly wider geographical distribution, whereas the species with greater shade preferences had significantly narrower geographical range. The stepwise analysis of multiple regressions between the diversity indices of shade groups of butterflies and vegetation density (PRIN 1) of closed forest shows a significant positive relationship, but the relationship was negative when similar analysis was carried out between species diversity indices of light preferred groups and vegetation density. Majority of closed canopy forest butterflies are sensitive to changes in moisture availability and humidity. Thus, changes in canopy cover and light penetration through microclimatic effects on adult and larval survival does have an impact on butterfly distributions and abundance. While the species richness and diversity are higher in degraded forest, the conservation value of primary forest lies more in the presence of species with restricted ranges. Owing to loss of diverse vegetation in degraded forest, the dense canopy cover and transparent ground cover has been reduced and thus leading to decline of forest butterflies species. Study has clearly indicated the strong and significant relationship that exists between the species of narrow range of geographical distribution and species shade preference. The restricted ranges species are affected due to forest degradation. Thus, clearly bringing into light, that increasing diversity in degraded forest is associated with the loss of species with restricted geographical distribution.   Key words: Nymphalid butterflies, forest degradation, primary forests, conservation value, endemic species, geographic distribution range, light and shade groups, phylogeny, tropical forests.