Local Habitat Characteristics Determine Butterfly Diversity and Community Structure in a Threatened Kihansi Gorge Forest, Southern Udzungwa Mountains, Tanzania

Background Many species inhabiting Kihansi gorge ecosystem in Southern Udzungwa mountains, Tanzania are threatened with extinction due to habitat loss caused by constructed hydropower plant that diverted over 90% of the water off the Kihansi River. Understanding ecological correlates and structure of an animal community in perturbed ecosystems is an important way to enhancing species conservation particularly in this system where several species are already threatened with extinction. This study assessed influences of local habitat characteristics on the butterfly abundance, species richness and diversity and examined how the butterfly community structures across three structurally heterogeneous habitats in the Kihansi gorge forest. Butterfly abundance data were collected using baited traps and measured environmental variables in the field where trapping occurred. To understand the diversity and butterfly richness, these parameters were computed under Primer software. Non-metric multidimensional scaling and analysis of community similarity were used to analyse the butterfly community structure. Further, the generalized linear models were used to assess how the measured variables explained observed species diversity, abundance, and richness. Results In total, 72 species of butterfly in five families were recorded. Butterfly, species diversity and richness did not vary across the habitat types or elevation gradient but showed strong correlation with some habitat characteristics. Also, there was evidence of butterfly communities structuring into distinct groups that showed greater separation associated with the habitat characteristics they utilise. Further, across the study area, butterfly species diversity was mostly likely to increase in high canopy and in trees with smaller diameter at breast height and at lower ground cover. Similarly, abundance significantly increased in the woodland and wooded grassland habitats, where there was high canopy and where tree density was high. Furthermore, butterfly species richness was strongly positively associated with high canopy cover and was mostly likely to increase in sites closer to water source. Conclusion Assessing habitat correlates of the butterfly communities provide important information on what components of the habitats are most useful to target when planning conservation especially in threatened ecosystems. This also helps to reveal existing gaps in important knowledge that would be useful to improving long-term monitoring of biodiversity in in fragile systems such as the Kihansi gorge forest.