Coleopteran diversity, its distribution and the influence of environmental factors on them in the Barak river basin of Assam, India

Abstract

The research aimed to assess beetle diversity across ecologically protected, semi-protected, and forested areas of Barak river basin area of Assam, India, with a focus on identifying species diversity and analysing its association with a variety of environmental parameters such as pH, temperature and precipitation. A total of 83 beetle species were identified, with Adoretus sinicus emerging as the most dominant species. Several rare species were also documented. Shannon-Wiener Diversity Index (H’) calculated to be 3.663, indicating a relatively high species diversity. Simpson’s diversity index (0.9704) indicated a well-balanced community. Shannon’s Equitability Index 0.829, indicate a fairly even distribution. Pielou’s Evenness Index (0.829) showed that species in the community are evenly distributed. Low value of Berger-Parker index (0.0725) explains that most abundant does not dominate the community, which complements the high diversity and evenness values. Whittaker’s Beta Diversity Index calculated (3.34), points towards significant species turnover, suggesting that each site has a relatively unique community composition and that overall biodiversity is high across the study sites. The CCA data variation in the community. In the first axis CCA1, soil pH and precipitation have strong but opposing influences. Soil pH positively contributed whereas precipitation negatively contributed towards variation. In the second axis CCA2, specific humidity showed an important role in determining the variation, suggesting that environmental parameters play a crucial role in shaping the spatial patterns of species assemblages. Adoretus sinicus and Anomala marginipennis were exceptionally common on the highly invasive plant Melastoma malabathricum and seemed to be frequently feeding on the nectar and leaves of this plant, though A. marginipennis is a non-specific consumer of most flowering plants. During late autumn months when the activity of these beetles was at the highest, not a single undamaged M. malabathricum was found in the study sites. Many species from families like Cerambycidae, Scarabaeidae and Chrysomelidae were collected during the post-monsoon and early summer months, from March to August, indicating a coherent seasonal pattern.