Diversity, Ecology and Significance of Formicidae in Selected Sites of Southern Western Ghats, Kerala, India

Abstract

The Southern Western Ghats of India, part of the globally recognized biodiversity hotspot and World Heritage landscape, represent one of the most significant centers of endemism and species richness in the tropics (Myers et al., 2000; Gunawardene et al., 2007). Within this region, the forested tracts of Thenmala, Aryankavu, Rosemala, Kulathupuzha, and Anchal in Kerala, falling under the Agasthyamalai Biosphere Reserve, encompass tropical evergreen, semi-evergreen, moist deciduous, riparian, plantation, and human-modified habitats across an elevational gradient of 100–1000 m, receiving 2500–3500 mm annual rainfall. Ants (Hymenoptera: Formicidae), which constitute a substantial proportion of terrestrial faunal biomass and perform critical ecosystem functions including soil engineering, nutrient cycling, predation, scavenging, seed dispersal, and mutualism, are widely acknowledged as sensitive bioindicators of habitat quality and disturbance (Hölldobler & Wilson, 1990; Andersen, 1997; Del Toro et al., 2012; Schultheiss et al., 2022). Despite the recognized ecological importance of ants in tropical forests, systematic documentation in the southern Western Ghats remains limited. The present year-long survey (April 2024–April 2025) employed standardized pitfall trapping, Winkler leaf-litter extraction, and active hand collection across stratified habitats (primary forest, secondary forest, riparian zones, plantations, and human-disturbed areas) to assess species richness, community composition, functional roles, and bioindicator potential of Formicidae. A total of 68 species belonging to six subfamilies—Myrmicinae (47%), Formicinae (28%), Ponerinae (12%), Dolichoderinae, Dorylinae, and Pseudomyrmicinae—were documented. Species richness varied markedly across sites, with Kulathupuzha (40 species) and Thenmala (38 species) supporting the highest diversity in structurally complex evergreen and semi-evergreen forests, whereas semi-urban Anchal exhibited the lowest richness (28 species) dominated by disturbance-tolerant taxa such as Paratrechina longicornis and Tapinoma melanocephalum. Forest-interior and litter-dependent predators including Diacamma rugosum and Odontomachus haematodus were restricted to relatively undisturbed habitats, indicating strong habitat specialization and high beta diversity among sites. Invasive and synanthropic species were more prevalent in fragmented landscapes, reflecting ecological homogenization under anthropogenic pressure. Biodiversity indices revealed a high Shannon–Wiener value (H′ = 6) and low Simpson dominance (D = 0.04), signifying high diversity and evenness, although a low Menhinick index (0.02) suggested numerical dominance of certain taxa relative to total individuals. Functional trait analysis highlighted the role of ants as ecosystem engineers influencing soil structure, trophic regulation, seed dispersal, and mutualistic networks (Folgarait, 1998; Giladi, 2006). Collectively, the findings demonstrate that ant assemblages in the southern Western Ghats respond sensitively to gradients of forest integrity, elevation, and anthropogenic disturbance, reinforcing their value as ecological indicators and emphasizing the necessity of multi-site conservation strategies to preserve functional diversity and ecosystem resilience in this globally important biodiversity hotspot.