Seasonal variation in spider abundance in Muthupet mangroves, South East coast of Tamilnadu, India

Abstract

The abundance, dominance and diversity of the arachnid population are influenced by their habitat’s microclimate and environmental variables. Here we evaluated a seasonal dominance, diversity and richness pattern of the arachnid population and their guild composition in the Muthupet mangrove forest. Most of the spiders were aggregated from specific mangrove plants such as Avicennia and Rhizophora species by adopting standard hand-picking and net-sweeping methods and employing bark traps, pitfall traps and leaf litter traps. A total of 14 families, 29 genera and 47 species of arachnids were recorded. The sequence of the abundance of the families was: Araneidae > Tetragnathidae > Lycosidae > Salticidae > Oxyopidae > Eresidae > Liniphidae > Clubionidae > Sparassidae > Uloboridae > Hersilidae > Gnaphosidae = Thomisidae > Miturgidae. The annual average population density of spiders was maximum (36.13%) during the post-monsoon (January, February, and March) and summer seasons. The minimum seasonal mean population density was during the pre-monsoon and monsoon periods, attributed to the changes in temperature, relative humidity and rainfall. The Muthupet mangrove forest registered six types of guilds. The dominant group was orb-weavers (62.44%), followed by foliage runners (15.11%). The rest of the guilds were represented by tunnel web builders (15.78%), ground runners (2.23%), communal web weavers (4.41%), and ambushers (0.03%). Thus, changes in environmental parameters produced alterations in arachnid abundance and diversity. Moreover, the predatory potential of the arachnids relies chiefly on the composition of spider assemblages, which in turn, gets impacted by abiotic factors of its environment.