A preliminary investigation on the dependence of arthropod diversity on vegetation diversity across four contrasting ecosystems in Hanthana mountain range of Sri Lanka

Abstract

Arthropods contribute significantly to biodiversity and vegetation provides a habitat and resources for them to survive, exist and propagate. We report a preliminary investigation on the extent to which arthropod diversity is dependent upon vegetation diversity across different ecosystems in a humid tropical climate. We determined the diversity of arthropods in four ecosystems closely-located ecosystems with different vegetation. Vegetation surrounding an aquatic environment (AQ), a broad-leaved wet, evergreen forest ecosystem (BL), a Pinus caribaea monoculture plantation (PN) and a Pinus plantation artificially enriched with indigenous broad-leaved tree species (PNEN) located in the Hanthana mountain range in Central Sri Lanka were selected. In each environment, arthropods were sampled in three randomlyselected sites (5 m x 5 m) using four sampling methods. Collected arthropods were identified upto the highest possible taxa using standard identification keys. Simultaneously, vegetation diversity was determined via a plant census. Arthropod and vegetation diversities were computed separately for each site using Shannon-Wiener Index (H).Within the 300 m 2 area of observation plots, arthropod individuals belonging to 68 species and 43 families were found. AQ had the greatest arthropod diversity (H=2.642), dominated by Olios spp. followed by BL (H=2.444), dominated by three arthropods, namely, a tettigonid species, Oxytate spp. and Psechrus spp. PN had the next highest arthropod diversity (H=1.411), dominated by Dicaldispa spp. The lowest arthropod diversity was found at PNEN (H=1.3500), dominated by an ant species. Contrastingly, PNEN had the highest plant diversity (H=2.614) and PN the lowest (H=0.879). AQ (H=1.810) and BL (H=1.871) had intermediate values.In a regression involving data from AQ, BL and PN, arthropod diversity was linearly dependent on plant diversity (R 2 =0.423) whereas it was not so when PNEN was also included (R 2 =0.008).This finding supports the hypothesis that while higher plant diversity contributes to greater arthropod diversity in ecosystems where human intervention is minimal, artificial enrichment of plant diversity does not necessarily increase arthropod diversity in the short-to medium-term.Further investigations are needed to substantiate these preliminary findings and validate the above hypothesis.