Impact of alien species on species composition, floristic and functional diversity of aquatic and terrestrial ecosystems

Abstract

Biotic homogenization is a major component of current biodiversity crisis involving increase in floristic, functional and genetic similarity of biotas resulting from species invasions and extirpations. Since habitat type is a good predictor of success of biological invasion at local scale, we studied distribution and abundance of native and alien plant species in eight habitat types namely lakes, wetlands, riparian, roadsides, orchards, grasslands, scrubs, and forests (06 sites each giving a total of 48 sites). For estimating taxonomic homogenization index, we calculated Jaccard’s similarity index separately for native, alien and alien + native species. We also calculated functional α, β, and γ diversity for three functional traits in three different ways i.e. with all species included, with only native species included and with only alien species included. We observed that habitats differ with respect to functional and floristic diversity. Aquatic habitats (species poor) were found to be more homogenous (average βA = 0.58) than terrestrial habitats (average βA = 0.68) with man-managed habitats (orchards) being taxonomically (average βA = 0.59) and functionally (FβA = 0.04) most homogenous among terrestrial habitats. Present study revealed that traits of alien plant species play an important role in determining the homogenization potential as invasives (in comparison to naturalized and casuals), perennials (in comparison to annual/biennials), herbaceous (in comparison to shrubs/sub-shrubs/lianas and trees) and submerged plants (in comparison to free floating, rooted floating and emergents) were found more homogenizing. These observations are crucial in understanding the homogenizing effects of alien species and in particular the underlying impact of taxonomic homogenization on functional stability of ecosystems.