Abstract
This year-long study, covering three main seasons of India, focused on enumerating the effect of varying cover of Alternanthera philoxeroides (alligator weed) on the associated macrophyte species diversity of the littoral region of natural pond ecosystem. A total of 192 quadrats were randomly placed in the littoral region of 12 similar ponds containing varying degrees of A. philoxeroides infestation to estimate A. philoxeroides ‘cover (%)’ and number of associated macrophyte species in each quadrat. Overall, 20 associated macrophyte species, including 16 aquatic/ littoral-associated, 2 non-aquatic species, and grasses and sedges, were found to be present. A. philoxeroides infestation was categorized into 4 cover grades (Grade I-IV) from lowest (no/negligible: 60% cover). For each season, significant differences in the total number of associated macrophyte species across the 4 A. philoxeroides cover grades were found. A Poisson-regression model showed that for each season, even when the effect of other invasive species was adjusted, the number of associated native macrophyte species in a quadrat decreases significantly with increase in A. philoxeroides cover. A comparison of the quadrat communities between the lowest grade (Grade I) and highest grade (Grade IV) of A. philoxeroides infestation showed a significant reduction of species richness, diversity and evenness from the lowest to the highest infestation grades. Again, Mann-Whitney U tests further revealed that the number of native macrophyte species was significantly lower at highest (Grade IV) A. philoxeroides infestation than that at lowest infestation (Grade I). The presence of multiple invaders in A. philoxeroides infested aquatic ecosystems is also reported, indicating probable facilitative interactions between A. philoxeroides and other invasive species. The socio-economic valuation of some important native plants, which were found to be significantly reduced at high infestation levels of A. philoxeroides, has also been highlighted.
Highlights
The introduction and spread of non-native species has become a global ecological and conservation crisis as invasive organisms are increasingly altering terrestrial and aquatic communities worldwide, causing catastrophes for the native ecosystems (McNeely 2001), leading to biodiversity loss (Powell et al 2011) and local extinction of native species (Butchart et al 2010)
This study aimed to investigate the impact of A. philoxeroides invasion on the associated macrophyte diversity of littoral zones of natural pond ecosystems
The box plots show that the mean cover (%) of A. philoxeroides was higher during monsoon (34.72%), followed by summer (26.79%), while it was lowest during winter (16.95%)
Summary
The introduction and spread of non-native species has become a global ecological and conservation crisis as invasive organisms are increasingly altering terrestrial and aquatic communities worldwide, causing catastrophes for the native ecosystems (McNeely 2001), leading to biodiversity loss (Powell et al 2011) and local extinction of native species (Butchart et al 2010). Invasive species may inflict harmful ecological and economic impacts upon ecosystems in non native regions (Pimentel et al 2005). They can lead towards ecosystem degradation and impairment of ecosystem services worldwide (Pysek and Richardson 2010), thereby inducing high conservation concerns (Wilcove et al 1998). Loss of native biodiversity threatens the productivity and sustainability of ecosystems (Tilman et al 1996), and has significant socioeconomic and environmental impacts, especially in developing, over-populated countries of Asia and Africa (Juffe-Bignoli et al 2012)
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