Invasion by alligator weed, Alternanthera philoxeroides, is associated with decreased species diversity across the latitudinal gradient in China

Aims Invasive species occurrence and their effects on biodiversity may vary along latitudes. We examined the occurrence (species cover) and relative dominance (importance value) of invasive alligator weed, Alternanthera philoxeroides, in its terrestrial habitat in China through a large-scale latitudinal field investigation. Methods We established 59 plots along the latitudinal transect from 21 degrees N to 37 degrees N. We recorded species name, abundance, height and individual species coverage of plants in every quadrat. We then measured alpha-species diversity variations associated with the A. philoxeroides community across the latitudinal range. We also analyzed the effect of latitude on plant species' distributions in this community by using canonical correspondence analysis (CCA). Important Findings We found that species cover and importance value of A. philoxeroides increased in areas <35 degrees N, but decreased at higher latitudes. Lower latitudes supported greater species diversity than higher latitudes. Small-scale invasion of A. philoxeroides was associated with higher species diversity, but community diversity was lower when A. philoxeroides species cover exceeded 36%. Community plant species changed from mesophyte to hygrophyte gradually from low to high latitude. Our research suggests that latitude had significant influences on community diversity which interacted with the biotic resistance of a community and impact of invasion. Consequently, A. philoxeroides may become more invasive and have greater negative impacts on community species diversity in higher latitudes as global climate changes.