Biotic interactions experienced by a new invader: effects of its close relatives at the community scale

Abstract

The success of nonindigenous species may be influenced by biotic interactions during the initial stages of invasion. Here, we investigated whether a potential invader, Solidago virgaurea L., would experience more damage by natural enemies in communities dominated by close relatives than those without them; interactions with mutualistic mycorrhizae might partially counteract these effects. We monitored damage experienced by S. virgaurea planted into communities with native congeners and without close relatives. Community type was crossed with a vegetation removal treatment to assess the combined effects of herbivory and competition on survival. We also evaluated growth of S. virgaurea in a greenhouse experiment where seedlings were exposed to soil biota sampled from these communities and compared with sterile controls. Overall, community type did not affect levels of herbivory or plant survival. Removal of surrounding vegetation resulted in reduced damage and increased survival; these effects were largest in grass-dominated communities. Soil sterilization reduced root growth and tended to reduce shoot growth, especially when compared with plants inoculated with biota collected near congeners. Overall, our results suggest that the presence of close relatives is unlikely to make old-field communities more resistant to invasion by S. virgaurea; instead, soil biota might facilitate growth in communities dominated by close relatives.