Abstract:
Plants inhabiting extremely stressful mine site environments tend to be specialized and localized, where they express lower performance than nonmine site plants from adjacent areas. However, such a cost may be concealed. In a previous study at a mine site, we found mine and adjacent nonmine plants of multiple species expressed similar performances in the absence of competition. However, a lower competitive ability may be a concealed driver. We aim to test whether costs under competition could explain specialization. In a glasshouse experiment, we measured the performance (i.e. vegetative and reproductive growth) of mine and nonmine potted plants under competition. The 6 herbaceous species tested were Anagallis arvensis 1., Cirsium vulgare (Savi) Ten., Conyza sumatrensis Retz., Echium vulgare L., Oxalis chnoodes Lourteig, and Senecio diaschides D.G.Drury. We exposed individuals to interspecific competition using a local grass (Polypogon monspeliensis), as well as to intraspecific competition. Plants were grown alone for the control group. For all treatments, the mine plants expressed similar performances to the nonmine plants, except for mine site O. chnoodes, which had lower performance under intraspecific competition. Mine plants of A. arvensis and C. sumatrensis had higher performance than nonmine plants. Overall, there was no evidence of specialization in the mine site plants. These results indicate that, under some circumstances, inhabiting a stressful metal habitat does not promote specialization in multiple species. Future research may focus on assessing the environmental conditions and population genetics that promote the evolution of generalists that inhabit extremely stressful environments.