Ecotypic variation in the competitive effects of Solidago gigantea: Plants from low elevations are better competitors than plants from high elevations

Background/Question/Methods

Invasive plant species often behave differently in their new geographic ranges than in their native ranges.  Plants from non-native populations can be larger, more reproductive, and exhibit greater competitive ability.  However, within ranges species can vary substantially in size and competitive ability among populations.  But whether ecotypic differences differ between ranges has not been explored.

We conducted a greenhouse experiment with 15 Solidago gigantea populations from the native range in North America, and 15 from the non-native range in Europe.  These collected from high and low altitudes, and from wet and dry habitats.  We grew plants alone, and with each of 11 commonly co-occurring species native to North America.  We calculated Relative Interaction Indices and compared them with a generalized mixed-effect linear model.

Results/Conclusions

Overall, Solidago from Europe did not exhibit greater competitive ability than North American populations.  In contrast, native populations were less inhibited by North American competitors than non-native populations (for belowground biomass, F_range = 3.088, P=0.088; for number of lateral shoots, F_range = 13.378, P=0.001).  The altitudinal origins of populations highly influenced competitive performance. Populations from low altitudes were less affected by competition than populations from high altitudes (for the number of lateral shoots, F_altitude = 6.622, P=0.015).  We also found a strong altitude × habitat interaction meaning that populations from low altitudes and wet habitats were more resistant to competition from other species than those from dry habitats, whereas populations from high altitudes and wet habitats were less resistant to competition than populations from dry habitats.  The performance of other North American species when competing with Solidago was significantly inhibited by competition of Solidago, but this did not vary with native vs.  non-native ranges, altitude or habitat.

Our results show strong ecotypic variation in competitive ability for Solidago gigantea and demonstrate that the effect of ecotypic variation is not consistent between the native and non-native ranges.

Acknowledgements The research was supported by the Marie Curie Actions of the European Union’s FP7/2007-2013 Programme under REA 300639 (R.W.P.), and the MJ Murdock Charitable Trust’s Partners in Science Program (P.M).