Competition among native and invasive Impatiens species: the roles of environmental factors, population density, and life stage

Impatiens glandulifera Royle has broader ecological niche than expected. Expansion from river banks is thus possible. Photo taken at castle ruins above the Jizera river. Photo: Jan Čuda.
Impatiens glandulifera Royle has a broader ecological niche than expected. Expansion from river banks is thus possible. Photo taken at castle ruins above the Jizera river. Photo: Jan Čuda.

Many invasive species are considered competitively superior to native species, with the strongest competition expected in species with similar niches and/or in closely related species. However, competition outcome is strongly context-dependent as competitive strength varies along environmental gradients and life stages, and also depends on abundances. In a recent study published in AoB PLANTS, Čuda et al. examined competition effects in an experiment with three Impatiens species (Balsaminaceae) sharing similar life-history characteristics and habitats: the native I. noli‑tangere, and two invasive species, I. parviflora and I. glandulifera. The results suggest that the effect of competition on the performance of invasive Impatiens species exceeds that of environmental factors, i.e. light and soil moisture. Competitive interactions with co-occurring congeners may thus be a more important predictor of the invasion success of an invasive species and its population dynamics than its response to abiotic factors, and should be taken into account when evaluating their invasion potential.