Abstract
Competition is commonly thought to underlie the impact of plant invasions. However, competitive effects of aliens and competitive response of natives may also change over time. Indeed, as with time, the novelty of an invader decreases, the accumulated eco-evolutionary experience of resident species may eventually limit invasion success. We aimed to gain insights on whether directional changes in biotic interactions over time or more general differences between natives and aliens, for instance, resulting from an introduction bias, are relevant in determining competitive ability. We conducted a pairwise competition experiment in a target-neighbour design, using 47 Asteraceae species with residence times between 8 years-12,000 years in Germany. We first tested whether there are differences in performance in intraspecific competition amongst invasion status groups, that is casual and established neophytes, archaeophytes or native species. We then evaluated whether competitive response and effects depend on residence time or invasion status. Lastly, we assessed whether competitive effects influence range sizes. We found only limited evidence that native target species tolerate neighbours with longer potential co-existence times better, whereas differences in competitive ability were mostly better explained by invasion status than residence time. Although casual neophytes produced most biomass in intraspecific competition, they had the weakest per-capita competitive effects on natives. Notably, we did not find differences between established neophytes and natives, both of which ranked highest in interspecific competitive ability. This lack of differences might be explained by a biased selection of highly invasive or rare native species in previous studies or because invasion success may result from mechanisms other than interspecific competitive superiority. Accordingly, interspecific per-capita competitive effects did not influence range sizes. Further studies across a broader range of environmental conditions, involving other biotic interactions that indirectly influence plant-plant interactions, may clarify when eco-evolutionary adaptations to new invaders are a relevant mechanism.
Highlights
Biological invasions are a major driver of global change, posing a threat to native species, communities and ecosystems (Simberloff et al 2013; Pyšek et al 2020)
Understanding whether alien species benefit from higher interspecific competitive ability and whether the resulting local dominance is linked to large-scale invasion success, is crucial for conservation management
Performance in intraspecific competition may be an important determinant of invasion success, given that alien species often dominate in dense monospecific stands
Summary
Biological invasions are a major driver of global change, posing a threat to native species, communities and ecosystems (Simberloff et al 2013; Pyšek et al 2020). Competition is the most commonly invoked mechanism by which alien species impact natives (Levine et al 2003). Understanding whether alien species benefit from higher interspecific competitive ability and whether the resulting local dominance is linked to large-scale invasion success, is crucial for conservation management. According to Parker et al (1999), an invader’s potential impact is the product of abundance, per-capita effect and range size. It has long been suggested that locally-abundant species are generally the ones that are widespread (Lawton 1993) and that rare species are competitively inferior (Griggs 1940). Some studies have found that alien species with higher local interspecific competitive ability may reach larger range sizes (Milla et al 2011; Sheppard 2019), other studies with native species have not consistently found such an effect Performance in intraspecific competition may be an important determinant of invasion success, given that alien species often dominate in dense monospecific stands
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