Resource competition in plant invasions: emerging patterns and research needs

Abstract

Invasions by alien plants provide a unique opportunity to examine competitive interactions among plants. While resource competition has long been regarded as a major mechanism responsible for successful invasions, given a well-known capacity for many invaders to become dominant and reduce plant diversity in the invaded communities, few studies have measured resource competition directly or have assessed its importance relative to that of other mechanisms, at different stages of an invasion process. Here, we review evidence comparing the competitive ability of invasive species vs. that of co-occurring native plants, along a range of environmental gradients, showing that many invasive species have a superior competitive ability over native species, although invasive congeners are not necessarily competitively superior over native congeners, nor are alien dominants are better competitors than native dominants. We discuss how the outcomes of competition depend on a number of factors, such as the heterogeneous distribution of resources, the stage of the invasion process, as well as phenotypic plasticity and evolutionary adaptation, which may result in increased or decreased competitive ability in both invasive and native species. Competitive advantages of invasive species over natives are often transient and only important at the early stages of an invasion process. It remains unclear how important resource competition is relative to other mechanisms (competition avoidance via phenological differences, niche differentiation in space associated with phylogenetic distance, recruitment and dispersal limitation, indirect competition, and allelopathy). Finally, we identify the conceptual and methodological issues characterizing competition studies in plant invasions, and we discuss future research needs, including examination of resource competition dynamics and the impact of global environmental change on competitive interactions between invasive and native species.

Indirect interactions in terrestrial plant communities: emerging patterns and research gaps

“…Indirect effects have also been examined to improve our understanding of the efficacy of the use of v www.esajournals.org biocontrol agents to control invasive populations, with studies showing that the presence of alternative hosts decreased the effectiveness of biological control, while increasing the richness of a particular guild of natural enemies can reduce the density of a widespread group of herbivorous pests and increase crop yields (Cardinale et al 2003). Overall, the importance of indirect interactions relative to direct interactions, such as resource competition, in promoting successful invasions is largely unknown (Gioria andOsborne 2014, but see Palladini and. Additional studies are required to examine the role of indirect interactions in promoting plant invasions and how indirect effects may be manipulated to control plant invasions.…”

Interactions between seedlings of the invasive treeAilanthus altissimaand the native treeRobinia pseudoacaciaunder low nutrient conditions

“…In fact, the ability to tolerate a low nitrogen environment is essential to the strong competitive ability of R. pseudoacacia (Boring & Swank 1984a;Gioria & Osborne 2014), and is a main reason why R. pseudoacacia is considered to be a good invasive species itself outside of its native range in the eastern USA (Castro-Díez et al 2008). The comparatively small size of A. altissima seedlings in this study suggested that the nutrient levels used may have been too low for A. altissima to thrive in a sandy environment.…”

“…Some researchers suggest that the superior competitive ability of invasive species over native species is closely related to more efficient resource acquisition or resource conservation (Tecco et al 2010;Gioria & Osborne 2014). A variety of invasive species have higher resource-use efficiency than native species, especially in low-resource environments (Funk & Vitousek 2007).…”

Interaction between invasive and potentially invasive shrub species does not influence relationships between their ecological success and distance from propagule sources

“…However, in studies concerning relationships between invasive and native species, authors frequently focused only on competition between the alien and native species, and intraspecific competition, neglecting relationships between two invaders (e.g., Mangla et al 2011;Rodríguez-Echeverría et al 2013). Studies concerning relationships between two alien species are relatively rare, but essential to better understanding the competitive interactions among alien species, and increase our knowledge of secondary invasions (Gioria and Osborne 2014). It is especially important when occurrence of earlier-established invaders modifies environments in ways which facilitate dispersal distance of secondary alien species, according to the invasional meltdown concept (Simberloff and Von Holle 1999;Simberloff 2006;Gioria et al 2011).…”