Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

A competition experiment of an invasive alien grass and two native species: are functionally similar species better competitors?

Abstract

Invasive plant species often outcompete natives when colonizing new areas, but the mechanisms behind their success are unclear. The limiting similarity hypothesis predicts that functionally similar species are more prone to compete than dissimilar ones. This ecological assumption can assist in the selection of a seed mixture for ecological restoration of disturbed sites, to control opportunistic exotic plants at early stages of establishment. We performed a greenhouse experiment to evaluate the competition effects of Stipa gigantea Link (Poaceae), a functionally similar species, and Lupinus luteus L. (Fabaceae), a dissimilar one, over the invasive Cortaderia selloana (Schultes & Schultes fil.) Asch. & Graebn (Poaceae). Our design included monospecific and mixed pots at three densities (one, two or four plants per pot) and different densities of the invader (0, 25, 50, 75 and 100%). We compared above-ground dry biomass, an indicator of resource limitation in growth, Specific Leaf Area (SLA), and several indexes obtained from the leaf reflectance spectrum, indicators of physiological stress. Cortaderia showed strong intraspecific competition, with lower plant biomass at higher densities. When grown in competition, Cortaderia was outcompeted by Stipa, which performed better than in unmixed pots, but was not affected by Lupinus. Slight variations in SLA and photosynthetic performance were observed in Cortaderia, demonstrating a higher plasticity than the native species, which did not show any response. Based on our results, we suggest that Cortaderia is a weak competitor compared to a similar native species, and its advantage must lie in other traits such as its facility to generate large amounts of propagules and its efficiency in early stages of seedling growth. Functionally similar species may be an adequate choice for restoration in order to outcompete invasive plants.