Impacts of marine invaders on biodiversity depend on trophic position and functional similarity

Abstract

Impacts of marine invaders on local biodiversity have not been analyzed across invasive species and invaded habitats. We conducted a meta-analysis of 56 field experiments published in 29 papers that examined the effects of marine invaders on local species richness, diversity, and/or evenness. We show that invaders, across studies, typically have negative effects on biodiversity within a trophic level but positive effects on biodiversity of higher trophic levels. For example, both plants and sessile filter-feeders had positive effects on richness and diversity of mobile consumers. The contrasting negative and positive effects on similar versus higher trophic levels are potentially manifested through community-wide antagonism (competition and consumption) versus facilitation (habitat and food provisioning) interactions, respectively. These relation ships extended to functional interactions, as sessile invaders had negative effects on the biodiversity of sessile communities (intra-functional interactions) but positive effects on the biodiversity of mobile communities (inter-functional interactions). Our analyses highlight the importance of pairing attributes of the invader and the impacted organisms to obtain simple predictions of how the diversity of entire communities may respond to species invasions on local scales. We also note that our analysis did not require information on co-evolutionary history but that such data, coupled with long-term large-scale mensurative data, are needed to gain a comprehensive predictive insight into invasion impact.

An invasive foundation species enhances multifunctionality in a coastal ecosystem

“…Related analyses also suggest biases that favor finding negative effects, and, as a consequence, the potential benefits of invasive species may have been overlooked (19,20). For example, most studies (i) examine impacts when invasive species are displacing functionally similar native species (21)(22)(23)(24), (ii) consider only one or few related response variables when assessing the impacts of invaders (19,20), (iii) are conducted on small spatial scales (e.g., in aquatic systems typically ≤1 m 2 ; refs. 25 and 26), and (iv) rarely incorporate multiple abundance levels, despite the fact that impacts depend fundamentally on the abundance of the invader (26,27).…”

Ecosystem impacts of the widespread non-indigenous species in the Baltic Sea: literature survey evidences major limitations in knowledge

“…Katsanevakis et al, 2014). However, these should be inevitably accompanied by relevant fieldworks at appropriate spatio-temporal scales as the NIS effects are expected to vary both in space and time, due to changes in population characteristics, local conditions, and scale dependent processes (Ruiz et al, 1999;Thomsen et al, 2014).…”

Variations in importance and intensity of competition underpin context dependency in the effects of an invasive seaweed on resident assemblages

“…It is worth stressing that the relevance of assessing variations in both the intensity and importance of species interactions is not limited to competition, but it extends to facilitation. There is, in fact, compelling evidence that species interactions can switch from negative to positive and vice versa according to environmental conditions (Bertness and Callaway 1994) and that the effects of invaders on native communities or species are not necessarily negative (Thomsen et al 2014;Maggi et al 2014). The use of indexes assessing variations in the intensity of competition is increasingly common in invasion studies (Vilà et al 2004;Xiao et al 2013).…”