Richard Field

Aim Ecological refuges buffer organisms against stressors and mediate a range of species interactions. However, their role in the context of biological invasions has yet to be synthesized, despite the increasing prevalence and impact of non‐native species. To address this, we conducted a systematic review aiming to determine the extent to which refuges are considered explicitly in the invasion literature and to synthesize their function. Location Global. Time period Present day. Major taxa studied All. Methods Our search of the literature was conducted using the SCOPUS and Web of Science databases and followed the preferred reporting items for systematic reviews and meta‐analyses (PRISMA) protocol. We obtained 315 records of refuge use in biological invasions from 300 studies. From each record, we extracted information relating to the experimental design, species characteristics and refuge type, where available. Results Refuges and refuge‐mediated processes are widely reported in the invasion literature. Native species commonly use refuges to avoid non‐native predation and competition, with spatial complexity and habitat heterogeneity key factors in facilitating their coexistence. Records show that artificial structures safeguard non‐natives in their introduced range. However, there were key differences in the use of such structures in marine and terrestrial environments. Moreover, the enhanced structural complexity created by non‐native plants and bivalves is often reported to act as a predation refuge for other species. Main conclusions The ubiquity of refuge‐based processes suggests that refuges can play an important role in affecting the persistence, spread and impacts of non‐native species, either through previously described mechanisms (i.e. refuge‐mediated apparent competition and the persistent pressure scenario) or through a mechanism we describe (i.e. when non‐native species use existing refuges), or both.

Questions Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non‐endemic species. We hypothesized that endemic species show lower intraspecific variation than non‐endemic species because they tend to have high rates of in situ speciation, whereas non‐endemic species are expected to have a larger gene pool and higher phenotypic plasticity. Location La Palma, Canary Islands. Methods We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non‐endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community‐weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient. Results The contribution of intraspecific variation to total variation was similar in endemic and non‐endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation. Conclusions Despite their distinct evolutionary history, endemic and non‐endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non‐endemic species compared with endemic species.