Environmental filtering governs the spatial distribution of alien fishes in a large, human‐impacted Mediterranean river

Abstract

Aim:To analyse the occurrence and abundance of native versus alien fish species in relation to climate, land use, hydrologic alteration and habitat fragmentation in a heavily invaded and human-impacted riverine ecosystem. To test whether co-occurrence patterns of native versus alien species are structured by environmental filtering or biotic associations.Location: Mediterranean, Iberian Peninsula, Ebro River catchment. Methods:We modelled freshwater fish distributions and their association with environmental conditions using a hurdle model-like approach involving boosted regression trees. Additionally, we applied a joint species distribution model to quantify the co-occurrence of native versus alien fish species that can be attributed to shared environmental responses or potentially to biotic interactions. Results:Our results point to environmental factors, rather than biotic associations, as major correlates of the increase of alien and the decline of native fishes in the Ebro River. We observed contrasting patterns of native versus alien species along the upstream-downstream gradient. Alien species dominated in the lower reaches associated with warmer temperatures, higher shares of intensive land use and appeared facilitated by dams and river regulation. Native species richness was highest in the larger tributaries followed by a strong decline in the main stem which was related to the river network position and land use type. Fragmentation played a subordinate role in explaining fish richness and abundance patterns.Main conclusions: Given the strong association with temperature, a further range expansion of alien fishes in the Ebro with future climate change may be expected.More local-scale factors related to habitat degradation and hydrologic alteration will further exacerbate the invasion success of many alien fishes. Further multiple, independent species introductions might mask isolation and fragmentation effects of dams on the future spread and distribution of alien fish. K E Y W O R D Sboosted regression trees, Ebro River, environmental filtering, freshwater fish, habitat degradation, invasive alien species, joint species distribution model, native species decline, species co-occurrence

Increasing climate‐driven taxonomic homogenization but functional differentiation among river macroinvertebrate assemblages

“…Although these New Zealand streams have seen an increase in functional diversity over the 25 year period, more intensified disturbances are likely to suppress or overturn this trend (Domisch et al., 2013; Kakouei et al., 2018). For example, an increasing number of colonizing warm water species could promote further species losses, by competitive exclusion (Buisson et al., 2008; Radinger et al., 2019). Moreover, the resilience of stream biodiversity in the face of continued global change could also be reduced if spatial insurance effects become less effective, as large‐scale disturbances promote greater synchrony among ecosystems (Shanafelt et al., 2015).…”

Species‐pair associations, null models, and tests of mechanisms structuring ecological communities

“…) and Radinger et al. () used a similar approach (joint species distribution models) to analyze the relative influence of biotic interactions or environmental responses of the co‐occurrence patterns of plant communities along an altitudinal gradient and native versus alien fish species, respectively. Both studies found a higher influence of the environment as well on the association patterns observed between species.…”

“…For example, using fossil pollen taxa, Blois et al (2014) found that biotic interactions were rarely the only cause of associations between species pairs, but climatic or spatial differences among locations were more frequently related to significant co-occurrence patterns. D'Amen et al 2018) and Radinger et al (2019) used a similar approach (joint species distribution models) to analyze the relative influence of biotic interactions or environmental responses of the co-occurrence patterns of plant communities along an altitudinal gradient and native versus alien fish species, respectively. Both studies found a higher influence of the environment as well on the association patterns observed between species.…”

Combining geostatistical and biotic interaction model to predict amphibian refuges under crayfish invasion across dendritic stream networks

“…Under biological invasion, many native species are becoming confined to refuges where invasive species are still absent or scarce, and thus may hold remnant populations of high conservation value (e.g. Chapman et al, 1996;Grabowski et al, 2009;Habit et al, 2010;Radinger et al, 2019). This study provides a framework to predict the location and environmental drivers of such refuges, using geostatistical tools to model native species responses to exotic species while controlling for environmental effects and spatial dependencies across dendritic stream networks (Filipe et al, 2017;Peterson et al, 2013).…”

“…Refuges may thus allow the persistence of at least some remnant populations of native species (e.g. Chapman et al, 1996;Grabowski, Bacela, Konopacka, & Jazdzewski, 2009;Habit et al, 2010;Radinger, Alcaraz-Hernández, & García-Berthou, 2019), making it a priority to understand where, why and how refuges can contribute to species conservation under biological invasion.…”