Abstract
Understanding how global change and connectivity will jointly modify the distribution of riverine species is crucial for conservation biology and environmental management. However, little is known about the interaction between climate change and fragmentation and how movement barriers might impede native species from adjusting their distributions versus limit the further spread of alien species. In this study, we modelled the current and future distributions of 11 native and five alien fishes in the large and heavily fragmented Ebro River, located within the Mediterranean region, which has many freshwater endemics severely threatened by global change. We considered 10 climate change models and five modelling algorithms and assessed the effects of connectivity on the accessibility of future suitable habitats. Thereby, we identify most conflict-prone river reaches, that is, where barriers pose a particular trade-off between isolating and negatively impacting native species versus potentially reducing the risk of alien species spread. Our results projected upstream habitat shifts for the vast majority of the species. Climate change affected species differently, with alien species generally showing larger habitat gains compared to natives. Most pronounced distributional changes (i.e. losses of native species and gains of alien species) and compositional turnover might be expected in the lower and mid reaches of large tributaries of the Ebro River. The role of anthropogenic barriers in this context is often ambiguous but rather unfavourable, as they not only restrict native fishes but also alter stream habitats and flow conditions. However, with our spatial modelling framework, we could identify specific river reaches where the connectivity trade-off in the context of climate change is particularly relevant. Overall, our findings emphasize the importance of the complex effects that climate change, riverine connectivity and alien species are expected to impose on river communities and the urgent need to adapt management strategies accordingly.
Highlights
Climate change has become a major driver of unprecedented rates of global biodiversity change (Bellard, Bertelsmeier, Leadley, Thuiller, & Courchamp, 2012)
It has become clear that invasive alien species pose a further dominant threat to biodiversity worldwide that interacts with climate change (Bellard, Jeschke, Leroy, & Mace, 2018; Ziska & Dukes, 2014)
33% of the European freshwater fishes, especially those in the Mediterranean, are already recognized as susceptible to climate change (Jarić, Lennox, Kalinkat, Cvijanović, & Radinger, 2019). In particular those of cold water river species, are commonly projected to shift to higher altitudes (Comte & Grenouillet, 2013; Isaak & Rieman, 2013; Pörtner & Farrell, 2008); specific spatial realizations of habitat shifts are further complicated by interactions with other anthropogenic drivers of global change such as land use change or habitat degradation and fragmentation by barriers (Grenouillet & Comte, 2014; Herrera-R et al, 2020; Radinger et al, 2016, 2017)
Summary
Climate change has become a major driver of unprecedented rates of global biodiversity change (Bellard, Bertelsmeier, Leadley, Thuiller, & Courchamp, 2012). There is an urgent need to better understand the interactive effects of climate change and the spread of alien species, especially in the context of riverine connectivity and the antithetical role of movement barriers To address this question, we focus on the Ebro River, Spain, which is highly fragmented by anthropogenic barriers (Radinger, Alcaraz-Hernández, Alcaraz-Hernández, & GarcíaBerthou, 2018), and located within the Mediterranean region, where many endemic species are threatened by future climate change (Jarić et al, 2019; Maceda-Veiga, 2013). We expect that barriers impede species from tracking suitable habitats in particular those species that show largest climate change induced habitat shifts
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