Functional landscape connectivity and cropland context influence spider abundance in the ecological infrastructure of Mediterranean agricultural floodplains

Agricultural intensification, particularly in water-scarce Mediterranean floodplains, threatens the provision of Ecosystem Services and natural habitats. Spiders (Arachnida: Araneae) are key natural enemies of pests in agricultural landscapes and contribute substantially to natural pest suppression, but they are vulnerable to habitat loss and fragmentation. Ecological Infrastructure (EI) – the network of natural and semi-natural vegetation patches in altered landscapes – provides crucial resources for these arthropods. While previous research has highlighted the importance of spatial scale and landscape composition, few studies have incorporated aspects of landscape configuration, such as functional habitat connectivity. To address this gap, we used Generalised Linear Mixed Models to investigate the local- and landscape-scale features of EI driving spider abundance in two Portuguese Mediterranean floodplains (Tagus and Sorraia). Functional connectivity was quantified using the Integral Index of Connectivity (IIC) with two dispersal distance thresholds (50 m and 300 m). Our multi-scale analysis revealed that functional connectivity was a significant positive driver of spider abundance at both local and landscape scales, underscoring the importance of landscape configuration. Furthermore, the local physiognomy of the EI patch (riparian vs. terrestrial) and the nearest crop type in the surrounding matrix were relevant variables. Spider abundance was significantly higher in riparian EI patches and in patches nearest to rice crops. Overall, this work clearly identifies that beyond spatial scale and composition, landscape configuration is a key environmental feature to support populations of natural enemies. Furthermore, the findings of this study emphasise that effective conservation strategies targeting pest natural enemies in Mediterranean floodplains must adopt a multi-scale approach, prioritising the preservation of the EI as well as the maintenance of functional connectivity and landscape composition characteristics. Future research directions include incorporating temporal dimensions and further exploring the role of landscape configuration and local crop management practices on spider predation. • Spider abundance was assessed in Portuguese Mediterranean agricultural floodplains. • Local- and landscape-scale features of ecological infrastructure influenced spiders. • These included nearest crop type, patch connectivity, physiognomy and size. • EI patches contributing more to functional landscape connectivity supported spiders. • Landscape configuration and patch characteristics determine spider abundance.