Aquatic-terrestrial linkages drive contrasting biodiversity patterns in tropical and temperate forests

Riparian ecosystems harbour unique biodiversity because of their close interconnections with adjacent aquatic ecosystems. Yet, how aquatic ecosystems influence terrestrial biodiversity over different spatial scales is poorly understood, particularly in the tropics. We conducted field campaigns to collect 235 terrestrial invertebrate assemblages along 150 m transects from 47 streams in both Brazil and the UK, compiling one of the largest known datasets of riparian invertebrate community composition at multiple spatial scales. Invertebrate densities increased towards water in both regions. In Brazil, this was driven by an increase in spiders, with a corresponding decrease in non-predators, resulting in higher predator : prey ratios near water. In the UK, non-predator densities increased towards water, decreasing predator : prey ratios. While pairwise dissimilarity increased with distance from water in both regions, β-diversity was significantly higher in tropical assemblages, with more β-diversity explained by turnover. Spider community composition was significantly structured by distance from water in the Brazilian sites, suggesting tropical assemblages were influenced more by emerging aquatic prey, with a distinct spider community replacing other predators, with possible top-down control of terrestrial prey. High turnover-driven dissimilarity among tropical assemblages suggests that Brazilian riparian ecosystems are better managed at the landscape scale, with an emphasis on in-stream measures preventing disruption of aquatic resource subsidies.