Data from: Fatty acid biomarkers reveal landscape influences on linkages between aquatic and terrestrial food webs

Stream and riparian habitats are meta-ecosystems that can be strongly
connected via the emergence of aquatic insects, which form an important
prey subsidy for terrestrial consumers. Anthropogenic perturbations that
impact these habitats may indirectly propagate across traditional
ecosystem boundaries, thus weakening aquatic-terrestrial food web
linkages. We investigated how algal production, aquatic invertebrates, and
terrestrial spiders influence cross-ecosystem connectivity in temperate
streams across four European catchments with varying levels of human
disturbance. We used fatty acid biomarkers to measure putative aquatic
linkages to riparian spiders. Variation partitioning analysis indicated
that aquatic insect dispersal traits explained a relatively large
proportion of variability in the fatty acid profile of spiders. Trophic
connectivity, as measured by the proportion of the polyunsaturated fatty
acid eicosapentaenoic acid (EPA) and the ratio of EPA to its chemical
precursor, alpha-linolenic acid (ALA), were positively associated with
abundances of ‘aerial active’ dispersing aquatic insects. However, this
positive influence was also associated with changes in environmental
context and arachnid beta diversity. Structural equation modelling
disentangled how aquatic insect communities influence trophic connectivity
with riparian predators after accounting for biological and environmental
contingencies. Our results show how subsidies of stream insects are a
putative source of essential fatty acids for adjacent terrestrial food
webs. Catchment-wide impacts indirectly propagated to the local scale
through impacts on aquatic invertebrate communities, thus affecting
stream-riparian food webs. Increased riparian tree cover enhanced stream
insect subsidies via dispersal traits despite reducing aquatic primary
production through shading. Consequently, ecosystem properties such as
woody riparian buffers that increase aquatic-terrestrial trophic
connectivity have the potential to affect a wide range of consumers in
modified landscapes.