The strength of ecological subsidies across ecosystems: a latitudinal gradient of direct and indirect impacts on food webs.

Material and energy flows among ecosystems can directly and indirectly drive ecosystem functions. Yet, how populations of consumers respond to allochthonous inputs at a macroecological scale is still unclear. Using a meta-analysis spanning several biomes, we show that the abundance of recipient populations is 36-57% larger with increased allochthonous inputs. The strength of direct effects on the recipients of these inputs as well as the indirect effects on the consumers of these recipients (i.e. ascending indirect effects) are constant across a latitudinal gradient spanning subtropical, arid, temperate, boreal and arctic ecosystems. However, indirect effect on the in situ resources of the input recipient (i.e. descending indirect effects) decreases with latitude. Our results suggest that the influence of allochthonous inputs can vary across large-scale gradients of ecosystem productivity and may be driven by the types of trophic interactions within recipient food webs.