Resource and Consumer Fluxes at the Water-Land Interface and Beyond: A Meta-Analysis

Resources and consumers move readily across the freshwater-land interface, causing competing bottom-up and top-down effects in recipient ecosystems. We assessed the relative impact of these two fluxes using a meta-analysis of 1426 observations from 166 studies that measured organism responses to resource or consumer fluxes across multiple ecosystem boundaries. Preliminary results suggest that resource subsidies and consumer fluxes at the freshwater-terrestrial interface have similar but opposing strengths, increasing or decreasing recipient organism abundance by ~1.5-fold, regardless of the direction of flux. These results were largely consistent across different ecosystem boundaries. Of the 40 observations that measured the contribution of terrestrial subsidies to the diets of aquatic organisms, 15 (38%) were of fish. In contrast, of 153 observations that measured the effect of terrestrial subsidies on aquatic organism abundance, only 6 (3.9%) were of fish. Thus, while terrestrial-derived resources are clearly important to fish diets, it is unclear how they affect fishes at the population and community level. Our preliminary results suggest two key findings: 1) the freshwater-terrestrial interface is a suitable model system, and 2) the effects of subsidies on fish populations and communities are not well-studied.