Characterizing Non-Linear Relationships in Marine Ecosystems: A Meta-Analysis

An important knowledge gap in ocean management is understanding quantitatively how ecosystem components respond to natural and anthropogenic stressors. A common assumption is that stressor-response relationships are linear. However, a growing body of literature demonstrates that many relationships are nonlinear, where small changes in a stressor prompt a disproportionately large ecological response. The goal of our work is to better understand the relationships between stressors and ecosystem properties and to identify where nonlinearities are likely to occur. To accomplish this we (1) conducted a wide literature search on single stressor-response relationships in pelagic ecosystems, (2) identified the degree of nonlinearity in these relationships using summary statistics from published regression models and models fit to available datasets, and (3) examined whether it is possible to glean general patterns in the shapes and strengths of the relationships and threshold responses across systems and stressors. Here, we present a characterization of stressor-response relationships in pelagic systems and address the potential risks associated with the simplifying assumption of linearity. In addition, we highlight important knowledge gaps that hinder our ability to gain insights into ecosystem thresholds and to help inform the selection of reference points for management to avoid tipping points in marine ecosystems.