Application of a predator-prey overlap metric to determine the impact of sub-grid scale feeding dynamics on ecosystem productivity

Abstract

Marine ecosystem models assume spatially homogeneous population dynamics at sub-grid scale resolution, despite evidence that marine systems are highly structured on fine scales. This structuring can influence the predator-prey interactions driving trophic transfer and thereby overall ecosystem production. Here we apply a statistic, the AB ratio (ζAB), to quantify increased predator production due to fine-scale overlap with its prey. We calculated ζAB from available literature sources (spatial observations of predator and prey) and from data obtained with a towed plankton imaging system, demonstrating that organisms from a range of trophic levels and oceanographic regions tended to overlap with their prey both in the horizontal and vertical dimensions. The values of ζAB indicate that spatially homogeneous calculations underestimate productivity. This pattern was accentuated when accounting for swimming over a diel cycle and by increasing sampling resolution, especially when prey were highly aggregated. We recommend that ecosystem models incorporate more fine-scale information both to more accurately capture trophic transfer processes and to capitalize on the increasing sampling resolution, data volume, and data sharing platforms from empirical studies.