Environmental heterogeneity enhances transfer efficiency in a model of the food chain from plankton to fish

Abstract

Conventionally, food web models have been developed based on the mean-field approach ignoring small-scale spatial variability. The closure modeling approach, which accounts for both fluctuations and spatial means, is an effective way to model the impact of heterogeneity on plankton ecosystem dynamics. The hypothesis “Environmental Heterogeneity (EH) supports higher trophic levels in plankton ecosystems and may sustain biodiversity” was previously proposed based on the analysis of NP, NPZ and NPZD plankton models. The present study extends previous results by analyzing a nutrient-phytoplankton-zooplankton-fish model, and finds support for the hypothesis that EH enlarges the parameter domain for stable solutions, which may promote coexistence. This study shows how top-down dynamics may influence both biomass and production ratios along the food chain, altering the trophic structure and transfer efficiency to higher trophic levels. The lower-trophic transfer efficiency (from P to Z) (TEPZ) decreases (increases) with increasing EH in the presence (absence) of fish while higher-trophic transfer efficiency from Z to F (TEZF) increases with the level of heterogeneity. These results suggest that previously under-appreciated micro-scale heterogeneity may explain how the low mean-field biomass of zooplankton often observed in oligotrophic waters is able to support the growth of larval fish.