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Trophic Relationships in Freshwater Pelagic Ecosystems
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1986
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Trophic ImpactBiogeochemistryTotal Phosphorus AvailabilityEngineeringBenthic-pelagic CouplingAquatic EcologyZooplankton EcologyFreshwater EcosystemTrophic InteractionsFood Web InteractionFood WebTrophic RelationshipsTrophic WebRelative Impacts
The study quantified how bottom‑up nutrient availability and top‑down predator effects jointly shape biomass and size structure across five key components of freshwater pelagic ecosystems. The model predicts that bottom‑up control of maximum biomass halves at each trophic step upward, while top‑down influence dominates near the top and weakens downward; variability around bottom‑up patterns is explained by top‑down forces, and the relative strength of these interactions shifts with lake trophic status, being strongest for piscivore‑to‑zooplankton in eutrophic lakes and for zooplankton‑to‑phytoplankton in oligotrophic lakes.
Relative impacts of bottom-up (producer controlled) and top-down (consumer controlled) forces on the biomass and size structure of five major components of freshwater pelagic systems (piscivores, planktivores, zooplankton, phytoplankton, and total phosphorus availability) were estimated. Predictions that emerge are (1) maximum biomass at each trophic level is controlled from below (bottom-up) by nutrient availability, (2) this bottom-up regulation is strongest at the bottom of the food web (i.e. phosphorus → phytoplankton) and weakens by a factor of 2 with each succeeding step up the food web, (3) as energy moves up a food web, the predictability of bottom-up interactions decreases, (4) near the top of the food web, top-down (predator mediated) interactions are strong and have low coefficients of variation, but weaken with every step down the food web, (5) variability around the bottom-up regressions can always be explained by top-down forces, and (6) interplay between top-down and bottom-up effects changes with the trophic status of lakes. In eutrophic lakes, top-down effects are strong for piscivore → zooplankton, weaker for planktivore → zooplankton, and have little impact for zooplankton → phytoplankton. For oligotrophic lakes, the model predicts that top-down effects are not strongly buffered, so that zooplankton → phytoplankton interactions are significant.