“Cascading impacts of nutrient availability on food webs and vice versa” 14 May 2015 LTER Science Council Meeting Roger Ruess, Dan Reed, Russ Schmitt, Sally Holbrook, Lydia Zeglin, Sherri Johnson

Background Within both grazing and detrital food webs, consumers and their predators are strongly influenced by, but also have strong influences on nutrient availability and biogeochemical cycling. Linkages between food webs and biogeochemical cycles vary across complex spatial and temporal scales, and are influenced by climate- disturbance interactions. Environmental change is affecting the coupling between nutrient availability and food web dynamics at most LTER sites. In many cases, abrupt changes in ecosystem state are tied to alterations in the dynamics of grazing and/or detrital food webs.

Potential cross-site questions: 1)Nature of feedbacks How do rates of biogeochemical cycling and the quantity and quality of forage change with increasing consumption rates? Under what conditions do consumers accelerate biogeochemical cycling and improve the quality and quantity of their own food resources? How can we measure and compare the strengths of these relationships across sites - both in terms of consumer effects on biogeochemical cycling, and feedbacks to consumer abundance and population dynamics? What determines the strength of these feedbacks? How does disturbance or trophic structure (e.g., predation, invasive consumers) modulate these feedbacks (either directly or indirectly)?

2)Spatial and Temporal Contexts Heterogeneity at multiple spatial scales strongly influences food web structure and function. Biotic factors (consumer density, composition, and movements) and abiotic factors (disturbance, habitat structure, and movement of materials) influence connectivity across multiple spatial scales. What is the relative importance of consumers in contributing to spatial heterogeneity – and at what spatial scales are they most important? How do consumers and disturbance interact within and across spatial scales to influence biogeochemical cycling? When/where do legacies of linkages between consumers and biogeochemical cycling play an important role in ecosystem structure and function?

Next steps: Refine questions and develop Hs Compile relevant Network data on consumer densities, offtake rates, and linkages to biogeochemical cycling. Develop ASM Working Group to move topic forward (Knut Kielland, BNZ Lead??)