Mast-seeding trees provide a pulsed resource that mediates the spatio-temporal structure of communities by both supporting and destabilizing consumer populations. Whereas a reliable resource is abundant on average, with limited variation in time and space, masting events are volatile and localized, and that variability ramifies throughout food webs. The life histories and foraging patterns of mast consumers must anticipate covariance structure in time, in space, and across a diverse diet. Theory is needed to gauge the capacity of forests to support food webs through regulation of consumers. Specifically, how does the space-time structure of masting interact with the capacities of consumers to exploit alternative hosts, to forage widely in space, and to store reserves in time? A solution to the theoretical challenge is of little use without a model that offers the necessary estimates. With the goal of understanding the types of consumers that forests can support, we incorporate and predict spatio-temporal covariance in the diverse diets of mast consumers with their capacities to withstand variation through movement in space, storage in time, and substitutable resources that vary asynchronously. We developed Mast Inference and Forecasting (MASTIF), a state-space autoregressive model, accommodating long-term lags, that predicts seed availability within the canopy, on the forest floor, and across sites in a regional network.
Results/Conclusions
Using a long-term network of seed rain data from eastern North America, we determined that the benefit of high average resource supply can be offset for many consumers by high space-time covariance. Even the most highly synchronized mast species offer canopy consumers (arboreal arthropods and rodents, song birds) a heterogeneous resource structure. A fitted dispersal kernel translates covariance experienced by canopy foragers to a different space-time covariance experienced by ground foragers (rodents, ground-nesting birds and vertebrates). For consumers lacking mobility, demographic storage in episodic recruitment following mast years is important for population persistence. Many consumers compensate this volatility with diet breadth. Depending on the dominant masting strategies of host tree species, habitats differentially limit specific life history strategies that are misaligned with the covariance structure of mast availability. For this reason, the range of mast producers in a habitat ‘predict’ (place bounds on) the life histories of consumers that persist there. Results can be used to rank habitats by their capacities to support wildlife from a resource perspective.