Resource waves: phenological diversity in prey resources enhances the foraging opportunities of wide-ranging consumers

Background/Question/Methods

A vast body of research has explored how phenology mediates trophic interactions. Much of this work falls into two categories: (1) trophic matching explores how synchrony between consumer and resource phenologies mediates the strength of trophic interactions, and (2) predator swamping explores how synchrony within prey populations affects predator-prey dynamics. These topics typically consider trophic interactions as singular relationships between a consumer and one homogenous resource stock (e.g., a population of prey). However, many trophic resources exhibit spatial variation in phenology, and wide-ranging consumers can integrate across this phenological diversity, sampling a portfolio of functionally distinct resource stocks. Spatial variation in resource phenology generates asynchrony in the resource portfolio, such that foraging opportunities propagate across landscapes rather than occurring as a single spatially synchronized pulse. This phenomenon has been coined a “resource wave”. Consumers benefit from resource waves if they can “surf” them by moving to track spatial variation in resource phenology. Here we review empirical evidence of resource waves and provide a quantitative model to explore their potential significance to wide-ranging consumers.

Results/Conclusions

We found evidence of resource waves in a variety of ecosystems. For example, spatial variation in the phenology of grasses and forbs generates “green waves” that are critical to migratory herbivores in several continents. Population and species-level variation in salmon breeding phenology creates “red waves” that benefit wide-ranging predators such as grizzly bears. Latitudinal gradients in herring spawn-timing propagate “silver waves” that entrain the migration stopovers of sea ducks. Our model confirms the significance of resource waves. Spatial variation in resource phenology had much stronger affects on consumer foraging potential than resource abundance. Further, attributes of the resource wave and consumer foraging behavior played relatively small roles in mediating the relationship between spatial variation in resource phenology and consumer foraging potential. This suggests that resource waves benefit most mobile consumers and not just specialists that exhibit high perceptual extent and resolution. Most of the resource wave examples we present face threats; for example, human development often diminishes resource waves or creates semi-permeable barriers that interfere with the ability of consumers to surf resource waves. Our results suggest that accounting for the significance of resource waves could substantially improve the management and conservation of wide-ranging consumers across the globe.