Spatial and Temporal Heterogeneity Creates a “Brown Tide” in Root Phenology and Nutrition

Abstract

Spatial and temporal heterogeneity in plant phenology and nutrition benefits herbivores by prolonging the period in which they can forage on nutritious plants. Landscape heterogeneity can therefore enhance population performance of herbivores and may be a critically important feature of their habitat. The benefits of resource heterogeneity over space and time should extend not only to large herbivores using above-ground vegetation but also to omnivores that utilize below-ground resources. We used generalized linear models to evaluate whether spatial heterogeneity influenced temporal variation in the crude protein content of alpine sweetvetch (Hedysarum alpinum) roots in west-central Alberta, Canada, thereby potentially offering nutritional benefits to grizzly bears (Ursus arctos). We demonstrated that temporal patterns in the crude protein content of alpine sweetvetch roots were influenced by spatial heterogeneity in annual growing season temperatures and soil moisture and nutrients. Spatial heterogeneity and asynchrony in the protein content of alpine sweetvetch roots likely benefit grizzly bears by prolonging the period they can forage on high quality resources. Therefore, we have presented evidence of what we termed a "brown wave" or "brown tide" in the phenology and nutrition of a below-ground plant resource, which is analogous to the previously described "green wave" in above-ground resources.

Foods, macronutrients and fibre in the diet of blue sheep (Psuedois nayaur) in the Annapurna Conservation Area of Nepal

“…As well, differences in the nutritional content of plants across an elevation gradient likely influences the timing of plant nutrition (Coogan et al. ), and therefore diet of blue sheep across different areas. Furthermore, a more complete nutritional profile of available vs. consumed foods will help determine whether blue sheep are actively foraging for a balance of nutrients different from what they would consume if they simply foraged (proportional to availability).…”

“…While our analysis detected differences in nutrient concentration between in plants sampled during different months, differences in species collected between periods confounds robust phenological comparisons and should be examined further. As well, differences in the nutritional content of plants across an elevation gradient likely influences the timing of plant nutrition (Coogan et al 2012), and therefore diet of blue sheep across different areas. Furthermore, a more complete nutritional profile of available vs. consumed foods will help determine whether blue sheep are actively foraging for a balance of nutrients different from what they would consume if they simply foraged (proportional to availability).…”

Resource waves: phenological diversity enhances foraging opportunities for mobile consumers

“…Variation has been studied primarily at the intra-population level and is often treated as statistical noise rather than as an ecologically significant attribute worthy of direct study (Diez et al 2012). Spatial variation in resource phenology, which occurs at multiple levels of biological organization, protracts foraging opportunities for animals ranging from grasshoppers (Caelifera; Searle et al 2010) to grizzly bears (Coogan et al 2012. The consumers that surf resource waves are often commercially and culturally important, yet existing management frameworks are typically inadequate for conserving either the underlying mechanisms of resource waves or the spatiotemporal aspects of habitat connectivity that enable consumers to surf them.…”

“…Plants often store energy overwinter in their roots, and then transfer this energy to aboveground tissues over the course of the growing season. landscape heterogeneity generates spatial variation in plant phenology, prolonging the period of profitable foraging opportunities on roots (Coogan et al 2012). grizzly bears appear to track the brown wave by moving to areas of delayed plant development (higher elevations and North facing slopes) as the growing season progresses (Hamer et al 1991).…”

Vegetation phenology can be captured with digital repeat photography and linked to variability of root nutrition inHedysarum alpinum

“…; Coogan et al. ). Once the above‐ground biomass component of H. alpinum has reached its peak, corresponding to the mid‐point of the growing season, the nutritional value of the roots substantially decreases when compared to the initial green‐up earlier in the season or senescence in the autumn (Coogan et al.…”