Climate structures bison dietary quality and composition at the continental scale

• Main Authors: Tami Jorns, Joseph Craine, E. Gene Towne, Margaret Knox
• Format: Article
• Language: English
• Published: Wiley 2020-01-01
• Series: Environmental DNA
• Subjects: bison; diet; fecal; herbivory; metabarcoding; near‐infrared spectroscopy
• Online Access: https://doi.org/10.1002/edn3.47

Abstract Background Nutrition is a key determinant of North American plains bison (Bison bison) weight gain and reproduction, yet little is known about what bison eat and the pattern of nutritional stress across their distribution. Aims In order to better understand patterns of bison nutrition across broad climatic gradients, bison fecal material was sampled from 50 sites across the United States in June and September of 2018. Materials and Methods For each sample, dietary composition and microbial composition were assessed with DNA metabarcoding, along with dietary quality via near‐infrared spectroscopy and elemental composition. Results Herds in cool, wet sites typically had diets with high crude protein but not necessarily higher or lower digestible organic matter than in hot, dry sites. Independent of climate and season, on average, 57% and 48% of protein intake was derived from non‐graminoids in June and September, respectively. Cool‐season grass abundance in the diet was greater in cooler climates in June and September, while N2‐fixing plant abundance in the diet was greater in warmer climates in June. Among multivariate patterns, bison eating a high‐quality diet had fecal material with higher concentrations of P, Mg, Mn, and Ca, and a higher relative abundances of cellulose‐digesting Ruminococcus. Discussion By sampling across broad geographic gradients and across seasons, the drivers of different components of bison diet are becoming clear. Our results show that climate is integral to structuring bison diet quality, diet composition, elemental intake, and their gut microbiomes. Conclusions Although future work remains to better understand seasonal patterns and inter‐annual variation in diet, North American plains bison should no longer be considered strict grazers. Also, given current geographic dietary patterns, bison in a warmer climate are likely to suffer increased nutritional stress unless actions are taken to increase protein availability.