Latitudinal and seasonal plasticity in American bison Bison bison diets

Abstract

In ecological niche theory, diet is a trait frequently used to place species along a continuum from specialists to generalists. A multidimensional approach to investigating species’ niches has been developed to incorporate nutrition. We apply the concepts of multidimensional nutritional niche theory to the dietary patterns of a widespread, large herbivore, the American bison Bison bison, at various levels of its nutritional niche. Specifically, we sought to estimate dietary niches for female bison at the levels of the forage items they consume and the macronutrients they acquire from those forage items. We assessed how these dietary niches changed seasonally and explored physical and climatic mechanisms that contribute to observed differences in the dietary niches. We also examined dietary differences between the two bison subspecies: wood bison Bison bison athabascae and plains bison Bison bison bison. We compiled data for 16 bison subpopulations using 26 peer‐reviewed publications, government reports, conference proceedings, and graduate theses that described the dietary composition of female bison for analysis of dietary niches. We found that the diets of female bison were, as expected, dominated by graminoids throughout the year, but during the growing season (spring and summer), dietary niches had greater breadth. Their diets were relatively high in carbohydrates, but percentages of dietary lipid and protein increased during the growing season. Further, we found significant increases in consumption of browse items, lipids, and proteins with increasing latitude (†N), and differences between American bison subspecies. Our study provides insight into the fundamental macronutrient niche of the American bison and also provides a framework for the nutritional targets of bison. We show that bison are able to adapt to availability of local forage and that they may consume different items in different proportions in order to regulate nutritional composition of their diet.

Assessing the nutritional consequences of switching foraging behavior in wood bison

“…Herbivore nutritional quality is typically defined in terms of energy, concentration of limited nutrients (i.e., protein), and limiting factors such as digestibility (i.e., structural carbohydrates’ concentration), all of which influence herbivore fitness (Hamel et al, 2012 ; Plumb et al, 2009 ; van Soest, 1994 ). Forbs and browse tend to have greater quantities of limited nutrients than graminoids, and graminoids have more structural carbohydrates, regardless of season (Craine et al, 2010 ; Hecker et al, 2021 ). The nutritional niche of herbivores has been estimated using a multidimensional approach known as nutritional geometry (Machovsky‐Capuska et al, 2016 ).…”

“…We chose bison because they have been described as obligate grazers and have the morphophysiology of a grazer (Hofmann, 1989 ; Strong & Gates, 2009 ). However, recently, forbs and browse have been found to contribute significant proportions to some bison diets, especially during summer (Bergman et al, 2015 ; Craine et al, 2015 ; Hecker et al, 2021 ; Leonard et al, 2017 ). We elected to examine the diets of females because female bison are known to have higher quality diets that are more diverse in composition than males (Jung, 2015 ; Mooring et al, 2005 ; Popp, 1981 ).…”

Buffalo on the Edge: Factors affecting Historical Distribution and Restoration of <em>Bison bison </em>in the Western Cordillera, North America

“…The success of these projects demonstrates that bison are clearly adapted to thrive in a broad range of climates, vegetation conditions, and predators, even if snow depth [40], forage quality and availability [105] and non-human predation [106] influence their localized spatial distribution. Recent studies have also demonstrated remarkable plasticity in bison diets across North America [107,108], providing further evidence that bison can thrive in a variety of conditions. Lastly, MaxEnt ecological niche modelling based on fossil records of bison and historic climates demonstrated that much of North America was suitable bison habitat over the past 20,000 years [30].…”

Buffalo on the Edge: Factors Affecting Historical Distribution and Restoration of <em>Bison bison </em>in the Western Cordillera, North America

“…The success of these projects demonstrates that bison can thrive in a broad range of climates, vegetation conditions, and predators, even if snow depth [48], forage quality and availability [116] and non-human predation [117] influence their localized spatial distribution. Recent studies have also demonstrated remarkable plasticity in bison diets across North America [118,119], and MaxEnt ecological niche modelling based on fossil records of bison and historic climates demonstrated that much of North America was suitable bison habitat over the past 20,000 years [13].…”