Original Research
Are Bison Intermediate Feeders? Unveiling Summer Diet Selection at the Northern Fringe of Historical Distribution
Introduction
Historically, bison (Bison bison) inhabited most of North America, ranging as far north as Alaska and the Northwest Territories, to Mexico in the south, and spanning coast to coast, from New Jersey to California (Truett, 1996, Lammers et al., 2013). Bison currently occupy most of these same regions in North America (for the most part, with herds ≤ 300 individuals restricted to small, fenced areas), but information on bison forage selection in the Boreal Plains Ecozone is lacking. On the basis of forage selection and ruminant physiology, Hofmann (1989) describes three overlapping morphophysiological ruminant feeding types: concentrate selectors; intermediate-opportunistic mixed feeders (hereafter, intermediate feeder); and grass-roughage feeders. Concentrate selectors, like moose (Alces alces) or white-tailed deer (Odocoileus virginianus), have evolved to digest nutritious, high-soluble plant material, such as forbs and browse (e.g., any part of a woody plant; Hofmann, 1989). Intermediate feeders, like elk (Cervus elapus), opportunistically forage between both extremes, consuming a mixed diet while displaying short-term or seasonal dietary shifts in response to forage quality (Hofmann, 1989). Plains bison (Bison bison bison; portrayed by domestic cattle in Hofmann’s, 1989 Fig. 2.) are typically classified as grass-roughage feeders, almost exclusively foraging on graminoids (Peden et al., 1974, Larter and Gates, 1991), such as grasses (Poaceae) and sedges (Cyperaceae). However, recent research in mixed-grass prairies of the Midwest contradicts this classification, with bison diets comprising high concentrations of eudicots, primarily forbs (Bergmann et al., 2015, Craine et al., 2015).
Diet selection of herbivores is typically determined through comparison of vegetative composition of use and forage cover-abundance (hereafter, availability; Larter and Gates, 1991). Selection of a food item can be assumed if use is greater than forage availability (Johnson, 1980). In contrast, avoidance of a food item can be assumed if use is less than availability (Klein, 1970, Johnson, 1980). Typically, herbivore diets are quantified using the microhistological analysis method, first described by Baumgartner and Martin (1939) and later verified in numerous studies (e.g., Denham, 1965, Sparks and Malechek, 1968). Microhistological analysis is popular and has been used to quantify ungulate diets worldwide (Jenks et al., 1996, Schuette et al., 1998, Gibbs et al., 2004, Beck and Peek, 2005, Forsyth and Davis, 2011). DNA barcoding is a relatively new technique currently in use for analysis of herbivore diets (Valentini et al., 2009) and is gaining popularity (Czernik et al., 2013, Bergmann et al., 2015, Craine et al., 2015, Kartzinel et al., 2015). The technique has proven more accurate for quantifying composition of complex plant mixtures; 75% of the plant DNA extracted from fecal samples was identifiable to the genus level versus 20% using microhistological analysis (Soininen et al., 2009).
Plains and wood bison (B. bison athabascae) diets have been analyzed across North America using microhistological analysis and observational forage bouts (Peden et al., 1974, Peden, 1976, Reynolds et al., 1978, Larter and Gates, 1991, Plumb and Dodd, 1993, Knapp et al., 1999). To our knowledge, only two studies have analyzed bison diets from feces using DNA barcoding (Bergmann et al., 2015; Craine et al., 2015); however, neither study analyzed forage availability to assess diet selection. Therefore, the objectives of our study were to determine forage selection patterns of herbaceous (nonwoody stem) plant material for bison in pastures among and within summer months (June–August) in central Manitoba. We hypothesized that vegetative composition of bison diets would be equal to availability and that bison diets would vary as the availability of forage shifted between pastures. Additionally, we hypothesized that bison would select for grass and sedge species as would be expected for a grass-roughage feeder (Hofmann, 1989).
Section snippets
Study Area
Our study was conducted June–August 2015 within the East, East-Center, South Sclater, and North Sclater pastures on the Pine River Ranch (lat 51o47′N, long 100o30′W), which is part of Olson’s Conservation Bison Ranches located within the Rural Municipality of Mountain (south), Manitoba, Canada. The privately operated ranch encompasses 12 500 ha of 9 cross-fenced pastures (range: 291 − 3 316 ha) and manages approximately 350 mature (≥ 3 yr old) female bison, which are rotationally grazed during
Results
Overall, bison diets were composed (mean ± SEM) of 44.3 ± 3.5% grass, 37.7 ± 2.6% forb, 16.3 ± 2.3% browse, 1.1 ± 2.4% sedge, and 0.6 ± 1.3% rush, while forage availability was 51.2 ± 1.9% grass, 28.3 ± 1.5% forb, 11.0 ± 1.3% sedge, and 7.6 ± 0.7% rush (Table 1). Bison use and availability differed (P ≤ 0.05) for each taxonomical group between months throughout the summer. Grass and forbs comprised > 80% of bison diets (see Table 1). However, bison selected grass during June (0.19; t24 = 2.22; P
Discussion
Change in dietary composition throughout the summer was not surprising as North American bison are temperate ruminants that take advantage of available vegetation throughout the summer (Schuler et al., 2006, Fortin and Fortin, 2009). However, bison diets did not shift according to availability as predicted. Grass became more abundant as summer progressed, but use declined, whereas use of forbs increased as availability decreased (see Fig. 1). This may be explained by plant phenology (Bergmann
Implications
We recognize that bison reintroductions across North America are becoming more popular (Alaska Department of Fish and Game, 2015, Banff National Park, 2015, Steenweg et al., 2016), thus increasing the need for better understanding diet selection across North America. To date, managers and biologist have used management plans and estimated stocking rates for bison that focus primarily on providing sufficient forage availability of monocots (e.g., grasses, sedges, rushes). However, the high
Acknowledgments
Research was funded in part by Olson’s Conservation Bison Ranches LTD and South Dakota State University’s Department of Natural Resource Management. We thank R. Metcalfe for field and logistical support. Thanks also to J. M. Craine and A. J. Beckley, Jonah Ventures, Boulder, Colorado, for analysis of bison fecal samples. N. Martorelli provided statistical assistance. Thanks to W. M. Inselman, W. M. Giuliano, and two anonymous reviewers for insightful comments that improved our manuscript
References (74)
- et al.
Diet composition, forage selection, and potential for forage competition among elk, deer, and livestock on aspen–sagebrush summer range
Rangeland Ecology & Management
(2005) - et al.
Group-size-dependent association between food profitability, predation risk and distribution of free-ranging bison
Animal Behavior
(2009) - et al.
Habitat selection by free-ranging bison in a mixed grazing system on public land
Rangeland Ecology & Management
(2015) Pre- and post-settlement palynology of southern Alberta
Review of Palaeobotany and Palynology
(1977)- et al.
DNA metabarcoding for ecologists
Trends in Ecology and Evolution
(2009) Wood bison free in Alaska
- et al.
The natural vegetation of Saskatchewan prior to agricultural settlement
Canadian Journal of Botany
(1980) Reintroduction plan: plains bison in Banff National Park. Parks Canada
- et al.
Plant histology as an aid in squirrel food habitat studies
Journal of Wildlife Management
(1939) Steer diets in southeastern Colorado
Journal of Range Management
(1975)
Nucleic Acids Research
GenBank
The last mile: how to sustain long-distance migration in mammals
Conservation Biology
Seasonal shifts in diet and gut microbiota of the American bison (Bison bison)
PloS One
Seasonality and patterns of natural selection for life histories
The American Naturalist
Bison grazing patterns on seasonally burned tallgrass prairie
Journal of Range Management
Plant-herbivore interactions in a North American mixed-grass prairie. II. Responses of bison to modification of vegetation by prairie dogs
Oecologia
Resource strategies of wild plants
Climatic warming and the future of bison as grazers
Scientific Reports
Fast and efficient DNA-based method for winter diet analysis from stools of three cervids: moose, red deer, and roe deer
Acta Theriology
A canopy-coverage method of vegetational analysis
Northwest Science
In vitro fermentation studies on native sandhill range forage as related to cattle selection
Search and clustering orders of magnitude faster than BLAST
Bioinformatics
UPARSE: highly accurate OTU sequences from microbial amplicon reads
Nature Methods
The soils of Manitoba
Diets of non-native deer in Australia estimated by macroscopic versus microhistological rumen analysis
Journal of Wildlife Management
Foraging ecology of bison at the landscape and plant community levels: the applicability of energy maximization principles
Oecologia
Predictive models of movement by Serengeti grazers
Ecology
Cervid forage utilization in noncommercially thinned ponderosa pine forests
Rangeland Ecology & Management
A multi-scale test of the forage maturation hypothesis in a partially migratory ungulate population
Ecological Monographs
Relationships between moisture deficiency and amount of tree cover on the pre-agricultural Canadian prairies
Prairie Forum
Choice of feeding sites by moose during summer, the influence of forest structure and plant phenology
Holarctic Ecology
Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of their digestive system
Oecologia
Foraging ecology of bison in aspen boreal habitats
Journal of Range Management
Competition in sympatric white-tailed deer and cattle populations in southern pine forests of Oklahoma and Arkansas, USA
Acta Theriology
The comparison of usage and availability measurements for evaluating resource selection
Ecology
Characteristics of plant cell walls affecting intake and digestibility of forages by ruminants
Journal of Animal Science
DNA metabarcoding illuminates dietary niche partitioning by African large herbivores
Proceedings of the National Academy of Science
Cited by (10)
-
Multiproxy analysis of permafrost preserved faeces provides an unprecedented insight into the diets and habitats of extinct and extant megafauna
2021, Quaternary Science ReviewsCitation Excerpt :The now extinct steppe bison (Bison priscus) was closely related to modern bison (Bison bison (Linnaeus, 1758); Marsolier-Kergoat et al., 2015). While modern bison are often thought of as grazers feeding for the majority on graminoids, their summer diets are more variable, consisting on average of 44% grass, 38% forb, 16% shrubs and <2% sedge (Leonard et al., 2017). This is similar to the DNA results of the Yakutian bison studied here, where forbs and shrubs are important components.
-
Behavioral habitat selection of wood bison (Bison bison athabascae) in boreal forests
2023, Mammal Research -
Reindeer Hunters of the Ice Age in Europe: Economy, Ecology, and the Annual Nomadic Cycle
2022, Reindeer Hunters of the Ice Age in Europe: Economy, Ecology, and the Annual Nomadic Cycle -
Seasonal patterns of bison diet across climate gradients in North America
2021, Scientific Reports -
Assessing the nutritional consequences of switching foraging behavior in wood bison
2021, Ecology and Evolution -
Latitudinal and seasonal plasticity in American bison Bison bison diets
2021, Mammal Review