Macronutrient optimization and seasonal diet mixing in a large omnivore, the grizzly bear: a geometric analysis - PubMed (original) (raw)

Macronutrient optimization and seasonal diet mixing in a large omnivore, the grizzly bear: a geometric analysis

Sean C P Coogan et al. PLoS One. 2014.

Erratum in

Abstract

Nutrient balance is a strong determinant of animal fitness and demography. It is therefore important to understand how the compositions of available foods relate to required balance of nutrients and habitat suitability for animals in the wild. These relationships are, however, complex, particularly for omnivores that often need to compose balanced diets by combining their intake from diverse nutritionally complementary foods. Here we apply geometric models to understand how the nutritional compositions of foods available to an omnivorous member of the order Carnivora, the grizzly bear (Ursus arctos L.), relate to optimal macronutrient intake, and assess the seasonal nutritional constraints on the study population in west-central Alberta, Canada. The models examined the proportion of macronutrients that bears could consume by mixing their diet from food available in each season, and assessed the extent to which bears could consume the ratio of protein to non-protein energy previously demonstrated using captive bears to optimize mass gain. We found that non-selective feeding on ungulate carcasses provided a non-optimal macronutrient balance with surplus protein relative to fat and carbohydrate, reflecting adaptation to an omnivorous lifestyle, and that optimization through feeding selectively on different tissues of ungulate carcasses is unlikely. Bears were, however, able to dilute protein intake to an optimal ratio by mixing their otherwise high-protein diet with carbohydrate-rich fruit. Some individual food items were close to optimally balanced in protein to non-protein energy (e.g. Hedysarum alpinum roots), which may help explain their dietary prevalence. Ants may be consumed particularly as a source of lipids. Overall, our analysis showed that most food available to bears in the study area were high in protein relative to lipid or carbohydrate, suggesting the lack of non-protein energy limits the fitness (e.g. body size and reproduction) and population density of grizzly bears in this ecosystem.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Right-angled mixture triangle (RMT) plots depicting the estimated macronutrient (lipid, available carbohydrate, and crude protein) content of seasonally available foods consumed by grizzly bears in west-central Alberta, given as a percentage of metabolizable energy.

Protein is represented by the third _z_-axis which varies inversely with distance from the origin. Seasons are defined based on major changes in grizzly bear diet, and include: a) pregreen-up; b) graminoid and forb season; c) berry season; and d) late fall. For reference, optimal diets self selected by captive grizzly bears are shown as black symbols and marked in the legend with an asterisk (*), while the 17% protein to 83% non-protein energy intake target is shown as a black line. The grey-shaded polygon indicates the estimated nutrient space available to grizzly bears consuming seasonal foods. Overlap between the nutrient space polygon and the intake target line indicates that an optimal diet may be achieved during a season. The food items plotted do not include variation and are meant to give a general perspective.

Similar articles

Cited by

References

    1. Lee KP, Simpson SJ, Clissold FJ, Brooks R, Ballard JW, et al. (2008) Lifespan and reproduction in Drosophilia: new insights from nutritional geometry. Proc Natl Acad Sci U S A 105: 2498–2503. - PMC - PubMed
    1. Piper MD, Partridge WL, Raubenheimer D, Simpson SJ (2011) Dietary restriction and aging: a unifying perspective. Cellular Metab 14: 154–160. - PMC - PubMed
    1. Cotter SC, Simpson SJ, Raubenheimer D, Wilson K (2010) Macronutrient balance mediates trade-offs between immune function and life history traits. Funct Ecol 25: 186–198.
    1. Simpson SJ, Raubenheimer D (2005) Obesity: the protein leverage hypothesis. Obes Rev 6: 133–142. - PubMed
    1. Maklakov AA, Simpson SJ, Zajitschek F, Hall MD, Dessmann J, et al. (2008) Sex-specific fitness effects of nutrient intake on reproduction and lifespan. Curr Biol 18: 1062–1066. - PubMed

Publication types

MeSH terms

Substances

Grants and funding

Funding for S. C. P. Coogan was provided by the Foothills Research Institute Grizzly Bear Program, Natural Sciences and Engineering Research Council (NSERC) of Canada, Alberta Innovates – Bio Solutions, and the Applied Conservation Ecology lab (http://www.ace-lab.org/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

LinkOut - more resources