Ursids evolved early and continuously to be low-protein macronutrient omnivores

Abstract

The eight species of bears world-wide consume a wide variety of diets. Some are specialists with extensive anatomical and physiological adaptations necessary to exploit specific foods or environments [e.g., polar bears (Ursus maritimus), giant pandas (Ailuropoda melanoleuca), and sloth bears (Melursus ursinus)], while the rest are generalists. Even though ursids evolved from a high-protein carnivore, we hypothesized that all have become low-protein macronutrient omnivores. While this dietary strategy has already been described for polar bears and brown bears (Ursus arctos), a recent study on giant pandas suggested their macronutrient selection was that of the ancestral high-protein carnivore. Consumption of diets with inappropriate macronutrient profiles has been associated with increased energy expenditure, ill health, failed reproduction, and premature death. Consequently, we conducted feeding and preference trials with giant pandas and sloth bears, a termite and ant-feeding specialist. Both giant pandas and sloth bears branched off from the ursid lineage a million or more years before polar bears and brown bears. We found that giant pandas are low-protein, high-carbohydrate omnivores, whereas sloth bears are low-protein, high-fat omnivores. The preference for low protein diets apparently occurred early in the evolution of ursids and may have been critical to their world-wide spread.

Nutrient intake and its possible drivers in free‐ranging European brown bears (Ursus arctos arctos)

“…Hence, the question poses itself whether we can perceive this minimal protein optimum as an optimum that bears strive toward throughout the year, or whether it is rather a fall optimum for efficient fat storage (fat storage is indeed most efficient from dietary fat, followed by carbohydrates and protein, respectively [McDonald et al, 2011]), that in its turn depends on population conditions. The reports on natural spring and summer diets, by Coogan et al (2018) and our own study, as well as the need for high protein diets for lactating bears (López-Alfaro et al, 2013) also draws into question whether seasonal protein levels higher than 20% actually may be a health hazard (kidney, liver and cardiovascular disease) for bears (Robbins, Christian, et al, 2022;Rode et al, 2021).…”

Testing foraging optimization models in brown bears: Time for a paradigm shift in nutritional ecology?

“…Even though annual diets most closely resembled predictions from the optimum foraging model, none of the three models fully described the relationship between foraging and community interactions in our system. In general, herbivorous diets may not be as protein limited as historically thought and overconsuming protein has negative health consequences for polyphagous species (Robbins et al, 2022; Rode et al, 2021; Rothman et al, 2011). Life histories are aggregates of complex interactions between energy acquisition and allocation, macronutrient balance, and nutrient limitations to which different species, populations, and even individuals within populations have adapted.…”

“…Diet greater than one‐third meat, as estimated from previous scat analyses, would indicate that brown bears were consuming protein quantities more like obligate carnivores, such as felids, rather than other polyphagous species (Clauss et al, 2010). Protein overconsumption is linked to kidney and liver disease, as well as an increased risk of cancer (Delimaris, 2013; Robbins et al, 2022; Rode et al, 2021). One issue related to estimating protein in diets of wild animals is that estimates often cannot differentiate between skeletal muscle, which is high in protein and deficient in fats and carbohydrates, and viscera, which has a more balanced macronutrient content (U. S. Department of Agriculture, Agricultural Research Service, 2018).…”

“…Food that provides predominately one macronutrient, such as berries and moose meat, are low‐quality foods whereas, ants, which offer more balanced ratios of proteins, carbohydrates, and lipids, are of higher quality (Raubenheimer et al, 2009; Appendix S1: Table S1). Under the balancing macronutrient model, bears should predominantly consume ants and, to a lesser extent, moose to meet protein demands and then use berries to meet energetic demands while avoiding protein overconsumption (Erlenbach et al, 2014; Robbins et al, 2022; Rode et al, 2021). This model predicts that brown bears are major predators of ants, minor predators of moose, and moderately interact with the plant community.…”

Trophic adaptation of large terrestrial omnivores to global change

“…We focus on the seven extant terrestrial bear species (Order: Carnivora, Family: Ursidae), which are the largest terrestrial omnivores and occupy a wide range of biomes from the arctic tundra to tropical rainforests. Unlike most other large carnivores, bears show a preference for low-protein diets and have relatively weak craniodental adaptations to carnivory (17, 18), which allows them to maintain a high degree of dietary flexibility. Owing to their broad dietary niches, bears contribute to a multitude of ecosystem processes, such as predation, scavenging, or frugivory that can have strong impacts on prey populations (19), plant regeneration (20, 21), nutrient cycling (22, 23) and energy fluxes (6) within and across terrestrial and aquatic ecosystems.…”