Optimizing protein intake as a foraging strategy to maximize mass gain in an omnivore

Abstract

Energy maximization, time minimization, and linear programming models subject to various constraints have dominated foraging ecology ideas and methods for decades. However, animals must use very complex physiological processes and foraging decisions to ensure fitness that in many cases may not be adequately described by these approaches. An example of this problem occurs when brown bears, Ursus arctos, have access to both abundant salmon and fruit. Salmon are one of the most energy and nutrient dense foods available to bears. Fruits are often high in soluble carbohydrates, low to deficient in many required nutrients, and more difficult to efficiently exploit. Therefore, wild brown bears that fatten primarily on fruits without access to salmon are 50% smaller than salmon-feeding bears. Thus, we predicted based on a linear, energy-maximizing model without dietary interaction effects that wild brown bears with access to both abundant salmon and fruit would feed almost exclusively on salmon. However, wild adult females with or without accompanying offspring foraged three times longer per day on fruit than on salmon. Similarly, the relative dry matter intake of ad libitum apples and salmon by captive, adult brown bears averaged 7695% fruit and 2495% salmon. Captive brown bears consuming mixed diets with intermediate dietary protein levels had 60% lower maintenance energy costs, 37% to 139% higher efficiencies of mass gain, and 72% to 520% higher maximum rates of gain than when they consumed either salmon or fruit alone. These relationships were nonlinear functions of dietary protein content in which salmon and fruit provided complementary nutritional resources. Both wild and captive bears attempted to regulate total protein, energy, and carbohydrate intake within a multidimensional intake target that both maximized energy intake and mass gain.

Predormancy omnivory in European cave bears evidenced by a dental microwear analysis of Ursus spelaeus from Goyet, Belgium

“…Between summer and fall, extant bears gain body mass by hyperphagia and accumulate fat to face the costs of dormancy and, in the case of females, reproduction and lactation (41)(42)(43)(44). This gain results from a balance between energy expenditure, intake, foraging time, and fat accumulation, depending primarily on availability, foraging efficiency, body size, and condition (45,46). As a result, a mixed diet is the most common one in extant bears in the fall, which may include one dominant item such as terrestrial vertebrates (mostly ungulates and rodents) (47-50), insects (especially ants) (51), roots (52), berries (50,52), or hard mast (53).…”

“…However, there is a limit to how much protein-rich food bears want to consume (45,46), which indicates that cave bears were probably not strictly carnivorous during the predormancy period. The other food categories inferred from dental microwear analysis for the diet of cave bears from Goyet are never frequent in extant bear diet.…”

Nutritional Ecology of Ateles chamek in lowland Bolivia: How Macronutrient Balancing Influences Food Choices

“…The Geometric Framework for nutrition (GF) is an analytical technique that enables an understanding of the nutritional strategies of animals (Simpson and Raubenheimer 1993;Raubenheimer and Simpson 2004) and the interpretation of food choices that are otherwise difficult to explain (Robbins et al 2007). Researchers have successfully applied the framework to a range of vertebrate and invertebrate taxa (Chambers et al 1995;Felton et al 2009b;Raubenheimer and Simpson 2006;Robbins et al 2007;Ruohonen et al 2007;Raubenheimer 2001, 2005).…”

“…Researchers have successfully applied the framework to a range of vertebrate and invertebrate taxa (Chambers et al 1995;Felton et al 2009b;Raubenheimer and Simpson 2006;Robbins et al 2007;Ruohonen et al 2007;Raubenheimer 2001, 2005). The GF describes feeding behavior within an n-dimensional space delineated by axes representing nutrients of interest (Raubenheimer and Simpson 2004).…”

Stable isotopes reveal an invasive plant contributes more than native sources to anuran larvae diets

“…To achieve a balanced diet, organisms choose to consume sources that maximize energy (Felton et al 2016), are nutrient rich (Felton et al 2009;Rothman et al 2011), and are void of toxins (Bryant & Kuropat 1980). Thus, organisms will discriminate against unpalatable and hard-to-digest foods, unless no other option is available (Felton et al 2009(Felton et al , 2016 and to compensate for limited availability of highly nutritious food sources, organisms will consume excess amounts of the available low-quality resources (Cruz-Rivera & Hay 2000; Simpson et al 2004;Robbins et al 2007;Felton et al 2016). Therefore, additional studies are required to explain complex foraging behavior in larger varieties of organisms and ecosystems.…”