Functional implications of omnivory for dietary nutrient balance

Abstract

Captive experiments have shown that many species regulate their macronutrient (i.e. protein, lipid and carbohydrate) intake by selecting complementary food types, but the relationships between foraging strategies in the wild and nutrient regulation remain poorly understood. Using the pine marten as a model species, we collated available data from the literature to investigate effects of seasonal and geographic variation in diet on dietary macronutrient balance. Our analysis showed that despite a high variety of foods comprising the diet, typical of a generalist predator, the macronutrient energy ratios of pine martens were limited to a range of 50–55% of protein, 38–42% of lipids and 5–10% of carbohydrates. This broad annual stabilisation of macronutrient ratios was achieved by using alternative animal foods to compensate for the high fluctuation of particular prey items, and sourcing non‐protein energy (carbohydrates and fats) from plant‐derived foods, particularly fruits. Macronutrient balance varied seasonally, with higher carbohydrate intake in summer–autumn, due to opportunistic fruit consumption, and higher protein intake in winter–spring. In terms of their proportional dietary carbohydrate intake the pine marten's nutritional strategy fell between that of true carnivores (e.g. the wolf) and more omnivorous feeders (e.g. the European badger). However, in terms of energy contributed by protein pine martens are equivalent to obligate carnivores such as the wolf and domesticated cat, and different to some omnivorous carnivores such as the domesticated dog and grizzly bears.

Motive for Killing: What Drives Prey Choice in Wild Predators?

“…; Remonti et al. ). In addition to nutrients, NG allows broader factors such as ‘animal fibre’ (e.g.…”

“…Remonti et al. ). In most cases, however, scat analysis provides only a snapshot of the diets of individuals and is susceptible to bias due to differential digestibility of foods (Marker et al.…”

“…While use of literature data to estimate the chemical compositions of prey can present obvious limitations, its use can also provide valuable information for understanding the nutritional ecology of wild predators when prey sampling is impractical or unattainable (Remonti et al. ).…”

Amphibians in Eurasian otterLutra lutradiet: osteological identification unveils hidden prey richness and male‐biased predation on anurans

“…Assessing the nutritional requirements of a predator and its position along the specialist–generalist continuum is essential for reconstructing food webs and understanding the predator's function in the ecosystem (Remonti et al. ). Unfortunately, the investigation in detail of the diversity of species preyed on by elusive mammalian carnivores is often hindered by the difficulty of identifying prey remains to the species level through the analysis of the undigested remains found in either faeces or, to a lesser extent, stomachs (Britton et al.…”

Omnivory does not preclude strong trophic cascades

“…Fixed omnivory may also manifest in other ways, for example, when organisms forage in a way that is suboptimal in terms of pure energetics but is otherwise required to maintain nutritional or stoichiometric balances (Berthoud and Seeley , Remonti et al. , Zhang et al. ).…”