Resource Availability and Quality Influence Patterns of Diet Mixing by Sheep

Abstract

In grazing systems, forage availability is a function of herbivore density, which can influence an animal's ability to be selective. In turn, the influence of food availability on selectivity has the potential to influence plant biodiversity. We hypothesized that the ability of herbivores to mix toxin-containing foods in their diets is a function of the availability of nontoxic foods and the nutritional characteristics of the toxin-containing foods. We evaluated this hypothesis in two trials simulating different diet qualities (high-quality foods in trial 1, low-quality foods in trial 2). Within each trial, the four treatment groups were offered with different amounts of nutritious, familiar foods-10, 30, 50, and 70% of ad libitum intake-but were offered with ad libitum access to toxin-containing foods. Each lamb was presented with five foods, including three toxin-containing unfamiliar foods (terpenes, tannins, and oxalates) and two nutritious familiar foods (alfalfa and barley). In trial 1, as the availability of nutritious familiar foods decreased, animals ate more of all three toxin-containing foods. As the availability of nutritious alternatives increased, the pattern of selection shifted from terpenes to tannins and oxalates. In trial 2, animals also ate more toxins as the availability of nutritious alternatives decreased, but their pattern of diet mixing changed. Low availability of nutritious alternatives resulted in the animals eating more oxalates. During preference tests when all five foods were offered ad libitum, animals fed with 10, 30, 50, and 70% of ad libitum intake from trial 1 ate 49, 47, 41, and 38% of the three toxin-containing foods, respectively. The lower diet quality in trial 2 affected intake of the toxin-containing foods such that animals fed with 10, 30, 50, and 70% of ad libitum intake ate 37, 36, 29, and 27%, respectively, of the three toxin-containing foods. Thus, the quality of toxin-containing foods and the availability of nutritious alternatives interacted to modify the pattern of diet mixing by lambs.

Using Sheep to Control Purple Loosestrife (Lythrum salicaria)

“…Alternatively, ungulate diets are commonly composed of only a few of the plant species available (Provenza et al 2003;Ruyle and Bowns 1985). Different ungulate species select different combinations of plants, apparently in response to physical and chemical attributes of the plant community (Fraker-Marble et al 2007;Provenza et al 2007;Shaw et al 2006). Although the debate surrounding the impacts of grazing domesticated livestock in wild ecosystems remains energetic (Bock et al 2006;Floyd et al 2003;Tadey and FarjiBrener 2007;Walter and Levin 2007), there is growing evidence that in grasslands at least, low-intensity grazing has minimal impacts (Brown and McDonald 1995;Marty 2005;Saberwal 1996).…”

Digestive Organ Size and Behavior of Red Knots (Calidris Canutus) Indicate the Quality of Their Benthic Food Stocks

“…When the mechanism yielding the digestive constraint is of such nature, there is one obvious way for digestively constrained foragers to enhance their rate of assimilating digestible food: by simply selecting food with a high ratio of digestible to indigestible components (this ratio will be called food quality from now on). Indeed, digestively constrained foragers have been shown to select their food on the basis of quality (Shaw et al, 2006), rather than other factors such as the (digestible) amount of energy per unit handling time (Van Gils et al, 2005b).…”

High Energy or Protein Concentrations in Food as Possible Offsets for Cyanide Consumption by Specialized Bamboo Lemurs in Madagascar

“…From the plants' perspective, production of PSMs is costly and therefore some PSMs 70 are only produced when plants are threatened by folivores (Dolch and Tscharntke 2000) or 71 after they have actually been fed upon (induced defences; Schuman and Baldwin 2012). From 72 the animals' point of view, detoxification also requires additional energy expenditure that 73 sometimes needs to be compensated for by ingestion of more or higher quality food (Glander 74 1982; Provenza et al 2003 Shaw et al 2006). A dramatic cost of detoxification of a 76 single PSM (benzoate) has been described for common brushtail possums (Trichosurus 77 vulpecula) where the costs for detoxification account for about 30% of the dietary nitrogen 78 intake (Au et al 2013).…”