Food choice by white-tailed deer in relation to protein and energy content of the diet: a field experiment

Optimality models of food selection by herbivores assume that individuals are capable of assessing forage value, either directly through the currency used in the model or indirectly through other variables correlated with the currency. Although energy and protein are the two currencies most often used, controversy exists regarding their respective influence on food choice. Part of the debate is due to the difficulty of teasing apart these two nutrients, which are closely correlated in most natural forages. Here we offer a test of the assumption that energy and protein contents of the forage are both currencies that large mammalian herbivores can use when selecting their food. We observed feeding behavior of 47 wild white-tailed deer (Odocoileusvirginianus) during winter while individuals were presented with four experimental foods representing two levels of energy and protein (dry matter digestibility: 40–50%; crude protein: 12–16%). Using experimental foods allowed us to separate the influences of energy and protein and clearly distinguish between the roles of these two nutrients. Deer discriminated between foods through partial selection, and selected diets higher in energy but lower in protein. The observed choices appeared consistent with physiological needs of deer wintering at the study site, where digestible energy was in short supply in the natural environment while protein was probably not. Results are in good agreement with recent findings on domesticated ruminants. They support a basic assumption of optimality models of food selection that use energy and/or protein as a currency, although the physiological mechanisms behind the food selection process remain unclear. We urge students of food selection by herbivores to replicate our experiment with other foods and/or in other circumstances before more general conclusions are drawn. Received: 1 September 1997 / Accepted: 22 February 1998     

Feeding-patch choice by red deer in relation to foraging efficiency

We tested the idea that ruminants allocate their feeding time to habitat patches in relation to foraging efficiency. We used five tame red deer (Cervus elaphus) in an enclosure planted with four treatment of timothy grass (Phleum pratense) differing in their stage of growth. Older swards offered higher biomass but lower nutritional quality than younger swards. We observed time spent feeding in each treatment during each of seven trials. We measured goodness-of-fit between observed times and predictions from two alternative hypotheses differing in optimization strategy (maximizing versus matching), and a third, null hypothesis. We tested the hypotheses using two alternative currecies: digestible protein, and digestible dry matter or energy. Although digestible protein concentration and dry-matter digestibility were highly correlated (r=0.763, P<0.001), the wider range of digestible protein made it the much more sensitive measure of forage quality. Distributions of feeding time closely matched estimated intake rates of digestible protein (R _infPred ^sup2 =0.899) across all animals and trials. The other hypotheses were rejected. The results have important ecological implications in showing the underlying role of food in the selection of habitat by ruminants, and that simple, mechanistic models of forage intake and digestion can be scaled up to the level of animal behavioural choices.     

Food choice in Siganus fuscescens: influence of macrophyte nutrient content and availability

Using multiple‐choice feeding experiments, the selection of six species of macrophytes by the herbivorous rabbitfish Siganus fuscescens was examined. The rabbitfish showed distinct food choice in the laboratory; however, selection of macrophytes by S. fuscescens was not related to their absolute nutrient content (nitrogen, carbon, energy and ash free dry mass). Nutrient assimilation estimates showed that the macrophytes which were most preferred were those that S. fuscescens assimilated best. In S. fuscescens , the macrophytes that were preferred passed through the gut significantly faster than the less preferred species. Gut transit time had a significant effect on the absolute value of a food item in terms of net nutrient gain per unit time. This study showed that food value could be inferred from the absolute nutrient content of the macrophytes. Thus both the ability to assimilate nutrients as well as the absolute nutrient content of macrophytes must be quantified when assessing food value.     

Food plant selection by reindeer during winter in relation to plant quality

The relative palatabilities of nine plant taxa used as winter food by reindeer were estimated by presenting them in cafeteria and pairwise tests Feeding p reference indices were then related to the chemical composition of the plants High preference indices were obtained for the lichens Bryoria spp, Cladina arbuscula, C rangiferina and C stellaris, while low values were obtained for the moss Pleurozium schrebel and the dwarf shrubs Empetrum hermaphroditum and Vaccinium myrttllus The grass Deschampsia flexuosa and the lichen Stereocaulon paschale received intermediate scores Feeding preferences showed a strong negative correlation with acid detergent fiber (ADF)-values No statistically significant correlations were found between feeding preferences and contents of nitrogen, in vitro organic matter digestibility (IVOMD) or neutral detergent fiber (NDF)     

Rotifer occurrence in relation to oxygen content

Information on the distribution of 204 species of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analyzed for details on relationships to the oxygen content of the environment. No sign of truly anoxybiontic appearance was traced, although some species may be encountered in high abundance at low O₂-values. Most cold-stenothermal species prefer an environment rich in oxygen, but there are a few exceptions. For the warm-stenothermal species no really close connections with oxygen exist. Several species combine a tolerance of low oxygen content with a preference of high Pt-values. No such connections were traced between oxygen content and trophic degree.     

Female mate choice in relation to heterozygosity in Tribolium castaneum

Abstract Female mate choice, both before and after copulation, is pervasive among insect species. It is often hypothesized that females would preferentially mate with males that are genetically dissimilar to promote the genetic variability of the offspring. We used various strains of red flour beetle, Tribolium castaneum, and tested the effect of male and female genetic backgrounds on precopulatory and post‐copulatory female mate choice. Simultaneous mate choice experiments using previously well established pheromone assays did not detect female preference for males of different strains. Post‐copulatory female mate choice was examined through paternity analysis. Two parameters were used to measure post‐copulatory female mate choice, including male defence capacity (P₁, proportion of offspring sired by the first male when a female mated with two males consecutively) and offence capacity (P₂, proportion of offspring sired by the second of two males to mate with a female). When female and male beetle strains were same, defence capacity was significantly higher than when female and male strains were different. However, such a pattern was not observed for offence capacity. The results suggest that female precopulatory mate choice is not affected by genetic background, but the outcome of post‐copulatory processes depends on the genetic background of male and female beetles.     

Food choice in the laboratory pigeon

Although food reward plays a large role in learning and behavioral experiments, there have been few studies examining the most motivating food reward for pigeons. Brown (1969) found that pigeons had a tendency to prefer peas, while Killeen et al. (1993) found pigeons to prefer peas and popcorn in Experiment 1A. We looked to further explore these options as well as expand upon the types of foods examined beyond mainly grains and seeds. Pigeons were presented with six novel foods (granulated peanuts, popping corn, freeze-dried mealworms, bread crumbs, split peas, and sunflower hearts) allocated into two sets of three food items. Once the most consumed food from each food set was determined, they were pooled together with sorghum seeds (a familiar food) to form a third set. Sunflower hearts were the most consumed of all the food items, followed by corn and granulated peanuts. We discuss the potential factors mediating consumption choice, including nutritional profile and food particle size.     

The moisture content of timber in relation to attack by Lyctus powder-post beetles

The relation between moisture content of oak sapwood and rate of development of Lyctus brunneus has been investigated at 23C. Oviposition took place normally in samples of various moisture contents between 5.5 and 23.5%. The eggs hatched in wood of 7.7% moisture content, but not of 61% moisture content, although the embryos developed fully. The rate of gain in weight of young larvae increased to a maximum as the moisture content of the wood rose to about 14.2% and then fell again. The rate of development from egg to adult followed a somewhat similar curve with a maximum at 16% moisture content. At all moisture contents the first male emerged a few days earlier than the first female. The average weight of the male beetles was less and their moisture content greater than those of the corresponding females. The average weight of the beetles showed a tendency to increase at moisture contents of the wood above 97%. The average moisture content of the males was fairly constant up to 156% moisture content of the wood, but that of the females rose slowly as the moisture content of the samples increased. In wood of 15.6% moisture content at 23C. the minimum period of development from egg to adult was 167 days; at 14.2% moisture content and 27.5 C. this was reduced to 142 days. Green timber was shown to be liable to infestation as soon as a superficial skin was formed of a suitable moisture content; the upper limiting moisture content is probably the fibre saturation point. Control of moisture content of timber cannot be achieved sufficiently easily for it to become an important method for the control of Lyctus infestation.     

Supercooling of Myzus persicae in relation to gut content

The supercooling distribution curves of Myzus persicae varied in response to feeding position, diet and age. Unfed instar I aphids supercooled to temperatures lower than –20 °C. Feeding aphids supercooled to higher temperatures, the earlier instars on subsidiary veins supercooling to lower temperatures than the late instars and adults on the main veins. Starvation decreased supercooling ability in some adult aphids. The supercooling ability of aphids feeding on sucrose solutions through a Parafilm membrane decreased in response to an increasing concentration, the position being reversed on 25% sucrose. Varying the amino acid concentration had no effect. The possible effects of this variable supercooling ability on the winter survival of the aphid are discussed.     

Rotifer distribution in relation to temperature and oxygen content

Lunzer Obersee, a small lake located at an altitude of 1100 m above sea level, was investigated from July 1985 to October 1987. The rotifer community consists of 7 dominant species, 7 subdominant species and 34 species which occasionally occurred in the plankton. The dominant species show rather different demands in relation to temperature and oxygen content; e.g.: Filinia hofmanni was found at a wide range of oxygen concentrations (0.6–13.3 mg O₂l^–1) and low temperatures (4–6 °O, living in the upper water layers (1–7 m) during spring and in the deeper, anoxic zone in summer. In contrast, Asplanchna priodonta was found at rather high oxygen contents (> 9 mg O₂ l^–1), ), and showed a wide range of temperature tolerance (4–15 °C).On the basis of field data the temperature and oxygen requirements of several species are described and discussed.     

Ribosome-DnaK interactions in relation to protein folding

Bacterial ribosomes or their 50S subunit can refold many unfolded proteins. The folding activity resides in domain V of 23S RNA of the 50S subunit. Here we show that ribosomes can also refold a denatured chaperone, DnaK, in vitro, and the activity may apply in the folding of nascent DnaK polypeptides in vivo. The chaperone was unusual as the native protein associated with the 50S subunit stably with a 1:1 stoichiometry in vitro. The binding site of the native protein appears to be different from the domain V of 23S RNA, the region with which denatured proteins interact. The DnaK binding influenced the protein folding activity of domain V modestly. Conversely, denatured protein binding to domain V led to dissociation of the native chaperone from the 50S subunit. DnaK thus appears to depend on ribosomes for its own folding, and upon folding, can rebind to ribosome to modulate its general protein folding activity.     

Food choice of Antarctic soil arthropods clarified by stable isotope signatures

Antarctic soil ecosystems are amongst the most simplified on Earth and include only few soil arthropod species, generally believed to be opportunistic omnivorous feeders. Using stable isotopic analyses, we investigated the food choice of two common and widely distributed Antarctic soil arthropod species using natural abundances of ¹³C and ¹⁵N and an isotope labelling study. In the laboratory we fed the isotomid springtail Cryptopygus antarcticus six potential food sources (one algal species, two lichens and three mosses). Our results showed a clear preference for algae and lichens rather than mosses. These results were corroborated by field data comparing stable isotope signatures from the most dominant cryptogams and soil arthropods (C. antarcticus and the oribatid mite Alaskozetes antarcticus). Thus, for the first time in an Antarctic study, we present clear evidence that these soil arthropods show selectivity in their choice of food and have a preference for algae and lichens above mosses.