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Bite Rate (bite + rate)
Selected AbstractsHow a mega-grazer copes with the dry season: food and nutrient intake rates by white rhinoceros in the wildFUNCTIONAL ECOLOGY, Issue 2 2006A. M. SHRADER Summary 1Few studies have investigated how free-ranging wild herbivores adjust their food intake rate and nutrient gains during the dry season. Our study focused on the largest extant grazer, the white rhinoceros (Ceratotherium simum Burchell 1817). Field measurements were made on changes in bite mass, bite rate and nutrient concentrations of food eaten during the dry season. 2As the dry season progressed, the quality and availability of food resources declined. During this time white rhinos foraged mainly in high-quality short and woodland grasslands. Late in the dry season they also used flushes of green grass in previously burnt Themeda grasslands. 3Bite mass increased linearly with increasing sward height, while bite rate declined. Intake rate was determined primarily by bite mass and thus tended to increase linearly with sward height. Maximum bite mass and intake rate was obtained in swards >20 cm. 4White rhinos did not compensate for seasonal declines in food quality by adjusting their food intake rate or diet breadth. We suggest that white rhinos mobilize fat reserves to help meet their nutritional needs during the dry season. [source] The effect of sward structure as influenced by ryegrass genotype on bite dimensions and short-term intake rate by dairy cowsGRASS & FORAGE SCIENCE, Issue 1 2003P. D. Barrett Abstract The effects of genotypic variation in ryegrasses on sward structure, bite dimensions and intake rate by dairy cows were investigated. Two experiments were conducted. In Experiment 1, swards were in a vegetative state whereas, in Experiment 2, they were partly reproductive and were taller with higher herbage mass but lower leaf proportion than in Experiment 1. Applicability of relationships between sward structure and bite characteristics, previously established from artificial or hand-constructed swards, to field conditions were tested. Additional short-term intake rates and/or sward structural characteristics were considered as indicators of potential intake for use in protocols for the evaluation of grass varieties. Four cultivars were studied: AberElan, Twins (diploid and tetraploid perennial ryegrasses respectively), Polly, a hybrid ryegrass (perennial × Italian ryegrass) and Multimo (Italian ryegrass), each established in 200-m2 plots in four replicated blocks. Herbage intake rate was determined by short-term liveweight change (taking account of insensible weight loss) using 16 dairy cows allocated to four balanced groups with each plot grazed by one group for a 1-h assessment period. One block was grazed per day, over a 4-d experimental period, with each group grazing each variety in a complete crossover design. Sward characteristics and bite rate were also measured in both experiments. Bite dimensions were subsequently estimated, with bite depth being determined as a function of extended tiller height (ETH) in both experiments. Within both experiments, bite mass and intake rate did not differ significantly between swards of different cultivars despite swards containing Multimo generally having a higher ETH and water-soluble carbohydrate concentration and lower green leaf mass, sward bulk density and neutral-detergent fibre concentration than the other swards. However, bite depth was significantly higher (P < 0·01) in swards containing Multimo swards than in the others and, in Experiment 1, bite depth, as a proportion of ETH, was higher in swards containing Multimo and lower in those containing Twins than in the other two cultivars, whereas there was no difference in Experiment 2. Taking both experiments together, the mean bite depth was 0·5 of ETH with sward bulk density accounting for almost half the variance in the relationship between bite depth and ETH. The bulk density of the bite (bite mass per unit bite volume), measured in Experiment 2, followed a similar pattern to sward bulk density, increasing in the order Multimo, Polly, AberElan and Twins. It is concluded that the relationships between sward characteristics and bite dimensions, derived from artificial swards, are applicable to field swards, although the range in natural ryegrass sward characteristics is usually not as wide as in experiments using artificial swards. Lack of precision in the measurement of short-term intake and in sward-based measurements is likely to preclude their use in the evaluation of grass varieties. [source] Longer guts and higher food quality increase energy intake in migratory swansJOURNAL OF ANIMAL ECOLOGY, Issue 6 2008Jan A. Van Gils Summary 1Within the broad field of optimal foraging, it is increasingly acknowledged that animals often face digestive constraints rather than constraints on rates of food collection. This therefore calls for a formalization of how animals could optimize food absorption rates. 2Here we generate predictions from a simple graphical optimal digestion model for foragers that aim to maximize their (true) metabolizable food intake over total time (i.e. including nonforaging bouts) under a digestive constraint. 3,The model predicts that such foragers should maintain a constant food retention time, even if gut length or food quality changes. For phenotypically flexible foragers, which are able to change the size of their digestive machinery, this means that an increase in gut length should go hand in hand with an increase in gross intake rate. It also means that better quality food should be digested more efficiently. 4These latter two predictions are tested in a large avian long-distance migrant, the Bewick's swan (Cygnus columbianus bewickii), feeding on grasslands in its Dutch wintering quarters. 5Throughout winter, free-ranging Bewick's swans, growing a longer gut and experiencing improved food quality, increased their gross intake rate (i.e. bite rate) and showed a higher digestive efficiency. These responses were in accordance with the model and suggest maintenance of a constant food retention time. 6These changes doubled the birds' absorption rate. Had only food quality changed (and not gut length), then absorption rate would have increased by only 67%; absorption rate would have increased by only 17% had only gut length changed (and not food quality). 7The prediction that gross intake rate should go up with gut length parallels the mechanism included in some proximate models of foraging that feeding motivation scales inversely to gut fullness. We plea for a tighter integration between ultimate and proximate foraging models. [source] Mechanisms of functional response and resource exploitation in browsing roe deerJOURNAL OF ANIMAL ECOLOGY, Issue 5 2002Andrew W. Illius Summary 1The functional responses of roe deer were examined using 11 plant species. A technique to discriminate between encounter- and handling-limited processes was used, and it can be concluded that the functional response applicable to patch browsing by roe deer is governed not by the rate of encounter but by the rate of oral processing. 2The large differences between plant species were due to variations in both parameters of the functional response: h , the time lost in biting, and Rmax , the maximum processing rate. Removing the thorns from three of the species affected these parameters differently, according to the size and density of thorns. 3Animals took larger bites from larger patches (branches), and bite mass declined as patch exploitation progressed, implying that animals were selecting the larger items to eat first. It was demonstrated experimentally that depletion of the larger bites does occur first, and it was concluded that prey selection is an important component of herbivore foraging behaviour. 4The gain curves for deer feeding on the different plant species are calculated as being virtually linear. Patch depression did not, in general, occur because increasing bite rate compensated for declining bite mass. Our mechanistic approach is contrasted with other approaches to describing the gain curve in the literature. 5A priori and empirical grounds are presented for rejecting the hypothesis that resource exploitation by browsing mammals is governed by optimal patch use. Diet optimization, involving a trade-off between diet quality and quantity, offers a better explanation of herbivore foraging behaviour. [source] |