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PubMed2002

Foraging ecology of bison at the landscape and plant community levels: the applicability of energy maximization principles.

Predictions of animal distribution and resource use require multi-scale consideration because animals can use different sets of selection criteria at different scales. We investigated whether patterns of distribution and resource use by free-ranging bison (Bison bison) in Prince Albert National Park, Saskatchewan, follow rules of energy maximization that hold across multiple scales. Optimality theory predicts specialization on Carex atherodes and frequency-independent selection among plant species; that is, local variation in C. atherodes biomass should not influence diet choice but only the time spent in individual patches. The summer use of resources within meadows was closely related to energy maximization principles. C. atherodes dominated the diet of bison, was selected in all meadows, and diet choice was frequency-independent among meadows in the bison range. In winter, diet was still dominated by C. atherodes, but frequency-dependent selection of Scolochloa festucacea and the relative use of Cirsium arvense were inconsistent with theoretical predictions. At a larger spatial scale, however, the probability of meadow use was not positively related to the abundance of Carex atherodes. During summer and winter, general landscape features within the daily radius of bison (2 km in summer and 1.3 km in winter), together with abiotic characteristics of meadows, had the major influence on the probability of meadow utilization. Our study suggests that bison distribution and resource use are influenced by abiotic and biotic factors which vary in importance at different spatio-temporal scales.

Adaptation, Physiological↗

PubMed2004

Habitat structural complexity mediates the foraging success of multiple predator species.

We investigated the role of freshwater macrophytes as refuge by testing the hypothesis that predators capture fewer prey in more dense and structurally complex habitats. We also tested the hypothesis that habitat structure not only affects the prey-capture success of a single predator in isolation, but also the effectiveness of two predators combined, particularly if it mediates interactions between the predators. We conducted a fully crossed four-factorial laboratory experiment using artificial plants to determine the separate quantitative (density) and qualitative (shape) components of macrophyte structure on the prey-capture success of a predatory damselfly, Ischnura heterosticta tasmanica, and the southern pygmy perch, Nannoperca australis. Contrary to our expectations, macrophyte density had no effect on the prey-capture success of either predator, but both predators were significantly less effective in the structurally complex Myriophyllum analogue than in the structurally simpler Triglochin and Eleocharis analogues. Furthermore, the greater structural complexity of Myriophyllum amplified the impact of the negative interaction between the predators on prey numbers; the habitat use by damselfly larvae in response to the presence of southern pygmy perch meant they captured less prey in Myriophyllum. These results demonstrate habitat structure can influence multiple predator effects, and support the mechanism of increased prey refuge in more structurally complex macrophytes.

Analysis of Variance↗

PubMed2005

Global and local spatial landmarks: their role during foraging by Columbian ground squirrels (Spermophilus columbianus).

Locating food and refuge is essential for an animal's survival. However, little is known how mammals navigate under natural conditions and cope with given environmental constraints. In a series of six experiments, I investigated landmark-based navigation in free-ranging Columbian ground squirrels (Spermophilus columbianus). Squirrels were trained individually to find a baited platform within an array of nine identical platforms and artificial landmarks set up on their territories. After animals learned the location of the food platform in the array, the position of the latter with respect to local artificial, local natural, and global landmarks was manipulated, and the animal's ability to find the food platform was tested. When only positions of local artificial landmarks were changed, squirrels located food with high accuracy. When the location of the array relative to global landmarks was altered, food-finding accuracy decreased but remained significant. In the absence of known global landmarks, the presence of a familiar route and natural local landmarks resulted in significant but not highly accurate performance. Squirrels likely relied on multiple types of cues when orienting towards a food platform. Local landmarks were used only as a secondary mechanism of navigation, and were not attended to when a familiar route and known global landmarks were present. This study provided insights into landmark use by a wild mammal in a natural situation, and it demonstrated that an array of platforms can be employed to investigate landmark-based navigation under such conditions.

Animals↗

PubMed2005

Foraging in chemically diverse environments: energy, protein, and alternative foods influence ingestion of plant secondary metabolites by lambs.

Interactions among nutrients and plant secondary metabolites (PSM) may influence how herbivores mix their diets and use food resources. We determined intake of a food containing a mix of terpenoids identified in sagebrush (Artemisia tridentata) when present in isoenergetic diets of increasing concentrations of protein (6, 9, 15, or 21% CP) or in isonitrogenous diets of increasing concentrations of energy (2.17, 2.55, 3.30, or 3.53 Mcal/kg). Lambs were offered choices between those diets with or without terpenes or between diets with terpenes and alfalfa hay. Intake of the diets with terpenes was lowest with the lowest concentrations of protein (6%) and energy (2.17 Mcal/kg) in the diets, and highest with diets of 15% CP and 3.53 Mcal/kg. In contrast, when terpenes were absent from the diets, lambs consumed similar amounts of all four diets with different concentrations of protein, and more of the diets with intermediate amounts of energy. When given a choice between the diet with or without terpenes, lambs preferred the diet without terpenes. When lambs were offered choices between terpene-containing diets and alfalfa, energy and protein concentrations influenced the amount of terpenes animals ingested. Energy densities higher than alfalfa, and protein concentrations higher than 6%, increased intake of the terpene-containing diet. Thus, the nutritional environment interacted with terpenes to influence preference such that lambs offered diets of higher energy or protein concentration ate more terpenes when forced, but not when offered alternative food without terpenes. The nutrients supplied by a plant and its neighbors likely influence how much PSM an animal can ingest, which in turn may affect the dynamics of plant communities, and the distribution of herbivores in a landscape. We discuss implications of these findings for traditional views of grazing refuges and varied diets in herbivores.

Animal Feed↗

PubMed1974