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The Value to Herbivores of Plant Physical and Chemical Diversity in Time and Space

^a Wildland Resources, Utah State Univ., Logan, UT 84322-5230
^b Plant, Soils, and Biometeorology, Utah State Univ., Logan, UT 84322-4820
^c Animal, Dairy, and Veterinary Sciences, Utah State Univ., Logan, UT 84322-4810

View larger version (20K): [in this window] [in a new window]   Fig. 1. Palatability is a complex phenomenon that integrates a food's odor, taste, and texture with the postingestive effects of nutrients and toxins in the food. The process of ingesting a food causes an animal to satiate on the foods it is eating, and the satiety hypothesis attributes changes in palatability to transient food aversions due to flavors, nutrients, and toxins interacting along temporal concentration gradients.

View larger version (15K): [in this window] [in a new window]   Fig. 2. Examples of objects with Euclidian and Fractal (non-integer) dimensions (adapted from Milne, 1997). Fractal and Euclidean geometry differ in that fractals do not require the value of dimensions (d) to be integers. Instead, they can be fractional values. For instance, if a cube was made of Swiss cheese, it would not completely fill the three-dimensional space. Instead of d assuming a value of three, the fractal dimension of the Swiss cheese cube would fall between two and three.

View larger version (73K): [in this window] [in a new window]   Fig. 3. Differential resource encounter by a forager when the environment is uniform (left column) or fractal (right column). The green box represents the area searched by a forager, while black boxes represent a resource such as food. N is a count of the number of resource cells encountered with the subscripts u and f representing uniform and fractal landscapes, respectively. A change in forager size and hence search area is represented by the green squares over the top of the resource distributions. Forager size, and therefore search area, increases down each column from a 3 x 3 square to a 9 x 9 square of arbitrary units. As search area increases, the number of cells occupied (Nu and Nf) increases in both distributions (columns), but it does so less quickly in the fractal distribution.

View larger version (14K): [in this window] [in a new window]   Fig. 4. Log-log plot showing the change in resource encounter by a forager with changing scale in a uniform and a fractal environment (see Fig. 3). The exponent in each regression approximates the resource dimension of the environment, which is close to 2 in the uniform environment and lower in the fractal environment. Realized resource density in the uniform distribution has an exponent of approximately 2 where y = 0.61x1.91 (r2 = 0.99), which indicates resource density is not strongly scale-dependent. On the other hand, realized food density within the fractal distribution has a much lower exponent y = 0.51x1.26 (r2 = 0.99), which suggests strong scale dependence.