Diet, dietary selectivity and density of South American grey fox, Lycalopex griseus, in Central Chile.
The South American grey fox Lycalopex griseus is a canid widely distributed in southern South America; however, some aspects of its biology are still poorly known. We studied the diet and density of L. griseus in the Lago Peñuelas Biosphere Reserve, in Central Chile. The trophic niche breadth was B = 6.16 (Bsta = 0.47) and prey diversity was H' = 2.46 (Hmax ' = 3.17, J' = 0.78). The highest proportions of prey consumed in the diet were Oryctolagus cuniculus (52.21%) and other mammals (32.78%). We compared these results with a latitudinal gradient of diet results for this species in Chile. L. griseus eats mostly mammals (>90% of total prey), consuming the rodent Phyllotis darwini and reptiles in the northern zone; Oryctolagus cuniculus, Octodon degus and Abrocoma bennetti in the central zone; Abrothrix spp. and lagomorphs in the southern zone; and Lepus capensis and Ovis aries in the austral zone. The estimated density of L. griseus in Lago Peñuelas NR was 1.3 foxes/km2 .
Food habits of barn owl Tyto alba in an agroecosystem in southern central Chile
The Barn owl (Tyto alba) diet is described in an agroecosystem located at 20 km South of Mulchén, in south-central Chile. This was studied through the systematic collection of pellets and further analysis in laboratory. It was emphasized the predominant presence of mammals (rodents; 81.9%), followed by birds (passerines; 9.6%), and to a lesser extent, by invertebrates (3.6%). Ecological elements involved in this pattern are discussed.
A Theory of Trophic Strategies: The Evolution of Facultative Specialists
An adaptation of Vandermeer's (1972) revision of niche theory based upon a generalization of the familiar logistic model describes optimal resource utilization patterns for populations at all stages of growth. These are focused into three trophic strategies, two of which are expected to evolve where the relationship between population size and resource abundance (or the rates of resource utilization and provision) is constant and one where this relationship is variable. When population size is constantly less than or equal to that which could be sustained by available resources, obligate specialization and generalization, respectively, are the optimal strategies. When this relationship varies, facultative strategists that could specialize when their population sizes were less than those that could be sustained by available resources and generalize when they were limited by resources would be at a selective advantage. Since such variation characterizes most environments and obligate strategists are limited to constant ones, most consumers should be facultative. Observations of trophic behavior (Murdoch and Oaten 1975) are consistent with this theory, although its evaluation awaits feeding experiments in which the abundance of predators relative to their prey, as well as the frequencies of alternatives, are varied. The results of Cook and Miller (1977) seem to corroborate this theory, but the potential importance of facultative strategists in shaping and maintaining the structure of communities (Glasser 1979, 1982) suggests that it warrants further attention.