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159 availability. Based on these studies on Santa Cruz and Pin- zon, it is suggested that tortoises throughout the islands, regardless of sex, size (except perhaps the smallest, from hatching to 4-5 years old), or island, maintain the same general activity patterns and time budgets as each other, uith seasonal changes consistent with changes in environmen- tal conditions.
160 CHAPTER FIVE - FEEDING BEHAVIOR INTRODUCTION Animals with wide food preferences, and in many cases, greater tolerance for aridity, appear especially favored for establishment on oceanic islands (Carlquist 1974). The aridity and unpredictability of the climate in the Galapagos Islands require that animals maintain these characteristics to survive. This does not mean that herbivores on oceanic islands need be strict generalists, eating each species in proportion to its presence (Chew 1974), but rather that they be facultative strategists, having the ability to shift along the continuum from generalist to specialist depending on the current conditions (Glasser 1984). Herbivores living in arid regions are often generalized feeders, in that they feed on a wide range of species, plant types, and plant parts, but often show distinct seasonal changes in prefer- ence (Noy-Heir 1974). Most turtles are opportunistic with some species changing their food habits according to avail- ability of food items in different seasons (Mahmoud and Klicka 1979)9 showing the strategy of flexible selectivity suggested by Noy-feir (1974). One hypothesis resulting from optimal foraging models is that animals should feed more selectively (ie., act as spe- cialists) when food is abundant and should feed on all potential food items when food is very scarce (Ivlev 1961, NacArthur and Pianka 1966, Emlen 1966, 1968, Schoener 1971).