Visual display of the Ecology of giant tortoises (Geochelone elephantopus) in the Galapagos Islands



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.






    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).