Eric Mellink andMnica E Riojas Lpez

Introduction

Consumption of Vegetative Structures Cladode Preferences Seasonal Effects for Herbivory Nutritional Qualitites of Cladodes Spine Effects on Herbivory Consumption of Reproductive Structures Flower Consumption Fruit Consumption Evolutionary and Ecological Context Past and Present Herbivory Pressures Galápagos Islands Alienized Relations Concluding Remarks Literature Cited

Introduction

In arid lands, platyopuntias (prickly pear cacti, also called nopales [singular, nopal]) often appear as lush, exhuberant forage and, during the proper time of the year, bear brightly colored fruits, which, as Gibson and Nobel (1986) indicate, "would be a welcome waterhole and restaurant for animals." Cladodes and fruits of platyopuntias are indeed consumed by a variety of vertebrates in ways that affect entire ecosystems (Anthony 1954; Janzen 1986).

This chapter presents an overview of the utilization of platyopuntias by wild vertebrates. It also includes a list of the vertebrate species reported to be consumers of platy-opuntias. Certainly this list is not complete, as many con sumers have not been reported in the formal literature. Because of the natural distribution of platyopuntias, the information about vertebrate consumption is biased toward the deserts of North America and the Galápagos Islands. Most sources indicating consumption of platy-opuntias by vertebrates present rather incidental information on the issue; only a few, notably those for the Galápagos Islands, derive from the study of ecological relations involving platyopuntias. Eighty-nine vertebrate species appear in the literature as consumers of platyopuntias: 9 species of reptiles, 26 of birds, and 54 of mammals (Table 7.1). Pads (cladodes) and fruits are the parts most often reported as consumed, although reports on the use of fruits may mask the use of seeds.

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