Island ecosystems are particularly vulnerable to biological invasions. Since the early 1800s, humans have introduced to the GaIapagosIslands animals andplants that threaten the native vegetation Goats are the most abundant and destructive feral animals. Endemic members of the Cactaceae and Asteraceae have been reduced drastically. A control program has completely eradicated goats on several islands, where vegetation has returned but sometimes the species composition diyfers from the original. Hunting continues on Santiago, where 80,000 goats exist, and fenced quudrats protect some native plants. Cattle damage vegetation, particularly the endemic sbrub, Miconia robinsoniana, by trampling and grazing. Ranchers on several islands have been urged to fence in cattle. Wild pigs dig up and eat the roots of tuoodyplants and some rare orchids. Donkeys trample and eat grasses and shrubs. Control of pigs has started; there is no control of donkeys. Between 20 and50 introduced

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 146. INTRODUCTIONIn 1966 investigations were begun by a research team led by P.A.C. into the environmental history of the Galapagos Islands. These semi-desert volcanic islands are attractive to the historical ecologist, both because of their celebrated biota and because their site is well suited to the study of climatic change. The islands lie on the equator, approximately 950 km west of Ecuador (Fig. 1), in the Central Pacific Dry Zone (Palmer & Pyle 1966), a region of unusual climate at the confluence of the wind and ocean current systems of the Eastern Pacific. It is likely, therefore, that global changes in climate like those associated with glacial advances might profoundly alter the conditions for life on the Galapagos, making a long history of the Galapagos environment of great interest. The whole archipelago has been searched for lakes and bogs (Colinvaux 1968). Cores were raised from the principal sediment basins, and the collections taken to Ohio State University in Columbus. These cores have yielded pollen and spore histories of some antiquity from the islands of San Cristobal (Chatham), Santa Cruz, Santiago, Isabela and Genovesa, together with other fossil and stratigraphic evidence of past climates and populations. The longest history goes back to times too ancient to be dated by the radiocarbon method. A series of ecological studies has also been carried out in association with those on environmental history (Boersma 1974, 1975; Maxwell 1974; Racine & Downhower 1974; Downhower & Racine 1975).Historical ecology suffers from an endless conflict of interests, between the necessity for using fossil data to reconstruct climate and the need to know climate in order to understand the community of fossils. The twin goals of the Galapagos research programme, the histories of the climate and of the biota, at once raise this dilemma of circular argument, for if the pollen records had to be used directly to infer climate, then the value of the pollen as a tool for testing biogeographic and ecological theory would be restricted. Fortunately, enough evidence of past climate was found in the gross stratigraphy and mineralogy of the San Cristobal sediments to reconstruct the outline climatic history of the Galapagos Archipelago throughout the last glacial cycle with very little reliance on the record of biota (Colinvaux 1972). Thus it has been possible to use the pollen data to study the response of plants to the changes in climate which have been deduced from other lines of evidence. Accordingly the emphasis throughout this and subsequent papers will be on the elucidation of ecological and biogeographic theory by means of the fossil traces of Galapagos ...

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