Historical Ecology in the Galapagos Islands: I. A Holocene Pollen Record from El Junco Lake, Isla San Cristobal

Abstract

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 ...

Detecting the initial impact of humans and introduced species on island environments in Remote Oceania using palaeoecology

“…As a result, the sites that were selected for analysis were mostly large and remote from early human habitation sites. For example, high elevation bogs or volcanic caldera lakes in the tropical Hawaiian Islands (Selling 1948;Selling in Massey 1979;Athens and Ward 1993) and Galápagos Islands (Colinvaux and Schofield 1976), subtropical Easter Island (Flenley 1979;Flenley and King 1984;Flenley et al 1991) and numerous bogs in temperate and subAntarctic New Zealand. While these records provide good regional pictures of vegetation change including, in many cases, deforestation by fire, they do not, and probably cannot, reveal more local and direct evidence of human activities such as the introduction of agriculture and the effects of invasive species.…”

Guatemalan forest synthesis after Pleistocene aridity

“…An early Holocene temperate forest preceded a mesic tropical forest with Brosimum (ramon). Thus "primeval" rain forests of Guatemala are no older than 10,000 to 11,000 years and are considerably younger Holocene (10,[0][1][2][3][4][5][6][7][8]500 B.P.) (3, 4) but are unsubstantiated by palynological data from Central America.…”

“…Evidence of late Glacial (15,000-10,000 B.P.) aridity in the Neotropics comes from pollen studies in the savannas of northern South America (5), the Galapagos Islands (where the lowest sections are devoid of pollen) (6), an undated diagram from the Amazon Basin (7), and Lake Valencia, Venezuela (8,9,36). Supporting data for the Neotropics come from geomorphic studies (10,11) and deep sea cores (12)(13)(14).…”

Arid landscapes and environmental transformations in ancient Southwestern Ecuador

“…Nevertheless, it would be hazardous to apply these findings uncritically to the data from Loma Alta, particularly as the synchrony of later Holocene events is still unclear (Markgraf 1989: 8;Markgraf and Bradbury 1982: 42). Still others suggest no significant climatic shifts during the Holocene (Colinvaux andSchofield 1976:1010;Ferdon 1981: 625 …”