Impacts of climate variability and human colonization on the vegetation of the Galápagos Islands

Authors

  • Alejandra Restrepo,

    1. Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida 32901 USA
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    • Present address: Center of Tropical Paleoecology and Archaeology, Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancon, Republic of Panamá.

  • Paul Colinvaux,

    1. Marine Biology Laboratory, Woods Hole, Massachusetts 02543 USA
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  • Mark Bush,

    Corresponding author
    1. Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida 32901 USA
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  • Alexander Correa-Metrio,

    1. Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida 32901 USA
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    • Present address: Instituto de Geología, Universidad Nacional Autónoma de México, Mexico, D.F. 04510 México.

  • Jessica Conroy,

    1. Department of Geosciences, The University of Arizona, Tucson, Arizona 85721 USA
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    • Present address: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332 USA.

  • Mark R. Gardener,

    1. Charles Darwin Foundation, Santa Cruz, Galápagos Islands, Ecuador
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    • Present address: Research Institute for Environment and Livelihoods, Charles Darwin University, NT 0909 Australia.

  • Patricia Jaramillo,

    1. Charles Darwin Foundation, Santa Cruz, Galápagos Islands, Ecuador
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  • Miriam Steinitz-Kannan,

    1. Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099 USA
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  • Jonathan Overpeck

    1. Department of Geosciences, The University of Arizona, Tucson, Arizona 85721 USA
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  • Corresponding Editor: F. S. Hu.

Abstract

A high-resolution (2–9 year sampling interval) fossil pollen record from the Galápagos Islands, which spans the last 2690 years, reveals considerable ecosystem stability. Vegetation changes associated with independently derived histories of El Niño Southern Oscillation variability provided evidence of shifts in the relative abundance of individual species rather than immigration or extinction. Droughts associated with the Medieval Climate Anomaly induced rapid ecological change that was followed by a reversion to the previous state. The paleoecological data suggested nonneutral responses to climatic forcing in this ecosystem prior to the period of human influence.

Human impacts on the islands are evident in the record. A marked decline in long-term codominants of the pollen record, Alternanthera and Acalypha, produced a flora without modern analogue before 1930. Intensified animal husbandry after ca. 1930 may have induced the local extinction of Acalypha and Alternanthera. Reductions in populations of grazing animals in the 1970s and 1980s did not result in the return of the native flora, but in invasions by exotic species. After ca. 1970 the trajectory of habitat change accelerated, continuously moving the ecosystem away from the observed range of variability in the previous 2690 years toward a novel ecosystem. The last 40 years of the record also suggest unprecedented transport of lowland pollen to the uplands, consistent with intensified convection and warmer wet seasons.

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