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Residence time and human-mediated propagule pressure at work in the alien flora of Galapagos

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Abstract

Introduced species present the greatest threat to the unique terrestrial biodiversity of the Galapagos Islands. We assess the current status of plant invasion in Galapagos, predict the likelihood of future naturalizations and invasions from the existing introduced flora, and suggest measures to help limit future invasions. There has been a 1.46 fold increase in plant biodiversity in Galapagos due to alien plant naturalizations, reflecting a similar trend on islands elsewhere. There are 870 alien plant species recorded in the archipelago. Of evaluated species, 34% species have naturalized. Within this group are the invasive species (16% of evaluated) and the transformers (3.3% of evaluated). We show that, as expected, naturalized species have been present in the archipelago longer than non-naturalized species. We also find that a higher human-mediated propagule pressure is associated with a greater human population and with properties that have been settled longer. This, combined with the relatively recent introduction of most species, leads us to the conclusion that Galapagos is at an early stage of plant invasion. We predict that more species from the existing alien flora will find an opportunity to naturalize and invade as propagule pressure increases alongside rapid human population growth associated with immigration to serve the booming tourism industry. In order to reduce future invasion risk, we suggest reviewing inter-island quarantine measures and continuing community education efforts to reduce human-mediated propagule pressure.

Resumen

Las especies introducidas representan la mayor amenaza a la biodiversidad terrestre única de las Islas Galápagos. En este estudio, evaluamos la condición actual de invasión de plantas en Galápagos, predecimos la posibilidad de nuevas naturalizaciones e invasiones de la flora introducida existente, y sugerimos maneras para limitar invasiones en el futuro. Ha habido un incremento de 1.46 veces en total de biodiversidad de plantas en Galápagos atribuido a las naturalizaciones de plantas introducidas; este patrón se refleja en otras islas del mundo. Han sido reportadas 870 especies de plantas introducidas en el archipiélago. De las especies evaluadas, 34% están naturalizadas; dentro de este grupo están las especies invasoras (16% de las evaluadas) y las transformadores (3.3% de las evaluadas). Como se esperaba, se muestra que las especies naturalizadas han estado presentes en el archipiélago más tiempo que las especies no-naturalizadas. También encontramos que el incremento del número de individuos de las especies introducidas sembradas por los seres humanos está directamente relacionado con el tamaño de la población humana y con la antigüedad de las propiedades privadas. Este hecho, en combinación con la introducción relativamente reciente de la mayoría de las especies, nos lleva a la conclusión de que Galápagos está en las primeras etapas de invasión. Predecimos que más de las especies introducidas ya presentes van a encontrar una oportunidad para naturalizarse a medida que se incrementa el número de individuos por el crecimiento acelerado de la población humana debido al turismo. Para limitar el riesgo de más invasiones en el futuro, sugerimos hacer una revisión del sistema de cuarentena inter-islas, y continuar con los esfuerzos con campañas de educación en la comunidad y de esta manera disminuir el incremento en el número de individuos de las especies ya presentes.

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Acknowledgments

This research originated as part of a Masters in Tropical Environmental Management at Charles Darwin University, Australia, carried out by MT, supervised by RA, PW and Dr Diane Pearson. Chris Buddenhagen and Alan Tye kindly supplied preliminary results from the GWRA for use in this study. Mark Gardener, Chris Buddenhagen and Richard Hobbs provided useful comments on a draft of the manuscript, and feedback from two anonymous referees significantly improved this work. Support for RA and AG comes from the Boston Environmental Fund. The inventory data and risk assessment were products of Project ECU/00/G31 “Control of Invasive Species in the Galapagos Archipelago”, a donation from the Global Environment Facility (GEF) to the Ecuadorian Government, represented by the Ministry of Environment. An early version of this work was presented at the 10th Conference on the Ecology and Management of Alien Plant Invasions in South Africa, August 2009. This paper is contribution number 2009 of the Charles Darwin Foundation for Galapagos Islands.

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  1. Mandy Trueman

    Present address: University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia

Authors and Affiliations

  1. Charles Darwin Foundation, Puerto Ayora, Galapagos, Ecuador

    Mandy Trueman, Rachel Atkinson & Anne Guézou

  2. Charles Darwin University, Darwin, NT, 0909, Australia

    Mandy Trueman & Penny Wurm

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  1. Mandy Trueman
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Correspondence to Mandy Trueman.

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Trueman, M., Atkinson, R., Guézou, A. et al. Residence time and human-mediated propagule pressure at work in the alien flora of Galapagos. Biol Invasions 12, 3949–3960 (2010). https://doi.org/10.1007/s10530-010-9822-8

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