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Effects of Urbanization on the Distribution and Abundance of Amphibians and Invasive Species in Southern California Streams

Authors

  • SETH P. D. RILEY,

    Corresponding author
    1. Santa Monica Mountains National Recreation Area, National Park Service, 401 W. Hillcrest Drive, Thousand Oaks, CA 91360, U.S.A.
      email seth_riley@nps.gov
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  • GARY T. BUSTEED,

    1. Santa Monica Mountains National Recreation Area, National Park Service, 401 W. Hillcrest Drive, Thousand Oaks, CA 91360, U.S.A.
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  • LEE B. KATS,

    1. Department of Biology, Pepperdine University, 24255 Pacific Coast Highway, Malibu, CA 90263, U.S.A.
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  • THOMAS L. VANDERGON,

    1. Department of Biology, Pepperdine University, 24255 Pacific Coast Highway, Malibu, CA 90263, U.S.A.
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  • LENA F. S. LEE,

    1. Santa Monica Mountains National Recreation Area, National Park Service, 401 W. Hillcrest Drive, Thousand Oaks, CA 91360, U.S.A.
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  • ROSI G. DAGIT,

    1. Resource Conservation District of the Santa Monica Mountains, 122 N. Topanga Canyon Blvd, Topanga, CA 90290, U.S.A.
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  • JACOB L. KERBY,

    Corresponding author
    1. Santa Monica Mountains National Recreation Area, National Park Service, 401 W. Hillcrest Drive, Thousand Oaks, CA 91360, U.S.A.
    2. Resource Conservation District of the Santa Monica Mountains, 122 N. Topanga Canyon Blvd, Topanga, CA 90290, U.S.A.
      Current address: Environmental Science and Policy, 1 Shields Avenue, University of California, Davis, CA 95616, U.S.A.
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  • ROBERT N. FISHER,

    1. U.S. Geological Survey, San Diego Field Station, 5745 Kearny Villa Drive, Suite M, San Diego, CA 92123, U.S.A.
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  • RAYMOND M. SAUVAJOT

    1. Santa Monica Mountains National Recreation Area, National Park Service, 401 W. Hillcrest Drive, Thousand Oaks, CA 91360, U.S.A.
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email seth_riley@nps.gov

Current address: Environmental Science and Policy, 1 Shields Avenue, University of California, Davis, CA 95616, U.S.A.

Abstract

Abstract: Urbanization negatively affects natural ecosystems in many ways, and aquatic systems in particular. Urbanization is also cited as one of the potential contributors to recent dramatic declines in amphibian populations. From 2000 to 2002 we determined the distribution and abundance of native amphibians and exotic predators and characterized stream habitat and invertebrate communities in 35 streams in an urbanized landscape north of Los Angeles (U.S.A.). We measured watershed development as the percentage of area within each watershed occupied by urban land uses. Streams in more developed watersheds often had exotic crayfish (Procambarus clarkii) and fish, and had fewer native species such as California newts (Taricha torosa) and California treefrogs (Hyla cadaverina). These effects seemed particularly evident above 8% development, a result coincident with other urban stream studies that show negative impacts beginning at 10–15% urbanization. For Pacific treefrogs (H. regilla), the most widespread native amphibian, abundance was lower in the presence of exotic crayfish, although direct urbanization effects were not found. Benthic macroinvertebrate communities were also less diverse in urban streams, especially for sensitive species. Faunal community changes in urban streams may be related to changes in physical stream habitat, such as fewer pool and more run habitats and increased water depth and flow, leading to more permanent streams. Variation in stream permanence was particularly evident in 2002, a dry year when many natural streams were dry but urban streams were relatively unchanged. Urbanization has significantly altered stream habitat in this region and may enhance invasion by exotic species and negatively affect diversity and abundance of native amphibians.

Abstract

Resumen: La urbanización afecta de muchas formas negativas a los ecosistemas naturales, particularmente a los sistemas acuáticos. La urbanización también está reconocida como uno de los potenciales causantes de las dramáticas declinaciones recientes en las poblaciones de anfibios. Entre 2000 y 2002 determinamos la distribución y abundancia de anfibios nativos y depredadores exóticos y caracterizamos el hábitat y las comunidades de invertebrados en 35 arroyos en un paisaje urbanizado al norte de Los Ángeles. Medimos el desarrollo de la cuenca como el porcentaje de la superficie ocupada por usos urbanos en cada cuenca. Los arroyos en cuencas más desarrolladas a menudo tenían cangrejos de río exóticos (Procambarus clarkii) y peces, y tenían menos especies nativas, como tritones (Taricha torosa) y ranas arborícolas (Hyla cadaverina). Estos efectos parecieron particularmente evidentes arriba de 8% de desarrollo, un resultado que coincide con otros estudios de arroyos urbanos que muestran impactos negativos a partir de 10-15% de urbanización. La abundancia de H. regilla, el anfibio nativo con mayor distribución, fue menor en presencia de cangrejos de río exóticos, aunque no encontramos efectos directos de la urbanización. Las comunidades de macroinvertebrados bentónicos también fueron menos diversas en los arroyos urbanos, especialmente las especies sensitivas, Los cambios en la comunidad de la fauna en arroyos urbanos se pueden relacionar con cambios en el hábitat físico del arroyo, tales como menos hábitat con pozas y más hábitat con corriente y una mayor profundidad y flujo de agua, lo que produce arroyos más permanentes. La variación en la permanencia de los arroyos fue particularmente evidente en 2002, año en el que muchos arroyos naturales se secaron y los arroyos urbanos permanecieron relativamente sin cambios. La urbanización ha alterado significativamente a los hábitats de arroyos en esta región y puede incrementar la invasión de especies exóticas e incidir negativamente en la diversidad y abundancia de anfibios nativos.

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