Effects of Invasive Cordgrass on Presence of Marsh Grassbird in an Area where It Is Not Native

Authors

  • ZHIJUN MA,

    Corresponding author
    1. Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, China
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  • XIAOJING GAN,

    1. Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, China
    Current affiliation:
    1. Nature Conservation Legislation Research Panel, Beijing, China
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  • CHI-YEUNG CHOI,

    1. Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, China
    Current affiliation:
    1. Ecology Group, Institute of Agriculture and Environment, PN 624, Massey University, Palmerston North, New Zealand
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  • BO LI

    1. Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, China
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Abstract

The threatened Marsh Grassbird (Locustella pryeri) first appeared in the salt marsh in east China after the salt marsh was invaded by cordgrass (Spartina alterniflora), a non-native invasive species. To understand the dependence of non-native Marsh Grassbird on the non-native cordgrass, we quantified habitat use, food source, and reproductive success of the Marsh Grassbird at the Chongming Dongtan (CMDT) salt marsh. In the breeding season, we used point counts and radio-tracking to determine habitat use by Marsh Grassbirds. We analyzed basal food sources of the Marsh Grassbirds by comparing the δ13C isotope signatures of feather and fecal samples of birds with those of local plants. We monitored the nests through the breeding season and determined the breeding success of the Marsh Grassbirds at CMDT. Density of Marsh Grassbirds was higher where cordgrass occurred than in areas of native reed (Phragmites australis) monoculture. The breeding territory of the Marsh Grassbird was composed mainly of cordgrass stands, and nests were built exclusively against cordgrass stems. Cordgrass was the major primary producer at the base of the Marsh Grassbird food chain. Breeding success of the Marsh Grassbird at CMDT was similar to breeding success within its native range. Our results suggest non-native cordgrass provides essential habitat and food for breeding Marsh Grassbirds at CMDT and that the increase in Marsh Grassbird abundance may reflect the rapid spread of cordgrass in the coastal regions of east China. Our study provides an example of how a primary invader (i.e., cordgrass) can alter an ecosystem and thus facilitate colonization by a second non-native species.

Efectos de Spartina alterniflora Invasora Sobre Locustella pryeri en un Área Donde No Es Nativa

Resumen

El ave amenazada Locustella pryeri apareció por primera vez en las marismas del este de China después de que fueran invadidas por el pasto Spartina alterniflora, una especie no nativa e invasora. Para entender la dependencia del ave no nativa con la planta no nativa, cuantificamos el uso de hábitat, la fuente de alimento y el éxito reproductivo del ave en la marisma Chongming Dongtan (CMDT). En la temporada reproductiva usamos puntos de conteo y radio-transmisores para determinar el uso de hábitat del ave. Analizamos las fuentes de alimento basales de las aves al comparar las firmas del isotopo δ13C de muestras de plumas y excretas de las aves con las de las plantas locales. Monitoreamos los nidos a lo largo de la temporada reproductiva y determinamos el éxito reproductivo del ave en la CMDT. La densidad de las aves fue más alta cuando la planta se encontraba en áreas de monocultivo de la caña nativa Phragmites australis. El territorio de reproducción del ave estuvo compuesto principalmente por parches de Spartina alterniflora y los nidos estaban construidos exclusivamente con tallos de esta planta. S. alterniflora fue el principal productor primario en la base de la cadena alimenticia de Locustella pryeri. El éxito reproductivo de L. pryeri en la CMDT fue similar al éxito reproductivo dentro de su extensión nativa. Nuestros resultados sugieren que la especie no nativa S. alterniflora proporciona un hábitat y alimento esenciales en la CMDT para individuos de la especie L. pryeri en temporada reproductiva y que el incremento en la abundancia de esta especie puede reflejar el esparcimiento rápido de la planta S. alterniflora en las regiones costeras del este de China. Nuestro estudio proporciona un ejemplo de cómo un invasor primario (p. ej.: S alterniflora) puede alterar un ecosistema y así facilitar la colonización de una segunda especie no nativa.

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