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      Nest-site competition and killing by invasive parakeets cause the decline of a threatened bat population


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          The identification of effects of invasive species is challenging owing to their multifaceted impacts on native biota. Negative impacts are most often reflected in individual fitness rather than in population dynamics of native species and are less expected in low-biodiversity habitats, such as urban environments. We report the long-term effects of invasive rose-ringed parakeets on the largest known population of a threatened bat species, the greater noctule, located in an urban park. Both species share preferences for the same tree cavities for breeding. While the number of parakeet nests increased by a factor of 20 in 14 years, the number of trees occupied by noctules declined by 81%. Parakeets occupied most cavities previously used by noctules, and spatial analyses showed that noctules tried to avoid cavities close to parakeets. Parakeets were highly aggressive towards noctules, trying to occupy their cavities, often resulting in noctule death. This led to a dramatic population decline, but also an unusual aggregation of the occupied trees, probably disrupting the complex social behaviour of this bat species. These results indicate a strong impact through site displacement and killing of competitors, and highlight the need for long-term research to identify unexpected impacts that would otherwise be overlooked.

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          Worldwide impact of alien parrots (Aves Psittaciformes) on native biodiversity and environment: a review

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            Experimental evidence for nest-site competition between invasive ring-necked parakeets (Psittacula krameri) and native nuthatches (Sitta europaea)

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              Crowding in the City: Losing and Winning Competitors of an Invasive Bird

              Invasive species can take advantage of resources unexploited by natives (opportunism hypothesis) or they can exploit the same resources but more aggressively or efficiently (competition hypothesis), thus impacting native species. However, invasive species tend to exploit anthropogenic habitats that are inefficiently used by natives such as urban environments. Focusing on the ring-necked parakeet (Psittacula krameri), one of the most invasive birds worldwide, we combined observations of interspecific aggressions, species-specific cavity-nest preferences and the spatial distribution of the native cavity-nesting vertebrate community to determine the invasion process as well as its potential impacts on native species in a Mediterranean city. Our results support the competition hypothesis, suggesting that ring-necked parakeets are outcompeting native species sharing nest-site preferences. Parakeets initiated and won most interspecific aggressions, which were directed towards competitors but also towards predators. This behaviour could explain the spatial arrangement of natives, with most bird species breeding close to parakeets possibly to take advantage of their effective antipredatory behaviour. However, temporal and spatial patterns of segregation suggest that a threatened bat species is negatively affected by parakeets. This demonstrates that common species gain benefits and threatened ones (in this study, a bat and possibly a falcon) lose nest sites due to invaders. Therefore, the conservation status of the native species that pay the costs of competition with invaders should be considered. This scenario of winners and losers may, however, shift towards more losers if the ring-necked parakeet population continues to grow, thus requiring close monitoring and control/eradication programs to avoid further impacts.

                Author and article information

                R Soc Open Sci
                R Soc Open Sci
                Royal Society Open Science
                The Royal Society Publishing
                May 2018
                9 May 2018
                9 May 2018
                : 5
                : 5
                [1 ]Department of Conservation Biology, Estación Biológica de Doñana (CSIC) , Avda. Américo Vespucio, 41092 Sevilla, Spain
                [2 ]Department of Evolutionary Ecology, Estación Biológica de Doñana (CSIC) , Avda. Américo Vespucio, 41092 Sevilla, Spain
                [3 ]Department of Physical, Chemical and Natural Systems, University Pablo de Olavide , Ctra. de Utrera, km. 1, 41013 Sevilla, Spain
                [4 ]CIBER of Epidemiología y Salud Pública (CIBERESP) , Barcelona, Catalunya, Spain
                Author notes
                Author for correspondence: Dailos Hernández-Brito e-mail: dailoshb@ 123456ebd.csic.es

                Electronic supplementary material is available online at https://dx.doi.org/10.6084/m9.figshare.c.4079990.

                © 2018 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                Funded by: Organismo Autónomo de Parques Nacionales (MMA);
                Award ID: 021/2002
                Funded by: Fundación Repsol;
                Funded by: Severo Ochoa Program;
                Award ID: SVP-2014-068732
                Funded by: Action COST;
                Award ID: ES1304
                Biology (Whole Organism)
                Research Article
                Custom metadata
                May, 2018

                biological invasions,interspecific competition,impact,urban habitats


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