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The effect of enemy-release and climate conditions on invasive birds: a regional test using the rose-ringed parakeet (Psittacula krameri) as a case study

Authors

  • Assaf Shwartz,

    Corresponding author
    1. The Biodiversity Research Group, Department of Evolution, Systematics and Ecology, The Silberman Institute Life Science, The Hebrew University of Jerusalem, Jerusalem 91904 Israel,
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  • Diederik Strubbe,

    1. Evolutionary Ecology Group, Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium,
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  • Chris John Butler,

    1. Department of Biology, College of Mathematics and Science, University of Central Oklahoma, 100 N University Drive, Edmond, OK 73034-5209, USA
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  • Erik Matthysen,

    1. Evolutionary Ecology Group, Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium,
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  • Salit Kark

    Corresponding author
    1. The Biodiversity Research Group, Department of Evolution, Systematics and Ecology, The Silberman Institute Life Science, The Hebrew University of Jerusalem, Jerusalem 91904 Israel,
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*Correspondence: Assaf Shwartz and Salit Kark, The Biodiversity Research Group, Department of Evolution, Systematics and Ecology, The Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel. E-mail: shwar.a@mail.huji.ac.il, salit@cc.huji.ac.il

ABSTRACT

Aim  Some invasive species succeed particularly well and manage to establish populations across a wide variety of regions and climatic conditions. Understanding how biotic and environmental factors facilitate their invasion success remains a challenge. Here, we assess the role of two major hypotheses explaining invasion success: (1) enemy-release, which argues that invasive species are freed from their native predators and parasites in the new areas; and (2) climate-matching, which argues that the climatic similarity between the exotic and native range determines the success of invasive populations.

Location  India, Israel and the UK.

Methods  We studied the reproductive success of one of the most successful avian invaders, the rose-ringed parakeet (Psittacula krameri), in its native range (India) and in two introduced regions, varying in their climate conditions (Israel and the UK). We combined literature and field data to evaluate the role of predation pressure and climatic conditions in explaining the differences in reproductive success between the three regions.

Results  We found significant differences in reproductive success between regions. In accordance with the enemy-release hypothesis, we discovered that while predation was the main factor responsible for the reduction of fecundity in India, it did not significantly affect the fecundities of parakeet populations in the two introduced regions. In accordance with the climate-matching hypothesis, we found that in the colder temperate UK, egg infertility was high, resulting in lower fecundities. Populations in both the warmer Mediterranean climate of Israel and in the native Indian range had significantly lower egg infertility and higher fecundities than the UK populations.

Main conclusions  Our findings support both the enemy-release and the climate-matching hypotheses. While release from predators facilitates the reproductive success and therefore the invasiveness of parakeets in both the UK and in Israel, colder climate impedes reproduction and therefore the spread of parakeets in the UK.

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