Ecological impacts of an invasive predator are mediated by the reproductive cycle
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INVASION NOTE
Ecological impacts of an invasive predator are mediated by the reproductive cycle Arpita Dalal . John Gallogly . Ross N. Cuthbert . Ciaran Laverty . James W. E. Dickey . Jaimie T. A. Dick
Received: 6 June 2020 / Accepted: 3 November 2020 Ó Springer Nature Switzerland AG 2020
Abstract Predicting the ecological impacts of invasive species is impeded by context-dependencies that can mediate the strength of trophic interactions. Reproductive status is a pervasive context across trophic and taxonomic groups, yet has mostly been neglected in studies of invader impact. The present study examines the influence of the reproductive cycle on predatory impacts of a known damaging invasive freshwater crustacean, Gammarus pulex (Amphipoda), using a comparative functional response approach. Across females that were non-ovigerous, or had immature- or mature-stage embryonic broods, all G. pulex exhibited potentially prey destabilising Type II functional responses towards chironomid larvae. Attack rates were highest by immature embryonic brood stages, and significantly lower by mature embryonic brood stages. Conversely, handling times were consistently lower, and hence maximum feeding A. Dalal (&) Department of Ecology and Environmental Science, Assam University, Silchar 788011, India e-mail: [email protected] J. Gallogly R. N. Cuthbert C. Laverty J. W. E. Dickey J. T. A. Dick Institute for Global Food Security, School of Biological Sciences, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, Northern Ireland BT9 5DL, UK R. N. Cuthbert GEOMAR, Helmholtz-Zentrum fu¨r Ozeanforschung Kiel, Du¨sternbrooker Weg 20, 24105 Kiel, Germany
rates higher, where broods were present as compared to absent. These predatory patterns may reflect changing resource demands for progeny development across the reproductive cycle, the influence of brood bulk, female moult stage and/or motivational aspects of feeding, such as avoidance of filial cannibalism. Accordingly, many aspects of reproduction may alter the intensity of predatory impacts by invasive species. Future studies considering invader impacts should consider the influence of sex and reproductive status to more holistically quantify and predict populationlevel invader impacts. Keywords Impact prediction Functional response Gammarus pulex Freshwaters Trophic interaction Reproductive status
Introduction Biological invasions continue to disrupt the functioning, structure and service provision of ecosystems globally, and are a major threat to biodiversity (Bellard et al. 2016). Invasive predators can be damaging to native prey communities through both trait- and density-mediated effects, which can disrupt stable predator-prey cycles and result in alterations to community composition (Dick et al. 2014, 2017). Quantifying the impacts of novel consumers, such as predators, on native prey communities has remained a
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fundamental challenge in invasion science, owing to the presence of multipl
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