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Factors influencing the relative abundance of invasive predators and omnivores on islands


Invasive alien species (IAS) are the major cause of native species extinctions on islands worldwide. To mitigate or eliminate IAS impacts, eradication is often the best alternative. However, IAS removal may result in cascading effects, through increase in prey abundance, mesopredator release, or competitor release. Our objective is to determine which ecological processes may influence the relative abundance of invasive carnivores and rodents on an insular system. We find that feral cat and mustelids relative abundance was strongly related by prey abundance, and for the feral cat, abundance was also controlled by habitat; these results suggest that bottom-up control through environmental filtering could be the mechanism explaining predator abundance. For rodents, we find that the abundance of the black rat was mostly controlled by the abundance of Norway rat and house mice, and food availability; the Norway rat by the abundance of black rat, a house mice and of mustelid predators; and house mouse by the other rodents and food availability. These results suggest that several mechanisms could be concurrently controlling abundance of these species; competition and predation for Norway rat, and competition and bottom-up control by environmental filtering for the other two rodents. While different factors explain the abundance of invasive species within the same functional group, food resource availability is, in general, the main controller of abundance of invasive rodents and carnivores in the Azores. Therefore, IAS management actions in these islands should focus on limiting the access to food resources and shelter, mainly near to human populations.

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We gratefully acknowledge the Natural Park and Agrarian Development Service of Terceira Island for logistic support, Rémi Fontaine, Manuel Aguiar, Fábio Raposo and Alejandra Ros for field assistance, Marco Ferrante and Jagoba Malumbres for the statistical analysis help and James Russell for the commentaries and suggestions in the first version of the manuscript.


LLL (SFRH/BD/115022/2016) was supported by the Fundação para a Ciência e Tecnologia—FCT. MJS was supported by the University Research Priority Program in Global Change and Biodiversity from the University of Zürich.

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LL-L and MJS contributed to the conception/design of the work. LL-L performed the field work and data analysis. LL-L and MJS contributed to manuscript writing.

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Correspondence to Lucas Lamelas-López.

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Our methods met all ethical guidelines stipulated by the standards and policies of Portuguese law and special care was taken in order to minimize disturbance of biota.

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Lamelas-López, L., Santos, M.J. Factors influencing the relative abundance of invasive predators and omnivores on islands. Biol Invasions 23, 2819–2830 (2021).

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  • Azores
  • Biological invasions
  • Bottom-up regulation
  • Camera-trapping
  • Carnivores
  • Mesopredator release effect
  • Oceanic islands
  • Rodents