Invasive Species Dynamics and Impact on Native Squirrel Populations

Invasive species exert profound pressures on native ecosystems by altering competitive hierarchies, introducing novel pathogens and disrupting established trophic interactions. The eastern grey squirrel (Sciurus carolinensis), introduced to parts of Europe, North America and beyond, has outcompeted the native red squirrel (Sciurus vulgaris) in many regions through superior resource exploitation and by serving as a reservoir for squirrelpox virus. This disease, generally fatal to red squirrels but tolerated by greys, accelerates native declines via apparent competition. Concurrently, recovery of native predators such as the European pine marten (Martes martes) has revealed a nature-based control mechanism, reversing grey dominance where predator densities rise. Landscape fragmentation and urban refugia, however, permit grey squirrel persistence despite predation pressure. Mathematical and epidemiological models combining field data have elucidated how partial immunity, host heterogeneity and seasonality drive disease-mediated invasion dynamics. Integrated management that combines pathogen surveillance, targeted grey squirrel control in urban strongholds and promotion of native predator recovery offers a multifaceted strategy for conserving red squirrel populations. Globally, this system exemplifies the complex interplay among invasive hosts, pathogens and trophic networks, underscoring the need for cross-disciplinary approaches in invasive species management.

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Invasive Species Dynamics and Impact on Native Squirrel Populations publication trend

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Technical terms

Apparent competition: Indirect negative interaction whereby two prey species share a common predator or pathogen, amplifying impacts on one another.

Occupancy modelling: Statistical framework estimating species presence across landscapes while accounting for detection probability and environmental covariates.

Seropositivity: Presence of detectable antibodies in an organism’s blood, indicating exposure to a specific pathogen.

Refugia: Areas that offer shelter or protection from predators or environmental stressors, enabling species persistence.

Partial immunity: Immunological state in which hosts retain some, but not full, resistance to reinfection, affecting outbreak dynamics.

References

1. Immune interactions and heterogeneity in transmission drives the pathogen‐mediated invasion of grey squirrels in the UK. Journal of Animal Ecology (2024).
2. Restoring vertebrate predator populations can provide landscape‐scale biological control of established invasive vertebrates: Insights from pine marten recovery in Europe. Global Change Biology (2022).
3. The enemy of my enemy is my friend: native pine marten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations. Proceedings of the Royal Society B (2018).
4. Declining invasive grey squirrel populations may persist in refugia as native predator recovery reverses squirrel species replacement. Journal of Applied Ecology (2020).