Poxvirus, red and grey squirrel dynamics: Is the recovery of a common predator affecting system equilibria? Insights from a predator-prey ecoepidemic model

Abstract

In Europe, the Eastern grey squirrel is an allochthonous species causing severe impacts on the native red squirrel. The invasive species establishes complex relationships with the native one, out-competing it through resource and disease-mediated competition. However, recent research shed light on the potential role of a predator, the pine marten, in reversing the outcome of the competition between squirrels. Here, we investigate this hypothesis developing a one predator-two prey ecoepidemic model, including disease (squirrel poxvirus) transmission. We assess the equilibria of the dynamical system and investigate their sensitivity to ecosystem parameters changes through numerical simulations.Our analysis reveals that the system is more likely to evolve toward points where the red squirrels thrive than toward a disease-and-red-squirrels-free point. Although the disease is likely to remain endemic in the system, the introduction of the pine marten destabilizes previous equilibria, favouring the native squirrel and facilitating wildlife managers in their efforts to protect it. Nevertheless, the complete eradication of grey squirrels could be achieved only for specified values of the predation rates and pine marten carrying capacity. The active management of grey squirrel populations remains therefore necessary to try to eradicate the invader from the system.

Infection dynamics in ecosystems: on the interaction between red and grey squirrels, pox virus, pine martens and trees

“…That model had no density-dependent regulation of the infected populations, and the thresholds for transition between infected steady states were presented in terms of the host population densities rather than the reproduction numbers that we employ. The study presented in [17] addressed two squirrel species, SQPV and the pine marten as predator, but did not explicitly model infection dynamics in the grey squirrel. One feature of our model that differs from most previous models is the inclusion of the infected but not infectious state A g .…”

“…It is possible that the predator has effects on grey and red squirrels that add to the direct effect of increased mortality. In the presence of an active predator, the squirrel species may experience stress in a landscape of fear to different degrees that may influence their competitive ability [17,[43][44][45][46]. The figure shows the regions in the (K r , K g ) plane where each steady state is stable.…”

“…We explore the dynamics and interaction of red squirrels (Sciurus vulgaris) and grey squirrels (S. carolinensis) in different regions of the UK, with and without squirrel pox virus (SQPV). It is decidedly not our aim to present a detailed model or analysis of this system; many excellent studies exist that merge SQPV models with data to yield insight into the prospects for the red squirrel and aid conservation efforts [10][11][12][13][14][15][16][17][18][19]. Our aim is to highlight how ecological processes influence the interaction between a pathogen and its host species.…”

Natural strongholds for red squirrel conservation in Scotland

“…The study also found a negative correlation between grey squirrels and pine marten (Martes martes), a native mustelid whose numbers are increasing, and a positive correlation between pine marten and red squirrels. Theoretical studies using a two prey-one predator ecoepidemic model have also shown that the predator (pine marten) can destabilise the previous grey squirrel dominant equilibria, favouring the native red squirrel (Travaglia et al 2020). Thus, the impact of a native predator could aid red squirrel survival in the United Kingdom and Ireland via a reduction in grey squirrel density and geographic spread (Twining et al 2020).…”

A viral transmission model for foxes-cottontails-hares interaction: Infection through predation

“…The replacement between the two species is mainly due to exploitation competition for food resources, with the American species being more efficient in their use [34]. In Great Britain, however, grey squirrels carry a squirrelpox virus which is lethal for the red squirrel and this diseases-mediated competition increases the speed of the replacement [30,31,25] Models to explore two species interaction have been recently investigated, [31,2,21]. Alien species could also act as amplifiers of local pathogens.…”