Habitat mediates coevolved but not novel species interactions

Abstract

Ongoing recovery of native predators has the potential to alter species interactions, with community and ecosystem wide implications. We estimated the co-occurrence of three species of conservation and management interest from a multi-species citizen science camera trap survey. We demonstrate fundamental differences in novel and coevolved predator–prey interactions that are mediated by habitat. Specifically, we demonstrate that anthropogenic habitat modification had no influence on the expansion of the recovering native pine marten in Ireland, nor does it affect the predator's suppressive influence on an invasive prey species, the grey squirrel. By contrast, the direction of the interaction between the pine marten and a native prey species, the red squirrel, is dependent on habitat. Pine martens had a positive influence on red squirrel occurrence at a landscape scale, especially in native broadleaf woodlands. However, in areas dominated by non-native conifer plantations, the pine marten reduced red squirrel occurrence. These findings suggest that following the recovery of a native predator, the benefits of competitive release are spatially structured and habitat-specific. The potential for past and future landscape modification to alter established interactions between predators and prey has global implications in the context of the ongoing recovery of predator populations in human-modified landscapes.

A temporal refuge from predation can change the outcome of prey species competition

“…Despite our strong caveats on the interpretation of modelled pine marten densities, our study reflects the results from field observations (Sheehy et al 2018, Twining et al 2020a that suggest that, at the level of pine marten density observed in the UK and Republic of Ireland, the impact of pine marten predation on red squirrel density is low. Note however, that recent evidence suggests that the impact of pine marten on red squirrel density in low resource conifer dominated habitats in Northern Ireland (where field voles are absent) may be high (Twining et al 2022).…”

“…Those species exhibit irregular outbreaks in density linked to tree seed masting events (Pucek et al 1993), however they do not reach the densities exhibited by field voles in mainland UK (Smal and Fairley 1980). Thus, the impact of a temporal refuge may be more pronounced in Scotland and northern England than in Ireland, which may explain why the grey squirrel decline that has coincided with the recovery of pine marten in Ireland has been rapid (Sheehy and Lawton 2014, Twining et al 2020a, 2022). Note also that, while we considered the known influence of the proportion of coniferous and deciduous tree cover on squirrel species carrying capacity, we implicitly held the amount of field vole habitat constant.…”

“…Pine martens predate on both red and grey squirrels, but grey squirrels typically compose a greater proportion of pine marten diet than reds squirrels, as measured by frequency of occurrence (Sheehy and Lawton 2014, Twining et al 2020b), with naivety of the invasive species regarding the predator being cited as a cause (Wanger et al 2011). Thus, a resurgence in pine marten density, and an expansion of their distribution in Scotland, Northern Ireland and the Republic of Ireland, has seen a concurrent reduction, and in some instances the local extirpation, of invasive grey squirrels that has allowed the re‐establishment of the native red squirrel (Sheehy and Lawton 2014, Sheehy et al 2018, Twining et al 2020b, 2022).…”

Indirect effects of pine marten recovery result in benefits to native prey through suppression of an invasive species and a shared pathogen

“…Recent research has indicated that the recovery of native predators can benefit native prey species that compete with invasive prey in circumstances where predation is more pronounced on the naïve invasive species (Sheehy and Lawton, 2014;Twining et al, 2022b). Pine martens (Martes martes) are generalist semi-arboreal predators, native to Great Britain and Ireland, that have been reported to prey upon grey squirrels at a greater frequency compared to red squirrels (Twining et al, 2020c), which is believed to occur due to evolutionary naïvety and a lack of anti-predator behaviours in grey squirrels (Twining et al, 2020a).…”

“…Recent legal protection has led to the on-going recovery of pine marten that has led to the recolonisation of much of their historical range in Scotland and Ireland. This recovery has resulted in landscape scale declines of established grey squirrel populations that has allowed the re-establishment of red squirrels in regions where they have previously been excluded (Sheehy and Lawton, 2014;Twining et al, 2022bTwining et al, , 2020cSheehy et al, 2018;Bamber et al, 2020). There remains a paucity of information on the impact of pine marten recovery on the prevalence of SQPV in squirrel populations (but see Roberts and Heesterbeek, 2021).…”