Population crash in an invasive species following the recovery of a native predator: the case of the American grey squirrel and the European pine marten in Ireland

  title={Population crash in an invasive species following the recovery of a native predator: the case of the American grey squirrel and the European pine marten in Ireland},
  author={Emma Sheehy and Colin Lawton},
  journal={Biodiversity and Conservation},
In Ireland, the UK and Italy, the invasive North American grey squirrel, Sciurus carolinensis, threatens the survival of the Eurasian red squirrel, Sciurus vulgaris, as the effects of competition and disease almost inevitably lead to total replacement of red squirrel populations. However the results of a recent national squirrel survey suggested that the normally invasive grey squirrel had gone into decline in the Irish midlands, which was anecdotally attributed to an increase in European pine… 

The dynamics of pine marten predation on red and grey squirrels

Evidence is provided for the mechanism driving the current decline in grey squirrels in Ireland and Scotland and supports the hypothesis that in the presence of a shared predator, direct predation influences the outcome of species interactions between native red and non-nativegrey squirrels.

The regional demise of a non-native invasive species: the decline of grey squirrels in Ireland

The aim of this study was to assess the current squirrel distribution in the area directly bordering the River Shannon, and to identify habitat types and landscape characteristics that could be facilitating or impeding the spread of grey squirrels in Ireland.

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

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, and the introduction of the pine marten destabilizes previous equilibria, favouring the native squirrel and facilitating wildlife managers in their efforts to protect it.

Declining invasive grey squirrel populations may persist in refugia as native predator recovery reverses squirrel species replacement

1. Invasive species pose one of the most serious global threats to biodiversity. Investigations into the interactions of native and non-native species focus on the impacts of single species, despite

Invasive genetic rescue: Dispersal following repeated culling reinforces the genetic diversity of an invasive mammal

High genetic diversity is found in both marker types, with six diverse mtDNA haplotypes found and relatively high levels of nuclear genetic diversity, even after repeated culling efforts, according to the results of this study.

Frontier population dynamics of an invasive squirrel species: Do introduced populations function differently than those in the native range?

Careful comparative demographic study of invading populations could improve management outcomes, indicate differential invasibility of invaded communities, and offer clues to enhance the design of conservation reintroduction projects.

Translocated native pine martens Martes martes alter short‐term space use by invasive non‐native grey squirrels Sciurus carolinensis

Investigation of the short-term effects of exposure to translocated martens on the space use and survival of resident grey squirrels presents direct evidence that pine marten translocations could play an influential role in the behaviour and dynamics of invasive non-native grey squirrel populations.

A genetic analysis of grey squirrel (Sciurus carolinensis) populations in Ireland

Low to moderate genetic diversity overall across Irish populations as well as the presence of inbreeding is found, which could indicate genetic isolation between Irish populations or a secondary introduction of S. carolinensis to Ireland.

Native and invasive squirrels show different behavioural responses to scent of a shared native predator

Differences in behavioural responses to a shared native predator may assist in explaining differing outcomes of species interactions between native and invasive prey species depending on the presence, abundance and exposure to native predators.



Disease threats posed by alien species: the role of a poxvirus in the decline of the native red squirrel in Britain

Analysis of the incidence of disease and changes in distribution of the two species in Cumbria, from 1993 to 2003 and the predictions of an individual-based (IB) spatially explicit disease model simulating the dynamics of both squirrel species and SQPV in the landscape show grey squirrels increased whilst red squirrels declined.

Alien species and interspecific competition: effects of introduced eastern grey squirrels on red squirrel population dynamics

The presence of grey squirrels resulted in a reduction in red squirrel fitness which was evident by lower population summer breeding and a lower recruitment, which will result in a decline in population size and eventually population extinction.

The emergence of squirrelpox in Ireland.

Serological evidence of the extent of poxvirus infection in the grey squirrels from both the Republic of Ireland and Northern Ireland, including an apparent increase in the seroprevalence of antibodies against the virus ingrey squirrels over the period of the study is presented.

Predicting grey squirrel expansion in North Italy: a spatially explicit modelling approach

There is growing concern about the spread of the North American grey squirrel (Sciurus carolinensis) in northern Italy which were introduced into Piedmont in 1948. They have since spread across the

Interspecific effects of grey squirrels (Sciurus carolinensis) on the space use and population demography of red squirrels (Sciurus vulgaris) in conifer plantations

The data suggest that adult red squirrels suffered little from interspecific competition with grey squirrels and that the key factor is decreased juvenile recruitment in red Squirrels.

Comparative demography of red squirrels ( Sciurus vulgaris ) and grey squirrels ( Sciurus carolinensis ) in deciduous and conifer woodland

Red squirrels had higher survival than grey squirrels in conifers, which may give them an advantage in that habitat, but could also have been explained by a lack of predators on their island study site.


  • C. LawtonJ. Rochford
  • Environmental Science
    Biology and Environment: Proceedings of the Royal Irish Academy
  • 2007
Grey squirrel, Sciurus carolinensis, populations have been subjected to various degrees of control in the woodlands of Ireland and Britain since their introduction, but the recolonisation rates and other ecological effects of the culls have not been fully examined.

Interspecific competition between native Eurasian red squirrels and alien grey squirrels: does resource partitioning occur?

It is suggested that, at moderate grey-squirrel densities, red squirrels are unable to avoid competition with grey squirrels, and that competition for food and/or space will occur when these resources become limiting.