Data from: The enemy of my enemy is my friend: native pine marten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations

  • Emma Sheehy (Creator)
  • Chris Sutherland (Creator)
  • Catherine O’Reilly (Creator)
  • Xavier Lambin (Creator)



Shared enemies may instigate or modify competitive interactions between species. The dis-equilibrium caused by non-native species introductions has revealed that the outcome of such indirect interactions can often be dramatic. However, studies of enemy mediated competition mostly consider the impact of a single enemy, despite species being embedded in complex networks of interactions. Here we demonstrate that native red and invasive grey squirrels in Britain, two terrestrial species linked by resource and disease-mediated apparent competition, are also now linked by a second enemy-mediated relationship involving a shared native predator recovering from historical persecution, the European pine marten. Through combining spatial capture recapture techniques to estimate pine marten density, and squirrel site occupancy data, we find that the impact of exposure to predation is highly asymmetrical, with non-native grey squirrel occupancy strongly negatively affected by exposure to pine martens. In contrast, exposure to pine marten predation has an indirect positive effect on red squirrel populations. Pine marten predation thus reverses the well-documented outcome of resource and apparent competition between red and grey squirrels.

Data type

Pine marten encounter histories for use in SCR analysis using oSCR package in R: Data collected in the field and processed in lab to obtain genotypes. id= pine marten id/genotype, occasion = visit (1-5), trapid = detector name, sex = f/m, session = region name, site = name of cluster in which detector was located

Pine marten trap locations and operational data for use with oSCR package: Pine marten detector data relating to location of detectors and whether they were operational. X = British National Grid easting, Y = British National Grid northing, o1-o5 = whether detector was operational for each session, site = name of cluster which detector belongs to, region = LL (Central Scotland), BO (Borders) or HI (Highlands)

Red squirrel detection histories and covariates for occupancy analysis in UNMARKED R package: Detection/non-detection data site and survey specific covariates for red squirrels. 0=name of cluster which detector belongs to, region = CS (Central Scotland), BO (Borders) and HI (Highlands), X = BNG easting, Y= BNG northing, species = red squirrel, visit1-5 = detection (1) /non detection (0), cover = % of 100m buffer which is forested, bl = % of cover which is broadleaved, gs = portion of feeders within 500m used by grey squirrels, tCov1-tCov5 = hair (feeder only used) or both (feeder and camera used)

Grey squirrel detection histories and covariates for use in occupancy analysis using UNMARKED R package: Same as red squirrel detection history file except species = grey squirrel

Copyright and Open Data Licencing

This work is licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication license.
Date made available16 Feb 2018
PublisherDryad Digital Repository
Geographical coverageScotland


  • apparent competition
  • Martes martes
  • Occupancy Modelling
  • pest-regulating ecosystem service
  • predator mediated competition
  • Sciurus carolinensis
  • Sciurus vulgaris
  • spatial capture recapture
  • Species Interactions

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