Competition for Conifer Cones as a Potential Mechanism of Endangerment for the Mount Graham Red Squirrel

Abstract

Non-native species are a major cause of endangerment for native species, but the mechanisms are often unclear. As species invasions continue to rise, it is important to understand how to mitigate this threat. Our field experiment quantified the impact of introduced Abert's squirrels (Sciurus aberti) on rates of food removal within the range of the critically endangered Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis). In the presence of Abert's squirrels, the time until 50% of cones were removed was 5.55 days faster than when Abert's squirrels were excluded (95% confidence interval 2.25 to 11.63 days). The impact on food availability as a result of cone removal by Abert's squirrels suggests the potential of food competition as a mechanism of endangerment for the Mount Graham red squirrel. Eradication of established non-native populations is rare. Management targeted at specific mechanisms by which non-natives cause endangerment is an essential tool for conservation.