Relating Red Squirrel Body Size to Different Conifer Cone Morphologies within the Same Geographic Location

Abstract

Red squirrels (Tamiasciurus) are hypothesized to be coevolving with pinecones (Pinus), whereby squirrel seed predation selects upon cone serotiny and seed number, which in turn select upon squirrel size and strength. I tested the hypothesis that cone morphology produces phenotypic size differentiation in red squirrels (T. hudsonicus). I measured body mass, hind-foot length, and jaw width of squirrels among spruce (smaller soft cones), lodgepole pine (larger serotinous cones), and mixed conifer (both cone types) habitats while controlling for variability in geographic isolation and latitude. I found identical average values among habitats for all body measurements: larger squirrels were not associated with larger tougher cones. Geographic isolation or a latitudinal gradient appear necessary to promote size differentiation in red squirrels, but how these factors interact with habitat (cone morphology) remains to be documented. As such, whether squirrels and pinecones actually are coevolving largely remains speculation.