The anatomy of a range expansion: changes in cranial morphology and rates of energy extraction for North American red squirrels from different latitudes

摘要: Species with expanding ranges provide unique opportunities to examine environmentally induced adaptations in ecological traits and anatomical characteristics. Since the late 1800s, North American red squirrel (Tamiasciurus hudsonicus) has expanded its range into central hardwoods of United States conjunction increasing agricultural fragmentation. We examined whether squirrels from (west-central Indiana, USA) displayed differences foraging behaviors morphology relative conifer-dominated environments (upper peninsula Michigan, USA), a biome which evolved. Specifically, we measured rates energy extraction, variation cranial morphology, diet preference between both regions. In addition, compared those competitor that coevolved nut-producing trees, gray (Sciurus carolinensis). Red Indiana Michigan differed significantly efficiency they used food items, individuals each region extracting calories at more rapid rate for items were common their region. The enhanced southern feeding on black walnuts (Juglans nigra) was correlated geographic morphology; skulls larger, longer jaws higher metrics associated greater mandibular force than northern squirrels. Contrary our expectations, did not differ qualitatively preferences suggesting choice may be governed by perishability rather extraction. Gray efficient using all only slightly regard items. Measures resource use, after accounting species-specific metabolic requirements, suggest are unlikely compensate ecologically declining populations fragmented portions hardwoods, potentially adverse effects forest regeneration succession. Our results demonstrate invading species can display significant flexibility adapting new environments, but flexible enough exploit resources manner comparable native species.