Many trees must shift their ranges to track changing climate conditions, but their movement often depends on animal dispersers, which are overlooked in range shift predictions. We addressed this knowledge gap by assessing the dispersal of novel (i.e., not previously encountered) seeds by gray squirrels (Sciurus carolinensis) and analyzing intraspecific variation in dispersal decisions. We established a field experiment spanning the northern range limits of multiple oak (Quercus) and hickory (Carya) species in Northeastern USA and measured personality of 222 squirrels, further recording seed decisions by 50 individuals. Squirrels dispersed novel seeds, illustrating their critical role in tree range shifts, with sociality and weight mediating decisions. Seed novelty mediated certain decisions such as the consumption of removed seeds, while other decisions were consistent regardless of novelty. Overall, individuals contributed to novel seed dispersal differently based on personality, highlighting the need to preserve behavioral diversity to facilitate tree range shifts.
