Harsh climate selects for small body size among Iceland's Arctic foxes

Abstract

We studied the eff ect of the two environmental indices, the sub-polar gyre (SPG), and winter and summer North Atlantic Oscillation (NAO), together with mean annual winter and summer temperatures and geographic location on mandible size and body mass of Arctic foxes in Iceland (6345 and 2732 specimens, respectively) during the year of their death. We predicted that when favorable conditions prevailed, large specimens would be selected for, and vice versa. Body size and body mass were signifi cantly aff ected by the environmental parameters (i.e. SPG, NAO, ambient temperature and cloud cover) prevailing during the year of death. Th e eff ect of environmental conditions on body size was much stronger in the less productive region of eastern Iceland, apparently because in areas where food availability is meager, even a small diff erence in climate may tilt the balance from food suffi ciency to food shortage. Western Iceland comprises only a quarter of the total surface area of the country, but its productive seashores are twice as long as those of all the rest of the country combined. It is interesting to note that the eff ect of the SPG, a marine phenomenon in the oceans surrounding Iceland, is refl ected in the condition of the foxes more than the other climatic variables we used in this study, which are largely land-related. Because Arctic foxes in Iceland feed largely on marine birds and invertebrates, the SPG seems to encompass more accurate information regarding the direct ocean forces that aff ect food availability to the foxes.