‘Island syndrome’ in a population of Arctic foxes (Alopex lagopus) from Mednyi Island

Abstract

Comparative analysis of the biology of insular and mainland populations has demonstrated a number of differences in characteristics of insular populations, termed the 'island syndrome'. A subspecies of Arctic fox on the Commander Islands (Alopex lagopus semenovi on Mednyi Island) has been isolated for an evolutionarily significant time in small territories at the periphery of the species' range. The number of foxes on Mednyi had been observed to be very high since the islands were discovered in 1741, but a drastic decline in population density in the late 1970s, owing to mange, has left the population low. The aim of the study was to determine whether the Mednyi Arctic fox population exhibited the features expected in an isolated insular population, such as difference in body size, increased population density, larger social groups, lower tendency to disperse and lower fertility, and whether any behavioural changes were evolutionarily reinforced or were a temporal response to current ecological factors on the island. Eight predictions were identified based on the island syndrome, of which the Mednyi Arctic foxes conformed to seven. We suggest a new prediction, namely that the tendency for increased sex dimorphism in dispersal may also be a distinguishing feature of insular populations. All the features displayed by the insular population on Mednyiconservative use of space, increased tendency to form complex groups, decreased fertility and dispersal -seemed to be preserved regardless of the currently comparatively low populations. Thus, although foxes have been below carrying capacity for at least 10 generations, island syndrome characteristics have persisted.

Life on the edge: carnivore body size variation is all over the place

“…Allen 1876). In fact, individuals inhabiting range edges are often larger than core-area conspecifics ( Thurber & Peterson 1991;Law et al 2002;Goltsman et al 2005; this study), but again this pattern is not general. Neither does there seem to be a general tendency for similar patterns to be obtained in relation to range size or absolute body size.…”

Morphological variation and integration of dentition in the Arctic fox (Vulpes lagopus): effects of island isolation

“…In particular, they feed primarily on seabirds and marine mammals. Further, both Mednyi and Bering Island Arctic foxes are significantly heavier and have larger craniums than their mainland conspecifics, with average winter body masses of 5.0-7.0 kg for males and 4.5-6.0 kg for females, whereas these values on the mainland are 3.2-4.5 kg for males and 3.0-3.5 kg for females (Goltsman et al, 2005). Average condylobasal length of skull for males and females on Mednyi Island Arctic foxes is 130.0 mm and 123.3 mm, respectively.…”

“…This result is surprising, because Mednyi and Bering Island foxes are genetically similar (Geffen et al, 2007). Moreover, both Commander Islands populations have been isolated in similar environments (Zagrebelnyi, 2000b;Goltsman et al, 2005). In particular, they feed primarily on seabirds and marine mammals.…”

“…(V. lagopus semenovi Ognev, 1931), have been isolated for approximately 10,000 years from mainland Arctic foxes (Goltsman et al, 1996;Goltsman et al, 2005;Geffen et al, 2007;Dzhykiya, 2008) by the icefree waters of the Bering Sea. The island environment is not typical Arctic fox habitat, exhibiting a mild climate and an absence of rodents (Goltsman et al, 2005). The two Commander Islands populations are genetically similar but show a genetically distant relationship with other Arctic fox populations (Geffen et al, 2007).…”

“…Island subspecies have larger body and cranial sizes than those on the mainland (Tsalkin, 1944;Goltsman et al, 2005;Zagrebelnyi & Puzachenko, 2006;Nanova, 2009Nanova, , 2010. The cranium differs among the subspecies not only in size but also in form, as it is wider at the carnassial teeth and zygomatic arches, with relatively stronger developed cranial sagittal crests, in both island subspecies (Nanova, 2009).…”