Small-scale spatial and temporal variation of life-history traits of common frogs (Rana temporaria) in sub-Arctic Finland

Small-scale spatial and temporal variation in abiotic and biotic environmental conditions can lead to large differences in mean values of important life-history traits in ectothermic vertebrates, such as amphibians. However, relatively little is known about small-scale variation in life-history traits of sub-Arctic amphibians. We studied the spatio-temporal variation of adult life-history traits linked to age and body size in the common frog (Rana temporaria) from low (i.e., valley at 480 m a.s.l.) and high (i.e., hill at 530–650 m a.s.l.) altitude sites in the sub-Arctic Kilpisjärvi area (Finland). Data on life-history traits of frogs from hill sites collected during a 3-year field study were compared with previously published data from the valley sites. The results showed spatio-temporal variation in life-history traits, frogs responding to spatio-temporal variation in the environmental conditions with variation in age, life span, survival rates, body size, and mass. Frogs from hill sites had shorter life span, both in terms of mean age (5.6 versus 10.5 years) and longevity (9–10 versus 18 years), smaller snout-vent length (63 versus 77 mm), and body mass (24 versus 45 g) than frogs from valley sites. The differences were more pronounced in females than in males indicating some sex-specific responses to environmental differences among sites. The results show that small differences in elevation (or elevation-related abiotic and biotic factors) can translate to large differences in mean values of important life-history traits in common frogs living at the edge of their distribution range.