Recent Changes in Body Size of the Eurasian Otter Lutra lutra in Sweden
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We studied geographical and temporal body size trends among 169 adult museum specimens of the Eurasian otter (Lutra lutra) collected in Sweden between 1962 and 2008, whose sex, year of collection, and locality were known. Skull size and body mass increased significantly in relation to the year of collection, and skull size (but not body mass) was significantly and negatively related to latitude, contrasting Bergmann’s rule and the trend found for Norwegian otters. Latitudinal differences in body size between the two countries may be due to differences in food availability. The temporal increase in body size among Swedish otters resembled that observed for Norway otters, though Swedish otters are smaller with respect to their Norwegian counterparts. Latitude and year represent a combination of environmental factors, including ambient temperature in the year of collection as well as the number of days of ice coverage. We replaced the above factors with mean annual temperature or the number of days of ice coverage, and found that each of these factors explains a similar proportion of the variation in body size as did latitude and year. We hypothesize that this temporal increase in body size is related to a combination of factors, including reduced energy expenditure resulting from increasing ambient temperature, and increased food availability from longer ice-free periods.
KeywordsEurasian otter Lutra lutra Sweden Body size Ambient temperature Ice coverage Food availability Global warming
Thanks are due to Olavi Grönwall for his warm hospitality to YYT and SYT during their visit to the NRM and to Per Ericson for his valuable support. We are grateful to Eli Geffen for advice and comments, to Naomi Paz for editing this article, and to two anonymous reviewers for their helpful suggestions. YYT and SYT would like to thank Nick Davies for his hospitality during their sabbatical in Cambridge, England. We are grateful to Else-Marie Wingqvist of the Swedish Meteorological Service and to Mark Lomas of Sheffield University for their help in obtaining climate data. We acknowledge the financial support of a SYNTHESYS grant to YYT (SE-TAF-1844) made available by the European Community Research Infrastructure Action under the FP6 Structuring the European Research Area Programme, and the Israel Cohen Chair of Environmental Zoology to YYT.
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