2014 | VOLUME 30 | ISSUES 1-4
(Almost) no trend in brown frog (Rana arvalis and Rana temporaria) breeding phenology in southern Sweden 1990-2010
Breeding phenology of Rana temporaria and R. arvalis was studied during 1990-2010 and analyzed for trends. Two approaches were used. One, that put equal weight on data from all years, found no trend for either species. The other approach gave more weight to those years when more ponds were studied. This found no trend for R. temporaria but a trend towards earlier breeding for R. arvalis. Both species tended to breed earlier in years with high February and March temperatures. These temperatures were both correlated to the NAO (North Atlantic Oscillation) index which thus in turn was negatively correlated to date of frog breeding. A lack of a long term trend could indicate no change in climate or that frogs are more governed by date than by spring temperature. The present study supports only the first hypothesis as there was no temperature trend during the study years.
Published: 31 January 2014