Monitoring brown frogs Rana arvalis and Rana temporaria in 120 south Swedish ponds 1989-2005. Mixed trends in different habitats

The two brown frogs Rana arvalis and Rana temporaria were monitored at 57 localities (that contained a total of 120 ponds) for up to 17 years each during the years 1989-2005. The analysis summarized below only accounts for trends within sites actually usable for frogs during the analysis period, large scale habitat losses are thus not accounted for. R. arvalis populations tended to increase over the study period. R. temporaria populations displayed no significant change. However, both species displayed significant fluctuations from year to year. These were not correlated between the two species. Localities with permanent ponds tended to display more positive population trends than localities with temporary ponds and ponds in pastures tended to display more positive trends than those in forests. For ponds in cropped fields, where only R. temporaria were found, the trend were also generally negative. Thus, long-term trends suggest that neither species is in decline. Nevertheless, the population trends observed in more exploited habitats are less positive than those in relatively unexploited habitats. We conclude frog populations in agricultural habitats should be more carefully studied to identify the factors behind the decline. The negative trend in temporary ponds are cause for a closer analysis of the effects of weather factors on frog population dynamics.