The apparent population crash in heath-hares Lepus timidus sylvaticus of southern Sweden : do complex ecological processes leave detectable fingerprints in long-term hunting bag records?

Sammanfattning: Scientific and circumstantial evidence of recent decades indicate decreasing population trends in the native mountain hares Lepus timidus of Fennoscandia (Finland, Sweden, Norway). It has been suggested that climate warming, habitat degradation, pathogens, predation and interspecific competition are potential candidates to drive this supposed decline. How these ecological mechanisms could function in detail, however, has not been clarified. In this study I use uncorrected hunting bag data (HBD) densities at the county level to test the relative importance of two hypotheses. First, predation by red foxes Vulpes vulpes on mountain hares and congeneric brown hares Lepus europaeus will be scrutinized in a historical perspective by means of correlation analysis on the long-term data set for Sweden. Secondly, the potentially competitive influence of brown hares will be studied by conducting a population trend analysis for the whole of Fennoscandia during 1996-2010. Furthermore, the reliability of parts of the HBD used will be evaluated and discussed. During 1996-2010 mountain hares were declining (OLS linear regression; b<0; pb<.1) in all but one county in Fennoscandia, for which significant population trends could be detected (96% of the sample units). Interregionally, the most negative population trend among mountain hares occurred in region A of southern Sweden (Kruskal-Wallis H test; p<.000), de-culminating within a distinct zone around the 58° N latitude. Brown hares were also diminishing in Sweden (region A), but at similar rates as mountain hares did in arctic and boreal Fennoscandia (region B and C). Historically (1960-2010), the majority of the correlated time series sequences of red foxes and either hare species before and after the sarcoptic mange epizootic was not significant. During 1984-1992 negative correlation coefficients between red foxes and mountain hares occur in 59% of all sample units in southern Sweden, whereas only 17% had significant correlation coefficients with brown hares (Spearman rank rs; p<.05). The complete absence of associations with mountain hares for this region during 2003-2010 is contrasted by 24% positive correlation coefficients with brown hares, which also show to be stronger than before the sarcoptic mange outbreak. The results support the importance of red foxes and brown hares for mountain hare population dynamics. The current, in some areas alarming, situation for mountain hares in southern Sweden appears to be initiated in most areas by ecological processes during the period 1984-1992. Apparent competition assemblages with red foxes, other predators or the viral disease European Brown Hare Syndrome (EBHS) as deterministic mortality factors might have been influential. During 1996-2010 though the recovery of mountain hares in southern Sweden may rather be prevented by habitat degradation, the Allee effect and possibly hybridization with brown hares. Mountain hare habitat quality in form of winter food and shelter plants as well as landscape stability is expected to be invaluable in coping with diverse threat factors. Based on the population trends detected for mountain hares, Sweden should be partitioned into northern, central and southernmost (below the 59° N latitude) management regions.