Cycles in voles and small game in relation to variations in plant production indices in Northern Sweden

Abstract

Population dynamics for voles (Cricetidae), Tengmalm's owl (Aegolius funereus (L.)), red fox (Vulpes vulpes (L.)) willow grouse (Lagopus lagopus (L.)), black grouse (Lyrurus tetrix (L.)), capercaillie (Tetrao urogallus L.), hazel hen (Tetrastes bonasia (L.)), mountain hare (Lepus timidus L.) and tularemia (Francisella tularensis (McCoy & Chapin)) and game bird recruitment were studied by index methods in northern Sweden. In addition contemporary temperature records and spruce (Picea abies (L.) Karst.) and pine (Pinus silvestris L.) cone crops (as indices for plant production) and the occurrence of forest damage, caused by voles eating bark, were studied.During 1970-80 two synchronous 4-year cycles were observed for voles, predators (Tengmalm's owl and red fox) and their alternative prey species (grouse and mountain hare). In grouse the change of numbers was correlated with that of recruitment. Autumn vole numbers peaked about a year before the other species and extensive forest damage occurred at winter peak densities of voles. These population fluctuations are consistent with a predator-prey model for their regulation. In short the model suggests that vole-food plant interactions trigger the cycle of voles, that voles generate the cycle of predators and that these in turn synchronize alternative prey populations to the others at vole declines.For voles, grouse and red fox the amplitude was higher in the first cycle compared to the second one whilst the opposite was true for the mountain hare. Although temperature and cone crops showed large interannual variations they still implied that herbivore food conditions were 'better' during the former cycle. Hence, the reduction of the amplitude of the vole cycle may be explained by inter-cyclic differences in plant food conditions, implying food shortage (as indicated by bark-eating) at different population levels. The similar decrease of grouse and red fox populations may also be explained by deteriorated food conditions and/or for the fox by an outbreak of sarcoptic mange (Sarcoptes scabiae var. vulpes). The increased amplitude of the mountain hare cycle was part of a long-term rise in numbers after a tularemia epidemic in 1967. This is interpreted as a recovery, probably towards the generally higher pre-epidemic population level.

The role of vole populations in prevalence of the parasite (Echinococcus multilocularis) in foxes

“…In Fennoscandia, however, several fluctuation patterns in red fox populations have been observed in connection with vole densities. Populations of foxes track vole populations (Hornfeldt et al 1986;Linden 1988;Lindstrom 1989;Small et al 1993); fox populations exhibit cyclic fluctuations in the north where fewer alternative prey are present, whereas it is more stable in the south where the diet is more diverse (Englund 1970;Angelstam et al 1984Angelstam et al , 1985. Hokkaido has a rich alternative prey community (hares, grouse, and frogs) like southern Fennoscandia (Henttonen et al 1992), though some vole populations in Hokkaido are cyclic as well as those in the north of Fennoscandia (Bj0rnstad et al 1996Stenseth et al 1996;Saitoh et al 1998b).…”

“…For instance, even the red fox (Vulpes vulpes (L.», which is a typical generalist predator (Lloyd 1980), selectively takes this vole like a specialist predator in Hokkaido (Yoneda 1979). In Fennoscandia, populations of foxes track vole populations (Hornfeldt et al 1986; Linden 1) E-mail: bedjord@jfpri-hkd.ajfrc.go.jp 2) E-mail: takaken@iph.prej.hokkaido.jp 1988;Lindstrom 1989;Small et al 1993) and reproduction and feeding pattern of predatory species are also greatly influenced by the population fluctuation of voles Korpimaki 1994;Lindstrom 1992Lindstrom , 1994. Thus the most common voles could be the keystone species that essentially influences the predator-prey system, and also could be essential for the host-parasite system with parasites that alternate hosts to complete their life cycle in wildlife.…”

Investigations and actions taken during 2011 due to the first finding of Echinococcus multilocularis in Sweden

“…However, the population recovered to the levels of the 1970s in the early 1990s, and monitoring has not revealed any dramatic change after this recovery [29,30]. The fox population density varies, from relatively high and stable in the nemoral and boreonemoral zones (south) to a lower density with a much higher degree of fluctuation in the boreal zone (north) [26,27,31,32] and the fluctuations in the north follow those of vole populations [33]. The three areas where EM has been found have suitable fox habitat characterised by a mixture of forest and agricultural land.…”

Predicting High Risk for Human Hantavirus Infections, Sweden

“…Collection of these data is part of the National Environmental Monitoring Programme under the administration of the Swedish Environmental Protection Agency (11)(12)(13).…”

“…During the 10 previous bank vole cycles studied in the same phase during fall of 2007, i.e., year 2 in the cycle, the population increased by a factor ranging from 3.4 to 13.1; median was >5 (11)(12)(13). Trapping indices of fall 2006 and spring 2007 show a striking resemblance to those in 1972-73, when the bank vole population subsequently increased 4-fold during the summer of 1973 (11)(12)(13). A 4-fold increase was thus conceived as a reasonable assumption of the growth rate during the summer of 2007, giving an estimated fall trapping index of 12.64 in 2007.…”