... (Lillj.)... red. Peatlands also support field vole populations, al-Water vole though densitie... more ... (Lillj.)... red. Peatlands also support field vole populations, al-Water vole though densities seem to remain at lower levels than in Arvicola ... 586 I I j 4 4 1 OIKOS 29:3 (1977) Page 7. water voles or their signs have been seen when other vole species have had low densities. ...
... The overwintering strategy of C. gapperi is unclear, but territoriality is reported by Merrit... more ... The overwintering strategy of C. gapperi is unclear, but territoriality is reported by Merritt & Merritt (1978). Communal nesting in winter is finally considered the common pattern in C. glareolus (eg, Gebcszynski 1969, Christiansen et al. ...
Demography of field vole (Microtus agrestis) was studied by live-trapping wild populations in an ... more Demography of field vole (Microtus agrestis) was studied by live-trapping wild populations in an abandoned field and a grassy spruce forest in Konnevesi, Central Finland. Population density had two peaks in the field during the summer. The intervening low coincided with colonization of the suboptimal forest. Reproductive success of females in the field correlated negatively with population density. Repro ductive females were distributed among the habitats according to ideal free distribution as the forest was inhabited when reproductive success in the field lowered to the same level as in the forest. 28% of females and 3% of males matured during the year of their birth. Maturation rate of females correlated negatively with density of reproductive females. Most males born in late spring disappeared from the field resulting in an excess of spring born males in the forest. The different life histories of the sexes are due to their different social organizational modes.
Cyclic population fluctuations of small rodents are characteristic in northern and central Fennos... more Cyclic population fluctuations of small rodents are characteristic in northern and central Fennoscandia. In Finland research addressing this problem was initiated in 1940s by professor Olavi Kalela, and the work is carried on by his co-workers and their students. One of the paramount questions is to what extent and by which ways social interactions among individuals contribute to the observed population dynamics. The focus at Konnevesi Research Station has — during its whole ten years of existence — been on social mechanisms of small rodents. This article is a review of our pending studies. It rather soon turned out that population cycles take place in spite of stabilising social mechanisms, not because of them. Our studies uncovered correlation between social organisation and quality of food and habitat. This led to comparisons between species and among populations, calling for experimental research both in large outdoor enclosures and in detailed laboratory tests. The questions st...
A method is given to calculate the Standardized Root Length (SRL) of molars. It can be used to ex... more A method is given to calculate the Standardized Root Length (SRL) of molars. It can be used to examine the changes in age structure of overwintered Clethrionomys without grouping the animals in separate cohorts. The age structure of overwintered animals indicated by mean SRL reacted on many different environmental factors. The oldest animals survived best in conditions with increasing mortality and in interspecific competitive situations. Thus the mean SRL seems to be a sensitive indicator of increased mortality. The examination revealed one decline starting earlier in oligotrophic and ohgo-mesotrophic heath woods, when the populations in eutrophic meadow woods were still unaffected, thus indicating possible causes of the decline. Resource competition between sexes during decline was indicated.
Social Systems and Population Cycles in Voles, 1990
Monogamy, polygyny, and promiscuity have been found in populations of M. oeconomus and M. agresti... more Monogamy, polygyny, and promiscuity have been found in populations of M. oeconomus and M. agrestis in different environmental situations in northern Finland. Thus the mating systems seem to be more variable both between and within species in Microtus than in Clethrionomys. Spacing behavior in Microtus caused a temporary decline in population density in mid-summer, but in Clethrionomys a decline occurred only in the beginning of the breeding season. Habitat quality affected spacing behavior in similar ways in Microtus and Clethrionomys but did not affect differences in breeding limitation. Despite the differences in population regulation, both Clethrionomys and Microtus populations cycle synchronously in northern Fennoscandia.
We studied overwintering in the bank vole Clethrionomys glareolus in four 0.5 ha enclosures in an... more We studied overwintering in the bank vole Clethrionomys glareolus in four 0.5 ha enclosures in an abandoned field in central Finland in the winter 1987/88. In two of the enclosures food was offered evenly distributed over the whole enclosed area (Even Enclosures = EE), in the two others food was offered in one feeding patch with four feeding chambers 2 m apart (Patchy Enclosures = PE). Food was provided in about the same amount in both enclosures. The experiment commenced in early October, with 13 females and 11 males in EEs and 12 + 13 voles in PEs. After two months the voles in the PEs were concentrated around the feeding patches. Territoriality was not observed in EEs, instead the voles formed small exclusive overwintering groups consisting of 2-3 females and at least one male. The size of the home range of the females and males was identical during mid-winter as the voles were non-breeding. By the onset of breeding, range size increased in both sexes, but significantly more in males, however. The survival was about the same in all populations. Every population showed a mid-winter decline suggesting the effect of the mustelid predators observed in and around the enclosures. In the PEs the overwintering aggregations lasted until the maturation of the first litters. Food distribution affected the spatial distribution of the populations. We conclude that the patchiness of the habitat and especially the availability of food are the most important factors determining the social structure of overwintering populations.
Kin clusters of philopatric females are thought to form the basic social organization of breeding... more Kin clusters of philopatric females are thought to form the basic social organization of breeding females in various vole species. The spatial association between young breeding females and their mothers was studied in five 2500-m* enclosures in natural habitats during mid-and late breeding season in summer 1992. The mothers (founder females) were introduced into the enclosures in die beginning of the study in June, whereas the young breeding females were born within the enclosures. Matrilineal kinship was determined by using radionudides. In July-August, 58% of young breeding females were philopatric, but 82% of the mother-daughter associations broke up until August-September. Of the young females that started to breed in August-September, only 12% were philopatric Thus the kin clusters found were short Hved and few in number during the late breeding season. The reduction in the incidence of the kin clusters coincided with an increase of population density. The mean reproductive success of females breeding in kin clusters was better than that of those breeding separately. In addition, among the nonphilopatric females there was a positive, significant correlation between reproductive success and the distance to the nearest unrelated founder female. Such correlation was not found among the philopatric females.
The influence of avian predators on bank vole (Clethrionomys glareolus) populations in four 0.5-h... more The influence of avian predators on bank vole (Clethrionomys glareolus) populations in four 0.5-ha enclosures was studied in central Finland in 1988. Two of the enclosures were covered with nets to keep out birds of prey, and two were left open to avian predation. A fence of metal sheet and continuous trapping kept out small mustelids during the breeding season. The only avian predators observed in the area throughout the year were the Ural owl (Strix uralensis) and the tawny owl (Strix aluco) and during summer the common buzzard (Buteo buteo). During autumn and winter pygmy owls (Glaucidium passerinum) was present in the study area. No Tengmalm's owls (Aegolius funereus) were observed around the area. During late winter and spring, the highest density of voles was observed in one of the open enclosures. No evidence of the influence of avian predators could be observed. During the summer the net covers had no effect on the survival of the voles; the highest density, with 100% survival of the young, was observed in an open enclosure. We suggest that avian predators have only a slight influence on breeding bank vole populations during a peak year in a patchy environment with boreal spruce forest. An explanation could be that bank voles are only an alternative prey for avian predators when field voles (Microtus agrestis) have high densities in more open habitats at the same time. The heterogeneity of the habitat and the dominance of the Ural owl in the owl community could also play a role.peerReviewe
Charnov & Finerty's (1980) hypothesis of the impact of relatedness between individuals on... more Charnov & Finerty's (1980) hypothesis of the impact of relatedness between individuals on the multiannual fluctuations of microtine populations (cyclicity) has initiated a number of field experiments in the Holarctic region (Kawata 1987; Boonstra & Hogg 1988, Ylönen, et al. 1990). During recent years, the Charnov-Finerty hypothesis has been shown to be insufficient in explaining population cycles (e.g. Kawata 1990, Pugh & Tamarin 1990, Stenseth & Lomnicki 1990). Lambin & Krebs (1991) presented a new general model for all microtines of the impact of relatedness on the population fluctuations. In the present paper we go through some of the assumptions of the Lambin-Krebs model about the formation of social spring groups, occurence of spring declines and their possible impact on the following summer's demography. The paper is based on our long-term data on social organization and demography of the bank vole Clethrinonomys glareolus but studies on other Clethrionomus species and the field vole Microtus agrestis are also referred to. We attempt to verify the general validity of the model and present some new data on the impact of kinship and familiarity on the population growth in cyclic bank vole (Clethrionomys glareolus) populations.peerReviewe
The JSTOR Archive is a trusted digital repository providing for long-term preservation and access... more The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact
Frugivores functioning as seed dispersers may have fundamental effects on the reproductive succes... more Frugivores functioning as seed dispersers may have fundamental effects on the reproductive success of fruiting plants. Studies on this interaction have, however, mostly ignored possible within-season and between-year variations in seed germination behaviour. The aim of this study was to assess how berry ingestion by thrushes (Turdus spp.) affects seed germination of bilberry (Vaccinium myrtillus). Specifically, we studied if the timing of dispersal within the fruiting season affects germination success of seeds and whether these effects vary between years. The germination rate of intact seeds declined in the course of the fruiting season both in 1997 and in 1999. Ingestion by thrushes accelerated the germination rate of passed seeds and the final germination percentages of passed seeds were higher than or similar to those of intact seeds. These effects varied within season and between years. Thus, when effects of frugivores on seed germination success are studied, experiments should...
... (Lillj.)... red. Peatlands also support field vole populations, al-Water vole though densitie... more ... (Lillj.)... red. Peatlands also support field vole populations, al-Water vole though densities seem to remain at lower levels than in Arvicola ... 586 I I j 4 4 1 OIKOS 29:3 (1977) Page 7. water voles or their signs have been seen when other vole species have had low densities. ...
... The overwintering strategy of C. gapperi is unclear, but territoriality is reported by Merrit... more ... The overwintering strategy of C. gapperi is unclear, but territoriality is reported by Merritt & Merritt (1978). Communal nesting in winter is finally considered the common pattern in C. glareolus (eg, Gebcszynski 1969, Christiansen et al. ...
Demography of field vole (Microtus agrestis) was studied by live-trapping wild populations in an ... more Demography of field vole (Microtus agrestis) was studied by live-trapping wild populations in an abandoned field and a grassy spruce forest in Konnevesi, Central Finland. Population density had two peaks in the field during the summer. The intervening low coincided with colonization of the suboptimal forest. Reproductive success of females in the field correlated negatively with population density. Repro ductive females were distributed among the habitats according to ideal free distribution as the forest was inhabited when reproductive success in the field lowered to the same level as in the forest. 28% of females and 3% of males matured during the year of their birth. Maturation rate of females correlated negatively with density of reproductive females. Most males born in late spring disappeared from the field resulting in an excess of spring born males in the forest. The different life histories of the sexes are due to their different social organizational modes.
Cyclic population fluctuations of small rodents are characteristic in northern and central Fennos... more Cyclic population fluctuations of small rodents are characteristic in northern and central Fennoscandia. In Finland research addressing this problem was initiated in 1940s by professor Olavi Kalela, and the work is carried on by his co-workers and their students. One of the paramount questions is to what extent and by which ways social interactions among individuals contribute to the observed population dynamics. The focus at Konnevesi Research Station has — during its whole ten years of existence — been on social mechanisms of small rodents. This article is a review of our pending studies. It rather soon turned out that population cycles take place in spite of stabilising social mechanisms, not because of them. Our studies uncovered correlation between social organisation and quality of food and habitat. This led to comparisons between species and among populations, calling for experimental research both in large outdoor enclosures and in detailed laboratory tests. The questions st...
A method is given to calculate the Standardized Root Length (SRL) of molars. It can be used to ex... more A method is given to calculate the Standardized Root Length (SRL) of molars. It can be used to examine the changes in age structure of overwintered Clethrionomys without grouping the animals in separate cohorts. The age structure of overwintered animals indicated by mean SRL reacted on many different environmental factors. The oldest animals survived best in conditions with increasing mortality and in interspecific competitive situations. Thus the mean SRL seems to be a sensitive indicator of increased mortality. The examination revealed one decline starting earlier in oligotrophic and ohgo-mesotrophic heath woods, when the populations in eutrophic meadow woods were still unaffected, thus indicating possible causes of the decline. Resource competition between sexes during decline was indicated.
Social Systems and Population Cycles in Voles, 1990
Monogamy, polygyny, and promiscuity have been found in populations of M. oeconomus and M. agresti... more Monogamy, polygyny, and promiscuity have been found in populations of M. oeconomus and M. agrestis in different environmental situations in northern Finland. Thus the mating systems seem to be more variable both between and within species in Microtus than in Clethrionomys. Spacing behavior in Microtus caused a temporary decline in population density in mid-summer, but in Clethrionomys a decline occurred only in the beginning of the breeding season. Habitat quality affected spacing behavior in similar ways in Microtus and Clethrionomys but did not affect differences in breeding limitation. Despite the differences in population regulation, both Clethrionomys and Microtus populations cycle synchronously in northern Fennoscandia.
We studied overwintering in the bank vole Clethrionomys glareolus in four 0.5 ha enclosures in an... more We studied overwintering in the bank vole Clethrionomys glareolus in four 0.5 ha enclosures in an abandoned field in central Finland in the winter 1987/88. In two of the enclosures food was offered evenly distributed over the whole enclosed area (Even Enclosures = EE), in the two others food was offered in one feeding patch with four feeding chambers 2 m apart (Patchy Enclosures = PE). Food was provided in about the same amount in both enclosures. The experiment commenced in early October, with 13 females and 11 males in EEs and 12 + 13 voles in PEs. After two months the voles in the PEs were concentrated around the feeding patches. Territoriality was not observed in EEs, instead the voles formed small exclusive overwintering groups consisting of 2-3 females and at least one male. The size of the home range of the females and males was identical during mid-winter as the voles were non-breeding. By the onset of breeding, range size increased in both sexes, but significantly more in males, however. The survival was about the same in all populations. Every population showed a mid-winter decline suggesting the effect of the mustelid predators observed in and around the enclosures. In the PEs the overwintering aggregations lasted until the maturation of the first litters. Food distribution affected the spatial distribution of the populations. We conclude that the patchiness of the habitat and especially the availability of food are the most important factors determining the social structure of overwintering populations.
Kin clusters of philopatric females are thought to form the basic social organization of breeding... more Kin clusters of philopatric females are thought to form the basic social organization of breeding females in various vole species. The spatial association between young breeding females and their mothers was studied in five 2500-m* enclosures in natural habitats during mid-and late breeding season in summer 1992. The mothers (founder females) were introduced into the enclosures in die beginning of the study in June, whereas the young breeding females were born within the enclosures. Matrilineal kinship was determined by using radionudides. In July-August, 58% of young breeding females were philopatric, but 82% of the mother-daughter associations broke up until August-September. Of the young females that started to breed in August-September, only 12% were philopatric Thus the kin clusters found were short Hved and few in number during the late breeding season. The reduction in the incidence of the kin clusters coincided with an increase of population density. The mean reproductive success of females breeding in kin clusters was better than that of those breeding separately. In addition, among the nonphilopatric females there was a positive, significant correlation between reproductive success and the distance to the nearest unrelated founder female. Such correlation was not found among the philopatric females.
The influence of avian predators on bank vole (Clethrionomys glareolus) populations in four 0.5-h... more The influence of avian predators on bank vole (Clethrionomys glareolus) populations in four 0.5-ha enclosures was studied in central Finland in 1988. Two of the enclosures were covered with nets to keep out birds of prey, and two were left open to avian predation. A fence of metal sheet and continuous trapping kept out small mustelids during the breeding season. The only avian predators observed in the area throughout the year were the Ural owl (Strix uralensis) and the tawny owl (Strix aluco) and during summer the common buzzard (Buteo buteo). During autumn and winter pygmy owls (Glaucidium passerinum) was present in the study area. No Tengmalm's owls (Aegolius funereus) were observed around the area. During late winter and spring, the highest density of voles was observed in one of the open enclosures. No evidence of the influence of avian predators could be observed. During the summer the net covers had no effect on the survival of the voles; the highest density, with 100% survival of the young, was observed in an open enclosure. We suggest that avian predators have only a slight influence on breeding bank vole populations during a peak year in a patchy environment with boreal spruce forest. An explanation could be that bank voles are only an alternative prey for avian predators when field voles (Microtus agrestis) have high densities in more open habitats at the same time. The heterogeneity of the habitat and the dominance of the Ural owl in the owl community could also play a role.peerReviewe
Charnov & Finerty's (1980) hypothesis of the impact of relatedness between individuals on... more Charnov & Finerty's (1980) hypothesis of the impact of relatedness between individuals on the multiannual fluctuations of microtine populations (cyclicity) has initiated a number of field experiments in the Holarctic region (Kawata 1987; Boonstra & Hogg 1988, Ylönen, et al. 1990). During recent years, the Charnov-Finerty hypothesis has been shown to be insufficient in explaining population cycles (e.g. Kawata 1990, Pugh & Tamarin 1990, Stenseth & Lomnicki 1990). Lambin & Krebs (1991) presented a new general model for all microtines of the impact of relatedness on the population fluctuations. In the present paper we go through some of the assumptions of the Lambin-Krebs model about the formation of social spring groups, occurence of spring declines and their possible impact on the following summer's demography. The paper is based on our long-term data on social organization and demography of the bank vole Clethrinonomys glareolus but studies on other Clethrionomus species and the field vole Microtus agrestis are also referred to. We attempt to verify the general validity of the model and present some new data on the impact of kinship and familiarity on the population growth in cyclic bank vole (Clethrionomys glareolus) populations.peerReviewe
The JSTOR Archive is a trusted digital repository providing for long-term preservation and access... more The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact
Frugivores functioning as seed dispersers may have fundamental effects on the reproductive succes... more Frugivores functioning as seed dispersers may have fundamental effects on the reproductive success of fruiting plants. Studies on this interaction have, however, mostly ignored possible within-season and between-year variations in seed germination behaviour. The aim of this study was to assess how berry ingestion by thrushes (Turdus spp.) affects seed germination of bilberry (Vaccinium myrtillus). Specifically, we studied if the timing of dispersal within the fruiting season affects germination success of seeds and whether these effects vary between years. The germination rate of intact seeds declined in the course of the fruiting season both in 1997 and in 1999. Ingestion by thrushes accelerated the germination rate of passed seeds and the final germination percentages of passed seeds were higher than or similar to those of intact seeds. These effects varied within season and between years. Thus, when effects of frugivores on seed germination success are studied, experiments should...
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