Overview:
Reproduction
We have shown that the wolverine exhibits a polygamous mating system where males produce offspring with more than one female in a single year (Hedmark et al. 2007). Female wolverines attain sexual maturity at about 15 months and exhibit delayed implantation, i.e. after the mating (April-August) parturition occurs in mainly in February and March. In general, wolverine females have a low reproductive rate. In Persson et al. (2006) we found that no 2-yr-old females reproduced successfully and that most females reproduced at 3 or 4 yrs of age. Furthermore, we found that the mean proportion of females (≥3 years old) reproducing was 0.53, and the annual mean was 0.58. Mean annual birth rate was 0.74 young per female. Mean size of 74 litters was 1.88. This data suggests that female wolverines have low productivity and low capacity to compensate for increased mortality. In Persson (2005) we showed that reproduction incurs costs on female wolverines that affects future reproduction, and that reproductive costs appears to be related to the duration of parental care. Reproduction was higher for food-supplemented females than for non-supplemented females. Our study suggests that reproduction is limited by winter food availability and that additional food can compensate for reproductive costs. Thus, that female wolverine reproduction is determined by their condition in winter, which is a result of the combined effect of reproductive costs and winter food availability.
For more details, see our peer-reviewed research below, and student theses here.
Reproduction
We have shown that the wolverine exhibits a polygamous mating system where males produce offspring with more than one female in a single year (Hedmark et al. 2007). Female wolverines attain sexual maturity at about 15 months and exhibit delayed implantation, i.e. after the mating (April-August) parturition occurs in mainly in February and March. In general, wolverine females have a low reproductive rate. In Persson et al. (2006) we found that no 2-yr-old females reproduced successfully and that most females reproduced at 3 or 4 yrs of age. Furthermore, we found that the mean proportion of females (≥3 years old) reproducing was 0.53, and the annual mean was 0.58. Mean annual birth rate was 0.74 young per female. Mean size of 74 litters was 1.88. This data suggests that female wolverines have low productivity and low capacity to compensate for increased mortality. In Persson (2005) we showed that reproduction incurs costs on female wolverines that affects future reproduction, and that reproductive costs appears to be related to the duration of parental care. Reproduction was higher for food-supplemented females than for non-supplemented females. Our study suggests that reproduction is limited by winter food availability and that additional food can compensate for reproductive costs. Thus, that female wolverine reproduction is determined by their condition in winter, which is a result of the combined effect of reproductive costs and winter food availability.
For more details, see our peer-reviewed research below, and student theses here.
Survival and mortality causes
Wolverine populations have a low reproductive potential and are thus relatively sensitive to changes in survival rates. Consequently, knowledge about survival and mortality causes in wolverines is important for a sound management of the species. In Persson et al. (2003) we estimated survival rates for juvenile wolverines and evaluated the relative importance of intraspecific predation compared to other mortality causes in northern Scandinavia during 1993-2001. We found that intraspecific predation was the most important cause of juvenile mortality and occurred during two periods: juveniles killed in May-June when still altricial (infanticide), and juvenile females killed by conspecifics outside their mothers’ territories after independence in August-September. There was a strong tendency for survival to be lower during the summer when juveniles were altricial,than after they became independent.
In the light of the available information on wolverine life history and infanticide patterns in other species,we suggest two, not mutually exclusive,hypotheses to consider for further investigation:1) males kill non-related juveniles to increase their reproductive success,and 2) females kill non-related juveniles to reduce competition for resources. In addition,attention should be given to the alternative hypothesis that infanticide in wolverines is non-adaptive. Finally,we suggest that independent juvenile females were killed (August-September) by resident females in territorial defense. In Persson et al. (2009) we recalculated the survival rate for juvenile wolverines based on a larger sample size. There we found that the average survival rate for 139 juveniles in our study area was 0.83 (from 1 June–28 February).
Furthermore, in Persson et al. (2009), we analyzed adult wolverine mortality causes and survival rates. We found that poaching forms a substantial part of wolverine population dynamics in northern Scandinavia causing up to 60% of adult mortality. Average annual adult survival rate was 0.91. Male and female survival rates did not differ. Fifty-two percent of confirmed adult mortality was human caused. The most important cause of adult mortality was poaching. Annual adult survival was lower (0.86) when 15 adult resident wolverines that were assumed to have died due to poaching were included in the analyses. Natural mortality among subadults and adults was less frequent in our study population compared to North American wolverine populations. Adult survival was significantly lower during the snow season (Dec–May) than during the snow-free season (June–Nov), while natural mortality was more evenly distributed between seasons. We explain this by the increased frequency of poaching during snow seasons. Our results underline the need to frame the underlying human dimension factors behind poaching to facilitate conservation and management of endangered populations.
Wolverine populations have a low reproductive potential and are thus relatively sensitive to changes in survival rates. Consequently, knowledge about survival and mortality causes in wolverines is important for a sound management of the species. In Persson et al. (2003) we estimated survival rates for juvenile wolverines and evaluated the relative importance of intraspecific predation compared to other mortality causes in northern Scandinavia during 1993-2001. We found that intraspecific predation was the most important cause of juvenile mortality and occurred during two periods: juveniles killed in May-June when still altricial (infanticide), and juvenile females killed by conspecifics outside their mothers’ territories after independence in August-September. There was a strong tendency for survival to be lower during the summer when juveniles were altricial,than after they became independent.
In the light of the available information on wolverine life history and infanticide patterns in other species,we suggest two, not mutually exclusive,hypotheses to consider for further investigation:1) males kill non-related juveniles to increase their reproductive success,and 2) females kill non-related juveniles to reduce competition for resources. In addition,attention should be given to the alternative hypothesis that infanticide in wolverines is non-adaptive. Finally,we suggest that independent juvenile females were killed (August-September) by resident females in territorial defense. In Persson et al. (2009) we recalculated the survival rate for juvenile wolverines based on a larger sample size. There we found that the average survival rate for 139 juveniles in our study area was 0.83 (from 1 June–28 February).
Furthermore, in Persson et al. (2009), we analyzed adult wolverine mortality causes and survival rates. We found that poaching forms a substantial part of wolverine population dynamics in northern Scandinavia causing up to 60% of adult mortality. Average annual adult survival rate was 0.91. Male and female survival rates did not differ. Fifty-two percent of confirmed adult mortality was human caused. The most important cause of adult mortality was poaching. Annual adult survival was lower (0.86) when 15 adult resident wolverines that were assumed to have died due to poaching were included in the analyses. Natural mortality among subadults and adults was less frequent in our study population compared to North American wolverine populations. Adult survival was significantly lower during the snow season (Dec–May) than during the snow-free season (June–Nov), while natural mortality was more evenly distributed between seasons. We explain this by the increased frequency of poaching during snow seasons. Our results underline the need to frame the underlying human dimension factors behind poaching to facilitate conservation and management of endangered populations.
Our Related Peer-Reviewed Research:
(For student theses, see here.)
(For student theses, see here.)
Poaching Effects in National Parks (2016):
Using individual-based long-term data, we show that three species of large carnivores, brown bear, Eurasian lynx, and wolverine, all suffered higher risk of illegal killing inside three large national parks than in surrounding unprotected areas in northern Sweden. We suggest that this illegal killing is the result of low enforcement and public presence in these remote parks, which results in a low probability for poachers to be discovered. Our results demonstrate that size of protected areas alone may be a poor predictor of their conservation value for large carnivores. We warn against passive national park management and advocate considering the ecological and socioeconomic context present inside as well as outside protected areas.
Rauset, G-R., Andrén, H., Swenson, J.E., Samelius, G., Segerström, P., Zedrosser, A. & Persson, J. 2016. National parks in northern Sweden as refuges for illegal killing of large carnivores. Conservation Letters, doi:10.1111/conl.12226 PDF
Causes of Variation in Reproductive Output (2015):
We used longitudinal demographic data from an 18‐year study of 53 breeding female wolverines to examine how age, resource availability, and reproductive costs interact as factors to cause variation in reproductive output. Females showed a typical age‐related pattern in reproductive output, with an initial increase followed by a senescent decline in later years. This pattern was largely driven by four processes: (1) physiological/behavioral maturation between ages two and three; (2) age‐related differences in the costs of reproduction resulting in an initial increase, and then a declining probability of breeding two years in a row as individuals aged; (3) resource availability (carcass abundance from other predators’ kills) in the months preceding parturition, which influenced the probability of having cubs, but only for individuals that had successfully bred in the previous year; and (4) resource availability also influenced the cost of reproduction in an age‐dependent manner, as prime-age females that had bred in the previous year were more responsive to resource availability than those at other ages. This study demonstrates that by examining how drivers of reproductive variation interact, we can get a much clearer understanding of the mechanisms responsible for age‐related patterns of reproduction.
Rauset, G.R., Low, M. and Persson. 2015. Reproductive patterns result from age-related sensitivity to resources and reproductive costs in a mammalian carnivore. Ecology 96(12): 3153-3164. PDF
Effect of Conservation Payments on Swedish Wolverine Population (2015):
We show that conservation performance payments to Sami reindeer herders for wolverine reproductions has been instrumental in the recovery of wolverines in Sweden. Adult female wolverines were significantly less exposed to illegal killing and this allowed the population to more than double in a decade. We argue that this program provides protection for adult female wolverines through a combination of direct monetary value and indirect protection because of monitoring activities. The program’s success, even in a system where livestock is the main prey for the predator, reveals an exceptional potential for future implementations in large carnivore conservation.
Persson, J., Rauset, G.R., and Chapron, G. 2015. Paying for an endangered predator leads to population recovery. Conservation Letters 8 (5): 345-350 doi:10.1111/conl.12171. PDF
Using individual-based long-term data, we show that three species of large carnivores, brown bear, Eurasian lynx, and wolverine, all suffered higher risk of illegal killing inside three large national parks than in surrounding unprotected areas in northern Sweden. We suggest that this illegal killing is the result of low enforcement and public presence in these remote parks, which results in a low probability for poachers to be discovered. Our results demonstrate that size of protected areas alone may be a poor predictor of their conservation value for large carnivores. We warn against passive national park management and advocate considering the ecological and socioeconomic context present inside as well as outside protected areas.
Rauset, G-R., Andrén, H., Swenson, J.E., Samelius, G., Segerström, P., Zedrosser, A. & Persson, J. 2016. National parks in northern Sweden as refuges for illegal killing of large carnivores. Conservation Letters, doi:10.1111/conl.12226 PDF
Causes of Variation in Reproductive Output (2015):
We used longitudinal demographic data from an 18‐year study of 53 breeding female wolverines to examine how age, resource availability, and reproductive costs interact as factors to cause variation in reproductive output. Females showed a typical age‐related pattern in reproductive output, with an initial increase followed by a senescent decline in later years. This pattern was largely driven by four processes: (1) physiological/behavioral maturation between ages two and three; (2) age‐related differences in the costs of reproduction resulting in an initial increase, and then a declining probability of breeding two years in a row as individuals aged; (3) resource availability (carcass abundance from other predators’ kills) in the months preceding parturition, which influenced the probability of having cubs, but only for individuals that had successfully bred in the previous year; and (4) resource availability also influenced the cost of reproduction in an age‐dependent manner, as prime-age females that had bred in the previous year were more responsive to resource availability than those at other ages. This study demonstrates that by examining how drivers of reproductive variation interact, we can get a much clearer understanding of the mechanisms responsible for age‐related patterns of reproduction.
Rauset, G.R., Low, M. and Persson. 2015. Reproductive patterns result from age-related sensitivity to resources and reproductive costs in a mammalian carnivore. Ecology 96(12): 3153-3164. PDF
Effect of Conservation Payments on Swedish Wolverine Population (2015):
We show that conservation performance payments to Sami reindeer herders for wolverine reproductions has been instrumental in the recovery of wolverines in Sweden. Adult female wolverines were significantly less exposed to illegal killing and this allowed the population to more than double in a decade. We argue that this program provides protection for adult female wolverines through a combination of direct monetary value and indirect protection because of monitoring activities. The program’s success, even in a system where livestock is the main prey for the predator, reveals an exceptional potential for future implementations in large carnivore conservation.
Persson, J., Rauset, G.R., and Chapron, G. 2015. Paying for an endangered predator leads to population recovery. Conservation Letters 8 (5): 345-350 doi:10.1111/conl.12171. PDF
Conservation Success For Large Carnivores in Europe (2014):
The conservation of large carnivores is a formidable challenge for biodiversity conservation. Using a data set on the past and current status of brown bears, Eurasian lynx, gray wolves, and wolverines in European countries, we show that roughly one-third of mainland Europe hosts at least one large carnivore species, with stable or increasing abundance in most cases in 21st-century records. The reasons for this overall conservation success include protective legislation, supportive public opinion, and a variety of practices making coexistence between large carnivores and people possible. The European situation reveals that large carnivores and people can share the same landscape.
Chapron et al. 2014. Recovery of large carnivores in Europe’s modern human-dominated landscapes. Science 346: 1517-1519. PDF
The Important Timing of Wolverine Reproduction (2012):
We synthesize information on the timing of both wolverine reproductive events and food availability to improve our understanding of the behaviors, habitat features, and foods that influence reproductive success. Wolverine births are constrained to a brief period of the year and occur at an earlier date than other non-hibernating, northern carnivores. We suggest that this timing is adaptive because it allows wolverines to take advantage of a cold, low-productivity niche. The wolverine’s reproductive strategy appears to require success in 2 stages. Fueling lactation (Feb–April) with caches amassed over winter or acquisition of a sudden food bonanza. Next, fueling post-weaning growth during the brief summer period of resource abundance. In some regions the 2nd stage may continue to be focused on scavenging. In other regions the 2nd stage may be focused on predation. During all seasons and regions, selecting habitat features facilitating caching in cold, structured microsites to inhibit competition with insects, bacteria, and other scavengers is likely a critical behavioral adaptation in their relatively limited food resource niche.
Inman, R., Magoun, A., Persson, J. & Mattisson, J. 2012. The wolverine’s niche: Linking reproductive chronology, caching, competition, and climate. Journal of Mammalogy 93 (3): 634-644. PDF
Survival Rates and Causes of Mortality (2009):
In a multi-year study we monitored 211 radio-marked wolverines to estimate age-specific survival rates and mortality causes in an endangered population. Our data suggests that poaching forms a substantial part of wolverine population dynamics in northern Scandinavia causing up to 60% of adult mortality. Average annual adult survival rate was 0.91. Fifty-two percent of adult wolverines who died during the study was human caused. The most important cause of adult mortality was poaching. Annual adult survival was lower (0.86) when 15 adult resident wolverines that were assumed to have died due to poaching were included in the analyses. Natural mortality among subadults and adults was less frequent in our study population compared to North American wolverine populations. Adult survival was significantly lower during the snow season (Dec–May) than during the snow-free season (June–Nov), while natural mortality was more evenly distributed between seasons. We explain this by the frequency of poaching which is higher during snow season.
Persson, J., Ericsson, G. & Segerström, P. 2009. Human caused mortality in an endangered wolverine population. Biological Conservation 142: 325-331. PDF
Mating Systems and Paternity (2007):
In this study, we use 20 microsatellite loci for paternity testing in 145 wolverine offspring with known mothers. Samples were collected over >10 years in two Scandinavian populations, mainly in connection with radio-telemetry studies and as part of long-term population monitoring. In total, 51% of the offspring were assigned a father. Our results demonstrate that the wolverine exhibits a polygamous mating system as some males were shown to produce offspring with more than one female in a single year. Females often reproduced with the same male in subsequent breeding years, but sometimes changed their partner, potentially as a consequence of a change in the territory-holding male in the area. In the majority of litters, siblings were unambiguously assigned the same father, indicating that multiple paternity is rare. 87% of had overlapping home ranges, suggesting that pair formation generally is consistent with the territories held by wolverine males and females.
Hedmark, E., Persson, J., Landa, A. & Segerström, P. 2007. Paternity and mating system in wolverines. Wildlife Biology 3 (Suppl. 2): 13-30. PDF
Reproductive Output (2006):
We studied reproduction of 56 female wolverines in 2 areas of northern Scandinavia. Minimum average age at 1st reproduction was 3.4 years. Mean proportion of females (≥3 years old) reproducing was 0.53, and the annual mean was 0.58. Mean annual birth rate was 0.74 young per female (≥3 years old). Mean size of 74 litters was 1.88. Examination of our data suggests that female wolverines have low productivity and low capacity to compensate for increased mortality. Therefore, wildlife managers should consider wolverine demographics, especially mortality of adult female wolverines, when developing and implementing conservation policies and harvest regulations.
Persson, J., Landa, A., Andersen, R. & Segerström, P. 2006. Reproductive characteristics of female wolverines (Gulo gulo) in Scandinavia. Journal of Mammalogy 87(1):75-79. PDF
Reproductive Costs and Winter Food Availability (2005):
This study addresses how female wolverine reproduction is limited. We tested two complementary hypotheses: (1) current reproduction is affected by the costs of reproduction in the preceding year and (2) current reproduction is affected by food availability in the current winter. The first was addressed by comparing reproductive rates of females in relation to their reproductive effort in the preceding year, and the second was tested by comparing reproductive rates of food-supplemented females versus non-supplemented females. Reproduction incurred costs on female wolverines that affected future reproduction, and reproductive costs appeared to be related to the duration of parental care. Reproduction was higher for food-supplemented females than for non-supplemented females, even though all food-supplemented females had reproduced the preceding year. This study suggests that reproduction is limited by winter food availability and that additional food can compensate for reproductive costs. Thus, we suggest female wolverine reproduction is determined by their condition in winter, which is a result of the combined effect of reproductive costs and winter food availability.
Persson, J. 2005. Wolverine female reproduction: reproductive costs and winter food availability. Canadian Journal of Zoology 83: 1453-1459. PDF
The conservation of large carnivores is a formidable challenge for biodiversity conservation. Using a data set on the past and current status of brown bears, Eurasian lynx, gray wolves, and wolverines in European countries, we show that roughly one-third of mainland Europe hosts at least one large carnivore species, with stable or increasing abundance in most cases in 21st-century records. The reasons for this overall conservation success include protective legislation, supportive public opinion, and a variety of practices making coexistence between large carnivores and people possible. The European situation reveals that large carnivores and people can share the same landscape.
Chapron et al. 2014. Recovery of large carnivores in Europe’s modern human-dominated landscapes. Science 346: 1517-1519. PDF
The Important Timing of Wolverine Reproduction (2012):
We synthesize information on the timing of both wolverine reproductive events and food availability to improve our understanding of the behaviors, habitat features, and foods that influence reproductive success. Wolverine births are constrained to a brief period of the year and occur at an earlier date than other non-hibernating, northern carnivores. We suggest that this timing is adaptive because it allows wolverines to take advantage of a cold, low-productivity niche. The wolverine’s reproductive strategy appears to require success in 2 stages. Fueling lactation (Feb–April) with caches amassed over winter or acquisition of a sudden food bonanza. Next, fueling post-weaning growth during the brief summer period of resource abundance. In some regions the 2nd stage may continue to be focused on scavenging. In other regions the 2nd stage may be focused on predation. During all seasons and regions, selecting habitat features facilitating caching in cold, structured microsites to inhibit competition with insects, bacteria, and other scavengers is likely a critical behavioral adaptation in their relatively limited food resource niche.
Inman, R., Magoun, A., Persson, J. & Mattisson, J. 2012. The wolverine’s niche: Linking reproductive chronology, caching, competition, and climate. Journal of Mammalogy 93 (3): 634-644. PDF
Survival Rates and Causes of Mortality (2009):
In a multi-year study we monitored 211 radio-marked wolverines to estimate age-specific survival rates and mortality causes in an endangered population. Our data suggests that poaching forms a substantial part of wolverine population dynamics in northern Scandinavia causing up to 60% of adult mortality. Average annual adult survival rate was 0.91. Fifty-two percent of adult wolverines who died during the study was human caused. The most important cause of adult mortality was poaching. Annual adult survival was lower (0.86) when 15 adult resident wolverines that were assumed to have died due to poaching were included in the analyses. Natural mortality among subadults and adults was less frequent in our study population compared to North American wolverine populations. Adult survival was significantly lower during the snow season (Dec–May) than during the snow-free season (June–Nov), while natural mortality was more evenly distributed between seasons. We explain this by the frequency of poaching which is higher during snow season.
Persson, J., Ericsson, G. & Segerström, P. 2009. Human caused mortality in an endangered wolverine population. Biological Conservation 142: 325-331. PDF
Mating Systems and Paternity (2007):
In this study, we use 20 microsatellite loci for paternity testing in 145 wolverine offspring with known mothers. Samples were collected over >10 years in two Scandinavian populations, mainly in connection with radio-telemetry studies and as part of long-term population monitoring. In total, 51% of the offspring were assigned a father. Our results demonstrate that the wolverine exhibits a polygamous mating system as some males were shown to produce offspring with more than one female in a single year. Females often reproduced with the same male in subsequent breeding years, but sometimes changed their partner, potentially as a consequence of a change in the territory-holding male in the area. In the majority of litters, siblings were unambiguously assigned the same father, indicating that multiple paternity is rare. 87% of had overlapping home ranges, suggesting that pair formation generally is consistent with the territories held by wolverine males and females.
Hedmark, E., Persson, J., Landa, A. & Segerström, P. 2007. Paternity and mating system in wolverines. Wildlife Biology 3 (Suppl. 2): 13-30. PDF
Reproductive Output (2006):
We studied reproduction of 56 female wolverines in 2 areas of northern Scandinavia. Minimum average age at 1st reproduction was 3.4 years. Mean proportion of females (≥3 years old) reproducing was 0.53, and the annual mean was 0.58. Mean annual birth rate was 0.74 young per female (≥3 years old). Mean size of 74 litters was 1.88. Examination of our data suggests that female wolverines have low productivity and low capacity to compensate for increased mortality. Therefore, wildlife managers should consider wolverine demographics, especially mortality of adult female wolverines, when developing and implementing conservation policies and harvest regulations.
Persson, J., Landa, A., Andersen, R. & Segerström, P. 2006. Reproductive characteristics of female wolverines (Gulo gulo) in Scandinavia. Journal of Mammalogy 87(1):75-79. PDF
Reproductive Costs and Winter Food Availability (2005):
This study addresses how female wolverine reproduction is limited. We tested two complementary hypotheses: (1) current reproduction is affected by the costs of reproduction in the preceding year and (2) current reproduction is affected by food availability in the current winter. The first was addressed by comparing reproductive rates of females in relation to their reproductive effort in the preceding year, and the second was tested by comparing reproductive rates of food-supplemented females versus non-supplemented females. Reproduction incurred costs on female wolverines that affected future reproduction, and reproductive costs appeared to be related to the duration of parental care. Reproduction was higher for food-supplemented females than for non-supplemented females, even though all food-supplemented females had reproduced the preceding year. This study suggests that reproduction is limited by winter food availability and that additional food can compensate for reproductive costs. Thus, we suggest female wolverine reproduction is determined by their condition in winter, which is a result of the combined effect of reproductive costs and winter food availability.
Persson, J. 2005. Wolverine female reproduction: reproductive costs and winter food availability. Canadian Journal of Zoology 83: 1453-1459. PDF
Population Viability Analysis Using Stochastic Models (2005):
We analyzed the viability of Scandinavian wolverine populations that allow for the inclusion of uncertainties in parameter estimates and stochastic effects on population dynamics. We used the insight gained from analyses of stochastic population models to quantitatively analyze different management options for the wolverine. Stochastic components in population dynamics of the wolverine were large. Strong density regulation occurred around the carrying capacity. The carrying capacity of populations must exceed 46 sexually mature (≥3-yr-old) females to be considered not vulnerable. Continuation of the current levels of offtake in Norway will lead to extinction of the wolverine over large parts of the country. Hence, current rates of mortality of female wolverine make the northern population endangered, whereas the southern population is classified as vulnerable. Management plans allowing harvest of individuals should be based on a proportional threshold harvest strategy.
Saether, B.-E., Engen, S., Persson, J., Brøseth, H., Landa, A. and Willebrand, T. 2005. Management strategies for the Scandinavian wolverine: practical application of stochastic models in Population Viability Analysis. Journal of Wildlife Management 63: 1001-1014. PDF
Colonization History and Non-Invasive Monitoring in Norway (2004):
The southern Norwegian wolverine population was considered functionally extinct in the 1960s but has partly recovered in recent years. We report on a large-scale population monitoring project assessing these parameters through genetic tagging of individuals, with feces as the source of DNA. Sixty-eight different individuals were detected among 147 successfully genotyped samples collected in 2000 and 2001. A capture-recapture estimate based on the observed resampling rates suggested a population size of 89 wolverines, which is approximately 35% higher than an estimate of 64 obtained from the number of active natal dens. Indirect estimates of dispersal distances inferred from mother-offspring relationships suggested that wolverine males have the ability to disperse up to 500 km, and dispersal distances of more than 100 km were detected for females. Bayesian clustering analysis and subsequent assessment of individual relationships suggest that immigrants from northern Scandinavia have contributed and still contribute to the southern Norwegian gene pool, counteracting genetic erosion and reducing the risk of inbreeding depression.
Flagstad, Ö., Hedmark, E., Landa, A., Brøseth, H., Persson, J., Andersen, R., Segerström, P. & Ellegren, H. 2004. Colonization history and non-invasive monitoring of a re-established wolverine (Gulo gulo) population. Conservation Biology 18(3): 1-13. PDF
Juvenile Survival Rates and Intraspecific Predation (2003):
We estimated survival rates for juvenile wolverines using 80 radio-marked juveniles and evaluated the relative importance of intraspecific predation compared to other mortality causes in northern Scandinavia during 1993–2001. Intraspecific predation was the most important cause of juvenile mortality and occurred during two periods. First, seven juveniles were killed in May-June when still altricial, i.e. infanticide. Second, four juvenile females were killed by conspecifics outside their mothers' territories after independence in August–September. The survival rate of radio-marked juveniles during May-February was 0.68. There was a strong tendency for survival to be lower during the summer when juveniles were altricial, than after they became independent. We suggest two, not mutually exclusive, hypotheses to consider for further investigation: 1) males kill non-related juveniles to increase their reproductive success, and 2) females kill non-related juveniles to reduce competition for resources. In addition, attention should be given to the alternative hypothesis that infanticide in wolverines is non-adaptive. Finally, we suggest that independent juvenile females were killed by resident females in territorial defense.
Persson, J., Willebrand, T., Landa, A., Andersen, R. & Segerström, P. 2003. The role of intraspecific predation in the survival of juvenile wolverines Gulo gulo. Wildlife Biology 9: 21-28. PDF
Juvenile Dispersal Patterns and Home Range Characteristics (2001):
We studied patterns of dispersal and sizes of home ranges of juvenile wolverines. Mean dispersal age was 13 months for both male and female wolverines. Females displayed more variation in dispersal age (7–26 months) than males (7–18 months). Of the animals used in the dispersal analyses, all males and 69% of females dispersed. All sedentary females occupied their mother’s territory when she died or shifted territory, and no females dispersed from a territory vacated by their mother. Competition for resources seemed to determine the female dispersal pattern, while competition for mates seemed to explain the male dispersal pattern. Eight cases of exploratory movements were observed, and on average, these immediately preceded dispersal movements. The size of juvenile home ranges of males and females corresponded to the home-range area of denning females during the summer period.
Vangen, K.M., Persson, J. Landa, A. Andersen, R. & Segerström, P. 2001. Characteristics of dispersal in wolverines. Canadian Journal of Zoology 79: 1641-1649. PDF
Genetic Variation and Population Structure (2001):
We report here the development of 15 polymorphic microsatellite markers in wolverine and their use to examine the population sub-structure and genetic variability in free-ranging Scandinavian wolverine populations as well as in a sample of individuals collected before 1970. Significant subdivision between extant populations was discovered, in particular for the small and isolated population of southern Norway, which represents a recent recolonization. Overall genetic variability was found to be lower than previously reported for other mustelids. Analysis of the mitochondrial DNA control region revealed no variation throughout the surveyed populations. As the historical sample did not show higher levels of genetic variability, our results are consistent with a reduction in the genetic variation in Scandinavian wolverines that pre-dates the demographic bottleneck observed during the last century.
Walker, C., Landa, A., Lindén, M. & Ellegren, H. 2001. Genetic variation and population structure in Scandinavian wolverine (Gulo gulo) populations. Molecular Ecology 10: 53-63. PDF
Total Population Estimate for Scandinavia (1998):
Minimum numbers of wolverines were estimated for Scandinavia, based on the average number of active dens recorded in 1995–1997. To estimate the proportion of females active at dens, we followed individual females using radio-telemetry in northern Sweden, northern Norway, and south-central Norway. The sex and age structure of the population was estimated based on a sample of wolverines harvested before the introduction of protective measures and harvest restrictions. Our results are compared with those found in other published wolverine studies, mostly from North America. The Scandinavian population of one-year-old and older wolverines was estimated at 413 individuals (265 in Sweden and 147 in Norway). This method gave a lower population estimate than those found in earlier surveys based on summation of local (municipality) estimates and on local tracking surveys. The differences may be explained by the existence of a large number of undiscovered natal dens, but the previous estimates were based on methodologies with sources of error that could inflate estimates.
Landa, A., Tufto, J., Franzén R., Bø, T., Lindén, M. & Swenson, J.E. 1998. Active wolverine Gulo gulo dens as a minimum population estimator in Scandinavia. Wildlife Biology 4:159-168. PDF
We analyzed the viability of Scandinavian wolverine populations that allow for the inclusion of uncertainties in parameter estimates and stochastic effects on population dynamics. We used the insight gained from analyses of stochastic population models to quantitatively analyze different management options for the wolverine. Stochastic components in population dynamics of the wolverine were large. Strong density regulation occurred around the carrying capacity. The carrying capacity of populations must exceed 46 sexually mature (≥3-yr-old) females to be considered not vulnerable. Continuation of the current levels of offtake in Norway will lead to extinction of the wolverine over large parts of the country. Hence, current rates of mortality of female wolverine make the northern population endangered, whereas the southern population is classified as vulnerable. Management plans allowing harvest of individuals should be based on a proportional threshold harvest strategy.
Saether, B.-E., Engen, S., Persson, J., Brøseth, H., Landa, A. and Willebrand, T. 2005. Management strategies for the Scandinavian wolverine: practical application of stochastic models in Population Viability Analysis. Journal of Wildlife Management 63: 1001-1014. PDF
Colonization History and Non-Invasive Monitoring in Norway (2004):
The southern Norwegian wolverine population was considered functionally extinct in the 1960s but has partly recovered in recent years. We report on a large-scale population monitoring project assessing these parameters through genetic tagging of individuals, with feces as the source of DNA. Sixty-eight different individuals were detected among 147 successfully genotyped samples collected in 2000 and 2001. A capture-recapture estimate based on the observed resampling rates suggested a population size of 89 wolverines, which is approximately 35% higher than an estimate of 64 obtained from the number of active natal dens. Indirect estimates of dispersal distances inferred from mother-offspring relationships suggested that wolverine males have the ability to disperse up to 500 km, and dispersal distances of more than 100 km were detected for females. Bayesian clustering analysis and subsequent assessment of individual relationships suggest that immigrants from northern Scandinavia have contributed and still contribute to the southern Norwegian gene pool, counteracting genetic erosion and reducing the risk of inbreeding depression.
Flagstad, Ö., Hedmark, E., Landa, A., Brøseth, H., Persson, J., Andersen, R., Segerström, P. & Ellegren, H. 2004. Colonization history and non-invasive monitoring of a re-established wolverine (Gulo gulo) population. Conservation Biology 18(3): 1-13. PDF
Juvenile Survival Rates and Intraspecific Predation (2003):
We estimated survival rates for juvenile wolverines using 80 radio-marked juveniles and evaluated the relative importance of intraspecific predation compared to other mortality causes in northern Scandinavia during 1993–2001. Intraspecific predation was the most important cause of juvenile mortality and occurred during two periods. First, seven juveniles were killed in May-June when still altricial, i.e. infanticide. Second, four juvenile females were killed by conspecifics outside their mothers' territories after independence in August–September. The survival rate of radio-marked juveniles during May-February was 0.68. There was a strong tendency for survival to be lower during the summer when juveniles were altricial, than after they became independent. We suggest two, not mutually exclusive, hypotheses to consider for further investigation: 1) males kill non-related juveniles to increase their reproductive success, and 2) females kill non-related juveniles to reduce competition for resources. In addition, attention should be given to the alternative hypothesis that infanticide in wolverines is non-adaptive. Finally, we suggest that independent juvenile females were killed by resident females in territorial defense.
Persson, J., Willebrand, T., Landa, A., Andersen, R. & Segerström, P. 2003. The role of intraspecific predation in the survival of juvenile wolverines Gulo gulo. Wildlife Biology 9: 21-28. PDF
Juvenile Dispersal Patterns and Home Range Characteristics (2001):
We studied patterns of dispersal and sizes of home ranges of juvenile wolverines. Mean dispersal age was 13 months for both male and female wolverines. Females displayed more variation in dispersal age (7–26 months) than males (7–18 months). Of the animals used in the dispersal analyses, all males and 69% of females dispersed. All sedentary females occupied their mother’s territory when she died or shifted territory, and no females dispersed from a territory vacated by their mother. Competition for resources seemed to determine the female dispersal pattern, while competition for mates seemed to explain the male dispersal pattern. Eight cases of exploratory movements were observed, and on average, these immediately preceded dispersal movements. The size of juvenile home ranges of males and females corresponded to the home-range area of denning females during the summer period.
Vangen, K.M., Persson, J. Landa, A. Andersen, R. & Segerström, P. 2001. Characteristics of dispersal in wolverines. Canadian Journal of Zoology 79: 1641-1649. PDF
Genetic Variation and Population Structure (2001):
We report here the development of 15 polymorphic microsatellite markers in wolverine and their use to examine the population sub-structure and genetic variability in free-ranging Scandinavian wolverine populations as well as in a sample of individuals collected before 1970. Significant subdivision between extant populations was discovered, in particular for the small and isolated population of southern Norway, which represents a recent recolonization. Overall genetic variability was found to be lower than previously reported for other mustelids. Analysis of the mitochondrial DNA control region revealed no variation throughout the surveyed populations. As the historical sample did not show higher levels of genetic variability, our results are consistent with a reduction in the genetic variation in Scandinavian wolverines that pre-dates the demographic bottleneck observed during the last century.
Walker, C., Landa, A., Lindén, M. & Ellegren, H. 2001. Genetic variation and population structure in Scandinavian wolverine (Gulo gulo) populations. Molecular Ecology 10: 53-63. PDF
Total Population Estimate for Scandinavia (1998):
Minimum numbers of wolverines were estimated for Scandinavia, based on the average number of active dens recorded in 1995–1997. To estimate the proportion of females active at dens, we followed individual females using radio-telemetry in northern Sweden, northern Norway, and south-central Norway. The sex and age structure of the population was estimated based on a sample of wolverines harvested before the introduction of protective measures and harvest restrictions. Our results are compared with those found in other published wolverine studies, mostly from North America. The Scandinavian population of one-year-old and older wolverines was estimated at 413 individuals (265 in Sweden and 147 in Norway). This method gave a lower population estimate than those found in earlier surveys based on summation of local (municipality) estimates and on local tracking surveys. The differences may be explained by the existence of a large number of undiscovered natal dens, but the previous estimates were based on methodologies with sources of error that could inflate estimates.
Landa, A., Tufto, J., Franzén R., Bø, T., Lindén, M. & Swenson, J.E. 1998. Active wolverine Gulo gulo dens as a minimum population estimator in Scandinavia. Wildlife Biology 4:159-168. PDF