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Janne Sundell - One of the best experts on this subject based on the ideXlab platform.
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Voles and Weasels in the boreal Fennoscandian small mammal community: what happens if the Least Weasel disappears due to climate change?
Integrative zoology, 2019Co-Authors: Marko Haapakoski, Thorbjörn Sievert, Janne SundellAbstract:Climate change, habitat loss and fragmentation are major threats for populations and a challenge for individual behavior, interactions and survival. Predator-prey interactions are modified by climate processes. In the northern latitudes, strong seasonality is changing and the main predicted feature is shortening and instability of winter. Vole populations in the boreal Fennoscandia exhibit multiannual cycles. High amplitude peak numbers of voles and dramatic population lows alternate in 3-5-year cycles shortening from North to South. One key factor, or driver, promoting the population crash and causing extreme extended lows, is suggested to be predation by the Least Weasel. We review the arms race between prey voles and Weasels through the multiannual density fluctuation, affected by climate change, and especially the changes in the duration and stability of snow cover. For ground-dwelling small mammals, snow provides thermoregulation and shelter for nest sites, and helps them hide from predators. Predicted increases in the instability of winter forms a major challenge for species with coat color change between brown summer camouflage and white winter coat. One of these is the Least Weasel, Mustela nivalis nivalis. Increased vulnerability of wrong-colored Weasels to predation affects vole populations and may have dramatic effects on vole dynamics. It may have cascading effects on other small rodent-predator interactions and even on plant-animal interactions and forest dynamics.
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DOI 10.1007/s00265-004-0777-6 ORIGINAL ARTICLE
2014Co-Authors: Janne Sundell, Hannu Ylönen, H. YlönenAbstract:Abstract Animals often show a strong antipredatory response when they are exposed to their most deadly predator. In northern vole populations, the Least Weasel, Mustela nivalis nivalis, is probably the most important predator of voles. Because of its small size and slender body shape, the Least Weasel is capable of hunting voles in their burrows. However, small voles can potentially escape Weasel predation by selecting holes smaller than those Weasels can enter. We studied the choice of nest holes and refuges by two species of voles under simulated predation risk. In a laboratory experiment, voles were provided with four nest boxes as refuges, with individually adjusted entrance sizes. When exposed to the odour of a Weasel, voles did not choose the smallest opening; they rather seemed to trade full protection for easy and immediate access by choosing the nest box with an intermediate entrance size. When outside the nest at the time when a Weasel entered the arena, voles avoided the refuges with the smallest holes. In addition to using refuges on ground level, voles climbed on top of the boxes as an escape reaction, as well as exhibiting a variety of behavioural responses, such as fast running, freezing and sneaking
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OIKOS 90: 501–508. Copenhagen 2000 Functional response of the Least Weasel, Mustela ni�alis ni�alis
2014Co-Authors: Janne Sundell, Kai Norrdahl, Erkki Korpimäki, Ilkka HanskiAbstract:We investigated the functional response of the Least Weasel (Mustela ni�alis ni�alis) in a series of experiments conducted in large outdoor enclosures (0.5 ha). Radiocollared Microtus voles were released in the enclosures at different densities (4, 8, 16 and 100/ha) three days before the release of a radiocollared Weasel. During the three-day experiment every vole killed was replaced with another one as soon as possible to retain constant prey density. The results demonstrated type II functional response with the predation rate reaching 50 % of the asymptotic rate at a vole density of 15 individuals per ha. More voles were killed at the highest densities than would be expected from the known energy demands of Weasels. Female and male voles were killed in proportion to their abundances in the enclosures, and no difference in predation risk was detected between voles released in the enclosure before the Weasel (residents) and during the experiment (transients)
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Species-specific limitation of vole population growth by Least Weasel predation: facilitation of coexistence?
2014Co-Authors: Elina Koivisto, Janne Sundell, Otso Huitu, Erkki KorpimäkiAbstract:Interspecific competition is usually understood as different species competing directly with each other for limited resources. However, predators can alter such competitive interactions substantially. Predation can promote the coexistence of species in a situation where it would otherwise be impossible, for example if a tradeoff between the competitive abilities and predation resistance of the prey species exists. The field vole Microtus agrestis and the sibling vole M. rossiaemeridionalis are sympatric grassland species, which compete for the same resources. At the population level sibling voles are suggested to be superior competitors to field voles, yet more vulnerable to predation. We tested the effects of predation on the two species in 0.5 ha outdoor enclosures by exposing vole populations to radiocollared freely-hunting Least Weasels Mustela nivalis nivalis for three weeks. Lethal and non-lethal impacts of predation limited population densities of both species during and after the experimental period, but the effect was more pronounced in sibling voles in which population densities decreased markedly during the treatment period and even after that. Field vole population densities remained stable under Weasel predation, while densities increased in controls. Survival in both species was lower in treatment populations compared to controls, but the effect tended to be more pronounced in sibling voles and in females of both species. The average mass of adults in both species declined in the treatment populations. These results suggest that predation by Least Weasels can limit vole populations locally, even during favourable summer conditions, and have extended negative effects on the dynamics of vole populations. In addition
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Different escape tactics of two vole species affect the success of the hunting predator, the Least Weasel
Behavioral Ecology and Sociobiology, 2013Co-Authors: Sanna Mäkeläinen, Lenka Trebatická, Janne SundellAbstract:In the ongoing evolutionary arms race between predators and their prey, successful escape from the predator leads to the evolution of improved escape tactics in prey, but also predators become more effective in following and attacking the prey. Antipredatory behavior of prey is considered to be the strongest towards their most dangerous predators. However, prey species can differ both in vulnerability and efficiency of escape to a shared predator. We studied escape reactions of two vole species, the bank vole (Myodes glareolus) and the field vole (Microtus agrestis), under a simulated predation risk of the Least Weasel (Mustela nivalis nivalis). We conducted a laboratory experiment where a vole was given a possibility to escape from a Weasel by fleeing to a horizontal tunnel or climbing the tree. Subsequently to the vole escape decision, we released a Weasel to the same tunnel system to test how the Weasel succeeded in following the vole. Weasel presence changed the behavior of voles as especially bank voles escaped by climbing. Instead, the majority of field voles fled into the ground-layer tunnel. The different escape tactics of the voles affected the success of the Weasel, because climbing voles were less often successfully followed. We suggest that the difference in escape tactics has evolved as an adaptation to different habitats; meadow-exploiting field voles using ground-level escape while bank voles living in three-dimensional forest habitat frequently use arboreal escape tactics. This is likely to lead to different habitat-dependent vulnerabilities to predation in Microtus and Myodes vole species.
Erkki Korpimäki - One of the best experts on this subject based on the ideXlab platform.
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Multiple predators induce risk reduction in coexisting vole species
2020Co-Authors: Erkki Korpimäki, Elina Koivisto, Otso Huitu, Katrine S Hoset, Hannu Ylö, E Koivisto, O Huitu, Á H YlönenAbstract:Large predators may affect the hunting efficiency of smaller ones directly by decreasing their numbers, or indirectly by altering their behaviour. Either way this may have positive effects on the density of shared prey. Using large outdoor enclosures, we experimentally studied whether the presence of the Tengmalm's owl Aegolius funereus affects the hunting efficiency of the smallest member of the vole-eating predator guild, the Least Weasel Mustela nivalis, as measured by population responses of coexisting prey species, the field vole Microtus agrestis and the sibling vole M. levis. We compared the density and survival probability of vole populations exposed to no predation, Weasel predation or combined predation by a Weasel and an owl. The combined predation of both owl and Weasel did not result in obvious changes in the density of sibling and field vole populations compared to the control populations without predators, while predation by Least Weasel alone decreased the densities of sibling voles and induced a similar trend in field vole densities. Survival of field voles was not affected by predator treatment while sibling vole survival was lower in predator treated populations than in control populations. Our results suggest that Weasels are intimidated by avian predators, but without changing the effects of predators on competitive situations between the two vole species. Non-lethal effects of intraguild predation therefore will not necessarily change competitive interactions between shared prey species
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Species-specific limitation of vole population growth by Least Weasel predation: facilitation of coexistence?
2014Co-Authors: Elina Koivisto, Janne Sundell, Otso Huitu, Erkki KorpimäkiAbstract:Interspecific competition is usually understood as different species competing directly with each other for limited resources. However, predators can alter such competitive interactions substantially. Predation can promote the coexistence of species in a situation where it would otherwise be impossible, for example if a tradeoff between the competitive abilities and predation resistance of the prey species exists. The field vole Microtus agrestis and the sibling vole M. rossiaemeridionalis are sympatric grassland species, which compete for the same resources. At the population level sibling voles are suggested to be superior competitors to field voles, yet more vulnerable to predation. We tested the effects of predation on the two species in 0.5 ha outdoor enclosures by exposing vole populations to radiocollared freely-hunting Least Weasels Mustela nivalis nivalis for three weeks. Lethal and non-lethal impacts of predation limited population densities of both species during and after the experimental period, but the effect was more pronounced in sibling voles in which population densities decreased markedly during the treatment period and even after that. Field vole population densities remained stable under Weasel predation, while densities increased in controls. Survival in both species was lower in treatment populations compared to controls, but the effect tended to be more pronounced in sibling voles and in females of both species. The average mass of adults in both species declined in the treatment populations. These results suggest that predation by Least Weasels can limit vole populations locally, even during favourable summer conditions, and have extended negative effects on the dynamics of vole populations. In addition
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OIKOS 90: 501–508. Copenhagen 2000 Functional response of the Least Weasel, Mustela ni�alis ni�alis
2014Co-Authors: Janne Sundell, Kai Norrdahl, Erkki Korpimäki, Ilkka HanskiAbstract:We investigated the functional response of the Least Weasel (Mustela ni�alis ni�alis) in a series of experiments conducted in large outdoor enclosures (0.5 ha). Radiocollared Microtus voles were released in the enclosures at different densities (4, 8, 16 and 100/ha) three days before the release of a radiocollared Weasel. During the three-day experiment every vole killed was replaced with another one as soon as possible to retain constant prey density. The results demonstrated type II functional response with the predation rate reaching 50 % of the asymptotic rate at a vole density of 15 individuals per ha. More voles were killed at the highest densities than would be expected from the known energy demands of Weasels. Female and male voles were killed in proportion to their abundances in the enclosures, and no difference in predation risk was detected between voles released in the enclosure before the Weasel (residents) and during the experiment (transients)
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species specific limitation of vole population growth by Least Weasel predation facilitation of coexistence
Oikos, 2008Co-Authors: Elina Koivisto, Janne Sundell, Otso Huitu, Erkki KorpimäkiAbstract:Interspecific competition is usually understood as different species competing directly with each other for limited resources. However, predators can alter such competitive interactions substantially. Predation can promote the coexistence of species in a situation where it would otherwise be impossible, for example if a tradeoff between the competitive abilities and predation resistance of the prey species exists. The field vole Microtus agrestis and the sibling vole M. rossiaemeridionalis are sympatric grassland species, which compete for the same resources. At the population level sibling voles are suggested to be superior competitors to field voles, yet more vulnerable to predation. We tested the effects of predation on the two species in 0.5 ha outdoor enclosures by exposing vole populations to radio-collared freely-hunting Least Weasels Mustela nivalis nivalis for three weeks. Lethal and non-lethal impacts of predation limited population densities of both species during and after the experimental period, but the effect was more pronounced in sibling voles in which population densities decreased markedly during the treatment period and even after that. Field vole population densities remained stable under Weasel predation, while densities increased in controls. Survival in both species was lower in treatment populations compared to controls, but the effect tended to be more pronounced in sibling voles and in females of both species. The average mass of adults in both species declined in the treatment populations. These results suggest that predation by Least Weasels can limit vole populations locally, even during favourable summer conditions, and have extended negative effects on the dynamics of vole populations. In addition, predation alleviated interspecific competition between the vole species and is, therefore, a potential factor enabling the coexistence of them.
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variation in the diet composition of a generalist predator the red fox in relation to season and density of main prey
Acta Oecologica-international Journal of Ecology, 2007Co-Authors: Graziella Lucia Dellarte, Kai Norrdahl, Toni Laaksonen, Erkki KorpimäkiAbstract:Abstract Diet composition of a generalist predator, the red fox ( Vulpes vulpes ) in relation to season (winter or summer) and abundance of multi-annually cyclic voles was studied in western Finland from 1983 to 1995. The proportion of scats (PS; a total of 58 scats) including each food category was calculated for each prey group. Microtus voles (the field vole M. agrestis and the sibling vole M. rossiaemeridionalis ) were the main prey group of foxes (PS = 0.55) and they frequently occurred in the scats both in the winter and summer (PSs 0.50 and 0.62, respectively). There was a positive correlation between the PSs of Microtus voles in the winter diet of foxes and the density indices of these voles in the previous autumn. Other microtine rodents (the bank vole Clethrionomys glareolus , the water vole Arvicola terrestris and the muskrat Ondatra zibethicus ) were consumed more in winter than in summer. The unusually high small mustelid predation by red foxes (PS = approx. 0.10) in our study area gives qualitative support for the hypothesis on the limiting impact of mammalian predators on Least Weasel and stoat populations. None of the important prey groups was preyed upon more at low than at high densities of main prey ( Microtus voles). This is consistent with the notion that red foxes are generalist predators that tend to opportunistically subsist on many prey groups. Among these prey groups, particularly hares and birds (including grouse), were frequently used as food by foxes.
Hannu Ylönen - One of the best experts on this subject based on the ideXlab platform.
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In utero behavioral imprinting to predation risk in pups of the bank vole
Behavioral Ecology and Sociobiology, 2020Co-Authors: Thorbjörn Sievert, Arjane Kerkhoven, Marko Haapakoski, Kevin D. Matson, Olga Ylönen, Hannu YlönenAbstract:In the predator–prey arms race, survival-enhancing adaptive behaviors are essential. Prey can perceive predator presence directly from visual, auditory, or chemical cues. Non-lethal encounters with a predator may trigger prey to produce special body odors, alarm pheromones, informing conspecifics about predation risks. Recent studies suggest that parental exposure to predation risk during reproduction affects offspring behavior cross-generationally. We compared behaviors of bank vole ( Myodes glareolus ) pups produced by parents exposed to one of three treatments: predator scent from the Least Weasel ( Mustela nivalis nivalis ); scent from Weasel-exposed voles, i.e., alarm pheromones; or a control treatment without added scents. Parents were treated in semi-natural field enclosures, but pups were born in the lab and assayed in an open-field arena. Before each behavioral test, one of the three scent treatments was spread throughout the test arena. The tests followed a full factorial design (3 parental treatments × 3 area treatments). Regardless of the parents’ treatment, pups exposed to predator odor in the arena moved more. Additionally, pups spend more time in the center of the arena when presented with predator odor or alarm pheromone compared with the control. Pups from predator odor–exposed parents avoided the center of the arena under control conditions, but they spent more time in the center when either predator odor or alarm pheromone was present. Our experiment shows that cross-generational effects are context-sensitive, depending on the perceived risk. Future studies should examine cross-generational behavioral effects in ecologically meaningful environments instead of only neutral ones. Significance statement We exposed bank voles to odors signaling predation risk to assess the effects parental predation exposure on the behavior of their offspring. Besides predator odor, we also assessed the role of a conspecific alarm cue as a novel way of spreading the predation risk information. Pup behaviors were assessed in the open-field arena, a standard way of assessing animal behavior in a wide range of contexts. We found that also alarm pheromone increased the time pups spend in the center of the arena similarly to predator odor. While previous studies suggested that offspring would be more fearful, our results indicate that the cross-generational effects are very context-dependent; i.e., they differ significantly depending on which scent cue is presented in the open-field arena. This shows the need for better tools or measurements to translate laboratory results into ecologically meaningful frameworks.
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DOI 10.1007/s00265-004-0777-6 ORIGINAL ARTICLE
2014Co-Authors: Janne Sundell, Hannu Ylönen, H. YlönenAbstract:Abstract Animals often show a strong antipredatory response when they are exposed to their most deadly predator. In northern vole populations, the Least Weasel, Mustela nivalis nivalis, is probably the most important predator of voles. Because of its small size and slender body shape, the Least Weasel is capable of hunting voles in their burrows. However, small voles can potentially escape Weasel predation by selecting holes smaller than those Weasels can enter. We studied the choice of nest holes and refuges by two species of voles under simulated predation risk. In a laboratory experiment, voles were provided with four nest boxes as refuges, with individually adjusted entrance sizes. When exposed to the odour of a Weasel, voles did not choose the smallest opening; they rather seemed to trade full protection for easy and immediate access by choosing the nest box with an intermediate entrance size. When outside the nest at the time when a Weasel entered the arena, voles avoided the refuges with the smallest holes. In addition to using refuges on ground level, voles climbed on top of the boxes as an escape reaction, as well as exhibiting a variety of behavioural responses, such as fast running, freezing and sneaking
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Predation and vole odour preference of Weasel.
2013Co-Authors: Susanna Saari, Janne Sundell, Otso Huitu, Marjo Helander, Elise Ketoja, Hannu Ylönen, Kari SaikkonenAbstract:The effects of endophyte infected (E+) and endophyte free (E−) grass diets on predation and vole odour preference of Least Weasel. Estimated percentages of captured voles (n = 17) and odour preference (n = 21).
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Fungal-mediated multitrophic interactions--do grass endophytes in diet protect voles from predators?
Public Library of Science (PLoS), 2010Co-Authors: Susanna Saari, Janne Sundell, Otso Huitu, Marjo Helander, Elise Ketoja, Hannu Ylönen, Kari SaikkonenAbstract:Plant-associated micro-organisms such as mycotoxin-producing endophytes commonly have direct negative effects on herbivores. These effects may be carried over to natural enemies of the herbivores, but this has been rarely explored. We examined how feeding on Neotyphodium endophyte infected (E+) and endophyte free (E-) meadow ryegrass (Scherodonus pratensis) affects body mass, population size and mobility of sibling voles (Microtus levis), and whether the diet mediates the vulnerability of voles to Least Weasel (Mustela nivalis nivalis) predation. Because Least Weasels are known to be olfactory hunters, we also examined whether they are able to distinguish olfactory cues of voles fed on E+ and E- diets. Neither body mass of voles nor population size differed between diets. However, contrary to our prediction, Least Weasels preyed more often on voles fed with E- grass than on voles fed with E+ grass. The mobility of voles fed on E+ grass was reduced compared to voles fed on E- grass, but this effect was unrelated to risk of predation. Least Weasels appeared unable to distinguish between excrement odours of voles between the two treatments. Our results suggest that consumption of endophytic grass is not directly deleterious to sibling voles. What's more, consumption of endophytes appears to be advantageous to voles by reducing risk of mammalian predation. Our study is thus the first to demonstrate an effect of plant-associated microbial symbionts on herbivore-predator interactions in vertebrate communities
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does risk of small mustelid predation affect the oestrous cycle in the bank vole clethrionomys glareolus
Animal Behaviour, 1996Co-Authors: Esa Koskela, Taina J. Horne, Tapio Mappes, Hannu YlönenAbstract:Female bank voles suppress their reproduction when the risk of small mustelid predation is high. The mechanism for this reproductive suppression is unknown. Because rodents are known to alter their oestrous cycle in response to changing environmental conditions, the eVect of predation risk on the oestrous cycle of bank vole females was studied. The oestrous cycles of 24 females divided into two treatments (predation risk and control) were observed for 20 days using female receptivity as an indication of oestrus. Voles exposed for 2-3 h a day for 20 days to the close presence of a Least Weasel, Mustela nivalis nivalis, had fewer oestrous cycles than control females exposed to a domestic rabbit, Oryctolagus cuniculus. Females under predation risk had more abnormally long cycles than did control females. The number of days females were in oestrus tended to be lower in the predator-exposure group than in the control group. For those females that performed lordosis, the latency to lordosis did not diVer between treatments. The amount of food consumed or weight change in females did not diVer between treatments. The results indicate that female bank voles may respond to predation risk by suppressing their oestrous cycle. Suppressed oestrus may be a mechanism for the breeding suppression observed under the risk of small mustelid predation in female voles. Whether females suppressing oestrus have selective advantage in terms of future survival requires further study. ? 1996 The Association for the Study of Animal Behaviour
Marko Haapakoski - One of the best experts on this subject based on the ideXlab platform.
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In utero behavioral imprinting to predation risk in pups of the bank vole
Behavioral Ecology and Sociobiology, 2020Co-Authors: Thorbjörn Sievert, Arjane Kerkhoven, Marko Haapakoski, Kevin D. Matson, Olga Ylönen, Hannu YlönenAbstract:In the predator–prey arms race, survival-enhancing adaptive behaviors are essential. Prey can perceive predator presence directly from visual, auditory, or chemical cues. Non-lethal encounters with a predator may trigger prey to produce special body odors, alarm pheromones, informing conspecifics about predation risks. Recent studies suggest that parental exposure to predation risk during reproduction affects offspring behavior cross-generationally. We compared behaviors of bank vole ( Myodes glareolus ) pups produced by parents exposed to one of three treatments: predator scent from the Least Weasel ( Mustela nivalis nivalis ); scent from Weasel-exposed voles, i.e., alarm pheromones; or a control treatment without added scents. Parents were treated in semi-natural field enclosures, but pups were born in the lab and assayed in an open-field arena. Before each behavioral test, one of the three scent treatments was spread throughout the test arena. The tests followed a full factorial design (3 parental treatments × 3 area treatments). Regardless of the parents’ treatment, pups exposed to predator odor in the arena moved more. Additionally, pups spend more time in the center of the arena when presented with predator odor or alarm pheromone compared with the control. Pups from predator odor–exposed parents avoided the center of the arena under control conditions, but they spent more time in the center when either predator odor or alarm pheromone was present. Our experiment shows that cross-generational effects are context-sensitive, depending on the perceived risk. Future studies should examine cross-generational behavioral effects in ecologically meaningful environments instead of only neutral ones. Significance statement We exposed bank voles to odors signaling predation risk to assess the effects parental predation exposure on the behavior of their offspring. Besides predator odor, we also assessed the role of a conspecific alarm cue as a novel way of spreading the predation risk information. Pup behaviors were assessed in the open-field arena, a standard way of assessing animal behavior in a wide range of contexts. We found that also alarm pheromone increased the time pups spend in the center of the arena similarly to predator odor. While previous studies suggested that offspring would be more fearful, our results indicate that the cross-generational effects are very context-dependent; i.e., they differ significantly depending on which scent cue is presented in the open-field arena. This shows the need for better tools or measurements to translate laboratory results into ecologically meaningful frameworks.
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Voles and Weasels in the boreal Fennoscandian small mammal community: what happens if the Least Weasel disappears due to climate change?
Integrative zoology, 2019Co-Authors: Marko Haapakoski, Thorbjörn Sievert, Janne SundellAbstract:Climate change, habitat loss and fragmentation are major threats for populations and a challenge for individual behavior, interactions and survival. Predator-prey interactions are modified by climate processes. In the northern latitudes, strong seasonality is changing and the main predicted feature is shortening and instability of winter. Vole populations in the boreal Fennoscandia exhibit multiannual cycles. High amplitude peak numbers of voles and dramatic population lows alternate in 3-5-year cycles shortening from North to South. One key factor, or driver, promoting the population crash and causing extreme extended lows, is suggested to be predation by the Least Weasel. We review the arms race between prey voles and Weasels through the multiannual density fluctuation, affected by climate change, and especially the changes in the duration and stability of snow cover. For ground-dwelling small mammals, snow provides thermoregulation and shelter for nest sites, and helps them hide from predators. Predicted increases in the instability of winter forms a major challenge for species with coat color change between brown summer camouflage and white winter coat. One of these is the Least Weasel, Mustela nivalis nivalis. Increased vulnerability of wrong-colored Weasels to predation affects vole populations and may have dramatic effects on vole dynamics. It may have cascading effects on other small rodent-predator interactions and even on plant-animal interactions and forest dynamics.
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Mammalian predator-prey interaction in a fragmented landscape: Weasels and voles.
Oecologia, 2013Co-Authors: Marko Haapakoski, Janne SundellAbstract:The relationship between predators and prey is thought to change due to habitat loss and fragmentation, but patterns regarding the direction of the effect are lacking. The common prediction is that specialized predators, often more dependent on a certain habitat type, should be more vulnerable to habitat loss compared to generalist predators, but actual fragmentation effects are unknown. If a predator is small and vulnerable to predation by other larger predators through intra-guild predation, habitat fragmentation will similarly affect both the prey and the small predator. In this case, the predator is predicted to behave similarly to the prey and avoid open and risky areas. We studied a specialist predator's, the Least Weasel, Mustela nivalis nivalis, spacing behavior and hunting efficiency on bank voles, Myodes glareolus, in an experimentally fragmented habitat. The habitat consisted of either one large habitat patch (non-fragmented) or four small habitat patches (fragmented) with the same total area. The study was replicated in summer and autumn during a year with high avian predation risk for both voles and Weasels. As predicted, Weasels under radio-surveillance killed more voles in the non-fragmented habitat which also provided cover from avian predators during their prey search. However, this was only during autumn, when the killing rate was also generally high due to cold weather. The movement areas were the same for both sexes and both fragmentation treatments, but Weasels of both sexes were more prone to take risks in crossing the open matrix in the fragmented treatment. Our results support the hypothesis that habitat fragmentation may increase the persistence of specialist predator and prey populations if predators are limited in the same habitat as their prey and they share the same risk from avian predation.
Kai Norrdahl - One of the best experts on this subject based on the ideXlab platform.
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OIKOS 90: 501–508. Copenhagen 2000 Functional response of the Least Weasel, Mustela ni�alis ni�alis
2014Co-Authors: Janne Sundell, Kai Norrdahl, Erkki Korpimäki, Ilkka HanskiAbstract:We investigated the functional response of the Least Weasel (Mustela ni�alis ni�alis) in a series of experiments conducted in large outdoor enclosures (0.5 ha). Radiocollared Microtus voles were released in the enclosures at different densities (4, 8, 16 and 100/ha) three days before the release of a radiocollared Weasel. During the three-day experiment every vole killed was replaced with another one as soon as possible to retain constant prey density. The results demonstrated type II functional response with the predation rate reaching 50 % of the asymptotic rate at a vole density of 15 individuals per ha. More voles were killed at the highest densities than would be expected from the known energy demands of Weasels. Female and male voles were killed in proportion to their abundances in the enclosures, and no difference in predation risk was detected between voles released in the enclosure before the Weasel (residents) and during the experiment (transients)
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variation in the diet composition of a generalist predator the red fox in relation to season and density of main prey
Acta Oecologica-international Journal of Ecology, 2007Co-Authors: Graziella Lucia Dellarte, Kai Norrdahl, Toni Laaksonen, Erkki KorpimäkiAbstract:Abstract Diet composition of a generalist predator, the red fox ( Vulpes vulpes ) in relation to season (winter or summer) and abundance of multi-annually cyclic voles was studied in western Finland from 1983 to 1995. The proportion of scats (PS; a total of 58 scats) including each food category was calculated for each prey group. Microtus voles (the field vole M. agrestis and the sibling vole M. rossiaemeridionalis ) were the main prey group of foxes (PS = 0.55) and they frequently occurred in the scats both in the winter and summer (PSs 0.50 and 0.62, respectively). There was a positive correlation between the PSs of Microtus voles in the winter diet of foxes and the density indices of these voles in the previous autumn. Other microtine rodents (the bank vole Clethrionomys glareolus , the water vole Arvicola terrestris and the muskrat Ondatra zibethicus ) were consumed more in winter than in summer. The unusually high small mustelid predation by red foxes (PS = approx. 0.10) in our study area gives qualitative support for the hypothesis on the limiting impact of mammalian predators on Least Weasel and stoat populations. None of the important prey groups was preyed upon more at low than at high densities of main prey ( Microtus voles). This is consistent with the notion that red foxes are generalist predators that tend to opportunistically subsist on many prey groups. Among these prey groups, particularly hares and birds (including grouse), were frequently used as food by foxes.
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Functional response of the Least Weasel, Mustela nivalis nivalis
Oikos, 2000Co-Authors: Janne Sundell, Kai Norrdahl, Erkki Korpimäki, Ilkka HanskiAbstract:We investigated the functional response of the Least Weasel (Mustela nivalis nivalis) in a series of experiments conducted in large outdoor enclosures (0.5 ha). Radiocollared Microtus voles were released in the enclosures at different densities (4, 8, 16 and 100/ha) three days before the release of a radiocollared Weasel. During the three-day experiment every vole killed was replaced with another one as soon as possible to retain constant prey density. The results demonstrated type II functional response with the predation rate reaching 50% of the asymptotic rate at a vole density of 15 individuals per ha. More voles were killed at the highest densities than would be expected from the known energy demands of Weasels. Female and male voles were killed in proportion to their abundances in the enclosures, and no difference in predation risk was detected between voles released in the enclosure before the Weasel (residents) and during the experiment (transients).
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small mustelid predation slows population growth of microtus voles a predator reduction experiment
Journal of Animal Ecology, 1997Co-Authors: Tero Klemola, Erkki Korpimäki, Minna Koivula, Kai NorrdahlAbstract:1. The effects of predator reduction on the breeding performance and sex ratio of Microtus voles were studied in a cyclically fluctuating vole assemblage in western Finland, where the field vole (Microtus agrestis) and the sibling vole (M. rossiaemeridionalis) are the main prey of small mustelids. 2. The densities of small mustelids [the Least Weasel (Mustela nivalis nivalis) and the stoat (M. erminea)] were reduced experimentally in three large (2-3 km 2 ) unfenced areas in 1992, during a crash phase of the vole cycle, and in three different areas during the following crash phase in 1995. The reproductive performance of Microtus voles was compared between control and manipulation areas before and after reducing predators. 3. The reduction of predators increased the productivity of female voles, mainly due to an increased proportion of pregnancies, whereas the body condition of voles was not affected by the manipulation. This suggests that high predation risk in control areas suppressed the breeding of free-living voles. 4. The sex ratio of trapped voles before the manipulation did not differ between reduction and control areas, but after predators were reduced the sex ratio was more male-biased in the control areas. This indicates that small mustelids selectively killed female voles. 5. Our results suggest two possible mechanisms which may have operated concurrently. An adaptive explanation is that voles traded their current reproductive investment against future breeding under high predation risk. A simpler explanation is that small mustelids selectively preyed on pregnant female voles. Both suppressed breeding and selective killing would lead to a lower proportion of reproducing individuals in the vole population. Therefore, our results show that the presence of small mustelid predators slowed the population growth of Microtus voles.
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Responses of stoats and Least Weasels to fluctuating food abundances: is the low phase of the vole cycle due to mustelid predation?
Oecologia, 1991Co-Authors: Erkki Korpimäki, Kai Norrdahl, Tuija Rinta-jaskariAbstract:We studied responses of stoats and Least Weasels to fluctuating vole abundances during seven winters in western Finland. Density indices of mustelids were derived from snow-tracking, diet composition from scat samples, and vole abundances from snap-trapping. Predation rate was estimated by the ratio of voles to mustelids and by the vole kill rate by predators (density of predator x percentage of voles in the diet). We tested the following four predictions of the hypothesis that small mustelids cause the low phase of the microtine cycle. (1) The densities of predators should lag well behind the prey abundances, as time lags tend to have destabilizing effects. The densities of stoats fluctuated in accordance with the vole abundances, whereas the spring densities of Least Weasels tracked the vole abundances with a half-year lag and the autumn densities with a 1-year lag. (2) Predators should not shift to alternative prey with declining vole densities. The yearly proportion of Microtus voles (the staple prey) in the diet of stoats varied widely (range 16-82%) and was positively correlated with the winter abundance of these voles. In contrast, the same proportion in the food of Least Weasels was independent of the vole abundance. (3) The ratio of voles to small mustelids should be smallest in poor vole years and largest in good ones. This was also observed. (4) Vole densities from autumn to spring should decrease more in those winters when vole kill rates are high than when they are low. The data on Least Weasels agreed with this prediction. Our results from Least Weasels were consistent with the predictions of the hypothesis, but stoats behaved like "semi-generalist" predators. Accordingly, declines and lows in the microtine cycle may be due to Least Weasel predation, but other extrinsic factors may also contribute to crashes.