Kai Norrdahl - Academia.edu (original) (raw)

Papers by Kai Norrdahl

Research paper thumbnail of The role of avian and mammalian predation in cyclic fluctuations of small mammals

Li s ens i aatintucki el-ma ratr-Â.È€tat3 ad l{a temaatti s-luonnonti e ree I I inen 1¡oor¡untuOa... more Li s ens i aatintucki el-ma ratr-Â.È€tat3 ad l{a temaatti s-luonnonti e ree I I inen 1¡oor¡untuOau¡o-F!¡u[rusatf oî Lokakuu 1992 3iäinciede (morf.ekologinen Li Ogpr¡r¡a-Lafoamna a)

Research paper thumbnail of Reverse influence of riparian buffer width on herbivorous and predatory Hemiptera

Journal of Applied Entomology, 2014

Insects are major contributors to farmland biodiversity, and their economic roles are also divers... more Insects are major contributors to farmland biodiversity, and their economic roles are also diverse. Many herbivorous species are crop pests, while predatory insects have the potential to act as biological controls against pests. Overall insect diversity has declined as a result of intensified agricultural practices. Riparian buffers may support insect populations in intensively cultivated areas, but their actual impact on the balance between harmful pests and beneficial predators is not known. It can be postulated that this impact may vary depending on the characteristics and location of the riparian buffer itself. We investigated the possibility that the biotic and abiotic attributes of agricultural riparian buffers adjoining crop fields and watercourses can explain the species composition of hemipteran assemblages. In particular, we were interested in the abundances of species belonging to the genus Nabis (generalist predators) and recognized and potential pests of cereal crops. Riparian buffer width and the presence or absence of woody plants were not associated with hemipteran species turnover among riparian buffers. In contrast, differences in the degree of dominance by grasses, in plant species turnover, and in which crop plant was cultivated in the adjacent field, explained a significant proportion of the variance in hemipteran species turnover. The abundance of predatory Nabis species increased with increasing riparian buffer width, whereas the abundance of recognized and potential crop pests decreased. The reverse patterns in the predatory and herbivorous Heteroptera suggest that increasing riparian buffer width might enhance biological control by Nabis predators.

Research paper thumbnail of Leaf Litter Decomposition of Nonnative Shrub Species in Nonnative and Native Shrub Environments: A Field Experiment with Three Rosaceae Shrubs

Invasive Plant Science and Management, 2015

Invasion by nonnative plants may have ecosystem-wide effects, altering the decomposition rate of ... more Invasion by nonnative plants may have ecosystem-wide effects, altering the decomposition rate of plant material via changes in litter quality or altered environment (abiotic conditions, associated biotic community), or both. Yet, the relative importance of these factors for decomposition rates is not clear. We studied decomposition using the leaves of related shrub species (nonnative Sorbaria sorbifolia and Rosa rugosa, native Rubus idaeus) with comparable physiognomy but different leaf characteristics and origin (alien vs. native) in patches formed by S. sorbifolia and Rubus idaeus in southwestern Finland. Decomposition of cellulose in the topsoils of the patches was also studied. Using litter bags, we found that S. sorbifolia leaf litter decomposed slowest and Rosa rugosa leaves fastest irrespective of patch type. Topsoils in S. sorbifolia patches were richer in carbon, nitrogen, and calcium than those of Rubus idaeus, but these differences did not affect decomposition rates. Very...

Research paper thumbnail of Antibiotic resistance - How wild are wild mammals?

Nature, 2001

In bacteria associated with humans, antimicrobial resistance is common, both in clinical isolates... more In bacteria associated with humans, antimicrobial resistance is common, both in clinical isolates and in the less-studied commensal flora, and it is thought that commensal and environmental bacteria might be a hidden reservoir of resistance. Gilliver et al. have reported that resistance is also prevalent in faecal bacteria from wild rodents living in northwest England. Here we test the faeces of moose, deer and vole in Finland and find an almost complete absence of resistance in enterobacteria. Resistance is thus not a universal property of enterobacterial populations, but may be a result of the human use of antibiotics.

Research paper thumbnail of Experimental tests of predation and food hypotheses for population cycles of voles

Proceedings of the Royal Society B: Biological Sciences, 2000

Pronounced population cycles are characteristic of many herbivorous small mammals in northern lat... more Pronounced population cycles are characteristic of many herbivorous small mammals in northern latitudes. Although delayed density-dependent e¡ects of predation and food shortage are often proposed as factors driving population cycles, ¢rm evidence for causality is rare because su¤ciently replicated, large-scale ¢eld experiments are lacking. We conducted two experiments on Microtus voles in four large predator-proof enclosures and four unfenced control areas in western Finland. Predator exclusion induced rapid population growth and increased the peak abundance of voles over 20-fold until the enclosed populations crashed during the second winter due to food shortage. Thereafter, voles introduced to enclosures which had su¡ered heavy grazing increased to higher densities than voles in previously ungrazed control areas which were exposed to predators. We concluded that predation inhibits an increase in vole populations until predation pressure declines, thus maintaining the low phase of the cycle, but also that population cycles in voles are not primarily driven by plant^herbivore interactions.

Research paper thumbnail of Does Predation Risk Constrain Maturation in Cyclic Vole Populations?

Research paper thumbnail of Low proportion of shrews in the diet of small mustelids in western Finland

Z. Säugetierkd, 1987

Seats and guts of stoat and least weasel collected after a decline of microtines in western Finla... more Seats and guts of stoat and least weasel collected after a decline of microtines in western Finland showed that these mustelids did not use shrews as their alternative prey, probably because of their distaste for shrews. Therefore it seems that small mustelids did not cause the synchronous decline phases in microtine and shrew populations observed in the transition zone of Fennoscandian microtine cycles. In this zone the most likely reason, especially for spring and summer declines, may be the predation by avian predators which frequently feed on shrews in addition to microtines.

Research paper thumbnail of Predation of Tengmalm's Owls: Numerical Responses, Functional Responses and Dampening Impact on Population Fluctuations of Microtines

Research paper thumbnail of Sex roles, parental effort and offspring desertion in the monogamous Eurasian Curlew Numenius arquata

Research paper thumbnail of Nonlinearity in the predation risk of prey mobility

Proceedings of the Royal Society B: Biological Sciences, 2000

Odorous waste products such as urine and faeces are unavoidable for most animals and are widely e... more Odorous waste products such as urine and faeces are unavoidable for most animals and are widely exploited by predators and their prey. Consequently, waste accumulations can be risky and prey which increase their mobility in order to disperse and dilute their waste should avoid a high predation risk until this bene¢t is balanced by the increasing risks of random predator encounter. This hypothesis was tested for voles (Microtus spp.) in Finland which are vulnerable to predation due to the scent and ultraviolet attractiveness of their urine. The mortality and mobility of radio-collared voles showed a U-shaped relationship, regardless of vole sex, species or population cycle phase. The low risks for prey making intermediate movements suggest that predation risk can exert strong selective pressures on prey such that they have little respite from the risk of being killed.

Research paper thumbnail of Blackwell Publishing, Ltd.Vole cycles and predation in temperate and boreal zones of Europe

Graham & Lambin (2002) have reported on a weasel-reduction experiment, concluding that the impact... more Graham & Lambin (2002) have reported on a weasel-reduction experiment, concluding that the impact of weasel predation on field vole survival was neither sufficient nor necessary to initiate and drive the cyclic decline of field vole populations in Kielder Forest, northern England. They also stated that their findings contradict conclusively the specialist predator hypothesis put forward to explain population cycles of voles in North Europe.

Research paper thumbnail of OIKOS 90: 501–508. Copenhagen 2000 Functional response of the least weasel, Mustela ni�alis ni�alis

We investigated the functional response of the least weasel (Mustela ni�alis ni�alis) in a series... more 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).

Research paper thumbnail of Within‐season changes in habitat use of forest‐dwelling boreal bats

Ecology and Evolution

The three-dimensional arrangement of vegetation has an essential influence on habitat quality and... more The three-dimensional arrangement of vegetation has an essential influence on habitat quality and, therefore, the presence and abundance of animal species at local scales (Tews et al., 2004). The complexity and diversity of vegetation determine the diversity and behavior of higher organisms by influencing the availability and diversity of resources and niches (Hekkala, Tarvainen,

Research paper thumbnail of Only extreme vole densities limit the establishment of long-lived plants in riparian field margins

Research paper thumbnail of Biotic filtering and mass effects in small shrub patches: is arthropod community structure predictable based on the quality of the vegetation?

Ecological Entomology

1. Community assembly is affected by four processes: dispersal, filtering effects (selection), ec... more 1. Community assembly is affected by four processes: dispersal, filtering effects (selection), ecological drift and evolution. The role of filtering relative to dispersal and drift should decline with patch size, hampering possibilities to predict which organisms will be observed within small‐sized patches. However, vegetation structure is known to have a marked impact on species assemblages, and plant quality may act as a biotic filter. This challenges the assumption of unpredictable species assemblages in small‐sized vegetation patches.

Research paper thumbnail of Dry paths effectively reduce road mortality of small and medium-sized terrestrial vertebrates

Journal of environmental management, 2014

Wildlife passages are widely used mitigation measures designed to reduce the adverse impacts of r... more Wildlife passages are widely used mitigation measures designed to reduce the adverse impacts of roads on animals. We investigated whether road kills of small and medium-sized terrestrial vertebrates can be reduced by constructing dry paths adjacent to streams that pass under road bridges. The study was carried out in southern Finland during the summer of 2008. We selected ten road bridges with dry paths and ten bridges without them, and an individual dry land reference site for each study bridge on the basis of landscape and traffic features. A total of 307 dead terrestrial vertebrates were identified during the ten-week study period. The presence of dry paths decreased the amount of road-killed terrestrial vertebrates (Poisson GLMM; p < 0.001). That was true also when considering amphibians alone (p < 0.001). The evidence on road-kills on mammals was not such clear. In the mammal model, a lack of dry paths increased the amount of carcasses (p = 0.001) whereas the number of ca...

Research paper thumbnail of Different response of two Hemiptera species groups to sown wildflower strips: True bugs and leafhoppers

Agriculture, Ecosystems & Environment, 2016

Research paper thumbnail of Non-native and native shrubs have differing impacts on species diversity and composition of associated plant communities

Research paper thumbnail of Size of internal organs and forage quality of herbivores: are there differences between cycle phases in Microtus voles?

Oikos, Nov 11, 1997

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

Research paper thumbnail of What you need is what you eat? Prey selection by the bat Myotis daubentonii

Molecular ecology, Jan 3, 2016

Optimal foraging theory predicts that predators are selective when faced with abundant prey, but ... more Optimal foraging theory predicts that predators are selective when faced with abundant prey, but become less picky when prey gets sparse. Insectivorous bats in temperate regions are faced with the challenge of building up fat reserves vital for hibernation during a period of decreasing arthropod abundances. According to optimal foraging theory, pre-hibernating bats should adopt a less selective feeding behavior - yet empirical studies have revealed many apparently generalized species to be composed of specialist individuals. Targeting the diet of the bat Myotis daubentonii, we used a combination of molecular techniques to test for seasonal changes in prey selectivity and individual-level variation in prey preferences. DNA metabarcoding was used to characterise both the prey contents of bat droppings and the insect community available as prey. To test for dietary differences among M. daubentonii individuals, we used ten microsatellite loci to assign droppings to individual bats. The ...

Research paper thumbnail of The role of avian and mammalian predation in cyclic fluctuations of small mammals

Li s ens i aatintucki el-ma ratr-Â.È€tat3 ad l{a temaatti s-luonnonti e ree I I inen 1¡oor¡untuOa... more Li s ens i aatintucki el-ma ratr-Â.È€tat3 ad l{a temaatti s-luonnonti e ree I I inen 1¡oor¡untuOau¡o-F!¡u[rusatf oî Lokakuu 1992 3iäinciede (morf.ekologinen Li Ogpr¡r¡a-Lafoamna a)

Research paper thumbnail of Reverse influence of riparian buffer width on herbivorous and predatory Hemiptera

Journal of Applied Entomology, 2014

Insects are major contributors to farmland biodiversity, and their economic roles are also divers... more Insects are major contributors to farmland biodiversity, and their economic roles are also diverse. Many herbivorous species are crop pests, while predatory insects have the potential to act as biological controls against pests. Overall insect diversity has declined as a result of intensified agricultural practices. Riparian buffers may support insect populations in intensively cultivated areas, but their actual impact on the balance between harmful pests and beneficial predators is not known. It can be postulated that this impact may vary depending on the characteristics and location of the riparian buffer itself. We investigated the possibility that the biotic and abiotic attributes of agricultural riparian buffers adjoining crop fields and watercourses can explain the species composition of hemipteran assemblages. In particular, we were interested in the abundances of species belonging to the genus Nabis (generalist predators) and recognized and potential pests of cereal crops. Riparian buffer width and the presence or absence of woody plants were not associated with hemipteran species turnover among riparian buffers. In contrast, differences in the degree of dominance by grasses, in plant species turnover, and in which crop plant was cultivated in the adjacent field, explained a significant proportion of the variance in hemipteran species turnover. The abundance of predatory Nabis species increased with increasing riparian buffer width, whereas the abundance of recognized and potential crop pests decreased. The reverse patterns in the predatory and herbivorous Heteroptera suggest that increasing riparian buffer width might enhance biological control by Nabis predators.

Research paper thumbnail of Leaf Litter Decomposition of Nonnative Shrub Species in Nonnative and Native Shrub Environments: A Field Experiment with Three Rosaceae Shrubs

Invasive Plant Science and Management, 2015

Invasion by nonnative plants may have ecosystem-wide effects, altering the decomposition rate of ... more Invasion by nonnative plants may have ecosystem-wide effects, altering the decomposition rate of plant material via changes in litter quality or altered environment (abiotic conditions, associated biotic community), or both. Yet, the relative importance of these factors for decomposition rates is not clear. We studied decomposition using the leaves of related shrub species (nonnative Sorbaria sorbifolia and Rosa rugosa, native Rubus idaeus) with comparable physiognomy but different leaf characteristics and origin (alien vs. native) in patches formed by S. sorbifolia and Rubus idaeus in southwestern Finland. Decomposition of cellulose in the topsoils of the patches was also studied. Using litter bags, we found that S. sorbifolia leaf litter decomposed slowest and Rosa rugosa leaves fastest irrespective of patch type. Topsoils in S. sorbifolia patches were richer in carbon, nitrogen, and calcium than those of Rubus idaeus, but these differences did not affect decomposition rates. Very...

Research paper thumbnail of Antibiotic resistance - How wild are wild mammals?

Nature, 2001

In bacteria associated with humans, antimicrobial resistance is common, both in clinical isolates... more In bacteria associated with humans, antimicrobial resistance is common, both in clinical isolates and in the less-studied commensal flora, and it is thought that commensal and environmental bacteria might be a hidden reservoir of resistance. Gilliver et al. have reported that resistance is also prevalent in faecal bacteria from wild rodents living in northwest England. Here we test the faeces of moose, deer and vole in Finland and find an almost complete absence of resistance in enterobacteria. Resistance is thus not a universal property of enterobacterial populations, but may be a result of the human use of antibiotics.

Research paper thumbnail of Experimental tests of predation and food hypotheses for population cycles of voles

Proceedings of the Royal Society B: Biological Sciences, 2000

Pronounced population cycles are characteristic of many herbivorous small mammals in northern lat... more Pronounced population cycles are characteristic of many herbivorous small mammals in northern latitudes. Although delayed density-dependent e¡ects of predation and food shortage are often proposed as factors driving population cycles, ¢rm evidence for causality is rare because su¤ciently replicated, large-scale ¢eld experiments are lacking. We conducted two experiments on Microtus voles in four large predator-proof enclosures and four unfenced control areas in western Finland. Predator exclusion induced rapid population growth and increased the peak abundance of voles over 20-fold until the enclosed populations crashed during the second winter due to food shortage. Thereafter, voles introduced to enclosures which had su¡ered heavy grazing increased to higher densities than voles in previously ungrazed control areas which were exposed to predators. We concluded that predation inhibits an increase in vole populations until predation pressure declines, thus maintaining the low phase of the cycle, but also that population cycles in voles are not primarily driven by plant^herbivore interactions.

Research paper thumbnail of Does Predation Risk Constrain Maturation in Cyclic Vole Populations?

Research paper thumbnail of Low proportion of shrews in the diet of small mustelids in western Finland

Z. Säugetierkd, 1987

Seats and guts of stoat and least weasel collected after a decline of microtines in western Finla... more Seats and guts of stoat and least weasel collected after a decline of microtines in western Finland showed that these mustelids did not use shrews as their alternative prey, probably because of their distaste for shrews. Therefore it seems that small mustelids did not cause the synchronous decline phases in microtine and shrew populations observed in the transition zone of Fennoscandian microtine cycles. In this zone the most likely reason, especially for spring and summer declines, may be the predation by avian predators which frequently feed on shrews in addition to microtines.

Research paper thumbnail of Predation of Tengmalm's Owls: Numerical Responses, Functional Responses and Dampening Impact on Population Fluctuations of Microtines

Research paper thumbnail of Sex roles, parental effort and offspring desertion in the monogamous Eurasian Curlew Numenius arquata

Research paper thumbnail of Nonlinearity in the predation risk of prey mobility

Proceedings of the Royal Society B: Biological Sciences, 2000

Odorous waste products such as urine and faeces are unavoidable for most animals and are widely e... more Odorous waste products such as urine and faeces are unavoidable for most animals and are widely exploited by predators and their prey. Consequently, waste accumulations can be risky and prey which increase their mobility in order to disperse and dilute their waste should avoid a high predation risk until this bene¢t is balanced by the increasing risks of random predator encounter. This hypothesis was tested for voles (Microtus spp.) in Finland which are vulnerable to predation due to the scent and ultraviolet attractiveness of their urine. The mortality and mobility of radio-collared voles showed a U-shaped relationship, regardless of vole sex, species or population cycle phase. The low risks for prey making intermediate movements suggest that predation risk can exert strong selective pressures on prey such that they have little respite from the risk of being killed.

Research paper thumbnail of Blackwell Publishing, Ltd.Vole cycles and predation in temperate and boreal zones of Europe

Graham & Lambin (2002) have reported on a weasel-reduction experiment, concluding that the impact... more Graham & Lambin (2002) have reported on a weasel-reduction experiment, concluding that the impact of weasel predation on field vole survival was neither sufficient nor necessary to initiate and drive the cyclic decline of field vole populations in Kielder Forest, northern England. They also stated that their findings contradict conclusively the specialist predator hypothesis put forward to explain population cycles of voles in North Europe.

Research paper thumbnail of OIKOS 90: 501–508. Copenhagen 2000 Functional response of the least weasel, Mustela ni�alis ni�alis

We investigated the functional response of the least weasel (Mustela ni�alis ni�alis) in a series... more 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).

Research paper thumbnail of Within‐season changes in habitat use of forest‐dwelling boreal bats

Ecology and Evolution

The three-dimensional arrangement of vegetation has an essential influence on habitat quality and... more The three-dimensional arrangement of vegetation has an essential influence on habitat quality and, therefore, the presence and abundance of animal species at local scales (Tews et al., 2004). The complexity and diversity of vegetation determine the diversity and behavior of higher organisms by influencing the availability and diversity of resources and niches (Hekkala, Tarvainen,

Research paper thumbnail of Only extreme vole densities limit the establishment of long-lived plants in riparian field margins

Research paper thumbnail of Biotic filtering and mass effects in small shrub patches: is arthropod community structure predictable based on the quality of the vegetation?

Ecological Entomology

1. Community assembly is affected by four processes: dispersal, filtering effects (selection), ec... more 1. Community assembly is affected by four processes: dispersal, filtering effects (selection), ecological drift and evolution. The role of filtering relative to dispersal and drift should decline with patch size, hampering possibilities to predict which organisms will be observed within small‐sized patches. However, vegetation structure is known to have a marked impact on species assemblages, and plant quality may act as a biotic filter. This challenges the assumption of unpredictable species assemblages in small‐sized vegetation patches.

Research paper thumbnail of Dry paths effectively reduce road mortality of small and medium-sized terrestrial vertebrates

Journal of environmental management, 2014

Wildlife passages are widely used mitigation measures designed to reduce the adverse impacts of r... more Wildlife passages are widely used mitigation measures designed to reduce the adverse impacts of roads on animals. We investigated whether road kills of small and medium-sized terrestrial vertebrates can be reduced by constructing dry paths adjacent to streams that pass under road bridges. The study was carried out in southern Finland during the summer of 2008. We selected ten road bridges with dry paths and ten bridges without them, and an individual dry land reference site for each study bridge on the basis of landscape and traffic features. A total of 307 dead terrestrial vertebrates were identified during the ten-week study period. The presence of dry paths decreased the amount of road-killed terrestrial vertebrates (Poisson GLMM; p < 0.001). That was true also when considering amphibians alone (p < 0.001). The evidence on road-kills on mammals was not such clear. In the mammal model, a lack of dry paths increased the amount of carcasses (p = 0.001) whereas the number of ca...

Research paper thumbnail of Different response of two Hemiptera species groups to sown wildflower strips: True bugs and leafhoppers

Agriculture, Ecosystems & Environment, 2016

Research paper thumbnail of Non-native and native shrubs have differing impacts on species diversity and composition of associated plant communities

Research paper thumbnail of Size of internal organs and forage quality of herbivores: are there differences between cycle phases in Microtus voles?

Oikos, Nov 11, 1997

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

Research paper thumbnail of What you need is what you eat? Prey selection by the bat Myotis daubentonii

Molecular ecology, Jan 3, 2016

Optimal foraging theory predicts that predators are selective when faced with abundant prey, but ... more Optimal foraging theory predicts that predators are selective when faced with abundant prey, but become less picky when prey gets sparse. Insectivorous bats in temperate regions are faced with the challenge of building up fat reserves vital for hibernation during a period of decreasing arthropod abundances. According to optimal foraging theory, pre-hibernating bats should adopt a less selective feeding behavior - yet empirical studies have revealed many apparently generalized species to be composed of specialist individuals. Targeting the diet of the bat Myotis daubentonii, we used a combination of molecular techniques to test for seasonal changes in prey selectivity and individual-level variation in prey preferences. DNA metabarcoding was used to characterise both the prey contents of bat droppings and the insect community available as prey. To test for dietary differences among M. daubentonii individuals, we used ten microsatellite loci to assign droppings to individual bats. The ...