Effects of spatial isolation, habitat quality, and supplemental food for population dynamics of t... more Effects of spatial isolation, habitat quality, and supplemental food for population dynamics of the grey-sided vole, Clethrionomys rufocanus
Stable isotope values of long-tailed and parasitic jaegers' chick feathers in nothern Fennosc... more Stable isotope values of long-tailed and parasitic jaegers' chick feathers in nothern Fennoscandian tundra. Values are arranged by year and study area. There were three study areas, scattered along a coast (Altafjord) - inland (highland tundra plateau of Joatka Reserch Area) gradient (see Figure 1 in Ruffino et al. 2015 in Ecography for details of study areas). Year 2011 was a rodent outbreak year (both Norwegian lemmings and voles) in our study areas, while in 2012 rodent abundances declined sharply. Values have been obtained after lipid extraction - Analyses were made at the Stable Isotope Laboratory of Environment Canada, Saskatoon, Canada. See also the supplementary files of Ruffino et al. 2015 for further details on how the stable isotopic analyses were conducted
Spatial variation in the strength of trophic cascades in arctic tundra has been related to flows ... more Spatial variation in the strength of trophic cascades in arctic tundra has been related to flows of subsidies across ecosystem boundaries. Here, we ask whether the input of marine subsidies in tundra systems would cause spatial variation in the strength of rodent-plant interactions between coastal areas, where predators have access to marine-derived resources, and non-subsidized inland areas of northern Fennoscandia. We present a detailed evaluation of predator-rodent-vegetation interactions along a coast-inland gradient, during the 2011 rodent outbreak and the two following decline years, by using direct assessments of rodent impacts and tracing of marine-derived nutrients in the food web. Our results revealed that the main rodent predator during summer, the long-tailed jaeger Stercorarius longicaudus, did not benefit from marine resources while breeding (relative dietary proportion in chicks’ diet = 0-3%). Contrary to this pattern, parasitic jaegers S. parasiticus, bred exclusively near the coast and preyed effectively on both marine resources (41% of chicks’ diet) and rodents (12%). Mammalian predators also showed a higher activity during winter near the coast. Despite overall higher predator numbers, no evidence was found for lower rodent population growth rates during the three monitoring summers and for weaker rodent grazing impacts in the coastal area. Instead, we documented pronounced damages caused by lemmings and voles on bryophytes and vascular plants, especially dwarf shrubs (e.g., Vaccinum myrtillus) all along the coast-inland gradient. Taken together, our results did not support the hypothesis that marine subsidies would trigger a trophic cascade in coastal tundra areas of northern Fennoscandia during a major rodent outbreak, probably due to a low diversity of marine-subsidized predators in the region. Comparative observational and experimental studies at large spatial scales in various arctic regions are absolutely necessary for a better understanding of factors causing regional variations in the functioning of arctic food webs
Long-term studies of cyclic rodent populations have contributed fundamentally to the development ... more Long-term studies of cyclic rodent populations have contributed fundamentally to the development of population ecology. Previous research has shown macroecological patterns of population dynamics in relation to latitude, but without disentangling the role of underlying ecological and climate drivers. We collected 26 rodent time-series from the tundra biome and assessed how population dynamics characteristics of the most prevalent species varied with latitude and environmental variables. While we could not find a relationship between latitude and population cycle peak interval, other characteristics of population dynamics had latitudinal patterns. The environmental predictor variables provided insight into causes of these patterns, as i) increased proportion of optimal habitat in the landscape led to higher population cycle amplitudes in all species and ii) mid-winter climate variability had negative impacts on cycle amplitude in Norwegian lemmings and grey-sided voles. These results...
1. Large herbivores can control plant community composition and, under certain conditions, even i... more 1. Large herbivores can control plant community composition and, under certain conditions, even induce vegetation shifts to alternative ecosystem states. As different plant assemblages maintain contrasting carbon (C) cycling patterns, herbivores have the potential to alter C sequestration at regional scales. Their influence is of particular interest in the Arctic tundra, where a large share of the world’s soil C reservoir is stored. 2. We analysed how grazing mammals influence tundra vegetation and how grazer-induced vegetation shifts affect tundra C stocks, by resampling two sites located along pasture rotation fences in northern Norway. These fences have separated lightly grazed areas from heavily grazed areas (in close proximity to the fences) and moderately grazed areas (further away from the fences) for the past 50 years. 14 years earlier, the lightly and moderately grazed areas were dominated by dwarf shrubs, whereas heavy grazing had promoted the establishment of graminoid-dominated vegetation. Since then, both reindeer densities and temperatures have increased, and more time has passed for transient dynamics to be expressed. We expected that the vegetation and C stocks would have changed under all grazing intensities, but not necessarily in the same way. 3. At the site where relative reindeer numbers and trampling intensity had increased the most, graminoid-dominated vegetation was now also found in the moderately grazed area. At the other site, the dominant vegetation types under all grazing intensities were the same as 14 years earlier. 4. We show that the heavily grazed, graminoid-dominated, areas stored less C aboveground than the lightly grazed, shrub-dominated, areas. Yet, the belowground consequences of grazing-induced grassification varied between the sites: Grazing did not alter organic soil C stocks at the site where both evergreen and deciduous shrubs were abundant in the lightly grazed area, whereas heavy grazing increased organic soil C stocks at the site where the deciduous shrub Betula nana was dominant. 5. Our results indicate that despite the negative impacts of grazers on aboveground C storage, their impact on belowground C may even be positive. We suggest that the site-specific responses of organic soil C stocks to grazing could be explained by the differences in vegetation under light grazing. This would imply that the replacement of deciduous shrubs by graminoids, as a consequence of grazing, could be beneficial for C sequestration in tundra soils
Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However... more Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However, herbivores can also influence the abundance of shrubs in arctic ecosystems. We addressed these alternative explanations by following the changes in plant community composition during the last 10 years in permanent plots inside and outside exclosures with different mesh sizes that exclude either only reindeer or all mammalian herbivores including voles and lemmings. The exclosures were replicated at three forest and tundra sites at four different locations along a climatic gradient (oceanic to continental) in northern Fennoscandia. Since the last 10 years have been exceptionally warm, we could study how warming has influenced the vegetation in different grazing treatments. Our results show that the abundance of the dominant shrub, Betula nana, has increased during the last decade, but that the increase was more pronounced when herbivores were excluded. Reindeer have the largest effect on shrubs in tundra, while voles and lemmings have a larger effect in the forest. The positive relationship between annual mean temperature and shrub growth in the absence of herbivores and the lack of relationships in grazed controls is another indication that shrub abundance is controlled by an interaction between herbivores and climate. In addition to their effects on taller shrubs (> 0.3 m), reindeer reduced the abundance of lichens, whereas microtine rodents reduced the abundance of dwarf shrubs (< 0.3 m) and mosses. In contrast to short-term responses, competitive interactions between dwarf shrubs and lichens were evident in the long term. These results show that herbivores have to be considered in order to understand how a changing climate will influence tundra ecosystems.
Our transdisciplinary research tackles the interaction between the ecological phenomenon of topdo... more Our transdisciplinary research tackles the interaction between the ecological phenomenon of topdown impacts in food webs and climate–vegetation interactions in a changing climate and integrates this perspective with the reindeer husbandry and the Sámi culture dependent on it1. The Arctic region will warm more rapidly than the global mean, and mean warming over land will be larger than over the ocean. These physical changes will influence the northern ecosystems. Potential impacts include the transformation of arctic-alpine tundra to forest or dense scrubland with global scale climate consequences due to decreasing albedo. As people and nature are closely coupled in a social-ecological system (SES), change in one element may trigger consequences in the other. Climate change will affect both the elements and the way they interact with each other. Sometimes administrative and ecological processes do not correspond (Figure 1): national and international management priorities may conflic...
Challenge or an Opportunity for Reindeer Herding? Jukka Käyhkö, Tim Horstkotte, Sonja Kivinen, Ja... more Challenge or an Opportunity for Reindeer Herding? Jukka Käyhkö, Tim Horstkotte, Sonja Kivinen, Jarmo Vehmas, Lauri Oksanen, Bruce C. Forbes, Bernt Johansen, Jane Uhd Jepsen, Annamari Markkola, Jouni Pulliainen, Johan Olofsson, Tarja Oksanen, Tove Aagnes Utsi, Erkki Korpimäki, Cecile Menard, Lars Ericson and Nordic Centre of Excellence 'Tundra', (1)University of Turku, Turku, Finland, (2)University of Lapland, Rovaniemi, Finland, (3)Norut Northern Research Institute, Tromsø, Norway, (4)Norwegian Institute for Nature Research (NINA), Tromsø, Norway, (5)University of Oulu, Oulu, Finland, (6)Finnish Meteorological Institute, Helsinki, Finland, (7)Umeå University, Umeå, Sweden, (8)University of Tromsø, Tromsø, Norway The Arctic region will warm more rapidly than the global mean, influencing dramatically the northern ecosystems. Simultaneously, our societies transform towards urbanized, highly educated, service-based culture, where a decreasing population will gain its livelihood ...
Effects of spatial isolation, habitat quality, and supplemental food for population dynamics of t... more Effects of spatial isolation, habitat quality, and supplemental food for population dynamics of the grey-sided vole, Clethrionomys rufocanus
Stable isotope values of long-tailed and parasitic jaegers' chick feathers in nothern Fennosc... more Stable isotope values of long-tailed and parasitic jaegers' chick feathers in nothern Fennoscandian tundra. Values are arranged by year and study area. There were three study areas, scattered along a coast (Altafjord) - inland (highland tundra plateau of Joatka Reserch Area) gradient (see Figure 1 in Ruffino et al. 2015 in Ecography for details of study areas). Year 2011 was a rodent outbreak year (both Norwegian lemmings and voles) in our study areas, while in 2012 rodent abundances declined sharply. Values have been obtained after lipid extraction - Analyses were made at the Stable Isotope Laboratory of Environment Canada, Saskatoon, Canada. See also the supplementary files of Ruffino et al. 2015 for further details on how the stable isotopic analyses were conducted
Spatial variation in the strength of trophic cascades in arctic tundra has been related to flows ... more Spatial variation in the strength of trophic cascades in arctic tundra has been related to flows of subsidies across ecosystem boundaries. Here, we ask whether the input of marine subsidies in tundra systems would cause spatial variation in the strength of rodent-plant interactions between coastal areas, where predators have access to marine-derived resources, and non-subsidized inland areas of northern Fennoscandia. We present a detailed evaluation of predator-rodent-vegetation interactions along a coast-inland gradient, during the 2011 rodent outbreak and the two following decline years, by using direct assessments of rodent impacts and tracing of marine-derived nutrients in the food web. Our results revealed that the main rodent predator during summer, the long-tailed jaeger Stercorarius longicaudus, did not benefit from marine resources while breeding (relative dietary proportion in chicks’ diet = 0-3%). Contrary to this pattern, parasitic jaegers S. parasiticus, bred exclusively near the coast and preyed effectively on both marine resources (41% of chicks’ diet) and rodents (12%). Mammalian predators also showed a higher activity during winter near the coast. Despite overall higher predator numbers, no evidence was found for lower rodent population growth rates during the three monitoring summers and for weaker rodent grazing impacts in the coastal area. Instead, we documented pronounced damages caused by lemmings and voles on bryophytes and vascular plants, especially dwarf shrubs (e.g., Vaccinum myrtillus) all along the coast-inland gradient. Taken together, our results did not support the hypothesis that marine subsidies would trigger a trophic cascade in coastal tundra areas of northern Fennoscandia during a major rodent outbreak, probably due to a low diversity of marine-subsidized predators in the region. Comparative observational and experimental studies at large spatial scales in various arctic regions are absolutely necessary for a better understanding of factors causing regional variations in the functioning of arctic food webs
Long-term studies of cyclic rodent populations have contributed fundamentally to the development ... more Long-term studies of cyclic rodent populations have contributed fundamentally to the development of population ecology. Previous research has shown macroecological patterns of population dynamics in relation to latitude, but without disentangling the role of underlying ecological and climate drivers. We collected 26 rodent time-series from the tundra biome and assessed how population dynamics characteristics of the most prevalent species varied with latitude and environmental variables. While we could not find a relationship between latitude and population cycle peak interval, other characteristics of population dynamics had latitudinal patterns. The environmental predictor variables provided insight into causes of these patterns, as i) increased proportion of optimal habitat in the landscape led to higher population cycle amplitudes in all species and ii) mid-winter climate variability had negative impacts on cycle amplitude in Norwegian lemmings and grey-sided voles. These results...
1. Large herbivores can control plant community composition and, under certain conditions, even i... more 1. Large herbivores can control plant community composition and, under certain conditions, even induce vegetation shifts to alternative ecosystem states. As different plant assemblages maintain contrasting carbon (C) cycling patterns, herbivores have the potential to alter C sequestration at regional scales. Their influence is of particular interest in the Arctic tundra, where a large share of the world’s soil C reservoir is stored. 2. We analysed how grazing mammals influence tundra vegetation and how grazer-induced vegetation shifts affect tundra C stocks, by resampling two sites located along pasture rotation fences in northern Norway. These fences have separated lightly grazed areas from heavily grazed areas (in close proximity to the fences) and moderately grazed areas (further away from the fences) for the past 50 years. 14 years earlier, the lightly and moderately grazed areas were dominated by dwarf shrubs, whereas heavy grazing had promoted the establishment of graminoid-dominated vegetation. Since then, both reindeer densities and temperatures have increased, and more time has passed for transient dynamics to be expressed. We expected that the vegetation and C stocks would have changed under all grazing intensities, but not necessarily in the same way. 3. At the site where relative reindeer numbers and trampling intensity had increased the most, graminoid-dominated vegetation was now also found in the moderately grazed area. At the other site, the dominant vegetation types under all grazing intensities were the same as 14 years earlier. 4. We show that the heavily grazed, graminoid-dominated, areas stored less C aboveground than the lightly grazed, shrub-dominated, areas. Yet, the belowground consequences of grazing-induced grassification varied between the sites: Grazing did not alter organic soil C stocks at the site where both evergreen and deciduous shrubs were abundant in the lightly grazed area, whereas heavy grazing increased organic soil C stocks at the site where the deciduous shrub Betula nana was dominant. 5. Our results indicate that despite the negative impacts of grazers on aboveground C storage, their impact on belowground C may even be positive. We suggest that the site-specific responses of organic soil C stocks to grazing could be explained by the differences in vegetation under light grazing. This would imply that the replacement of deciduous shrubs by graminoids, as a consequence of grazing, could be beneficial for C sequestration in tundra soils
Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However... more Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However, herbivores can also influence the abundance of shrubs in arctic ecosystems. We addressed these alternative explanations by following the changes in plant community composition during the last 10 years in permanent plots inside and outside exclosures with different mesh sizes that exclude either only reindeer or all mammalian herbivores including voles and lemmings. The exclosures were replicated at three forest and tundra sites at four different locations along a climatic gradient (oceanic to continental) in northern Fennoscandia. Since the last 10 years have been exceptionally warm, we could study how warming has influenced the vegetation in different grazing treatments. Our results show that the abundance of the dominant shrub, Betula nana, has increased during the last decade, but that the increase was more pronounced when herbivores were excluded. Reindeer have the largest effect on shrubs in tundra, while voles and lemmings have a larger effect in the forest. The positive relationship between annual mean temperature and shrub growth in the absence of herbivores and the lack of relationships in grazed controls is another indication that shrub abundance is controlled by an interaction between herbivores and climate. In addition to their effects on taller shrubs (> 0.3 m), reindeer reduced the abundance of lichens, whereas microtine rodents reduced the abundance of dwarf shrubs (< 0.3 m) and mosses. In contrast to short-term responses, competitive interactions between dwarf shrubs and lichens were evident in the long term. These results show that herbivores have to be considered in order to understand how a changing climate will influence tundra ecosystems.
Our transdisciplinary research tackles the interaction between the ecological phenomenon of topdo... more Our transdisciplinary research tackles the interaction between the ecological phenomenon of topdown impacts in food webs and climate–vegetation interactions in a changing climate and integrates this perspective with the reindeer husbandry and the Sámi culture dependent on it1. The Arctic region will warm more rapidly than the global mean, and mean warming over land will be larger than over the ocean. These physical changes will influence the northern ecosystems. Potential impacts include the transformation of arctic-alpine tundra to forest or dense scrubland with global scale climate consequences due to decreasing albedo. As people and nature are closely coupled in a social-ecological system (SES), change in one element may trigger consequences in the other. Climate change will affect both the elements and the way they interact with each other. Sometimes administrative and ecological processes do not correspond (Figure 1): national and international management priorities may conflic...
Challenge or an Opportunity for Reindeer Herding? Jukka Käyhkö, Tim Horstkotte, Sonja Kivinen, Ja... more Challenge or an Opportunity for Reindeer Herding? Jukka Käyhkö, Tim Horstkotte, Sonja Kivinen, Jarmo Vehmas, Lauri Oksanen, Bruce C. Forbes, Bernt Johansen, Jane Uhd Jepsen, Annamari Markkola, Jouni Pulliainen, Johan Olofsson, Tarja Oksanen, Tove Aagnes Utsi, Erkki Korpimäki, Cecile Menard, Lars Ericson and Nordic Centre of Excellence 'Tundra', (1)University of Turku, Turku, Finland, (2)University of Lapland, Rovaniemi, Finland, (3)Norut Northern Research Institute, Tromsø, Norway, (4)Norwegian Institute for Nature Research (NINA), Tromsø, Norway, (5)University of Oulu, Oulu, Finland, (6)Finnish Meteorological Institute, Helsinki, Finland, (7)Umeå University, Umeå, Sweden, (8)University of Tromsø, Tromsø, Norway The Arctic region will warm more rapidly than the global mean, influencing dramatically the northern ecosystems. Simultaneously, our societies transform towards urbanized, highly educated, service-based culture, where a decreasing population will gain its livelihood ...
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