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- Sivertsen, Therese, et al.
(författare)
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Reindeer green-wave surfing constrained by predators
- 2018
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Ingår i: Ecosphere. - : Wiley. - 2150-8925. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Migratory large herbivores in seasonal environments are known to follow the onset of new growth during spring, so-called green-wave surfing. This ensures prolonged access to forage with an optimal balance between forage quality and quantity. Many studies have focused on herbivores' ability to follow the spring flush, but without considering potential constraints to surfing the green wave. The presence of predators is likely to be such a limitation, which could force herbivores to deviate from the optimal movement patterns in terms of forage access. We compared how well 319 reindeer (Rangifer tarandus) from seven different populations followed the green-up at different population densities of brown bear (Ursus arctos). We found that reindeer at higher bear densities selected movement paths with lower access to high-quality forage and deviated more in time from following the peak of the green wave, thus missing out on valuable forage. In addition, reindeer generally moved faster at higher bear densities, but this pattern was more consistent in forest habitats. Our results indicate that reindeer are forced to deviate from following the spring flush and alter their movement pattern in areas with high bear densities, which may lead to reduced body condition for reindeer experiencing high predation risk. With the recent recolonization of large carnivores in northern ecosystems, it is critical to understand the direct and indirect effects of predators on large herbivores in order to assess effects on population dynamics and potentially cascading consequences on ecosystem function.
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| 4. |
- Sivertsen, Therese, et al.
(författare)
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Reindeer habitat selection under the risk of brown bear predation during calving season
- 2016
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Ingår i: Ecosphere. - : Wiley. - 2150-8925 .- 2150-8925. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- The depredation of semi-domesticated reindeer by large carnivores reflects an important human-wildlife conflict in Fennoscandia. Recent studies have revealed that brown bears (Ursus arctos) may kill substantial numbers of reindeer calves (Rangifer tarandus tarandus) in forest areas in Sweden. Several authors have suggested that predation risk is an important driver of habitat selection in wild Rangifer populations where predation is a limiting factor, but little is known about these mechanisms in semi-domesticated populations. We examined the habitat selection of female reindeer in relation to spatial and temporal variations in brown bear predation risk on the reindeer calving grounds and evaluated the simultaneous responses of brown bears and reindeer to landscape characteristics. We used GPS data from 110 reindeer years (97 individuals) and 29 brown bear years (19 individuals), from two reindeer herding districts in the forest area of northern Sweden. Our results did not indicate that reindeer alter their behavior in response to spatiotemporal variation in brown bear predation risk, on the scale of the calving range. Instead, we suggest that spatiotemporal behavioral adjustments by brown bears were the main driver of prey-predator interactions in our study system. Contrasting responses by brown bears and reindeer to clear-cuts and young forest indicate that forestry can influence species interactions and possibly yield negative consequences for the reindeer herd. Even if clear-cuts may be beneficial in terms of calf survival, logging activity will eventually cause greater abundance of young regenerating forest, reducing available reindeer habitats and increasing habitat preferred by brown bears. Domestication may have made semi-domesticated reindeer in Fennoscandia less adapted to cope with predators. Areal restrictions, limiting the opportunity for dispersion and escape, possibly make the calves more susceptible to predation. Also, a generally higher population density in semi-domesticated herds compared to wild populations can make dispersion a less efficient strategy and the reindeer calves easier prey. Overall, the lack of ability of the reindeer females to reduce brown bear encounter risk on the scale of the calving range is probably an important reason for the high brown bear predation rates on reindeer calves documented in our study areas.
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- Sivertsen, Therese
(författare)
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The influence of natural and anthropogenic factors in Rangifer movements and habitat use
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rangifer tarandus (reindeer and caribou) is a circumpolar species inhabiting the Arctic and sub-arctic regions of Eurasia and North America. It is a key species in the northern hemisphere and has for centuries been a vital resource for many communities and indigenous peoples in the Arctic. In Fennoscandia most reindeer are semi-domesticated, while smaller herds of wild reindeer exist in mountainous areas in southern Norway and forested areas in eastern Finland. Reindeer herding forms a basis for the Sámi cultural heritage and is an essential economic income to many people within the Sámi society in Fennoscandia. In accordance with international agreements, there is a management goal in Norway and Sweden to ensure the livelihood of the Sámi people, including a sustainable reindeer husbandry, alongside with conservation of landscapes and biodiversity (Nilsson-Dahlström 2003). Although reindeer are domesticated they are freely ranged within the borders of the herding districts, and their behaviour and habitat selection are comparable to wild reindeer and caribou. Rangifer have developed in areas with high spatial and temporal heterogeneity in resource availability. Throughout the year the animals follow the seasonal changes in forage quantity and quality, and depend on access to large heterogeneous land areas to meet their energetic demands (Klein 1970). A constantly increasing infrastructure development has largely changed the terms for the reindeer and the reindeer husbandry in Fennoscandia. Further challenges are caused by the recent 20-30 years of growing predator populations, with a consequent need for management to find compromises between the conflicting interests of carnivore conservation and a sustainable reindeer husbandry. The main predators of semi-domesticated reindeer in Fennoscandia are the large carnivores: lynx (Lynx lynx), wolverine (Gulo gulo), brown bear (Ursus arctos), wolves (Canis lupus) and golden eagle (Aquila chrysaetos). Direct losses of reindeer to predation can be substantial (Danell 2011, Hobbs et al. 2012). However, the total effect of predation on herd productivity is still subject to debate. Also, we lack knowledge about behavioural interactions with predators and antipredator strategies in semi-domesticated reindeer. Anthropogenic activity and infrastructure development is threatening Rangifer in large parts of its range. Human development can cause habitat loss by direct cover of areas, 7 indirectly from avoidance effects or by making movements barriers. This can lead to important transport corridors being cut off, and loss of feeding grounds and critical habitats such as calving areas. Changes in foraging conditions do not only have immediate effects on the animal but also affect future performance and its progeny during several years ( Gaillard et al. 2000). The aim of the present review is to give an overview of the existing knowledge of Rangifer foraging and antipredator behaviour, and impact of human disturbance on Rangifer habitat use. As a theoretical framework I briefly summarize the main theories of foraging and antipredator behaviour in ecology. Finally I discuss the current and future challenges and knowledge gaps related to management of reindeer herding areas in Fennoscandia.
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| 7. |
- Stoen, Ole-Gunnar, et al.
(författare)
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Brown bear predation on semi-domesticated reindeer and depredation compensations
- 2022
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Ingår i: Global Ecology and Conservation. - : Elsevier BV. - 2351-9894. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- The recovery and conservation of large carnivores can negatively impact the economy of traditional pastoralist societies, including indigenous reindeer (Rangifer tarandus) herding communities. Quantifying the magnitude of predation on livestock is critical to evaluating governmental carnivore compensation schemes. We collaborated with two Sami herding communities in northern Sweden (2010-2012) to examine brown bear (Ursus arctos) predation patterns on semi-domesticated reindeer and quantify the economic impact of bear predation. Predation patterns were estimated by following 21 GPS proximity-collared bears and similar to 2500 transmitter-collared female reindeer during calving season. We calculated economic impact by multiplying the monetary value of reindeer by the expected number lost to bears. On average, bears killed 10.2 [8.6, 11.5] calves per bear, accounting for 39-62% of all calf mortality, while few adult reindeer were killed. Bear kill rates increased with time spent in the calving area, and varied widely by individual and reproductive status, e.g., females with cubs-of-the-year did not kill calves. Kill intervals increased over the parturition season, and were larger for sub-adults than adults. The mean reindeer calf predation rate was 16-27%, which resulted in an annual loss between similar to(sic)50,000 and similar to(sic)62,000 per herding group. Current compensation schemes for herding communities in Sweden are calculated as a fixed rate based on herding community land-area. The herding groups in our study were reimbursed for similar to 2% of realized monetary loss. Compensation schemes based on herding community area, rather than realized predation patterns, may be less effective at mitigating the economic impact of living with large carnivores.
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