Reindeer green‐wave surfing constrained by predators

• Published in: Ecosphere
• Main Authors: Rivrud, Inger Maren, Sivertsen, Therese Ramberg, Mysterud, Atle, Åhman, Birgitta, Støen, Ole‐Gunnar, Skarin, Anna
• Other Authors: Centre for Advanced Study, Oslo
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: Rangifer tarandus; Ursus arctos
• Online Access: http://dx.doi.org/10.1002/ecs2.2210; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fecs2.2210; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.2210; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ecs2.2210; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.2210

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.