Bilberry seed production explains spatiotemporal synchronicity in bank vole population fluctuations in Norway

Abstract

Population fluctuations of small rodents are often synchronized over larger areas (>100 km) than what could be explained by dispersal, suggesting that the synchronizing factor is weather‐related and possibly mediated through changes in food quality. Because bank vole (Myodes glareolus) populations usually peak 1 year after peaks in reproduction of the staple winter food plant bilberry (Vaccinium myrtillus), we tested for a possible link between food and spatial synchrony by comparing the synchrony in bank vole population indices and bilberry seed production indices between three study areas across about 20,000 km2 in South Norway during a four decade period (1979–2019). There were subperiods of spatial synchrony and asynchrony between the study areas in the fluctuations of bank vole numbers and bilberry seed production, with the latter part of the study period displaying more pronounced synchrony than the first and middle part. However, with a few marked exceptions, when vole fluctuations were spatially out of phase across study areas so was bilberry seed production. Thus, we conclude that bilberry seed production to a large extent explained the spatiotemporal synchronicity in bank vole population fluctuations. Although bilberry seed production seems to be a causal driver of vole fluctuations, it remains to be seen to what extent the chemical composition of bilberry plants influences vole performance. Finally, certain weather factors may still influence voles directly, or indirectly by triggering bilberry seed production.

Hawk owl irruptions: spatial and temporal variation in rodent abundance drive push and pull dynamics

“…One possible reason may be the return of more regular rodent cycles with larger peaks from ca. 2005–2010 after a period of dampened cycles starting around 1990 (Brommer et al 2010 ; Wegge and Rolstad 2018 ; Selås et al 2021 ; Sonerud 2022 ).…”

“…If conditions are predictably negatively correlated between source and destination areas, irruptive birds may be drawn to areas with better conditions than where they originate. Synchrony in masting years of trees and peak rodent years may range over hundreds or even thousands of kilometres (Koenig and Knops 1998 ; Sundell et al 2004 ; Gallego Zamorano et al 2018 ; Fay et al 2020 ; Selås et al 2021 ). Irruptive birds may therefore need to travel long distances to find areas with higher food availability than where they came from, i.e.…”

Climate influence on plant–pollinator interactions in the keystone species Vaccinium myrtillus

“…V . myrtillus is a keystone species in boreal and low‐alpine areas as it is highly abundant and both the fleshy fruits and vegetative parts provide an important food source for animals (Hegland et al, 2010 and references therein, Selås et al, 2021 ). This early‐flowering, deciduous, clonal dwarf‐shrub is partly selfing, and its main pollinators are bumblebees, bees, and wasps (Ritchie, 1956 ), of which bumblebees are dominant in alpine habitats.…”

Annual variation in breeding success in boreal forest grouse: Four decades of monitoring reveals bottom‐up drivers to be more important than predation

“…After correcting for ramet coverage, berry abundance was indexed as numbers per 1 m 2 of bilberry plants. We also had access to bilberry fruit indices in the study area for the whole period of 41 years, based on newspaper records (Selås et al, 2021). Parallel analyses for the final 17 years, using either our field measurements or the newspaper index, gave very similar results (Appendix S1: Chick food)—we therefore used the latter here.…”

“…Likewise, while the prediction of the Plant Stress sub-hypothesis that previous year's bilberry production should be related to breeding success was clearly verified, path analysis showed that this was due in part to an indirect relationship via voles. It may have been that high bilberry fruit crops increased the overwinter survival of bank voles (Selås et al, 2021), which subsist mainly on bilberry shoots during winter (Hansson, 1983), thereby buffering predation on nests and chicks via APH.…”