Population fluctuations and spatial synchrony in an arboreal rodent

Abstract

Climatic conditions, trophic links between species and dispersal may induce spatial synchrony in population fluctuations. Spatial synchrony increases the extinction risk of populations and, thus, it is important to understand how synchrony-inducing mechanisms affect populations already threatened by habitat loss and climate change. For many species, it is unclear how population fluctuations vary over time and space, and what factors potentially drive this variation. In this study, we focus on factors determining population fluctuations and spatial synchrony in the Siberian flying squirrel, Pteromys volans, using long-term monitoring data from 16 Finnish populations located 2–400 km apart. We found an indication of synchronous population dynamics on a large scale in flying squirrels. However, the synchrony was not found to be clearly related to distance between study sites because the populations seemed to be strongly affected by small-scale local factors. The regularity of population fluctuations varied over time. The fluctuations were linked to changes in winter precipitation, which has previously been linked to the reproductive success of flying squirrels. Food abundance (tree mast) and predator abundance were not related to population fluctuations in this study. We conclude that spatial synchrony was not unequivocally related to distance in flying squirrels, as has been observed in earlier studies for more abundant rodent species. Our study also emphasises the role of climate in population fluctuations and the synchrony of the species.Electronic supplementary materialThe online version of this article (10.1007/s00442-019-04537-3) contains supplementary material, which is available to authorized users.

Weather and biotic interactions as determinants of seasonal shifts in abundance measured through nest-box occupancy in the Siberian flying squirrel

“…However, these previously observed correlations between weather and the species might result from the indirect effects of weather on the food resources of flying squirrels, not the direct effect of weather on individuals 25,26 . Accordingly, in this study summer temperature was positively linked to apparent overwinter survival, which may be related to the fact that warm summers predict good catkin mast for the following winter 26 . This is possible, because our winter food indexes measured the variation in catkin mast at very coarse level.…”

“…For example, the winter weather had little or no direct effect on apparent overwinter survival in flying squirrels. In earlier studies on flying squirrels, increased winter precipitation increased the reproductive output 25,26 , and there is an optimum winter temperature that determines regional occurrence patterns of flying squirrels ( 27 , see also 33 ). However, these previously observed correlations between weather and the species might result from the indirect effects of weather on the food resources of flying squirrels, not the direct effect of weather on individuals 25,26 .…”

“…In earlier studies on flying squirrels, increased winter precipitation increased the reproductive output 25,26 , and there is an optimum winter temperature that determines regional occurrence patterns of flying squirrels ( 27 , see also 33 ). However, these previously observed correlations between weather and the species might result from the indirect effects of weather on the food resources of flying squirrels, not the direct effect of weather on individuals 25,26 . Accordingly, in this study summer temperature was positively linked to apparent overwinter survival, which may be related to the fact that warm summers predict good catkin mast for the following winter 26 .…”

“…The winter food availability (catkin mast of deciduous trees) determines reproductive success in flying squirrels by advancing spring reproduction and allowing production of second litters in summer 22,25 . Increased precipitation in winter is also positively correlated with both the reproductive success 25 and the population growth rate 26 , possibly due to increased spring foliage growth in moist conditions. The nocturnal Ural owl (Strix uralensis) is the main predator of the night-active flying squirrel, and they have been shown to detrimentally impact the occurrence of flying squirrels in the landscape 23,27 .…”

“…For summer survival model (ii), presence of the Ural owl 23 should decrease and moist summer weather might increase oversummer survival of adults, because drought (interaction of warm weather and little precipitation) likely has adverse effects on food availability for flying squirrels in summer. Warm summer temperature may be advantageous during summer, but it also increase catkin availability in next winter 26,30 . For winter survival model (iii), we predict that warm winter temperature and high birch catkin availability increase overwinter survival.…”