Abstract:
Spatially synchronous fluctuations of animal populations have profound
ecological consequences, especially in northern latitudes. Spatially coupled
fluctuations are often seen in small rodent populations, albeit with local and
regional variations. While both resource limitation and predation influence
rodent dynamics, their relative importance for generating spatial variation is less
clear, particularly during winter. In this study, we quantify spatial variation in
winter abundance of the Norwegian lemming (Lemmus lemmus) across three
ecologically connected mountain areas in northern Sweden and evaluate
whether the relative strength of bottom-up and top-down regulation influences
such variation. Our data included observations of predated and nonpredated
winter nests as well as environmental characteristics of nest locations and nest
predation. While the direction of annual changes in lemming nest abundance
was perfectly synchronized among the three areas, there were differences in nest
abundance, potentially caused by contrasting amplitudes of temporal fluctuations
in lemming winter populations. Mustelid predation was positively associated
with decreasing lemming populations but did not differ in occurrence among the
three areas. Lemming nests were predominantly observed in meadows, whereas areas prone to flooding and close to the tree line were underrepresented. Mustelid
predation was most common close to the tree line, but not associated with
geomorphological characteristics related to snow depth. We suggest that the
observed differences in lemming winter abundances were caused by variations in
the relative strength of bottom-up and top-down regulation in the threemountain
areas. We encourage further studies evaluating how the relative strength of different
processes influence local population regulation, and how such processes influence
spatial variation in animal population dynamics at different spatial scales.
