Landscape effects on temporal and spatial properties of vole population fluctuations

Abstract

Populations of northern small rodents have previously been observed to fluctuate in spatial synchrony over distances ranging from tens to hundreds of kilometers between sites. It has been suggested that this phenomenon is caused by common environmental perturbations, mobile predators or dispersal movements. However, very little focus has been given to how the physical properties of the geographic area over which synchrony occurs, such as landscape composition and climate, affect spatial population dynamics. This study reports on the spatial and temporal properties of vole population fluctuations in two areas of western Finland: one composed of large interconnected areas of agricultural farmland interspersed by forests and the other highly dominated by forest areas, containing more isolated patches of agricultural land. Furthermore, the more agricultural area exhibits somewhat milder winters with less snow than the forested area. We found the amplitude of vole cycles to be essentially the same in the two areas, suggesting that the relative amount of predation on small rodents by generalist versus specialist predators is similar in both areas. No seasonal differences in the timing of synchronization were observable for Microtus voles, whereas bank vole populations in field habitats appeared to become synchronized primarily during winter. Microtus populations in field habitats exhibited smaller spatial variation and a higher degree of synchrony in the more continuous agricultural landscape than in the forest-dominated landscape. We suggest that this inter-areal difference is due to differences in the degree of inter-patch connectivity, with predators and dispersal acting as the primary synchronizing agents. Bank vole populations in field habitats were more synchronized within the forest-dominated landscape, most likely reflecting the suitability of the inter-patch matrix and the possibility of dispersal. Our study clearly indicates that landscape composition needs to be taken into account when describing the spatial properties of small rodent population dynamics.

Competitive interactions among raptors in boreal forests

“…Reif et al 2001;Huitu et al 2003). Annual changes in vole numbers were analogous to changes in the fledgling production of common buzzards in the same study area during the same study period (Reif et al, unpublished data).…”

How do variations in seasonality affect population cycles?

“…The north-south gradient in Fennoscandia corresponds to a curve in this parameter plane. There is currently insufficient data to enable a detailed formulation of this curve, but it is likely to be nonlinear, especially when factors such as landscape fragmentation [22,35,36] are taken into account. Our results suggest that more information on the form of this nonlinear curve would be a key step in understanding the complexities in vole dynamics, such as the sudden change from annual to multi-year cycles that occurs in mid-Fennoscandia [7].…”

Habitat requirements of weasels Mustela nivalis constrain their impact on prey populations in complex ecosystems of the temperate zone

“…Theoretical models and some empirical data predict that sub-optimal habitats can provide refuges from predation during the bottleneck phase of the vole cycle and inXuence population dynamics of rodents (Huitu et al 2003;Ylönen et al 2003). This idea is mainly supported by data from boreal ecosystems, where Weld voles, the main prey of weasels, can go extinct due to predation in optimal habitats, but survive in wet habitats, where weasel predation is lower .…”