Spatial dynamics of Microtus vole populations in continuous and fragmented agricultural landscapes

Abstract

Small mammal populations often exhibit large-scale spatial synchrony, which is purportedly caused by stochastic weather-related environmental perturbations, predation or dispersal. To elucidate the relative synchronizing effects of environmental perturbations from those of dispersal movements of small mammalian prey or their predators, we investigated the spatial dynamics of Microtus vole populations in two differently structured landscapes which experience similar patterns of weather and climatic conditions. Vole and predator abundances were monitored for three years on 28 agricultural field sites arranged into two 120-km-long transect lines in western Finland. Sites on one transect were interconnected by continuous agricultural farmland (continuous landscape), while sites on the other were isolated from one another to a varying degree by mainly forests (fragmented landscape). Vole populations exhibited large-scale (>120 km) spatial synchrony in fluctuations, which did not differ in degree between the landscapes or decline with increasing distance between trapping sites. However, spatial variation in vole population growth rates was higher in the fragmented than in the continuous landscape. Although vole-eating predators were more numerous in the continuous agricultural landscape than in the fragmented, our results suggest that predators do not exert a great influence on the degree of spatial synchrony of vole population fluctuations, but they may contribute to bringing out-of-phase prey patches towards a regional density level. The spatial dynamics of vole populations were similar in both fragmented and continuous landscapes despite inter-landscape differences in both predator abundance and possibilities of vole dispersal. This implies that the primary source of synchronization lies in a common weather-related environment.

How Predation and Landscape Fragmentation Affect Vole Population Dynamics

“…To an extent this concurs with previous interpretations, which have usually considered predation the main factor driving the population dynamics of Fennoscandian microtines [1], [3], [22], [24]. In the past fragmentation has received less attention (but see [33], [34], [69]). However our results suggest that low fragmentation levels as well as the presence of specialist predators are necessary for the occurrence of population cycles.…”

“…Consequently, both direct and delayed density dependence may be affected by habitat fragmentation. This has received attention in some studies [33], [34]. A spatially diverse landscape makes it more difficult for a predator to control its environment and potentially decreases the degree of synchronisation between patches, by allowing prey outbreaks to remain undiscovered by predators [35]–[37].…”

Dissecting geographic variation in population synchrony using the common vole in central Europe as a test bed

“…2001; Huitu et al. 2008). In the Czech Republic, we observed a moderate decay with geographical distance, where the regional level of synchrony was attained at a separation of around 150 km.…”

The impact of climate and cyclic food abundance on the timing of breeding and brood size in four boreal owl species

“…Broods that were situated within a 50-km radius around the trapping sites were used for model Wtting (data was annually pooled and locations with less than three broods were omitted). The spatial scale of the synchrony of vole dynamics exceeds this 50 km (Sundell et al 2004;Huitu et al 2008). By using data of the nearest weather station (n = 70 stations) of each brood, we calculated the mean monthly temperature both before and during laying (February and March; March and April in pygmy owl) and at the time of brood rearing (May; June in pygmy owl).…”