The effect of landscape structure on dispersal distances of the Eurasian red squirrel

Abstract

Landscape structure can affect dispersal and gene flow in a species. In urban areas, buildings, roads, and small habitat patches make the landscape highly fragmented and can inhibit movement and affect dispersal behavior. Similarly, in rural forested areas, large open areas, such as fields, may act as barriers to movement. We studied how landscape structure affects natal dispersal distances of Eurasian red squirrels (Sciurus vulgaris) in an urban area and a rural area in Finland, by monitoring juvenile red squirrels with radio telemetry. We observed extremely long dispersal distances—up to 16 km—in the rural study area, but shorter distances—on average only half a kilometer—in the urban study area. The landscape structure affected the eventual dispersal paths; in the rural landscape, dispersers favored spruce dominated areas and avoided fields along their dispersal route, although they occasionally even crossed wide fields. In the urban landscape, squirrels preferred areas with deciduous or coniferous trees. The movement steps made by dispersers were longer in the more hostile landscape compared to forested areas. Despite these effects on movement path, the landscape structure only had a minor effect on straight line dispersal distances moved from the natal nest. In other words, individuals moved longer distances and were likely to circumvent barriers in their path, but this did not affect how far they settled from their natal home. This result indicates that, although landscape structure has obvious effects on movement, it still may have only a small effect on other aspects of the population, for example, gene flow.

Large-scale spatial synchrony in red squirrel populations driven by a bottom-up effect

“…The goshawk preys on red squirrels regularly (Penteriani 1997), and in some habitats, red squirrels are the most common prey item, especially in winter diet (Kenward et al 1981;Widén 1987), but red squirrel populations do not seem to be suppressed by the predation (Petty et al 2003). Dispersal distances of red squirrels in boreal forests are typically 2-4 km (Hämäläinen et al 2019).…”

Search strategies in rural and urban environment during natal dispersal of the red squirrel

“…The revisit behavior, however, varied between individuals as females revisited less than males and red squirrels with longer dispersal distance made less revisits than shortdistance dispersers. There is a major difference in dispersal distances between the two study areas, average distances with standard deviation being in Turku 431 ± 363 m and 3638 ± 3774 m in Kauhava (Hämäläinen et al 2019). But even though the study area was taken into account in the models, we found a significant difference in the amount of revisits between short-and long-distance dispersers.…”

“…At this age, red squirrels have not yet accomplished dispersal movements but move in close proximity of their birth place. Body mass at capture did not affect observed dispersal distances (Selonen et al 2018a; for more information on our data, see Fey et al 2016;Hämäläinen et al 2019). After collaring, individuals were followed with portable receiver (Biotrack) and Yagi antenna.…”

“…The cutoff value of 300 m was selected to correspond double the radius of the observed average home range size, being 7 ha (Hämäläinen et al 2018). The settlement site was determined to be the last area where the red squirrel was observed until the end of the tracking period (Hämäläinen et al 2018(Hämäläinen et al , 2019. After the settlement, the individual did not visit new sites and the movement distances between consecutive points were shortened.…”

“…In addition, urbanization modifies the landscape composition and alters the costs of moving in the landscape (Bonte et al 2012) and the quality of the habitat, for example, in the form of new resources, like artificial nest structures (Jokimäki et al 2017). Consequently, the dispersal behavior may differ between urban and rural landscapes (Hämäläinen et al 2019), which may also affect the search strategies of individuals in these habitats.…”