Patch occupancy, population density and dynamics in a fragmented red squirrelSciurusvulgarispopulation

Abstract

We studied population dynamics of red squirrels in a group of small forest fragments, that cover only 6.5% of the total study area (4664 ha) and where distances to the nearest source population were up to 2.2 km. We tested effects of patch size, quality and isolation and supplementary feeding on patch occupation during 1995–99. Larger patches and patches with supplementary feeding had a higher probability of being occupied. No patch <3.5 ha was ever occupied. No effects of isolation were found, suggesting that the forest habitat in the study area is not sufficiently fragmented to influence red squirrel distribution across patches. For medium sized patches (3.7–21 ha), that were occupied some years, there was an increase in patch occupation over the years, even though overall population size tended to decrease. These patches had a high turnover, especially of males. Patches in which the squirrel population went extinct were recolonized within a year. For patches that were at least some years occupied, squirrel density depended on patch quality only. No effects of patch size, isolation and winter temperature on population density were found. These data suggest that in our study area habitat fragmentation has no effect on local squirrel density and that the random sample hypothesis explains the distribution pattern across patches.

Responses of small mammals to clear-cutting in temperate and boreal forests of Europe: a meta-analysis and review

“…Moderately intense forest harvest is not considered to be a threat because populations of red squirrels often remain viable in fragmented landscapes (Andrén and Delin 1994;Delin and Andrén 1999;Verbeylen et al 2003). Red squirrels are able to travel relatively long distances on open ground, thus are not as strongly affected by fragmentation as are other arboreal species (Wauters et al 2010;Mortelliti et al 2011).…”

The response of tree squirrels to fragmentation: a review and synthesis

“…1), a strong negative relationship was detected for S. carolinensis (F 1,9 = 70.38, P < 0.0001, R 2 = 0.898) and S. niger (F 1,13 = 127.97, P < 0.0001, R 2 = 0.914), a moderately negative relationship was found for T. hudsonicus (F 1,9 = 3.21, P = 0.111, R 2 = 0.286), and no relationship for S. vulgaris (F 1,21 = 1.22, P = 0.281, R 2 = 0.0525). Sciurus vulgaris was rarely found in small woodlots and appears to require continuous forests or high levels of food supplementation or habitat connectivity to persist in fragmentated environs (Celada et al, 1994;Magris & Gurnell, 2002;Verbeylen et al, 2003).…”

“…Consequences of fragmentation for abiotic and biotic components of ecosystems are varied (for reviews, see Yahner, 1988;Tscharntke et al, 2002). Most major ecosystems have been fragmented through anthropogenic activities in the last 200 years; however, forested ecosystems have undergone excessively high levels of fragmentation (Nixon, Havera & Hansen, 1978;Middleton & Merriam, 1983;Harris, 1984;Nixon & Hansen, 1987;Sheperd & Swihart, 1995;Verbeylen, De Bruyn & Matthysen, 2003). Genetic variation is often, but not always, lost with habitat fragmentation (Avise, Neigel & Arnold, 1984;Wauters et al, 1994b;Frankham, 1997;Eldridge et al, 1999;Small, Stone & Cook, 2003).…”

A grey future for Europe: Sciurus carolinensis is replacing native red squirrels in Italy

“…Red squirrel presence in fragmented landscapes may be negatively influenced by the increase in forest fragmentation or by a source-sink dynamics with the disappearance from the smaller and isolated patches (Celada et al 1994;Verbeylen et al 2003). However, red squirrels have a high probability (>90%) to persist in forest patches > 10 ha (Rodríguez and Andrén 1999), and both sexes can easily disperse between forest fragments, with dispersal distances of up to 4.1 km (Wauters et al , 2011.…”