The causes and consequences of population declines of two boreal forest species : the case of the willow tit (<em>Parus montanus</em>) and the Siberian flying squirrel (<em>Pteromys volans</em>)

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>I used individual-based capture-mark-recapture data and genetic markers to gain understanding of the demographic and genetic processes operating in small and declining populations of two different species, the willow tit <em>Parus montanus</em> and the Siberian flying squirrel <em>Pteromys volans</em>. Both species have declined in Finland and the flying squirrel has been considered to be vulnerable. The willow tit study was conducted in northern Finland, near city of Oulu. The population size in the studied area has on average been stable during the past decade. Adult survival in the willow tit was high and fairly stable and was positively correlated with recruitment. Adult survival has been the most influential vital rate to the population growth rate. Local recruitment and immigration have high variation, inducing variation in the population growth rate. Female willow tits use extrapair copulations to maximise offspring heterozygosity. Heterozygous individuals are supposedly of higher quality than homozygous ones. I found weak negative association between individual homozygosity and recruitment probability. The flying squirrel populations have declined during the past ten years. Furthermore, adult survival has declined in one of the populations, most likely due to habitat loss and fragmentation that decrease the adult survival and limit dispersal. The flying squirrel populations were studied in western Finland. The flying squirrel densities in the studied areas are the highest in Finland and therefore these areas have been regarded as favourable for the flying squirrel. My results question this view. Microsatellite analyses strengthen the view of populations doing poorly, because the heterozygosities in all the populations and particularly in the most isolated one were rather low. High F_ST values indicate low dispersal even between adjacent populations. Following work should investigate the spatial variation in individual performance and the dispersal processes in these populations. For the flying squirrel it is vital to determine the size and quality of the patches that can support flying squirrels and the ones that apparently can not. Present estimates of survival and genetic diversity can be used to reconstruct a meaningful PVA and projections for these populations.</p></div>