Measures for phenology and range shifts
The start of the growing season in Europe, including Finland, has advanced over the past decades (Menzel & Fabian 1999; Helama et al. 2020), and suitable conditions for seasonally recurring life-history events now often occur earlier than before. To investigate the strategy of adjusting phenology in situ, we focus on the phenological timing of adult flight period, with the assumption of advanced flight period mirroring an adaptive response.
The area of Finland extends over a ca. 1100 km latitudinal gradient across boreal and subarctic climates and is topographically relatively homogenous. The climatic isoclines roughly follow latitudes (Ahtiet al. 1968), but they are currently shifting northwards due to climate change (Jylhä et al. 2010). Species range shifts as a response to climate change should thus be observable in Finland through colonization of new suitable areas north of their previous distribution (cf. Pöyry et al. 2009). To study the strategy of colonizing new suitable areas, we focus on measuring shifts in the northern range boundary (NRB).