Population trends of Finnish Lepidoptera during 1961-1996
DOI:
https://doi.org/10.33338/ef.83932Abstract
Based on a query and on a literature review, the population trends of Finnish Lepidoptera since Kaisila's (1962) thorough overview are analysed. Changes in the belt of three coastal biogeographical provinces (V-EK) show significant correlations with those in three inland provinces (St-ES). Furthermore, positive trends in these belts are reflected as new provincial finds north of them. The spatial synchrony is supposedly caused by spatially conelated climatic conditions. This is supported by evidence of synchronous trends in species grouped according to their overwintering stages (Marttila 1991, Bruun 1992). The increased migration rate, indicated by the new provincial finds, is probably a consequence of high population densities, and does not explain the synchrony itself. Kaisila's division into expansive and fluctuant species is considered to be a historical rather than a biological characterization. During the 19th century, the reporting of new lepidopteran species was delayed by about 50 years if they were night-active vs. day-active. The low numbers of observers and slow development of collecting methods have caused further analytical uncertainties. Some of Kaisila's expansive species may actually have been inhabitants of Finland for long periods of time. At present, drainage of peatlands and overgrowth of meadows are the most adverse environmental changes causing a decline of lepidopterans, particularly of the butterflies. Increase of bushiness and reeds appear to have positively affected many geometrid and noctuid species. The high incidence of new provincial finds and of species new to the country in the 1990s as well as positive trends in late-autumn and early-spring species supposedly reflect the ongoing climatic change. The Finnish lepidopteran fauna is undergoing a dynamic phase: around 30 recent invaders and 40 older expansive species are spreading, while fewer are retreating; the declining species are mainly habitat specialists while the expansive ones are generalists, mainly feeding on bushes and trees. Fewer expansions are evident among micro- than macrolepidopterans.
