Discovery of continental-scale travelling waves and lagged synchrony in geometrid moth outbreaks prompt a re-evaluation of mountain birch/geometrid studies

Abstract

The spatio-temporal dynamics of populations of two 9-10 year cyclic-outbreaking geometrids, Operophtera brumata and Epirrita autumnata in mountain birch forests in northern Fennoscandia, have been studied since the 1970´s by a Swedish-Norwegian research team and, during the last decade, by Norwegian and Finnish research teams. Some of the early results have been challenged by the Norwegian team. To examine the base for disagreements, five of the papers published by the Norwegian team (2004-2011) are reviewed. It is found that conclusions in these papers are questionable or data could not be interpreted fully because two decisive traits in the spatio-temporal behaviour of outbreaks of the two species were not considered.

Continental‐scale travelling waves in forest geometrids in Europe: an evaluation of the evidence

“… A wave with a wave speed of 330 km year −1 and a wave length of 3135 km travels across Europe in an ESE‐WNW direction from the Ural to the North Atlantic coast. Local population dynamics of forest geometrids cannot be understood without knowledge and understanding of the continental wave. This has led Tenow () to criticize a whole body of work on local moth dynamics. …”

“…), perfect synchrony would be equivalent to infinite wave speed, which clearly does not imply that individuals are travelling at that speed. Secondly, Tenow () stated that the presence of travelling waves would invalidate small‐scale research on geometrid population dynamics. In our view, this has no theoretical basis.…”

A response to Jepsen et al. (2016)

“…In an article (Tenow ), I refuted challenges to earlier work by me and others (Tenow ; Tenow et al . ) posed in five articles by the Norwegian team.…”