Geometrid outbreak waves travel across Europe

Tenow, Olle and Nilssen, Arne C. and Bylund, Helena and Pettersson, Rickard and Battisti, Andrea and Bohn, Udo and Caroulle, Fabien and Ciornei, Constantin and Csoka, Gyoergy and Delb, Horst and De Prins, Willy and Glavendekic, Milka and Gninenko, Yuri I. and Hrasovec, Boris and Matosevic, Dinka and Meshkova, Valentyna and Moraal, Leen and Netoiu, Constantin and Pajares, Juan and Rubtsov, Vasily and Tomescu, Romica and Utkina, Irina (2013) Geometrid outbreak waves travel across Europe. Journal of Animal Ecology, 82 (1). pp. 84-95. ISSN 0021-8790

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We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESEWNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 910 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year-1 and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight EW direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved NS. In analogy, outbreaks described previously as moving SN or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal hostherbivoreenemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

Item Type: Article
Language: English
Depositing User: Christer Enkvist
Date Deposited: 28 Feb 2017 14:31
Last Modified: 28 Feb 2017 14:31

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