Dark-bellied Brent geese aggregate to cope with increased levels of primary production


  • Daan Bos,

  • Johan Van De Koppel,

  • Franz J. Weissing

D. Bos, Community and Conservation Ecology Group, Univ. of Groningen, Kerklaan 30, NL-9751 NN Haren, the Netherlands. Present address: Altenburg & Wymenga Ecological Consultants, P.O. Box 32, NL-9269 ZR Veenwouden, the Netherlands (d.bos@altwym.nl). – J. van de Koppel, Netherlands Inst. of Ecology, Centre for Estuarine and Coastal Ecology, P.O. Box 140, NL-4400 AC Yerseke, the Netherlands. – F. J. Weissing, Theoretical Biology, Centre for Ecological and Evolutionary Studies, Univ. of Groningen, Kerklaan 30, NL-9751 NN Haren, the Netherlands.


We report on an aggregative response of Dark-bellied Brent geese to increased productivity of the vegetation during the growing season on agricultural fields on the island of Schiermonnikoog, the Netherlands. Plant standing crop was found to be maintained at low levels in the fields where geese activity focussed, whereas the remainder of the fields escaped herbivore control and developed a high standing crop. This pattern can be explained by a decreased efficiency of grazing in vegetation with a high standing crop. In other words, the functional response of the geese is not monotonically increasing but dome-shaped. As a consequence, continuously grazed swards are more suitable for feeding than temporarily ungrazed swards. We present a model showing that, for a dome-shaped functional response, optimal foraging under increasing primary productivity leads to spatial heterogeneity in standing crop. Beyond a certain threshold value, a further increase in productivity leads to a progressive release of vegetation from herbivore control and to the development of a high standing crop. Interestingly, our model suggests that only in a stable and predictable environment the aggregative behaviour of herbivores is able to maintain the intake rate close to its potential maximum. Misjudgement of patch quality by the herbivore or any other process disrupting the match between local primary production and consumption leads to a less than optimal intake, as suitable vegetation becomes depleted. This has important implications for ecological inferences, such as the prediction of carrying capacities in herbivore-dominated ecosystems.