Nigel G. Yoccoz Institute of Statistical Biology, University of Tromso Title Monitoring impacts of global change on ecosystems: we need better mechanistic hypotheses, sampling designs and statistical models Abstract In a paper published in 2001 (Yoccoz et al. 2001; see also 2003) we presented some general principles intended to improve current practices related to monitoring programmes. Our interests in the Ecology research group at the University of Tromsø focus on consequences of global change (warming climate, land use changes, reindeer husbandry practices) on ecosystems in northern Norway. In particular we work on effects of reindeer grazing on tundra ecosystems, competition between red and arctic fox and the effects of small rodents population cycles, and consequences of insect defoliators on birch forests. I will illustrate some of the difficulties associated with setting up a monitoring programme of these impacts, stressing the need for better mechanistic hypotheses, sampling designs and statistical models. CV • PhD in Biometry, University of Lyon, France 1988 • Post-doctoral fellow, University of Oslo, Norway, 1988-1990 • Lecturer (1990-93) and Senior Lecturer (1993-97) in Biometry at the University of Lyon. • Adjunct Professor of Biostatistics, University of Oslo, 2000-2002, Tromsø 2002-03. • Research Scientist at NINA, Tromsø, 1997-2003 (Senior Scientist 2000-03), adjunct after 2003 • Professor of Statistical Biology, University of Tromsø, 2003-present Selected recent Publications Bråthen, K. A., R. A. Ims, N. G. Yoccoz, P. Fauchald, T. Tveraa, and V. H. Hausner. 2007. Density-dependent productivity regimes among reindeer herds: A case for induced shift in ecosystem productivity? Ecosystems in press Ims, R. A., N. G. Yoccoz, K. A. Bråthen, P. Fauchald, T. Tveraa, and V. Hausner. 2007. Can reindeer overabundance cause a trophic cascade? Ecosystems in press Tveraa, T., P. Fauchald, N. G. Yoccoz, R. A. Ims, R. Aanes, and K. A. Høgda. 2007. What regulate and limit reindeer populations in Norway? Oikos 116:706-715. Killengreen, S. T., R. A. Ims, N. G. Yoccoz, K. A. Bråthen, J. A. Henden, and T. Schott. 2007. Structural characteristics of a low Arctic tundra ecosystem and the retreat of the Arctic fox. Biological Conservation 135:459-472. Hagen, S. B., J. U. Jepsen, R. A. Ims, and N. G. Yoccoz. 2007. Shifting altitudinal distribution of outbreak zones of winter moth Operophtera brumata in sub-arctic birch forest: a response to recent climate warming? Ecography 30:299-307. Mysterud, A., N. G. Yoccoz, R. Langvatn, N. Pettorelli, and N. C. Stenseth. 2007. Hierarchical path analysis of deer responses to direct and indirect effects of climate in northern forest. Philosophical Transactions of the Royal Society B-Biological Sciences in press. Institution address Nigel G. Yoccoz Institute of Biology University of Tromso, Norway http://www.ib.uit.no/~nigel/ nigel.yoccoz@ib.uit.no