Basic and Applied Ecology 5 (2004) 505—514 How does global change affect the strength of trophic interactions? Mark Emmerson a,Ã , T. Martijn Bezemer b,1 , MarkD. Hunter c , T. Hefin Jones d , GregoryJ. Masters e , Nicole M. Van Dam b a Department of Zoology, Ecology and Plant Sciences, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland b Netherlands Institute of Ecology (NIOO-KNAW), P.O. Box 40, 6666 ZG Heteren, The Netherlands c Institute of Ecology, University of Georgia, Ecology Building, Athens, GA 30602-2202, USA d Cardiff School of Biosciences, Cardiff University, P.O. Box 915, Cardiff CF10 3TL, UK e Ecological Applications, CABI Bioscience, Bakeham Lane, Egham, Surrey, TW20 9TY, UK Received 4 July 2004; accepted 4 September 2004 Summary Recent research has generally shown that a small change in the number of species in a food web can have consequences both for community structure and ecosystem processes. However ‘change’ is not limited to just the number of species in a community, but might include an alteration to such properties as precipitation, nutrient cycling and temperature, all of which are correlated with productivity. Here we argue that predicted scenarios of global change will result in increased plant productivity. We model three scenarios of change using simple Lotka–Volterra dynamics, which explore how a global change in productivity might affect the strength of local species interactions and detail the consequences for community and ecosystem level stability. Our results indicate that (i) at local scales the average population size of consumers may decline because of poor quality food resources, (ii) that the strength of species interactions at equilibrium may become weaker because of reduced population size, and (iii) that species populations may become more variable and may take longer to recover from environmental or anthropogenic disturbances. At local scales interaction strengths encompass such properties as feeding rates and assimilation efficiencies, and encapsulate functionally important information with regard to ecosystem processes. Interaction strengths represent the pathways and transfer of energy through an ecosystem. We examine how such local patterns might be affected given various scenarios of ‘global change’ and discuss the consequences for community stability and ecosystem functioning. & 2004 Elsevier GmbH. All rights reserved. ARTICLE IN PRESS www.elsevier.de/baae KEYWORDS Community; Ecosystems; Food webs; Herbivore; Plant; Predators; Prey; Stability 1439-1791/$ - see front matter & 2004 Elsevier GmbH. All rights reserved. doi:10.1016/j.baae.2004.09.001 Ã Corresponding author. Tel.: +353 21 490 4190; fax: +353 21 427 0562. E-mail address: m.emmerson@ucc.ie (M. Emmerson). 1 Present address: Nature Conservation and Plant Ecology Group, Wageningen University and Research Centre, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands.