Original article Biodiversity and abundance of terrestrial isopods along a gradient of disturbance in Sabah, East Malaysia M. Hassall a, * , D.T. Jones b , S. Taiti c , Z. Latipi d , S.L. Sutton d , M. Mohammed d a Centre for Ecology Evolution and Conservation, School of Environmental Sciences, University of East Anglia, Norwich NR4 7JT, UK b Soil Biodiversity Research Group, Entomology Department, British Natural History Museum, Cromwell Road, London SW7 5BD, UK c Istituto per lo Studio degli Ecosistemi, Consiglio Nazionale delle Ricerche, Via Madonna del Piano, 50019 Sesto Fiorentino, Florence, Italy d Tropical Biology and Conservation Institute, University of Malaysia Sabah, Beg Berkunci 2073, 88999 Kota Kinabalu, Sabah, Malaysia Available online 20 July 2006 Abstract Connell’s intermediate disturbance hypothesis predicts that the highest diversity is maintained at intermediate levels of dis- turbance. We have examined this hypothesis by observing differences in biodiversity of terrestrial isopods along a gradient of disturbance from two undisturbed primary tropical rainforest sites, to a logged site, a mixed native fruit orchard and a commercial oil palm plantation, in Sabah, East Malaysia. We describe a standardised protocol for the rapid assessment of isopod biodiversity on tropical forest floor sites and for measuring environmental variables to which we have related differences in species richness and relative abundance of the isopods. The results do not support Connell’s hypothesis because there were no significant differ- ences in diversity, species richness or equitability between disturbed sites and the nearest primary forests. The relative abundance of individual species was highest in the most disturbed environment. We suggest that this may be because particular species are well adapted to exploiting resources under the more ‘r’ selection conditions created by disturbance. Possible reasons for why the observations do not conform with predictions from the intermediate disturbance hypothesis are discussed. We conclude that Huston’s dynamic equilibrium model is more appropriate than the intermediate disturbance hypothesis in predicting the effects of disturbance of tropical rainforests on these arthropod macro-decomposers. © 2006 Published by Elsevier Masson SAS. Keywords: Diversity; Species richness; Equitability; Tropical rain forest; Logging; Deforestation; Dynamic equilibrium hypothesis 1. Introduction Primary tropical forests contain the highest biodiver- sity of any ecosystem on earth, but they are currently being lost at an unprecedented rate of 200,000 km 2 each year [44]. In many systems disturbance creates spaces more suitable for earlier successional species. If disturbance is uniform and severe it can result in a relatively simple community of pioneer species with good colonising ability. When the disturbance is vari- able in time and/or space it may result in a mosaic of habitat patches at different successional stages. At a landscape scale such patchy communities are often more diverse than either uniformly heavily disturbed ones or completely undisturbed communities dominated by fewer highly competitive species. This principle is encapsulated in the ‘intermediate disturbance hypothesis’ [9] initially formulated in rela- tion to tropical rainforests and coral reefs [8] but sub- sequently supported by studies of many other ecosys- tems [4,17,19,57,72] and recently thoroughly evaluated http://france.elsevier.com/direct/ejsobi European Journal of Soil Biology 42 (2006) S197–S207 * Corresponding author. Fax: +44 1603 59 1327. E-mail address: m.hassall@uea.ac.uk (M. Hassall). 1164-5563/$ - see front matter © 2006 Published by Elsevier Masson SAS. doi:10.1016/j.ejsobi.2006.07.002