ORIGINAL ARTICLE Animal species diversity driven by habitat heterogeneity/diversity: the importance of keystone structures J. Tews 1 *, U. Brose 2 , V. Grimm 3 , K. Tielbo ¨rger 1 , M. C. Wichmann 1 , M. Schwager 1 and F. Jeltsch 1 INTRODUCTION The ‘habitat heterogeneity hypothesis’ is one of the corner- stones of ecology (e.g. Simpson, 1949; MacArthur & Wilson, 1967; Lack, 1969). It assumes that structurally complex habitats may provide more niches and diverse ways of exploiting the environmental resources and thus increase species diversity (Bazzaz, 1975). In most habitats, plant communities determine the physical structure of the environ- ment, and therefore, have a considerable influence on the distributions and interactions of animal species (reviews in Lawton, 1983; McCoy & Bell, 1991). For example, for bird species diversity in forests, MacArthur & MacArthur (1961) evidenced that the physical structure of a plant community, i.e. how the foliage is distributed vertically, may be more important than the actual composition of plant species. Although positive relationships between vegetation-shaped habitat heterogeneity and animal species diversity are well documented on both local and regional scales (Davidowitz & Rosenzweig, 1998), empirical and theoretical studies have yielded contradictory results. Depending on the taxonomic group, the structural parameter of the vegetation and the 1 Institute of Biochemistry and Biology, Plant Ecology and Nature Conservation, University of Potsdam, Potsdam, Germany, 2 Department of Biology, Romberg Tiburon Center, San Francisco State University, Tiburon, CA, USA and 3 Department of Ecological Modelling, Center for Environmental Research Leipzig- Halle, Leipzig, Germany. *Correspondence: J. Tews, Institute of Biochemistry and Biology, Plant Ecology and Nature Conservation, University of Potsdam, Maulbeerallee 2, 14467 Potsdam, Germany. E-mail: jtews@rz.uni-potsdam.de ABSTRACT Aim In a selected literature survey we reviewed studies on the habitat heterogeneity–animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support. Location World-wide. Methods We reviewed 85 publications for the period 1960–2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study. Main conclusions The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to ‘keystone structures’ that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management. Keywords Habitat heterogeneity hypothesis, structural diversity, structural heterogeneity, foliage height diversity, species richness, biodiversity, spatial scale, habitat fragmentation. Journal of Biogeography (J. Biogeogr.) (2004) 31, 79–92 ª 2004 Blackwell Publishing Ltd www.blackwellpublishing.com/jbi 79