attention (McNaughton 1985; Huntly 1991; Brown 1995; Pickett et al. 2000). Physical ecosystem engineering by organisms – the creation or modification of habitat structure – has been postulated to be an important mechanism generating landscape-level heterogeneity and thus high species richness (Jones et al. 1997). For a physical ecosystem engineer to increase species richness at the landscape scale – defined explicitly here as a scale that encompasses multiple patch types – two conditions must be fulfilled. First, an engineer must create a patch with a combination of conditions not present elsewhere in the landscape. Second, there must be species that can live in the engineered patches that are not present in patches unmodified by the engineer. There are no a priori reasons to assume that an engineered patch should be more or less species rich than an unengineered patch (Jones et al. 1997). Previous research on organisms that modify the environment has found that modified patches can have both higher (e.g., Martinsen et al. 1990; Crooks 1998) and lower (e.g., Bratton 1975; Collins and Uno 1983) species richness than unmodified patches. Without knowing how an ecosystem engineer modifies the resource flows in a system and how all of the species in the system respond to such modifications, it is difficult to predict the effect of an engineer on between-patch richness (Jones et al. 1997). However, if the engineer creates patches that are sufficiently different from surrounding patches so that species otherwise excluded from the landscape can persist, one would predict that the addition of an engineer to the landscape should increase species richness by increasing habitat heterogeneity.