Key words Positive interactions · Indirect effects ·

Abstract We examined the potential of a common her-bivore to indirectly influence other diverse community members by providing habitat. Larvae of the leafroller Anacampsis niveopulvella commonly construct shelters by rolling leaves of cottonwood trees. These leaf rolls are later colonized by other arthropods. We first docu-mented 4 times greater species richness and 7 times greater abundance on cottonwood shoots that contained a rolled leaf compared to adjacent shoots without leaf rolls. Second, with both removal and addition experi-ments, we showed that leaf rolls are responsible for these differences in arthropod assemblages. Leaf roll removal caused a 5-fold decline in richness and a 7-fold decline in abundance; leaf roll addition resulted in a 2.5-fold in-crease in richness and a 6-fold increase in abundance. Third, to determine whether rolled leaves are colonized for food or for shelter, we compared colonization of nat-ural and artificial leaf rolls. Both richness and abundance were approximately 2-fold greater in artificial leaf rolls, indicating that leaf rolls are colonized primarily for shel-ter. Fourth, in a natural hybrid zone we found that leaf-roller densities were 2-fold greater on backcross hybrids than on F1 hybrids. These differences are likely associat-ed with genetically-based differences in leaf morphology and/or leaf chemistry. Ultimately, plant genotype affects positive indirect interactions that have the potential to af-fect community structure. This study and others demon-strate that shelter builders (i.e., leafrollers and gall for-mers) enhance biodiversity, while free-feeders are more likely to negatively affect biodiversity