Although habitat amount, fragmentation, and connectivity are thought to be important drivers of biodiversity, their independent effects have not been evaluated. We selected 70 forested sites in Ontario, Canada, such that forest amount, fragmentation (number of patches), and structural connectivity (treed corridors) in the surrounding landscapes were uncorrelated. We surveyed forest small mammals at each site and estimated the relative effects of the three landscape variables on individual species' abundance and occurrence and total species diversity. Most responses had high variability, with 95% confidence intervals crossing zero. Configuration variables (fragmentation and connectivity) generally had stronger effects on small mammals than forest amount. Fragmentation increased small mammal diversity but had variable effects on individual species responses. Unexpectedly, species diversity and individual species occurrence declined with structural connectivity. Therefore, landscape management aimed at decreasing fragmentation or increasing structural connectivity will not benefit all forest small mammals in this region.