The distribution of resources should influence mate availability and the costs and benefits of pursuing different mating strategies. Where resources are dispersed, males may be constrained in the extent to which they can monopolize more than 1 partner, resulting in social and genetic monogamy. There is abundant correlational evidence that resource distribution influences social and mating systems, but experiments that demonstrate a causal link between these variables are relatively rare. Here, we used a replicated experiment involving 160 animals to examine how the distribution of a key resource, crevice sites used as nesting habitat, shapes social and mating behavior of a family living lizard, Liopholis whitii. The distribution of crevice sites had significant effects on several important aspects of the social and mating system. When habitat was aggregated, adults had larger home ranges and overlapped with more individuals of the opposite sex, resulting in increased opportunity for social polygyny. Aggressive female territoriality appears to impose upper limits on opportunities for polygyny by restricting female–female home range overlap. Despite this, males in aggregated habitats still formed polygynous social groups more often than males in dispersed habitat. Aggregated habitat also increased the opportunity for sexual selection, resulting in greater variance in male reproductive success and a steeper Bateman gradient compared with males occupying dispersed habitat. These effects were independent of the increase in social polygyny. Overall, our study is consistent with the hypothesis that habitat structure is fundamentally important to the evolution of social and mating systems.