Top predators that negatively influence prey coexistence can simultaneously increase both stochastic and deterministic contributions to community assembly. When deterministic processes predominate, the site-to-site variability (e.g.,β-diversity) among otherwise environmentally similar sites should be low, whereas when stochastic processes predominate, β -diversity should be higher. Alternatively, predators that promote local prey coexistence (keystone predators) are predicted to enhance only deterministic contributions to community assembly leading to greater similarity in prey communities. We explored this prediction by investigating how keystone collared lizard predators influenced the assembly of grasshopper prey communities in glade habitats.

Results/Conclusions

We found that lizards altered the partitioning of local (α) and regional (γ) grasshopper diversity within metacommunities, thereby decreasing β-diversity. These predator-driven increases in the similarity of local communities were consistent with our predicted effects of keystone predators on community assembly. By enhancing deterministic contributions to community assembly, keystone predators simultaneously increase local diversity and erode compositional diversity leading to changes in the scaling of prey diversity within metacommunities.