AN EMPIRICAL TEST OF RAPOPORT’S RULE: ELEVATIONAL GRADIENTS IN MONTANE BUTTERFLY COMMUNITIES

We examined the response of montane butterflies to a 1300‐m elevational gradient in the Toiyabe Range, a mountain range in the central Great Basin. We tested whether elevational ranges of montane butterflies conform to Rapoport’s elevational rule (species at higher elevations have greater elevational ranges). We also tested whether the Rapoport‐rescue hypothesis (emigrants from higher elevation populations inflate the species richness of lower‐elevation sites) could explain the species richness patterns we observed. In addition, we predicted whether global climate change is likely to perturb current elevational gradients in butterfly species richness. Species presence data were collected from 105 100‐m vertical elevational bands in 17 canyons. Elevation and species richness were significantly negatively correlated, although species richness peaked at intermediate elevations, and butterflies in species‐rich areas had significantly narrower elevational ranges than species in more depauperate areas. Toiyabe Range butterflies conformed to Rapoport’s elevational rule. The Rapoport effect we documented did not result from sampling bias. However, the Rapoport‐rescue hypothesis cannot fully explain the elevational gradient in species richness. Environmental severity at either end and favorable conditions near the middle of the elevational gradient likely contributed to high species richness at intermediate elevations. Our models indicated that few butterfly taxa will be lost from the Toiyabe Range in the face of climate change. To maintain present species richness and maximize the potential of Great Basin butterflies to adapt to rapid climate change, we recommend that habitat protection and restoration efforts target not only high elevation Wilderness Areas but also intermediate elevations.