Why Montane Anolis Lizards Are Moving Downhill While Puerto Rico Warms

1Because Puerto Rico has warmed in recent decades, ectotherms there should have shifted their elevational ranges uphill. However, by comparing historical versus recent distributional records of Anolis lizards, we found that three \"montane-forest\" species have instead moved downhill in recent decades, almost to sea level. This downward shift appears related to the massive regeneration of Puerto Rican forests - especially in lowland areas - which started in the mid-20th century when the islands economy began shifting from agriculture to manufacturing. The magnitude of local cooling caused by regenerated forests swamps recent climate warming, seemingly enabling cool-adapted \"montane\" lizards to track forests as they spread downhill from mountain refugia into abandoned plantations. Thus, contemporary distributional patterns are likely converging to those prior to the arrival of European settlers, who cleared most lowland forests for agriculture, thereby restricting forests and associated fauna to high-elevation remnants. In contrast with the montane species, three lowland species expanded their ranges to higher elevations in recent decades; but whether this movement reflects warming, land-use shifts, or hurricane-induced destruction of upland forests is unclear.