Physiological tolerance, climate change, and a northward range shift in the spittlebug, Philaenus spumarius

1. Considerable evidence indicates that the Earth's climate has warmed over the past 20 years and most models predict that this process will continue or accelerate. Previous studies involving butterflies and other species have shown that ranges have shifted towards the poles although the mechanisms responsible for these range shifts have not been demonstrated conclusively. 2. Here it is reported that the range of the meadow spittlebug has moved northward along the California coast since 1988. 3. Survival and reproduction of this species in previous laboratory experiments were very sensitive to humidity and temperature. Small deviations from optimal conditions resulted in high mortality. 4. These laboratory results were corroborated by annual field censuses from one location since 1983 in which population densities of spittlebug nymphs were positively correlated with summer humidity and negatively correlated with temperature deviations from the published optimum. Thus it is shown that there are strong links between physiological tolerance and a geographic range shift associated with climatic change.