Abstract

While global warming has clearly affected the phenology of species and contributed to range expansions, contractions of species’ ranges are less well documented despite forecasts of massive future extinctions from climate envelop models. Assessments of effects of recent climate change on the distribution of biodiversity have been limited by use of historical surveys of short time spans with low spatial resolution, or by confounding effects of land use change. Furthermore, range shifts are uncertain when confounded by false absences due to limited historic sampling, and the inability to control for changes in detectability between sampling periods. We repeated a detailed, early 20th century surveys of small mammals and birds across elevation gradients spanning the long-protected landscapes of Yosemite National Park (YNP), Lassen National Park (LNP) and Kings-Canyon-Sequoia National Park. Climate change over the past century was variable at these transects, ranging from a 3C increase in average annual minimum temperate at YNP to cooler, wetter conditions at LNP . Using occupancy modeling to control for variation in detectability, we show substantial (~500m on average) upward shifts in elevation limits for half of 28 small mammal species monitored. Ranges of formerly low elevation species expanded and high elevation species contracted, leading to changed community composition at mid and high elevations. Responses were idiosyncratic among closely-related and ecologically-similar species. Nearly 50% of 70 bird species moved upward in elevational range, 10% moved downward, and 40% showed no change. Local colonizations and extinctions of birds followed the trends predicted by their climatic niche based on long-term temperature and precipitation shifts.