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Climate and land-use change could exhibit concordant effects that favor or disfavor the same species, which would amplify their impacts, or species may respond to each threat in a divergent manner, causing opposing effects that moderate their impacts in isolation. We used early 20th century surveys of birds conducted by Joseph Grinnell paired with modern resurveys and land-use change reconstructed from historic maps to examine avian change in Los Angeles and California's Central Valley (and their surrounding foothills). Occupancy and species richness declined greatly in Los Angeles from urbanization, strong warming (+1.8°C), and drying (-77.2 millimeters) but remained stable in the Central Valley, despite large-scale agricultural development, average warming (+0.9°C), and increased precipitation (+11.2 millimeters). While climate was the main driver of species distributions a century ago, the combined impacts of land-use and climate change drove temporal changes in occupancy, with similar numbers of species experiencing concordant and opposing effects.

High exposure to warming from climate change is expected to threaten biodiversity by pushing many species toward extinction. Such exposure is often assessed for all taxa at a location from climate projections, yet species have diverse strategies for buffering against temperature extremes. We compared changes in species occupancy and site-level richness of small mammal and bird communities in protected areas of the Mojave Desert using surveys spanning a century. Small mammal communities remained remarkably stable, whereas birds declined markedly in response to warming and drying. Simulations of heat flux identified different exposure to warming for birds and mammals, which we attribute to microhabitat use. Estimates from climate projections are unlikely to accurately reflect species' exposure without accounting for the effects of microhabitat buffering on heat flux., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

We provide a century-scale view of small-mammal responses to global warming, without confounding effects of land-use change, by repeating Grinnell's early-20th century survey across a 3000-meter-elevation gradient that spans Yosemite National Park, California, USA. Using occupancy modeling to control for variation in detectability, we show substantial ( approximately 500 meters on average) upward changes in elevational limits for half of 28 species monitored, consistent with the observed approximately 3 degrees C increase in minimum temperatures. Formerly low-elevation species expanded their ranges and high-elevation species contracted theirs, leading to changed community composition at mid- and high elevations. Elevational replacement among congeners changed because species' responses were idiosyncratic. Though some high-elevation species are threatened, protection of elevation gradients allows other species to respond via migration.