Biotic and climatic velocity identify contrasting areas of vulnerability to climate change
The velocity of climate change is commonly used to estimate the speed at which species must migrate over the surface of the earth to maintain constant climatic conditions. Although climatic velocity may reflect the exposure of organisms to climate change, resultant biotic effects are dependent on the sensitivity of individual species as reflected in their climatic niche width. We calculated climatic velocity for the Western Hemisphere for 1961-2100 using a recently developed metric based on the actual distance to where similar climates will be found in the future. We compared climatic velocity with biotic velocity, a metric based on projected species range shifts which estimates the velocity at which species must move to track their climatic niche, for 2954 species of birds, mammals, and amphibians.
Geographic patterns of biotic velocity showed greatest contrast with climatic velocity in north temperate and boreal regions. Both biotic and climatic velocities were greatest at low latitudes, implying that threats to equatorial species arise from both the future magnitude of climatic velocities and the narrow climatic tolerances of species in these regions which have historically experienced low climatic velocity. Whereas consideration of biotic and climatic velocity can inform conservation of species and locally-adapted populations, respectively, backward velocity (a function of distance to a source of colonizers adapted to a site’s future climate) allows assessment of vulnerability at the scale of ecosystems. Planners can use the suite of complementary velocity metrics to inform regional planning efforts that seek to conserve ecological diversity at multiple scales in the face of climate change.