Dispersal will limit ability of mammals to track climate change in the Western Hemisphere

Abstract

As they have in response to past climatic changes, many species will shift their distributions in response to modern climate change. However, due to the unprecedented rapidity of projected climatic changes, some species may not be able to move their ranges fast enough to track shifts in suitable climates and associated habitats. Here, we investigate the ability of 493 mammals to keep pace with projected climatic changes in the Western Hemisphere. We modeled the velocities at which species will likely need to move to keep pace with projected changes in suitable climates. We compared these velocities with the velocities at which species are able to move as a function of dispersal distances and dispersal frequencies. Across the Western Hemisphere, on average, 9.2% of mammals at a given location will likely be unable to keep pace with climate change. In some places, up to 39% of mammals may be unable to track shifts in suitable climates. Eighty-seven percent of mammalian species are expected to experience reductions in range size and 20% of these range reductions will likely be due to limited dispersal abilities as opposed to reductions in the area of suitable climate. Because climate change will likely outpace the response capacity of many mammals, mammalian vulnerability to climate change may be more extensive than previously anticipated. R ecent changes in climate have already caused discernible shifts in species distributions (1, 2). In general, these shifts have been toward the poles or upwards in elevation and have occurred at an average rate of 6.1 km and 6.1 m per decade, respectively (3). Given the projected rates of future climatic changes, rates of range shifts over the coming century are likely to be even greater (4-6). Several studies have projected potential shifts in species distributions in response to forecasted climatic changes. Because these range-shift projections rarely account for dispersal abilities, they indicate areas that may be climatically suitable for species in the future, but they do not tell us whether species will be able to expand their ranges into these newly suitable regions.In the coming century, the survival of species will in part depend on their abilities to track geographic changes in suitable climates (7,8). This ability to keep pace with climate change depends on both the velocity of the climatic changes a species will face and species-specific dispersal abilities. Loarie et al. (8) mapped the velocity of climate change as the ratio of temporal and spatial gradients of changes in mean temperature, and separately, in annual precipitation. Temperature and precipitation are expected to change globally at average velocities of 0.42 and 0.22 km/y, respectively, and the velocities of changes in both of these climatic variables also vary spatially. The velocity of climate change that a species will face, or the velocity at which a species will need to move to keep pace with shifts in suitable climates, therefore, depends on the location of the species and the velocities of changes...

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