There is enormous variation in the sizes of geographic ranges of individual species. Some large-range species can occupy habitats with area of more than 100,000,000 km², while some small-range species only occur in area of less than 100 m2. Understanding factors that influence geographic range sizes of species can not only provide important insight into the mechanisms for the distribution of biodiversity, but also is crucial for predicting shifts in species ranges in response to climate change. It is widely recognized that current climates (e.g. intra-annual climate variability and climate extremes) control species range size. Species that experience large magnitudes of climate variability or climate extremes would occupy larger range size. Other factors, such as long-term climate change velocity, topographic heterogeneity, land area, and species traits like physiological thermal limits, dispersal ability, fecundity and body size, have been shown to influence range size. Species able to cope with long-term climate change would occupy large range size. High topographic heterogeneity (e.g. mountains or coasts) will exert barriers to dispersal of species, thus limit the range size. Larger habitat area (e.g. continent area for terrestrial species) may harbor higher proportions of large-range species. Broader range of physiological thermal limits (e.g. upper and lower thermal tolerance) would result in a larger geographic range size. Species with high dispersal ability or large body size would also be more likely to occupy larger range size. However, few studies have examined the generality of each of these factors among different taxa, or have simultaneously evaluated the strength of relationships between range size and these factors at a global scale.

A group led by Prof. Yiming Li from Institute of Zoology, Chinese Academy of Sciences, quantifies contributions of these factors to range sizes of terrestrial vertebrates (three taxa: reptiles, mammals and birds) at a global scale. They find that range sizes of birds are larger than mammals and reptiles. Consistent determinants of range size for the three taxa include monthly extremes of maximum or minimum temperature within species’ ranges, long-term climate velocity since the Last Glacial Maximum, topographic heterogeneity and precipitation seasonality. A species would have large range size if it experiences greater monthly extremes of maximum or minimum temperature within their ranges, or it occurs in areas with higher long-term climate velocity and lower topographic heterogeneity or lower precipitation seasonality. Flight ability and body mass or continent width are important only for particular taxa. Weak evidence is detected for the effect of temperature seasonality, physiological thermal limits and clutch/litter size on range sizes. Larger range sizes for birds than for mammals or reptiles might be partly because birds experience lower minimum temperature than mammals or experience higher maximum temperature, and occur in areas with higher long-term climate velocity than reptiles. This study highlights the dominant effects of climate and topography in shaping range sizes of terrestrial vertebrates. The results suggest that conservation efforts should be focused on small-range species that experience lower temperature extremes or occur in regions with increased precipitation variability under climate change.

This study is conducted in collaboration between Chinese and Danish scientists, and has been published in advance online in Nature Climate Change (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2895.html). Prof. Yiming Li (corresponding author) and Ph.D. student Xianping Li are the first coauthors contributing equally to this work. This research is funded by the National Natural Science Foundation of China (31530088 and 31200416) and the Ministry of Science and Technology of the People´s Republic of China (2013FY110300).