Global correlates of range contractions and expansions in terrestrial mammals

Abstract

Understanding changes in species distributions is essential to disentangle the mechanisms that drive their responses to anthropogenic habitat modification. Here we analyse the past (1970s) and current (2017) distribution of 204 species of terrestrial non-volant mammals to identify drivers of recent contraction and expansion in their range. We find 106 species lost part of their past range, and 40 of them declined by >50%. The key correlates of this contraction are large body mass, increase in air temperature, loss of natural land, and high human population density. At the same time, 44 species have some expansion in their range, which correlates with small body size, generalist diet, and high reproductive rates. Our findings clearly show that human activity and life history interact to influence range changes in mammals. While the former plays a major role in determining contraction in species' distribution, the latter is important for both contraction and expansion.

Fig. 1. Scatterplot showing the relationship between increase and decrease in the range of each species.

Classes refer to the percentage range change with respect to the 1970s: large decrease (>50%), moderate decrease (between 49 and 5%), stable (within 5%), moderate increase (between 5 and 49%) and large increase (>50%).

Fig. 2. Random forest variable importance plots for selected predictors in the range contraction and expansion models.

The plot shows the decreasing importance of intrinsic and extrinsic variables at 10-km resolution in predicting proportional loss (upper panel) and gains (lower panel) in species’ ranges. Big changes in these measures indicate important variables. Yellow bars indicate life-history traits, blue bars human-pressure variables and red bars other variables. n = 204 species have been analysed.

Fig. 3. Partial dependence plots to show the effects of selected pairs of predictors on range contraction.

Top-left plot shows the negative interaction of change in natural lands with mean annual temperature; the top-right plot represents the negative interaction of human population density in the past with the size of the past range on range contraction; the bottom-left plot describes the positive interaction of change in mean annual temperature with past human population density; the bottom-right plot illustrates the positive interaction of body mass with mean annual temperature change on range contraction.

Fig. 4. Partial dependence plots to show the effects of selected pairs of predictors on range expansion.

Top-left plot represents the positive interaction of dietary breadth with habitat breadth; the top-right plot shows the positive interaction of dietary breadth with litters per year; the bottom-left plot describes the positive interaction of change in mean annual temperature with habitat breadth; the bottom-right plot illustrates the positive interaction of habitat breadth with the size of the past range on range expansion.