Colloquium paper: phylogenetic trees and the future of mammalian biodiversity

Abstract

Phylogenies describe the origins and history of species. However, they can also help to predict species' fates and so can be useful tools for managing the future of biodiversity. This article starts by sketching how phylogenetic, geographic, and trait information can be combined to elucidate present mammalian diversity patterns and how they arose. Recent diversification rates and standing diversity show different geographic patterns, indicating that cradles of diversity have moved over time. Patterns in extinction risk reflect both biological differences among mammalian lineages and differences in threat intensity among regions. Phylogenetic comparative analyses indicate that for small-bodied mammals, extinction risk is governed mostly by where the species live and the intensity of the threats, whereas for large-bodied mammals, ecological differences also play an important role. This modeling approach identifies species whose intrinsic biology renders them particularly vulnerable to increased human pressure. We outline how the approach might be extended to consider future trends in anthropogenic drivers, to identify likely future battlegrounds of mammalian conservation, and the likely casualties. This framework could help to highlight consequences of choosing among different future climatic and socioeconomic scenarios. We end by discussing priority-setting, showing how alternative currencies for diversity can suggest very different priorities. We argue that aiming to maximize long-term evolutionary responses is inappropriate, that conservation planning needs to consider costs as well as benefits, and that proactive conservation of largely intact systems should be part of a balanced strategy.

Fig. 1.

Geographic patterns in mammalian biodiversity. (a) The latitudinal gradient in species-richness. The solid line shows the median; gray bands demarcate the interquartile range; species are counted in every latitudinal band (100 km north to south) in which they occur. (b) A map of species richness within 100 × 100-km grid cells, ranging from deep blue (minimum = 0 species) to deep red (maximum = 258 species). (c) The latitudinal pattern of mean geographic range size; details as for a.

Fig. 2.

Maps showing four aspects of mammalian diversification and diversity. (a) Mean numbers of species per genus within cells. (b) Proportion of species with shorter terminal branch lengths than the overall median (phylogeny from ref. , with branch lengths corrected and modified as explained in the previous page). (c) Residuals from a loess regression of cell total evolutionary history against cell species number (phylogeny as above). (d) Variance in log(body mass) (unpublished data), with missing data inferred as the mean of all closest relatives with data.

Fig. 3.

Strength and significance of clumping in extinction risk within WWF ecoregions. Scale bar below the map indicates clumping strength. A value of 1 indicates randomness, and clumping is stronger for lower values. Circle size indicates the p value [radius is proportional to −ln(p)]; circle size for P = 0.05 is shown at the lower left.

Fig. 4.

The surface relating extinction-risk prevalence to urban and agricultural land use and human population density (HPD), controlling for two indices of biological susceptibility, among ecoregions. White regions in the upper left and lower right corners contain no ecoregions. Blue, low risk; purple, high risk.