The changing fates of the world's mammals

Abstract

A recent complete assessment of the conservation status of 5487 mammal species demonstrated that at least one-fifth are at risk of extinction in the wild. We retrospectively identified genuine changes in extinction risk for mammals between 1996 and 2008 to calculate changes in the International Union for Conservation of Nature (IUCN) Red List Index (RLI). Species-level trends in the conservation status of mammalian diversity reveal that extinction risk in large-bodied species is increasing, and that the rate of deterioration has been most accelerated in the Indomalayan and Australasian realms. Expanding agriculture and hunting have been the main drivers of increased extinction risk in mammals. Site-based protection and management, legislation, and captive-breeding and reintroduction programmes have led to improvements in 24 species. We contextualize these changes, and explain why both deteriorations and improvements may be under-reported. Although this study highlights where conservation actions are leading to improvements, it fails to account for instances where conservation has prevented further deteriorations in the status of the world's mammals. The continued utility of the RLI is dependent on sustained investment to ensure repeated assessments of mammals over time and to facilitate future calculations of the RLI and measurement against global targets.

Figure 1.

Red List Indices for mammals during 1996–2008 in different biogeographic realms (sensu [48]). An RLI value of 1 equates to all species being Least Concern; an RLI value of 0 equates to all species being Extinct. Improvements in species conservation status lead to increases in the RLI; deteriorations lead to declines. A downward trend in the RLI value means that the net expected rate of species extinctions is increasing. Sample sizes: all mammals = 195 genuine status changes/4556 non-Data Deficient species (excluding EX and PE in 1996); Afrotropical = 19/1044; Antarctic = 3/17; Australasian = 52/619; Indomalayan = 72/823; Neotropical = 26/1333; Nearctic = 11/470; Oceanian = 4/31; and Palaearctic = 36/776. See Butchart et al. [33] for the methodology on disaggregating the RLI.

Figure 2.

Red List Indices for mammals during 1996–2008 in different body mass classes. Sample sizes: 0–1 kg = 73 genuine status changes/3374 non-Data Deficient species (excluding EX and PE in 1996; dotted line with cross); 1–10 kg = 57/639 (dashed line with square); 10–100 kg = 60/521 (dashed line with circle); more than 100 kg = 5/22 (dashed line with triangle); and all mammals (solid line with diamond).

Figure 3.

Number of mammal species changing IUCN Red List categories between 1996 and 2008. EX, Extinct; EW, Extinct in the Wild; CR(PE), Critically Endangered (Possibly Extinct); CR, Critically Endangered; EN, Endangered; VU, Vulnerable; NT, Near Threatened; LC, Least Concern. Species undergoing an improvement (i.e. moving from a higher to a lower category of threat) appear above the line; species deteriorating in status (i.e. moving from a lower to a higher category of threat) appear below the line. Species changing categories for non-genuine reasons (improved knowledge, taxonomy) are excluded.

Figure 4.

The main drivers for deteriorating mammal species (1996–2008) coded according to the Red List category of the species in 2008. EX, Extinct; EW, Extinct in the Wild; CR(PE), Critically Endangered (Possibly Extinct); CR, Critically Endangered; EN, Endangered; VU, Vulnerable; NT, Near Threatened.

Figure 5.

Cumulative proportion of species undergoing Red List category changes. Non-Data Deficient extant species at start of the period (n = 4556).

Figure 6.

Conservation actions implemented that led to improvements in IUCN Red List Status for mammals (figure reproduced from Hoffmann et al. [47], with permission from AAAS/Science). Dark grey, major conservation actions; light grey, minor conservation actions.