The decline of mammal functional and evolutionary diversity worldwide

Abstract

Biodiversity is declining worldwide. Because species interact with one another and with their environment, losses of particular organisms alter the function of ecosystems. Our understanding of the global rates and specific causes of functional decline remains limited, however. Species losses also reduce the cumulative amount of extant evolutionary history ("phylogenetic diversity" [PD]) in communities-our biodiversity heritage. Here we provide a global assessment of how each known anthropogenic threat is driving declines in functional diversity (FD) and PD, using terrestrial mammals as a case study. We find that habitat loss and harvest (e.g., legal hunting, poaching, snaring) are by far the biggest drivers of ongoing FD and PD loss. Declines in FD in high-biodiversity countries, particularly in Southeast Asia and South America, are greater than would be expected if species losses were random with respect to ecological function. Among functional guilds, herbivores are disproportionately likely to be declining from harvest, with important implications for plant communities and nutrient cycling. Frugivores are particularly likely to be declining from both harvest and habitat loss, with potential ramifications for seed dispersal and even forest carbon storage. Globally, phylogenetically unique species do not have an elevated risk of decline, but in areas such as Australia and parts of Southeast Asia, both habitat loss and harvest are biased toward phylogenetically unique species. Enhanced conservation efforts, including a renewed focus on harvest sustainability, are urgently needed to prevent the deterioration of ecosystem function, especially in the South American and equatorial Asian tropics.

Keywords: bushmeat hunting; conservation; habitat loss; harvest; phylogenetic diversity.

Fig. 1.

Anthropogenic threats vary strongly in their impacts on FD (A) and PD (B) diversity (P < < 0.001 in both cases) across countries. Box edges show 25th and 75th quartiles; the thick inner line represents the 50th quartile; and whiskers show the largest value ≤1.5 times the interquartile range. Threats with the same lowercase letter are not significantly different based on Tukey’s honest significant difference test.

Fig. 2.

(A–D) Effects of habitat loss on absolute declines in FD (A) and PD (B; units are millions of years of cumulative evolutionary history) and proportional declines in FD (C) and PD (D). (E and F) Maps of where declines in SR associated with habitat loss are significantly biased toward functionally (E) and phylogenetically (F) unique species (red) or toward redundant species (blue) or are unbiased with respect to ecological function or phylogeny (white).

Fig. 3.

(A–D) Effects of harvest on absolute declines in FD (A; units are cumulative dendrogram branch-lengths) and PD (B; units are millions of years of cumulative evolutionary history) and proportional declines in FD (C) and PD (D). (E and F) Maps of where declines in SP associated with harvest are significantly biased toward functionally (E) and phylogenetically (F) unique species (red) or toward redundant species (blue), or are unbiased with respect to ecological function or phylogeny (white).

Fig. 4.

Probability that habitat loss (A) and harvest (B) across countries are biased toward functionally unique mammal species as a function of the current SR of the country. Mean estimate (solid lines) and SEs (dashed lines) are shown; P < 0.001.