Abstract
Neotropical mammal diversity is currently threatened by several chronic human-induced pressures. We compiled 1,029 contemporary mammal assemblages surveyed across the Neotropics to quantify the continental-scale extent and intensity of defaunation and understand their determinants based on environmental covariates. We calculated a local defaunation index for all assemblages—adjusted by a false-absence ratio—which was examined using structural equation models. We propose a hunting index based on socioenvironmental co-variables that either intensify or inhibit hunting, which we used as an additional predictor of defaunation. Mammal defaunation intensity across the Neotropics on average erased 56.5% of the local source fauna, with ungulates comprising the most ubiquitous losses. The extent of defaunation is widespread, but more incipient in hitherto relatively intact major biomes that are rapidly succumbing to encroaching deforestation frontiers. Assemblage-wide mammal body mass distribution was greatly reduced from a historical 95th-percentile of ~ 14 kg to only ~ 4 kg in modern assemblages. Defaunation and depletion of large-bodied species were primarily driven by hunting pressure and remaining habitat area. Our findings can inform guidelines to design transnational conservation policies to safeguard native vertebrates, and ensure that the “empty ecosystem” syndrome will be deterred from reaching much of the New World tropics.
Highlights
Neotropical mammal diversity is currently threatened by several chronic human-induced pressures
Interpolated values throughout the Neotropics shows that a vast fraction of this terrestrial realm has experienced fairly high Hunting pressure index (HPI) values from 0.2 to 0.4, spanning a total area of ~ 17 million km[2], which largely includes the Amazon, Cerrado, Caatinga and Patagonian regions (Fig. 2)
Only 4% (~ 850,000 km2) of the Neotropics experienced HPI values of 0.2 or lower; these areas are mainly concentrated in naturally species-poor regions or those that had been historically most depleted (Fig. 2)
Summary
Neotropical mammal diversity is currently threatened by several chronic human-induced pressures. Several chronic anthropogenic drivers, including habitat loss, overhunting, intentional or accidental wildfires, diseases and the introduction of alien species[9,10] increasingly threaten the Neotropical mammal fauna. Chief anthropogenic disturbances that lead to declines, local extinctions, and cascade-effects of vertebrate species losses include access to previously remote forested areas via new roads[12], expansion of agribusiness frontiers[13], wildfires fueled by climate change[14], mounting hunting pressure[15], relaxation of environmental law e nforcement[16], and synergistic combinations between these and socioeconomic stressors that limits access to dietary protein. Since the European conquest, defaunation either in terms of population depletion or complete local extirpation can result from several chronic to cumulative processes including habitat loss and fragmentation, overharvesting, and disease outbreaks[17]. Undisturbed equatorial rainforests may contain assemblages of up to 180 sympatric mammal species—more than 20% of which may consist of medium- to large-bodied species24,25—while diversity gradually decays at higher latitudes and elevations
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