Extent, intensity and drivers of mammal defaunation: a continental-scale analysis across the Neotropics

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.

Where Might We Find Ecologically Intact Communities?

“…Along the Gabon and Congo coastline, chimpanzees but not gorillas are considered taboo, and this is reversed in some areas of Cameroon; a factor "eat gorillas" or "eat chimpanzees" was included in the spatial model that predicted the density of both taxa in western Equatorial Africa (Strindberg et al, 2018). Predicting the impacts of hunting needs much more detailed analysis (Benítez-López et al, 2019;Bogoni et al, 2020;Romero-Muñoz et al, 2020) than making assumptions about impacts from access distance to road and river networks. Similarly, the impacts of introduced species cannot be assessed from maps such as the Human Footprint but have had a major impact on extirpated species numbers in places such as Australia (Woinarski et al, 2015).…”

Impending anthropogenic threats and protected area prioritization for the largest Neotropical apex predator in its Amazonian stronghold

“…Across the Neotropics, drivers of local biotic depletion have accelerated since the 1970s. Dominant anthropogenic disturbances that lead to species declines and local extinctions include access to hitherto isolated forested areas via new roads [60], wildfires fueled by climate change [61], deforestation due to agribusiness frontiers expansion [62], relaxation of environmental law enforcement [63], increasing hunting pressure [64], and synergistic combinations between these and other socioeconomic stressors [23]. The Brazilian Amazon experienced an overwhelming and multifaceted spike in environmental degradation over the last decade, exacerbated by a renewed acceleration in deforestation and human-induced fires [34], exerting further pressure on Amazonian forest wildlife and native ethnic groups [37, 65].…”

“…Previous studies in human-modified landscapes showed that habitat loss and fragmentation have a strong detrimental impact on jaguar populations, which are now locally extinct in several Neotropical ecoregions [22][23]. For instance, the few remaining jaguar subpopulations in the Atlantic Forest are small, dispersed, and highly isolated into a few sufficiently large forest remnants [22,69].…”

Diversity and activity patterns of medium- and large-sized terrestrial mammals at the Los Tuxtlas Biosphere Reserve, México

“…At the landscape level, studies provide insights on the local conservation status of species, and provide a better understanding of patterns on the local effects of habitat loss and fragmentation on biodiversity (Bogoni et al 2020). In this context, it is important to gather information on the status of the terrestrial mammal community to establish adequate conservation and management programs to promote a sustainable use of the natural resources by local inhabitants and to ensure the protection of biodiversity.…”