Hunting and Forest Modification Have Distinct Defaunation Impacts on Tropical Mammals and Birds

Anand M Osuri,Shahid Naeem,Rohit Naniwadekar,Varun Varma,Uttara Mendiratta

doi:10.3389/ffgc.2019.00087

Abstract

The mammalian and avian assemblages of intact tropical forests are among the most diverse vertebrate communities on Earth and influence the structure, composition and functioning of these forests in myriad ways. Over recent centuries, however, increasing human domination of the tropics has led to widespread defaunation, or the decline, local- or global extinction of tropical animal species. Defaunation is one of the defining features of the Anthropocene and is best documented for vertebrate species, especially mammals and birds. Defaunation is driven by several direct (e.g., hunting) and indirect (e.g., habitat alteration) anthropogenic threats, but how these threats differ in the nature and magnitude of their impacts on tropical mammal and bird species remains unclear. Using a meta-analysis of 82 studies on 254 mammal and 1640 bird species from across the tropics, we assess the effects of three major regional-scale drivers of tropical defaunation, namely hunting, forest degradation and forest conversion, on measures of abundance for tropical mammal and bird species belonging to different dietary guilds and IUCN conservation status groups. Mammal species across dietary guilds declined or did not vary, on average, in response to the three drivers, with hunting having the most consistent negative impacts on abundances of carnivores, frugivores, herbivores/granivores, large-bodied species, and species of high conservation importance. By contrast, bird species declined most strongly in response to forest conversion, with responses varying widely across different dietary and conservation importance groups, and not consistently related to body size. Our results reveal that hunting, forest degradation and conversion are associated with distinct types of defaunation of mammal and bird species, and are therefore likely to have distinct implications for animal-mediated interactions and processes, ecosystem functions, and conservation of tropical forests. Addressing major gaps in our empirical understanding of defaunation effects – e.g., hunting impacts on smaller-bodied mammals and birds, and responses of species in southeast Asian forests – is key to better understanding, predicting, and mitigating the impacts of this pervasive global threat.

Highlights

Tropical forests are among the most biodiverse global biomes and harbor c. 50–70% of all terrestrial vertebrate diversity (Whitmore, 1990; Pimm and Raven, 2000)
We examined all the publications included in the above meta-analysis and retained those studies that were in English, available online, and which explicitly compared and reported metrics of abundance or relative abundance for at least one mammal or bird species from hunted forests and forests experiencing little to no hunting
Forest conversion was associated with consistent declines of frugivores and insectivores and increases of herbivores/granivores and nectarivores, and inconsistent declines of insectivores, while guild-wise responses to hunting and forest degradation were weaker and more variable (Figure 3B)

Summary

Introduction

Tropical forests are among the most biodiverse global biomes and harbor c. 50–70% of all terrestrial vertebrate diversity (Whitmore, 1990; Pimm and Raven, 2000). The rapidly expanding footprint of anthropogenic disturbance is a leading driver of species population declines, resulting in widespread losses of tropical biodiversity (Gibson et al, 2011; Lewis et al, 2015; Watson et al, 2018) Such anthropogenic biodiversity loss, termed defaunation when focusing on animal species, is pervasive among all biomes, terrestrial, freshwater, or marine, and is one of the defining features of this epoch, commonly referred to as the Anthropocene (Dirzo et al, 2014; Young et al, 2016). Direct harvest for commercial and subsistence hunting is prevalent in most tropical forest regions (Fa et al, 2002; Peres and Palacios, 2007), including within protected reserves (Harrison, 2011; Laurance et al, 2012). Indirect drivers of faunal change in tropical forests include forest degradation (e.g., fragmentation and unsustainable logging) (Potapov et al, 2008; Malhi et al, 2014), and conversion of forests to plantations, cropland and pastures (Gibson et al, 2011; Young et al, 2016), which affect virtually all tropical landscapes

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Conclusion