The exposure and contribution of predators and scavengers to humans

Abstract

Humans are exerting unparalleled pressures on terrestrial vertebrates through overexploitation and development. The patterns of human destruction on the natural environment are especially prevalent within carnivore distributions because they are subject to not only habitat fragmentation and loss, but they are also perceived as a threat to human societies leading to direct conflict. Although the perceived negative impacts of predators and scavengers dominate policy and individual action towards carnivores, there is a growing body of literature pointing to the potential benefits that predators and scavengers provide within shared landscapes. The overall aim of this thesis is to address key gaps in our knowledge on the exposure and contribution of predators and scavengers to humans and how this information can be used to enhance conservation initiatives.Human pressures cause species extinction. These pressures range from over-hunting and urbanization to other forms of habitat loss such as agricultural development. While human pressures and their threatening processes have been increasingly documented across a range of species and ecosystems, we do not know the extent of intense cumulative human pressures within species’ geographic ranges globally. In Chapter 2, I aim to quantify the exposure of terrestrial vertebrates to intense human pressure, including carnivores. I use the most up-to-date spatial dataset on cumulative human pressure, which takes into account eight pressures known to cause species decline. I find that 85% of the terrestrial vertebrates assessed have more than half of their range exposed to these cumulative pressures, with carnivores having similar exposure. Specifically, carnivores have on average 75% of their ranges overlapping with intense human pressures. This work provides a useful starting point for assessing species at risk of decline, especially for species with limited information on threats.Carnivore declines impact ecosystem stability that can result in negative impacts on human well-being. In Chapter 3, I aim to provide the first review of the benefits provided by predators and scavengers in shared landscapes with humans. I find that predators and scavengers have been shown to reduce zoonotic disease risk, increase agricultural output, and limit species known to cause injury and death to humans. Through the review process, I found considerable gaps in knowledge regarding the potential benefits of predators and scavengers in shared landscapes, and I discuss future avenues of research, its caveats, and opportunities.An important knowledge gap identified during the review was the ecological and human well-being implications of losing apex scavengers. Although there is a great deal of information about the ecological repercussions of losing apex predators, we know relatively little about the role of apex scavengers at regulating lower trophic levels and how this can impact ecosystem health and human well-being. In Chapter 4, I describe the mesoscavenger release hypothesis, the competitive release of mesoscavengers in the absence of apex scavengers. This work sets the foundation for future studies investigating the consequences of apex scavenger decline on ecosystems and human health and provides a springboard for conservation action on imperiled apex scavengers.Another key question asked during the review was the potential role of large carnivores at benefitting humans. Chapters 5-7 focus on addressing this gap. Chapter 5 provides a case study of one of the most widespread large carnivores, leopards (Panthera pardus), at reducing bites and rabies risk from feral dogs in Mumbai, India. I discuss the implications of large carnivores at providing similar services around the world, especially where feral dogs are a considerable human health hazard in peri-urban environments. In Chapter 6 I quantify the predation value of two large carnivore species on an overabundant invasive species, wild pigs (Sus scrofa), known to cause substantial damage to agricultural lands. This chapter offers important information for assessing the benefits of large carnivore conservation on agricultural productivity while accounting for livestock loss. In Chapter 7 I assess the global ramifications of expanding wild pig populations, utilizing information on predicted wild pig densities and data on soil organic carbon (SOC) storage to quantify their relative impacts on SOC vulnerability. I discuss that wild pig control could be promoted through human-induced management and conservation of native predators. These case studies provide a foundation for future work investigating links between natural predation and human well-being through mitigating health hazards and increasing agricultural productivity in shared landscapes. These studies will also deliver conservation practitioners additional information on the consequences of large carnivore recovery.This thesis highlights the state of carnivores in shared landscapes with humans and the potential crucial services they provide. I address key gaps in our knowledge on the exposure and contribution of predators and scavengers to humans and how this information can be used to enhance conservation initiatives.