https://orcid.org/0000-0002-6472-6957
One of the greatest challenges for achieving the United Nation's Sustainable Development Goals is ensuring human communities and biodiversity can flourish simultaneously. Recognizing this challenge, global leaders have converged on environmental agreements that explicitly call for fostering nature's contribution to people. Although our understanding of the broad importance of nature to human health and well-being is established, emerging literature is pointing to lesser known but critical benefits of some of the most imperiled and controversial species on Earth—predators and scavengers (Ripple et al. 2014, O'Bryan et al. 2018, Palacios-Pacheco et al. 2024). Predators and scavengers are ecosystem regulators that consume other animals either alive or dead, and their exclusion as indicators for these environmental agreements may be detrimental to planetary health.
Predators and scavengers—species ranging from bats and vultures to wolves and reptiles—include some of the most iconic animals that are often associated with conflict and harm to society. Although the negative impacts of these species are well documented in the literature (Lozano et al. 2019, Palacios-Pacheco et al. 2024), there is growing evidence of their positive contributions to human health and well-being, given their regulatory roles in ecosystems (Ripple and Beschta 2012, Buechley and Şekercioğlu 2016). For instance, because of their top-down effects on species via predation and behavioral shifts, large carnivores such as wolves (Canis lupus) in North America and Europe have been linked to reduced vehicle collisions with wildlife that save human lives and millions of dollars in insurance premiums and hospital fees each year (Raynor et al. 2021, Sèbe et al. 2023). Predators have also been documented to contribute to food production by reducing pest populations that destroy crops or compete with valuable livestock (O'Bryan et al. 2018, Palacios-Pacheco et al. 2024). For example, the reintroduction of the threatened New Zealand falcon (Falco novaeseelandiae) saved wineries hundreds of dollars per hectare in grape production because the falcons preyed on passerines that fed on grapes (Kross et al. 2012). Furthermore, in North America, insectivorous bats may save farmers money by preying on pest insects; the widespread decline of insectivorous bats from white-nose syndrome between 2006 and 2014 revealed potential agricultural losses to farmers worth $26.9 billion (Frank 2024). And lesser-known species such as the heath goanna (Varanus rosenbergi), a reptilian scavenger of coastal mallee ecosystems of Australia, have been shown to significantly reduce numbers of rat carcasses, which carry harmful blowflies (Jameson et al. 2024). Blowflies cause $280 million in losses to the Australian sheep industry annually (Smith 2024), and Jameson and colleagues (2024) argued that native scavengers such as heath goannas may reduce these losses.
Beyond their contributions to agriculture, predators and scavengers may also reduce disease-related deaths in people. For example, the bat declines mentioned above resulted in farmers using 31% more insecticides on their crops to supplant the role of the bats, which translated to a potential 8% increase in human infant mortality in the affected counties (Frank 2024). Also, the multicontinental decline of amphibians due to the fungal pathogen Batrachochytrium dendrobatidis was empirically linked to the significant rise in human malaria incidents in Costa Rica and Panama (Springborn et al. 2022), suggesting their predation of mosquitos as an important regulatory mechanism of the disease. And a recent analysis indicates that the near extinction of vultures, obligate scavengers, in India in the 1990s was associated with the deaths of over half a million people and economic damages of $69.4 billion due to sanitation shocks from livestock carcasses not being scavenged efficiently (Frank and Sudarshan 2023). These examples are a few of many emerging case studies of the roles that these species play for hazard reduction, food production, and disease mitigation.
Given our growing understanding of the services provided by predators and scavengers, now is the time to consider their benefits as indictors for achieving global biodiversity commitments. A salient opportunity is the Kunming-Montreal Global Biodiversity Framework of the Convention on Biological Diversity, which seeks to achieve a world where people live in harmony with nature by 2050 (United Nations Environment Programme 2022). As part of reaching this goal, the near 200 signatory countries agreed to 23 action-oriented targets for the year 2030. One such target, target 11, explicitly calls for integrating natural ecosystem functioning in food production, disease prevention, and protection from natural hazards and disasters. Although the target contains the headline indicator of “services provided by ecosystems,” component indicators are currently broadly focused on climate, water quality, and air quality. For example, the number of people affected by natural disasters, the mortality rate attributed to unsafe water, and the annual mean levels of fine particulate matter in cities (www.cbd.int/gbf/targets/11). Although these indicators are important, they do not fully match the directive of target 11 and are not SMART—that is, specific, measurable, ambitious, realistic, and timebound (Hughes and Grumbine 2023). Given the global richness of ecosystem regulators such as predators and scavengers (figure 1) coupled with the known benefits they provide, signals opportunity for considering them as indicators. Example indicators include the livestock live weight gain associated with the presence of large carnivores via reduction of native herbivore competition and infection rates or supplanted costs attributed to organic waste removal from the presence of scavenger species. Although there are many more possible indicators, they nevertheless require a multidisciplinary approach that integrates predator–prey ecology or scavenging ecology with disease dynamics, agricultural production, or public health.
Species richness of predators and scavengers by country and example indicators. For illustration purposes, we only show the mammalian order of Carnivora and the avian raptor guild (orders Accipitriformes, Cathartiformes, Falconiformes, Strigiformes, and Cariamiformes). The map insets show an example species along with example indicators. The insets also show the number of species threatened in that country according to the IUCN Red List of Threatened Species. The spatial data were obtained from the IUCN and BirdLife International (IUCN 2025). Image credits: Adobe Stock, except for the black-and-chestnut eagle, which is credited to Thibaud Aronson.
Incorporating the contributions of predators and scavengers into global environmental agreements requires accounting not only for their benefits but also for their costs to human communities. Consider the case of the African lion (Panthera leo), which may provide benefits to livestock production by reducing native herbivore competition; however, they can also jeopardize a family's income by preying on livestock (Braczkowski et al. 2023). As such, considering whether and how predators and scavengers contribute to human health and well-being is challenging in areas where they are thought to be a real or perceived threat to people, game species, and valuable livestock. And people living alongside predators and scavengers tend to persecute them directly via shooting, trapping, and poisoning or indirectly via exclusionary methods (Lozano et al. 2019). This persecution has led to dramatic declines in range size and population health of many species, with predictions that they will soon be functionally extinct if not reversed (figure 1; Ripple et al. 2014). Therefore, an accounting approach for indicators that produces figures of net benefit can capture the full picture of the contributions of predators and scavengers in shared landscapes.
A core tenant of planetary health is recognizing and promoting opportunities for people and nature to thrive together—and realizing that our health is inextricably linked with the health of our environment (Martens 2024). Conserving predators and scavengers—and the services they provide—is a good example of the opportunity and challenge for achieving planetary health. Given that many predator and scavenger species are in state of rapid decline and that their declines are the proximal cause for ecosystem collapse (Ripple et al. 2014) and human loss (Frank and Sudarshan 2023, Frank 2024), we must act quickly to ensure their services are incorporated into global environmental agreements.
Data availability
All data used for the figure can be freely obtained from the IUCN and Birdlife International (IUCN 2025).
Author Biography
Christopher J. O'Bryan ([email protected]) and Pim Martens are affiliated with the System Earth Science Institute at Maastricht University in Venlo, the Netherlands. Alexander R. Braczkowski is affiliated with the Centre for Planetary Health and Food Security at Griffith University in Nathan, Queensland, Australia.
