Today marks Endangered Species Day, when people around the world are encouraged to discover more about threatened species and their habitats. For conservation efforts to succeed, it is necessary to understand how animals interact with each other, with their environment – and with humans. Lauren White (University of Minnesota) addresses this by studying the idea of One Health – the intersection of human, animal, and environmental health. Here, she discusses the relevance of this to conservation.
When I was in the third grade, I decided that I would become a field biologist who spent her time studying lemurs in Madagascar. I was particularly enraptured by aye-ayes—somewhat ungainly nocturnal lemurs with huge luminous eyes and an extremely long middle finger that aids their search for insects in rotting wood. When I found out that aye-ayes were often persecuted by local people because they were thought to bring bad luck, I was about as incensed as a third grader could be. This was my first confrontation with the realities of conservation—that human culture, beliefs, and needs do not always align with the conservation needs of other species on the planet.
My projected career path has changed somewhat since my elementary school days. As a disease ecologist, I now spend most of my time thinking about how we can better understand how infectious diseases spread through livestock and wildlife populations. What is interesting to me is that, I usually justify my research based on its relevance for humans, despite my original motivating interest in conservation as a child. As a society, we tend to care about diseases in wildlife because they might spread to livestock (e.g., foot and mouth disease from wild ruminants into livestock, bovine tuberculosis spilling over from badger into cattle) or because diseases originating in wildlife have the potential to spill over into people (e.g., Ebola, SARS, Hendra Virus). Emerging infectious diseases are on the rise, and we know that most of these diseases are starting in wildlife (Jones et al. 2008). Others have already pointed out that this trend might change the role of wildlife from a valued resource to that of pests to be eliminated (Evensen, 2008). For example, culling (reducing population size) is a common strategy used to fight zoonotic outbreaks in both domestic and wildlife populations. This raises a pivotal question in the realm of conservation: what happens if the dictates of human health and wildlife conservation are at odds?
This apparent dichotomy between human health and wildlife conservation is summarized nicely by two approaches to conservation: an ecocentric vs. an ecosystem services approach. An ecocentric approach argues that we should conserve species and green spaces for their inherent value, while ecosystem services monetizes both the current and the projected future value of the environment in order to justify conservation efforts (Piccolo et al. 2018).
The relationship between disease emergence and biodiversity is an important one. As we expand our reach into the environment through urbanization, habitat fragmentation, and changes in land use, we are making new human-livestock-wildlife interfaces for potential disease emergence (Hassell et al. 2017). Climate change will also contribute to changes in how host and vector species overlap, potentially leading to new diseases or the spread of existing diseases in new places. With the advent of the One Health field—which acknowledges the inherent relationship between human, animal and environmental well-being—there has been a recent push to combine expertise across fields like ecology, veterinary science, human medicine and public health. One idea promoted by this holistic approach is that preserving biodiversity may lower the risk of new diseases emerging. Research, however, describes a more complicated story so far, only supporting this “dilution effect” at certain scales and for certain systems (Young et al. 2017).
So, if conserving wildlife, green space, and biodiversity does not guarantee us some disease-buffering benefits, why study disease in wildlife, if not for its direct impacts on people?
- Parasites make up a huge part of biodiversity, and we haven’t even begun to catalog most of them. Parasites function similarly to predators in maintaining populations and ecosystems. In some ecosystems, they substantially outweigh predators in terms of biomass, and with climate change, up to one in three parasites may become extinct. It is hard to predict what the long-term consequences of such a massive extinction event might be.
- Emerging diseases pose risks to wildlife too! Such diseases can contribute to extinctions in already vulnerable or threatened wildlife populations (Smith et al. 2009). Some examples of this are Chytrid fungus (Batrachochytrium dendrobatidis), which has caused major declines in amphibian populations worldwide or West Nile Virus which has caused substantial declines in North American bird populations (Kilpatrick et al. 2010).
- As we continue to promote conservation through ventures like eco-tourism, reverse zoonoses/anthroponoses (transmission of diseases to animals from humans) or “pathogen pollution” will be of increasing concern for threatened wildlife populations. This is of particular concern in primate populations (Zachariah et al. 2017), but has been confirmed in other species as well—for example, a recent study confirmed that humans likely transmitted tuberculosis (Mycobacterium tuberculosis) to wild Asian elephants (Zachariah et al. 2017).
As a scientist, I am a pragmatist—I will use whatever tools are at my disposal to promote conservation, including an ecosystem service approach if that is persuasive to others. It is also likely that I will continue to pitch my research based on its applicability for human health. However, personally, it is my profound belief that each species has inherent value and that when we contribute to the extinction of a single species we cannot fully understand or predict the ramifications on the ecosystem at large. As ecological stewards, it should be our responsibility to mitigate the effects of our actions on other species. Increasingly, this includes the introduction of new pathogens or new invasive species to the detriment of native species (Thompson et al. 2010). This obligation to conservation should come regardless of whether it helps us stay healthy or not, but if we are lucky, we might benefit from both.
Evensen DT (2008) Wildlife disease can put conservation at risk. Nature 452(7185): 282.
Hassell JM, Begon M, Ward MJ, Fèvre EM (2017) Urbanization and disease emergence: Dynamics at the wildlife–livestock–human interface. Trends Ecol Evol 32(1): 55–67.
Jones KE, et al. (2008) Global trends in emerging infectious diseases. Nature 451(7181): 990–993.
Kilpatrick AM, Briggs CJ, Daszak P (2010) The ecology and impact of chytridiomycosis: an emerging disease of amphibians. Trends Ecol Evol 25(2): 109–18.
Piccolo JJ, Washington H, Kopnina H, Taylor B (2018) Why conservation scientists should re-embrace their ecocentric roots. Conserv Biol 0(0): 1–3.
Smith KF, Acevedo-Whitehouse K, Pedersen AB (2009) The role of infectious diseases in biological conservation. Anim Conserv 12(1): 1–12.
Thompson R, Lymbery A, Smith A (2010) Parasites, emerging disease and wildlife conservation. Int J Parasitol 40(10): 1163–1170.
Young HS, et al. (2017) Conservation, biodiversity and infectious disease: scientific evidence and policy implications. Philos Trans R Soc Lond B Biol Sci 372(1722): 20160124.
Zachariah A, et al. (2017) Mycobacterium tuberculosis in wild Asian Elephants, Southern India. Emerg Infect Dis 23(3): 504–506.