On Behalf of the Amphibians

An ecologist's perspective on the current mass extinction, human apathy, and frogs.

//jennifer rowe

We are in the midst of the planet’s sixth mass extinction. Fossil fuel emissions have driven unnaturally high carbon dioxide levels and undeniable human-caused climate change. Forests have been converted into fragmented matrices of agricultural fields and pavement. Our air and water are polluted, our natural resources exploited. Homo sapiens has really messed things up. The International Union for the Conservation of Nature (IUCN) listed 22,413 species — out of a sample of 4% of the total estimated number of described species — as threatened with extinction in 2014. We are losing species roughly 1,000 times faster than the background extinction rate, or the historic average species loss. [1][2] As a wildlife ecologist, this “Anthropocene Defaunation” keeps me awake at night.

Since I left Michigan for grad school in Oregon in 2010, I’ve been studying the factors contributing to species declines in the Pacific Northwest. Of particular interest to me is amphibian conservation; amphibians are among the most vulnerable taxonomic groups and are disappearing at an unprecedented rate. As of 2014, 41% of known amphibian species are threatened with extinction — more than the percentage for mammal (26%) and bird (13.43%) species combined. In the Pacific Northwest, native amphibians face myriad threats including habitat loss and degradation, disease, climate change, and non-native species — particularly warmwater fish and invasive American bullfrogs.    

The American bullfrog (Lithobates catesbeianus) is considered one of the world’s 100 worst invasive species; it has been widely introduced via aquaculture to over 40 countries. In the bullfrog’s native range throughout eastern North America, their numbers are put in check by limited resources and natural enemies (predators, competitors, and pathogens). They have co-evolved with other native species to occupy a balanced position in the predator-prey continuum, and they play a vital role within ecosystems by controlling algae growth, reducing the abundance of insect pests, and contributing to nutrient cycling. In the Western US invasive range, however, bullfrogs are having devastating impacts on naiive native fauna, including other amphibians, via competition and predation. [3][4][5][6] It’s a frog-eat-frog world out there, and just about everything is on the bullfrog’s menu.   

My research has largely focused on the mechanisms behind bullfrog success in novel habitats and their context-dependent interactions with native amphibian species. During field seasons, I can be found in waders surveying wetland amphibians in order to understand their habitat use. At Oregon State University, our lab spent months rearing bullfrog tadpoles in temperature-controlled rooms and conducting research on behaviors that might limit their success in their invasive range. There were entire days that I paced around the lab with a clipboard, stealthily peeking through slits cut in a makeshift blind to monitor bullfrog tadpole responses to predator chemical cues or UV-B radiation. I thought about bringing a sleeping bag to the lab when I spent nights pouring over a microscope and sifting through bullfrog stomach contents to assess their predatory impact. And I probably lost years of my life to spreadsheets and statistical coding. Don’t be misled by the lab-coat-clad caricature peering over beakers of bubbling blue liquid … science is rarely that glamorous. But it’s rewarding.

These research endeavors are part of the global effort by herpetologists to guide amphibian conservation. All around the world, native amphibians are facing a grim future. The factors driving their declines often interact synergistically to exacerbate the effect of a singular threat, so the research can quickly get messy. Notwithstanding direct threats to their habitat, the amphibian life history is wrought with unique obstacles. Amphibians have certain morphological and behavioral traits that make them particularly sensitive to environmental change. Many species are directly tied to both aquatic and terrestrial habitats, which must be connected and of high quality in order to support a self-sustaining population. Their unshelled eggs are prone to desiccation, and their semi-permeable skin, which promotes cutaneous respiration and water exchange, also allows for uptake of chemical contaminants. For these reasons, amphibians are often touted as “canaries in a coalmine” — harbingers of habitat degradation, with consequences that can resonate through the food chain.

But evolutionarily speaking, amphibians, have overcome a lot of challenges. To start, almost 400 million years ago, their earliest tetrapod ancestor made the transition from life in water to life on land. [7] A very diverse group, amphibians have since radiated to occupy almost any moist habitat on every continent except for Antarctica. Species have developed a wide variety of adaptations and reproductive strategies to suit their environments. Wood frogs produce their own antifreeze in the form of electrolyte-rich blood which enables them to hibernate through harsh arctic winters. Many dendrobatid frogs (poison dart frogs) exhibit parental care by transporting newly-hatched tadpoles on their backs to small, protected pools of water accumulating in bromeliads of rainforest canopies. [8] Salamanders are capable of regenerating a lost tail, limb, jaw, or other structures — a unique adaptation that is invaluable to evading predators and surviving wounds that might otherwise prove fatal. [9] A recently discovered species of rainfrog (Pristimantis mutabilis) in Ecuador even has the remarkable ability to change its skin texture to better camouflage against its surroundings.

These species are the precarious product of millions of years of random genetic variation and natural selection. A precise combination of interactions with local predators, competitors, and environmental conditions has shaped the various strategies they employ. Homo sapiens, a highly successful invasive species like the bullfrog in the West, has been disrupting these carefully matched dynamics since it originated in the Pleistocene a mere 200,000 years ago. [10] Invasive species are often incredibly successful in the new habitats they invade because they possess traits that are advantageous to their survival and proliferation. Humans, equipped with large brains and industrial power, are successful in exploiting new habitats and outcompeting pre-existing species. A rainforest-dwelling frog is certainly no match for a chainsaw.

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Working in the applied sciences requires a lot of outreach and “people management.” As a person who would much rather spend my days in wilderness, admittedly I’m still developing this skillset. I work with many well intentioned landowners who often ask, “Why should I care if I have frogs on my property?” This is certainly a legitimate question prompted by perhaps an innate desire to ascertain a species’ place within a system. With limited government resources, it’s natural to organize scientific endeavors within a hierarchy of importance. Taxpayer funding is largely dependent on the strength of the argument that a particular research endeavor will benefit people. “Describe the broader implications of this research” is a question every scientist encounters in funding applications. Essentially, it means that unless your research will directly benefit the economy or lead to a medical breakthrough or solve world hunger, you probably won’t be seeing any of that grant money. Gone are the days when scientific observations were made purely to advance our understanding of the natural world — the modern scientist must also be a humanitarian.

Many ecologists comply with this bias toward applied science because we also recognize the importance of convincing people to care. When a landowner asks me about the value of amphibians, I’m prepared to respond with anthropocentric examples. First of all, there are new species of amphibians described almost every other day, so we can’t even begin to know the extent of their importance for medicine, biotechnology, and agriculture. For instance, the biological mechanisms (presence of healing macrophages and the plastic reprogramming of cells) behind the salamander’s limb regrowth superpower have applications in regenerative medicine, making salamanders a valuable research model. [11][12][13] Certain compounds found on the skin of amphibians have proved useful in the development of pharmaceuticals and antimicrobials. [14] And let’s not forget that amphibians can be indicators of environmental health. If farmers have frogs on their property, chances are they also have unpolluted water sources for irrigation and livestock, an abundance of beneficial insects indicative of high quality soil, and fewer crop pests.

It’s ironic that a large component of the wildlife professional’s job is to justify the usefulness of such a job. After all, it’s a deep appreciation of the natural world — not grant money — that drives ecologists and conservationists to devote their lives to the imbroglio of field work and spreadsheets. “Why should I care?” The truth is, I really want to respond with a long-winded philosophical diatribe about how it shouldn’t matter that amphibians might serve some human purpose. The question contains a connotation of entitlement, a superficial elevation of Homo sapiens above all other beings. Isn’t it enough that amphibians, and every other species group, have a right to exist just as much as we do? They arrived the same way we did: by the process of evolution. Is there not inherent value to life? To biodiversity? To natural aesthetics?  

Biodiversity is critical for ecosystem function, productivity, and stability. A healthy ecosystem provides many services such as water and nutrient cycling, carbon sequestration, climate regulation, and crop pollination. [15] Any disruption (stochastic or human-caused) to the configuration of organisms in a carefully orchestrated web of interactions can resonate through the entire ecosystem, consequently affecting the services it provides. But we humans are meddlers, and we are living in an engineered world. Human interference has led to unnaturally high instability in ecosystem properties; in fact, our modification of species composition and system functions is so great that ecologists now recognize “novel ecosystems” in the new management paradigm. Invasive species are so prevalent that eradication is often unfeasible, and it is increasingly common for them to become integrated within a system. [16] Time and again we are challenging the fidelity of historic processes and embracing change (when it suits us).

Biodiversity is an incredibly important insurance policy; the greater the species pool, the greater the likelihood of one species filling the role of another if it is extirpated from the system. [17] Diverse native communities can even offer biotic resistance against invasive species by reducing the availability of unoccupied niches for the invader to colonize or regulating invader densities through competition and predation. John Muir wrote in My First Summer in the Sierra (published in 1911), “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” This statement, perhaps, has never been as evident as it is now in the age of novel ecosystems. The addition of one invasive species, the loss of one native species, a change in the frequency or intensity of abiotic conditions – these seemingly minor modifications can alter the entire trajectory of a system.  

Unfortunately, a conservation ethic is often suppressed by lack of knowledge; we fail to understand that environmental issues and social conflict are intimately intertwined. Biodiversity loss negatively impacts food and energy security, access to clean water, resilience to natural disasters, and human physical and spiritual health. [18] Destruction of mangroves, coral reefs, dunes, and salt marshes results in a loss of barriers to abate tropical storms and flooding, threatening roughly a third of the world’s coast-dwelling population. [19] Deforestation is associated with a rise in vector-borne diseases such as malaria, yellow fever, dengue, and Lyme disease. [20][21] Furthermore, the negative impacts of biodiversity loss are often disproportionately felt by impoverished groups. The global decline of fisheries exacerbated by commercial overexploitation has prompted an increase in child labor, piracy, and political conflict in West Africa, where people are reliant on fish for sustenance. The effects of climate change (reduced agricultural productivity, loss of fish stocks, and intensification of water stress) are projected to be most devastating in developing nations of the tropics under multiple scenarios. [22] Worldwide, the loss of ecosystem services is consistently followed by a decrease in ecological and socio-cultural wellbeing. We have even attempted to place monetary value on the practical and cultural benefits of ecosystem services; in 1997, the average annual economic value of biodiversity was estimated at $33 trillion. [23] But how does one place a dollar amount on the spiritual and aesthetic aspects of nature?

We need nature for its intangible, unquantifiable qualities. We need it for its curiosities, its beauty, its tranquil refuge. Exposure to the natural world is crucial for emotional and physical health, and we rely on it for philosophical and recreational escapes. Our evolutionary history suggests that we are not fully adapted to urban environments. Hominins originated in forested habitats of Africa; thus, there may be some truth that we are wired to prefer these natural ancestral surroundings.  [24] A growing body of research acknowledges “nature deficit disorder” as a true epidemic that is linked to higher rates of childhood obesity, attention deficit hyperactive disorder, anxiety, and depression. A child’s intellectual, social, and physical development, as well as empathy toward nature, can be hindered in the absence of exposure to the natural world. E.O. Wilson proposed the “biophilia hypothesis” to explain the seemingly innate bond with nature that children often possess. [25] Children engage with nature more holistically than adults, placing value on sensory experiences rather than aesthetics. [26] If we tend to only care about what we see, then it is good practice to look at the world through a child’s eyes.

A collaborative integration of legislation, stakeholder involvement, and education can foster connections between people and the land. In the U.S., the USDA Conservation Reserve Program allows farmers to enter a cost-share agreement in exchange for removing ecologically valuable land from production. Various incentive programs exist in other regions to mitigate the destruction of habitats. In Bolivia and Costa Rica, for example, landowners are compensated for the estimated value of ecosystem services (such as carbon sequestration) provided by their land. In the Indonesian island of Lombok, villagers manage a community forest to protect the watershed of a downstream city. In exchange, they receive payments subsidized by the city’s water fees, and they’re allowed to sustainably harvest forest fruits, cacao, and coffee beans. Ecotourism engages local communities to participate in conservation stewardship by providing jobs and tourist dollars (although it also contributes a large carbon footprint and increased traffic to sensitive habitats). As of 2010, 83% of developing nations relied on ecotourism as a major export, with global annual revenue exceeding $77 billion. Even the federally-threatened Oregon spotted frog (a species of high conservation concern in the Northwest) has its place within a collaborative social-conservation program; the Sustainability in Prisons Project is a partnership between The Evergreen State College, community members, and the Washington State Department of Corrections bringing conservation stewardship to prisons. Inmate technicians conduct field surveys to monitor spotted frog populations and help with captive rearing and reintroduction of the frogs to suitable sites. In a mutually beneficial relationship, the incarcerated are educated and motivated to contribute to research and recovery of the species.  

International partnerships are imperative for developing broad solutions to our current environmental crisis, and innovative programs offer hope for species and habitats that now desperately require our intervention. Although Homo sapiens is driving mass extinctions, we are the only species with the ability to make conscious decisions every day about how we want to leave this world for future generations. Besides, we need nature as much as nature needs us — to clean up our messes.

Footnotes:

[1] Pimm SL, Jenkins CN, Abell R, Brooks TM, Gittleman JL, Joppa LN, et al. The biodiversity of species and their rates of extinction, distribution, and protection. Science. 2014;344: 987–996.
[2] Millenium Ecosystem Assessment Program. Ecosystems and Human Well-Being: Synthesis. Washington, DC: Island Press; 2005.
[3] Snow N, Witmer G. American Bullfrogs as invasive species: a review of the introduction, subsequent problems, management options, and future directions. 2010; Available: http://digitalcommons.unl.edu/icwdm_usdanwrc/1288/
[4] Adams MJ, Pearl CA, Galvan S, Mccreary B. Non-native species impacts on pond occupancy by an anuran. The Journal of Wildlife Management. 2011;75: 30–35. doi:10.1002/jwmg.29
[5] Adams M, Pearl C. Problems and opportunities managing invasive bullfrogs: Is there any hope? Biological invaders in inland waters: Profiles, distribution, and threats. 2007;2: 679–693.
[6] Pearl CA, Adams MJ, Bury RB, McCreary B. Asymmetrical effects of introduced bullfrogs (Rana catesbeiana) on native ranid frogs in Oregon. Copeia. 2004;2004: 11–20.
[7] Hoskins S. The Rise of Amphibians: 365 Million Years of Evolution. Zoological Journal of the Linnean Society. 2011;161: 693–694. doi:10.1111/j.1096-3642.2011.00694.x
[8] Weygoldt P. Evolution of parental care in dart poison frogs (Amphibia: Anura: Dendrobatidae). Journal of Zoological Systematics and Evolutionary Research. 1987;25: 51–67. doi:10.1111/j.1439-0469.1987.tb00913.x
[9] Brockes JP, Kumar A. Plasticity and reprogramming of differentiated cells in amphibian regeneration. Nature Reviews Molecular Cell Biology. 2002;3: 566–574.
[10] White TD, Asfaw B, DeGusta D, Gilbert H, Richards GD, Suwa G, et al. Pleistocene Homo sapiens from Middle Awash, Ethiopia. Nature. 2003;423: 742–747. doi:10.1038/nature01669
[11] Brockes JP, Kumar A. Appendage regeneration in adult vertebrates and implications for regenerative medicine. Science. 2005;310: 1919–1923.
[12] Godwin JW, Pinto AR, Rosenthal NA. Macrophages are required for adult salamander limb regeneration. Proceedings of the National Academy of Sciences. 2013;110: 9415–9420. doi:10.1073/pnas.1300290110
[13] Song F, Li B, Stocum DL. Amphibians as research models for regenerative medicine. Organogenesis. 2010;6: 141–150.
[14] Barra D, Simmaco M. Amphibian skin: a promising resource for antimicrobial peptides. Trends in Biotechnology. 1995;13: 205–209.
[15] Millenium Ecosystem Assessment Program. Ecosystems and Human Well-Being: Synthesis. Washington, DC: Island Press; 2005.
[16] Hobbs RJ, Higgs E, Harris JA. Novel ecosystems: implications for conservation and restoration. Trends in Ecology & Evolution. 2009;24: 599–605. doi:10.1016/j.tree.2009.05.012
[17] Wilson EO. The Future of Life. 1st ed. New York: Random House, Inc.; 2002
[18] Millenium Ecosystem Assessment Program. Ecosystems and Human Well-Being: Synthesis. Washington, DC: Island Press; 2005.
[19] Barbier EB, Koch EW, Silliman BR, Hacker SD, Wolanski E, Primavera J, et al. Coastal ecosystem-based management with nonlinear ecological functions and values. Science. 2008;319: 321–323.
[20] Millenium Ecosystem Assessment Program. Ecosystems and Human Well-Being: Synthesis. Washington, DC: Island Press; 2005.
[21] Cohuet A, Simard F, Wondji CS, Antonio-Nkondjio C, Awono-Ambene P, Fontenille D. High malaria transmission intensity due to Anopheles funestus (Diptera: Culicidae) in a village of savannah-forest transition area in Cameroon. Journal of Medical Entomology. 2004;41: 901–905.
[22] Millenium Ecosystem Assessment Program. Ecosystems and Human Well-Being: Synthesis. Washington, DC: Island Press; 2005.
[23] De Groot RS, Alkemade R, Braat L, Hein L, Willemen L. Challenges in integrating the concept of ecosystem services and values in landscape planning, management and decision making. Ecological Complexity. 2010;7: 260–272.
[24] Wilson EO. The Future of Life. 1st ed. New York: Random House, Inc.; 2002
[25] Wilson EO. The Future of Life. 1st ed. New York: Random House, Inc.; 2002
[26] Gibson JJ. The theory of affordances. In R Shaw & J Bransford (Eds.),  Perceiving, acting, and knowing: Toward an ecological Psychology. Hillsdale, NJ: Erlbaum. 1977;67-82.

//Jennifer Rowe is a Michigan transplant currently living in the beautiful state of Oregon. Having recently received her Master's in Wildlife Science, she spends her free time hiking, herping, mushroom hunting and cooking, and creating nature-inspired art. To view more of Jennifer's work, please click here.