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Amphibian Conservation 
in Changing Habitats

4/18/2020

From Wetland to Farmland:

Understanding Amphibian Conservation in Changing Ecosystems

 

Introduction

            Development of natural lands has been increasing significantly since the Industrial Revolution. This has led to a great loss in ecological resources. Wetlands are one of the most important of these ecological resources and their number has decreased especially due to farming and cattle ranching. Since the 1970s, governments have initiated programs to attempt to limit the loss of wetlands. This has been completed primarily via the formation of Mitigation Wetlands: restored or created ecosystems that simulate a naturally formed wetland. Conservationists and Wetland Ecologists have expressed fears about the effectiveness of this method for restoring the number of ecological services that natural wetlands serve. Alternative methods have been explored for mitigation on pastureland, but the same problems persist. I am interested in evaluating the literature that assesses the efficacy of these mitigation methods that are intended to reestablish these necessary ecological resources. I will be using studies that assess amphibian presence and richness in reconstructed wetlands due to their correlation with high quality wetland environments. Furthermore, amphibians being present is one of the most important factors that are used to evaluate the formation of Mitigation Wetlands (Bookout, 2019).

            This is because amphibians’ biphasic lifestyle relies on wetlands for habitat, food, shelter, moisture, and breeding; this is beyond the normal reliance of other animal classes. They are also especially sensitive to a variety of wetland quality indicators: Dissolved Oxygen, Nitrate, and Sediment Load (Rouse, 1999; Carter, 2001). As a vital part of the ecosystem, amphibian presence and health are highly correlated with the overall health of a wetland. Wetland drainage has uprooted amphibians and forced them to find alternate breeding locations and resources. We will explore in the following pages how amphibian habitat has changed due to human development, the benefits and drawbacks to this change, and finally ways in which proper wetland use can restore (or at least improve) the habitats (and thus lives) of the amphibians native to these wetlands.

 

I.  Ecosystem Transformation: Wetland to Farmland

            The destruction of natural areas that provide ecological services is well recorded in history. However, despite efforts to educate the public, businesses continue to fail to understand the incredible value that we lose when loss of an ecological resource or service occurs. According to a 1997 study, “the annual value of these services is US$16-54 trillion, with an estimated average of US$33 trillion” (Costanza). I do not have an exact number for the monetary value that wetlands contribute to this estimated annual value, but we do know that they make up an important proportion of ecological services provided by the biosphere. Wetlands take up approximately 3-6% of Earth’s surface, yet they complete a disproportionate number of these ecological services, making them especially valuable (Hook, 1993). Ecotoxicologists note that wetlands filter water of toxic biowaste and have been successfully used to treat wastewater in many municipalities (Kadlec, 1990).

            Mangrove swamps and saltmarshes especially have some of the highest primary productivity rates, second only to monoculture cornfields. This contributes to the sequestration of carbon from the atmosphere. They also have high biodiversity due to specific stresses that promote heavy niche partitioning (e.g.: acidic environment of bogs and fens). However, despite the inordinate monetary, ecological, and cultural benefit of protecting wetlands, these ecosystems are subject to some of the most development due to their fertile soil. Development requires that the wetland be drained before building or farming commences on a property. This practice of drainage was unregulated in America until the 1970s, meaning that hundreds of wetlands were legally drained and transformed into farmland for crops or cattle. Furthermore, conservation efforts have proven difficult due to the ephemerality of some wetlands and the changing legal definitions for what can be protected from development. For instance: vernal pools are often little more than shallow depressions in the landscape for most of a year, only filling for a few weeks in Spring, yet they represent high-quality spawning sites for amphibians (Previant, 2016).

            The USA primarily uses a rule from 1989 that is referred to as “No Net Loss”. This means that a person can drain a wetland so long as they restore or create a wetland of the same area or larger; this is referred to as a mitigation wetland (U.S. EPA, 1990; Swartz 2019). This is ultimately a product of the dualistic notion of nature that has been perpetuated by the dominant conservationist culture that ignores other cultures that live in harmony with the land in heavily forested regions without deforestation or habitat degradation (Smith, 2014). Knowing this, we can make the statement that the loss of natural areas is not related directly to human habitation, but rather the specific practices of our culture and legislation that reinforces a human divide from nature. This particular legislation has been flouted by property owners and large companies (e.g.: the Rapanos Decision, Solid Waste Agency of Northern Cook County v. Army Corps of Engineers, etc.). 

 

            Ergo, the loose nature of wetland law enabled the ecosystem transformation of wetlands to farmlands even after the Clean Water Act (1972). Twenty-six percent of Earth’s ice-free land is now used as pasture for cattle (Howell, 2019). Much of this land is drained wetland and is at high risk for overgrazing due to unstable soil (Mysterud, 2006), degrading the habitat even further. The changed ecosystem now appears as a prairie-like ecosystem and does not house proper accommodations for wetland plants or amphibians. An estimated fifteen percent of wetlands are affected by rice production (Hook, 1993). These wetlands have been channelized and formed into rice monocultures, limiting diversity and thus niche/habitat for amphibians and other animals. These two examples highlight the ways in which development affects these habitats negatively.

            As noted in the introduction, amphibian presence is crucial to the perceived success of a restored wetland. Amphibians require both aquatic and terrestrial environments throughout their life cycles, making them especially vulnerable to development across all fronts (Beebee, 2005). Breeding is almost always completed in a wetland (Mushet, 2012). Amphibian larvae typically require aquatic environments to mature (though paedomorphic salamanders will spend their entire lives in aquatic areas). Adults use terrestrial habitats to move between wetlands. This means that connectivity of habitat is crucial to allow sufficient migration pathways and to prevent inbreeding. Wetland Connectivity is also an important metric used to determine the quality of a wetland itself, as low connectivity suggests that the water regime is unable to settle across a large area. So, what happens when an amphibian is left in a pastureland or farmland? Do mitigation wetlands do anything to conserve the populations of these creatures?

            In the following section, we will be focusing on recent studies that have elucidated some of the possibilities for conservation of amphibians. The most important of these discoveries has been the potential viability of the pasture drainage ditch and mitigation wetlands as new habitats for amphibians to breed and thrive in the Meghalayan age.

 

II. Conservation of Amphibians in Systemically Developed Regions

            Let us begin on a ranch. Cows graze in the distance and the ground is generally dry, with some wet ditches. This environment is a far cry from the wet forest that was sitting here only 200 years ago. One might assume that the wildlife has mostly left for the “protected” regions that the government has labeled as wilderness. This is not the case. Despite the lack of connectivity between high-quality environments, amphibians continue to attempt to live in habitats that are less than stellar. 40% of threatened amphibians are subject to this fragmentation of their original habitat (Stuart, 2004). This has led some populations of amphibians to breed in man-made locations such as: constructed ponds, drainage ditches, and even water troughs (Buono, 2019). In fact, according to this 2019 study completed in the Tolfa Mountains of Italy, amphibians used

Picture2.png

drinking troughs at approximately

the same rate as natural, permanent

sites (Figure to the Immediate Right).

This indicates that H. sapiens can

live in accord with surviving

amphibians, even on farmland.

However, the Tolfa Mountain

Region has breeding site options

that include permanent, naturally

formed bodies of water in a

protected Riverine Forest.

This is not the highest stress situation for an amphibian. Nonetheless, this study notes that a practical shift towards traditional farming could alleviate much of the stress on amphibian breeding populations. There has been a shift, especially in America and the European Union towards modernizing farming in order to strip the Earth of as much as it can produce at a given time (Benayas, 2012).

          Buono, et. al’s study is the exception, not the rule. Negative responses from taxa have been recorded in many instances of livestock grazing overtaking an ecosystem, especially in Western North America (Fleischner, 1994). Further complicating matters, certain taxa have experienced positive responses to livestock grazing, indicating that the issue is quite complicated. The intermediate disturbance hypothesis is just one example of how a stressor can lead to an increase in the viability of a species. Cattle presence can increase nitrate concentrations and sediment loads, which amphibians are quite sensitive to. This increase can be beneficial or highly destructive to the fitness of amphibians. In naturally low-nutrient areas, the new inflow of nitrate and sediment can provide more food for amphibian larvae. In areas that become eutrophic, breeding ponds may become completely uninhabitable. This variability in the response that amphibians can have to livestock has made studying this exceedingly difficult and has left little substantial data. Furthermore, data is lacking in Africa and Asia. Globally, negative amphibian responses to grazing were detected most prevalently in North America while positive responses were detected in Europe. Positive responses were caused by increased hydroperiods and prevention of ecological succession while negative responses were caused by increases in nitrate concentration and a reduction in dissolved oxygen (Howell, 2019). Ultimately, more studies need to be completed in order to make any kind of definitive statement about how to specifically manage livestock placement with regard to amphibian biodiversity.

            Mitigation wetlands represent the opposite problem as livestock grazing locations. They are areas where humans are attempting, explicitly, to create suitable habitat for amphibians (as their presence represents a high quality wetland). Bookout and Bruland hypothesized that once hydrology and vegetation were restored in their study site (Jersey County, Illinois), amphibians would repopulate the site. They observed 11 amphibian species which was significantly higher than similar studies that reported an average of 3.6 (Lehtinen, 2001) and 4.2 (Porej, 2005) species. The stable hydroperiod represented in two of the cells in the studied mitigation wetland yielded standing water for long enough to allow for larvae maturation (Bookout, 2019). This study shows that using the Gleasonian Succession Model and striving to return abiotic factors (e.g.: hydroperiod) to their natural state is a promising management strategy for these systems.

In a Yellowstone-based study

that compared created wetlands,

impacted wetlands, and reference

(undisturbed) wetlands, there was

a variable difference found

between the different groups with

regard to a selection of

amphibians’ occupancy (Figure to

the Immediate Right). The created wetlands were shallow, small, had a shorter hydologic regime, and had less aquatic vegetation. Tiger salamander occupancy was consistent across all types of wetland (Swartz, 2019). This went directly against the authors’ hypothesis, demonstrating the often-confusing nature of attempting to evaluate the effectiveness of a wetland before the creation process is completed. However, other studies have shown that the snout-vent length of salamanders (an indicator of health) in created wetlands was similar to that of extant populations (Valdez, 2017). So, the viability of repopulated wetlands for amphibian occupancy appears to be similar to that of natural areas, though long-term studies have never been completed.

Picture3.png

     

             Connectivity of wetlands has proved to be fragmented by years of development, leading to a difficulty in even finding a large enough area to create a new wetland. Choosing a location for a mitigation wetland can be a difficult process as well, due to the number of abiotic and biotic factors that must be analyzed before beginning the costly process of ecosystem transformation. Optimization models have been created to help in the selection, but the decision-making remains an expansive and time-consuming activity for those developers that care enough to interact meaningfully with the mitigation wetland creation (Scroggie, 2019). Amphibian biodiversity is most greatly influenced by this connectivity value. Isolated parks and created wetlands experience a lower species richness due to the lack of viable migration pathways allowing repopulation by extant populations of amphibians (Wright, 2020). The metacommunity of amphibians in a region must be considered before selection of a mitigation wetland location is completed for optimal results. To further complicate the selection process, connectivity and suitability of the to-be-created wetland are not correlated. This means that each factor must be considered holistically, without aggregating them into one selection process (Zaffaroni, 2019).

 

III Discussion and Conclusions

            Assessing the quality of a wetland can be an extremely taxing process that many businesses refuse to complete due to budget constraints or a lack of care. Furthermore, amphibians complicate the processes of survey and analysis due to unique lifestyles and a reliance on abiotic factors for survival. This was most prominently seen in the difficulty of assessing pasture-grazing amphibian population occupancy and viability of water trough lifestyles.

            The current dominant relationship to nature in the public imagination reinforces these difficulties, as the biphasic understanding of wilderness prevents humans from considering agricultural practices that allow for harmonious accordance with the environment and its other denizens. Upon the current trajectory, habitat fragmentation, degradation, pollution, and climate change will continue to decrease the habitat suitability and connectivity of wetland ecosystems, limiting amphibian population growth and initiating further decline. This ecosystem transformation that favors human comfort and ease over all other lives must stop in order for populations of other animals to return to previous levels. Even such a drastic course correction, will surely take decades or centuries to see true change that reestablishes non-human animal populations.

            More research should be completed concerning the selection of mitigation wetlands, practical changes that promote amphibian health in pastureland ecosystems, and studies that elucidate the underlying abiotic factors that are required for suitable amphibian life. We hold the power to change the lives of all the organisms around us, to transform whole ecosystems. Will our roots reach too far below the Earth like the trees of the mid-Devonian, destroying the world? Or will we learn from the past and come together as one people to become the bodhisattvas of the whole world? Only time will tell, but now is our call to action.

 

 

Works Cited

Beebee, T. J. C., & Griffiths, R. A. (2005). The amphibian decline crisis: A watershed for conservation biology? Biological Conservation 125: 271–285.

 

Benayas, R., & Bullock, J. M. (2012). Restoration of biodiversity and ecosystem services on agricultural land. Ecosystems 15: 883–899.

 

Bookout, T. and Bruland, G.L. (2019). Assessment of a Restored Wetland in West-Central Illinois. Northeastern Naturalist 26(2): 392-409.

 

Buono, V., Bissattini, A.M., & Vignoli L. (2019). Can a cow save a newt? The role of cattle drinking troughs in amphibian conservation. Aquatic Conservation-Marine and Freshwater Ecosystems 29(6): 964-975.

 

Carter, J. G. 2001. Livestock and water quality. Report to Western Watersheds Project, Utah. www.westernwatersheds.org/reports/grazeWQ_JCarter/WQWWP.doc

 

Costanza, R., dArge, R., deGroot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem, S., ONeill, R.V., Paruelo, J., Raskin, R.G., Sutton, P., and VandenBelt, M. (1997). The value of the world's ecosystem services and natural capital. Nature 387(6630): 253-260.

 

Fleischner, T. L. 1994. Ecological costs of livestock grazing in western North America. Conservation Biology 83: 629–644.

 

Hook, D.D. (1993). Wetlands: History, Current Status, and Future. Environmental Toxicology and Chemistry 12: 2157-2166.

 

Howell, H.J., Mothes, C.C., Clements, S.L., Catania, S.V., Rothermel, B.B., & Searcy, C.A. (2019). Amphibian responses to livestock use of wetlands: new empirical data and a global review. Ecological Applications 29(8), DOI: e01976.

 

Kadlec, R.H. and Bevis, F.B. (1990). Wetlands and Wastewater: Kinross, Michigan. Wetlands 10: 77-92.

 

Lehtinen, R.M.  and Galatowitsch, S.M. (2001).  Colonization of restored wetlands by amphibians in Minnesota. American Midland Naturalist 145:388–396.

 

Mushet, D.M., N.H. Euliss, and C.A. Stockwell. (2012). Mapping Anuran Habitat Suitability to Estimate Effects of Grassland and Wetland Conservation Programs. Copeia 2012: 321–   30.

 

Mysterud, A. (2006). The concept of overgrazing and its role in management of large herbivores. Wildlife Biology 12:129– 141.

 

Porej, D. and Hetherington, T.E. (2005).  Designing wetlands for amphibians: The  importance of predatory fish and shallow littoral zones in structuring of amphibian communities. Wetlands and Ecological Management 13(4):445–455.

 

Previant, W.J. and Nagel, L.M. (2016). Vernal Pool Inventory and Classification at Pictured Rocks National Lakeshore, Michigan. USA Natural Areas Association 36(2), doi: 043.036.0203.

 

Rouse, J. D., Bishop C. A., and J. Struger. 1999. Nitrogen pollution: An assessment of its threats to amphibian survival. Environmental Health Perspectives 107:799 803.

 

Scroggie, M.P., Preece, K., Nicholson, E., McCarthy, M.A., Parris, K.M., & Heard, G.W. (2019). Optimizing habitat management for amphibians: From simple models to complex decisions. Biological Conservation 236: 60-69.

 

Smith, T. R. (2014). "Humanity and Its Place in Nature: Rethinking the Reality of 'Wilderness'." Inquiries Journal/Student Pulse, 6(09). Retrieved from http://www.inquiriesjournal.com/a?id=911

 

Stuart, S.N., Chanson, J.S., Cox, N.A., Young, B.E., Rodrigues, A.S.L., Fischman, D.L., and Waller, R.W. (2004). Status and Trends of Amphibian Declines and Extinctions Worldwide. Science 306(5702): 1783-1786.

 

Swartz, L.K., Lowe, W.H., Muths, E.L., & Hossack, B.R. (2019). Species-specific responses to wetland mitigation among amphibians in the Greater Yellowstone Ecosystem. Restoration Ecology 28(1): 206-214.

 

U.S. EPA. (1990). Memorandum of agreement between the Environmental Protection Agency and the Department of the Army concerning the determination of mitigation under the Clean Water Act Section 404(b)(1) guidelines. Washington D.C.

 

Valdez, JW., Klop-Toker, K., Stockwell, M.P., Fardell, L., Clulow, S., Clulow, J., and Mahoney, M.J. (2017). Informing compensatory habitat creation with experimental trials: a 3-year study of a threatened amphibian.

Oryx 53(2): 310-320.

 

Wright, A.D., Campbell Grant, E.H., and Zipkin E.F. (2020). A hierarchical analysis of habitat area, connectivity, and quality on amphibian diversity across spatial scales. Landscape Ecology 35(2): 529-544.

 

Zaffaroni, M., Zamberletti, P., Creed, I.F., Accatino, F., De Michele, C., & DeVries, B. (2019). Safeguarding Wetlands and Their Connections within Wetlandscapes to Improve Conservation Outcomes for Threatened Amphibian Species. Journal of the American Water Resources Association 55(3): 641-656.  

                Water Resources Association 55(3): 641-656.  

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