Not All Frogs Can Make It in the City: Using the Landscape for Targeted Conservation
Like many places across the world, Northwest Arkansas is a growing urban area with a population size that has doubled over the last 30 years and is expected to be home to nearly 1 million people by 2045. Such a rapid growth in population size can result in equally rapid habitat destruction and modification, usually at the expense of local wildlife. How do wildlife populations respond to such rapid change? Well, with a handful of historic population records collected over the last 30 years and some enthusiasm, we set out to (at least partially) answer that question as it pertains to Crawfish Frogs.
Why Crawfish Frogs? They may not be an icon of the American prairie, but the Crawfish Frog is found throughout the eastern prairies and river valleys of the Central US and, like many amphibian species, the species is in decline. Crawfish Frogs have a distinct call described as a short snore that can be heard during breeding, a time when Crawfish Frogs can be found relatively easy. The Crawfish Frog is unique among many of its True Frog relatives because they do not spend much time in, or even near, wetlands, instead relying on crayfish burrows most of the year. However, their unique habitat needs require large tracts of relatively intact open-canopy habitat and access to crayfish burrows. As a result of habitat loss, the Crawfish Frog has gone extinct in one of the 13 states (i.e. Iowa) it historically occurred in, and is a species of greatest conservation need in the remaining 12 states. Like many species of the American prairie, Crawfish Frogs need targeted conservation action.
Crawfish Frogs have a distinct call described as a short snore that can be heard during breeding, a time when Crawfish Frogs can be found relatively easy.
We identified 81 potential breeding locations, including 16 sites known to have actively breeding Crawfish Frogs within the last 30 years, covering a range of prairie remnant, cattle pasture, row crops, and urban habitats. At each site, we completed repeated call surveys (i.e. we listened for calling males) and recorded environmental factors that might be related to calling activity. Our results provide important insights on Crawfish Frog population persistence in rapidly developing areas. Historical breeding populations, nearly 40%, had likely gone locally extinct, with no calling activity over the study period and much of the surrounding areas heavily developed for human-use. However, we also detected new breeding locations, primarily in cattle grazing and pasture habitat types. While Crawfish Frog populations do not persist in urban areas, they seem to persist in low-intensity agriculture habitats. We also identified landscape factors associated with Crawfish Frog presence to increase the probability of finding new breeding populations. Surprisingly, prairie mound density, an important topological feature common in open-canopy habitats and easily identifiable using remote-sensing tools, was a good predictor of Crawfish Frog presence. Additionally, the presence of mounds in agricultural areas indicates that while degraded, the habitat has not been extensively plowed or destroyed.
When we expanded our study area in Northwest Arkansas to cover more counties and a broader community of reptiles and amphibians, this trend remained true. Prairie mounds were important predictors of occurrence for not only Crawfish Frogs, but also other prairie-associated species.
Globally, temperate grasslands are the most endangered ecosystem with the highest risk of future biodiversity loss and amphibians are the most threatened vertebrate group, with over a third of all known species threatened with extinction. Our study helps contribute to a growing knowledge base that shows low-intensity agricultural habitats can serve as important reservoirs for many open-canopy species in rapidly changing landscapes. However in agricultural areas near or converted for urban use, wildlife populations with low mobility and specific habitat requirements, such as the Crawfish Frog, are more likely to go extinct. Additionally, having easily accessible metrics that can be used to narrow down survey locations to improve the probability of identifying new populations is valuable for species conservation. Prairie mounds and other mima-like mounds are found on every continent except Antarctica, and are often indicative of historic grassland habitat. Our study provides some evidence that these easy to identify topological features could be a useful tool for predicting grassland-associated species occurrence. With species-specific associations, mound density might also be a useful metric for identifying and targeting critical habitats for grassland conservation and restoration.
This response is in reference to:
Ichthyology & Herpetology, 110(1): 50-58 (2022).
Chelsea S. Kross, John D. Willson
Dr. Chelsea Kross
What drew you to the research topic you explored in your submission?
During the first year of my PhD, I spent the field season using radio-telemetry to track Crawfish Frogs in an urban wetland prairie sanctuary. Almost half of my transmittered frogs died during the three month study or left the sanctuary to nearby agricultural land that was about to be developed for residential housing. These observations and conversations with my PhD advisor, JD Willson, led us to ask “how are Crawfish Frog populations faring in Northwest Arkansas?”
How do you see your work contributing to public policy, citizen science, and/or science education more broadly?
Our work has contributed to multiple science education events in the Northwest Arkansas region, which has resulted in increased awareness of the Crawfish Frog and the loss of prairie habitat. Our work has also led to other projects funded by the Arkansas Game and Fish Commission to determine the specific habitat needs of Crawfish Frogs in Northwest Arkansas. The ultimate goal of these projects is to provided greater protection to the remaining Crawfish Frog populations in the region through land protection and easements, as well as increased community support for conservation.
What are your continuing research goals for the future (near and/or far)? What topics, areas, subjects are you interested in exploring?
We are currently wrapping up a three-year radio-telemetry project evaluating the specific habitat-use of Crawfish Frogs in restored and remnant prairies. Additionally, I am most interested in identifying the factors that allow Crawfish Frog populations to persist in low-intensity agricultural areas. It could be that land area is a primary factor associated with their persistence since these agricultural lands are some of the largest least-fragmented habitats available, but there could also be other factors such as metapopulation dynamics at play. I am also interested in validating the prairie mound density and species occupancy predictive relationship because I feel this could be really useful for identifying land parcels that might be especially valuable for grassland conservation.
Is there anything else you want to share about you and/or your research?
Some of the work I have been most proud of was having the opportunity to contribute the long-term conservation of the species with the Memphis Zoo by helping in the collection of Crawfish Frog sperm for future reproduction and captive-rearing efforts. Also, Crawfish Frogs are just awesome frogs and everyone should know what one sounds like.
Dr. Chelsea Kross
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