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Feb. 26, 2020

MSU scientists develop models to evaluate amphibian biodiversity

These days, a lot of people are vying for territory in the nation’s capital, but you may be surprised to know that since 2005, the National Capital Region Network, or MCRN, of 11 national parks in and around Washington, D.C. has been paying very close attention to the thin-skinned constituents who also live and breathe there – amphibians.

Frogs, toads, salamanders and newts breathe and absorb water through their skin, making them key vital signs of a healthy park. But for the past 10-15 years, these vital signs have been declining.

Two researchers in MSU’s Department of Integrative Biology in the College of Natural ScienceElise Zipkin, assistant professor, and Alex Wright, fourth-year doctoral student – are developing statistical models to understand why.

In a recently published paper in Landscape Ecology, Wright and Zipkin, along with Evan Grant, director of the U.S. Geological Survey’s Northeast Amphibian Research and Monitoring Initiative, integrated amphibian biodiversity data across spatial scales into a statistical analysis to evaluate the factors influencing amphibian communities and inform management decisions across the NCRN.

“Models like this can help us evaluate species trends through time as well as the specific factors that influence their distributions across space,” Zipkin, lead investigator of the Zipkin Quantitative Ecology Lab, said.

The team used the natural fragmentation of the NCRN as a case study to understand how scale mediates relationships between biodiversity and landscape variables such as connectivity between parks, habitat quality and the total area of a park.

“Amphibians are indicators of biological integrity, so when they decline, we know there is a larger problem with the ecosystem – whether that is driven by urbanization, climate change or other drivers,” said Wright, who has participated in data collection at the NCRN parks every summer for the past four years. “We also know from almost 15 years of monitoring in the NCRN that habitat fragmentation is occurring in this very urban region, but there is a lot of conflict in the scientific literature about the effect of fragmentation on species richness.”

With some amphibians active earlier in the year, like the spotted salamander, and some later, like the spring peeper, determining species richness with accuracy is tricky, but the team’s model was able to account for all species and parks across the NCRN, even estimating the number of species that were unobserved during data collection.

“Even though detection and wetland occupancy rates varied across species, our community occupancy model allowed us to estimate trends for both common and rare species across the network of parks,” Wright explained. “Being able to analyze these data at a large scale and to understand spatial variation among parks is a novel statistical advancement.”

Using the model, the scientists were able to ask: What species of amphibians live in the wetlands and parks? How many are there in each park? And what factors, at both wetland and park levels, influence species occurrences?

“Amphibians have dynamic populations, so at the park scale we found that the more permeable the boundary is between parks the more species are present,” Wright said. “The size of the park is also important—the bigger the area, the more species it can harbor. At the local scale, the rate at which wetland habitats dry up and the quality of the water in wetlands both impacted species trends.”

“These results are critical for conservation,” Zipkin added. “Understanding how and why amphibians use wetland habitat can help scientists and managers develop effective management plans and take actions to prevent species declines in the future.”

When previous naturalists like John Muir, Rachel Carson and Aldo Leopold set out as individuals to observe granite cliffs, eastern seashores and sandy hills, their observations were limited. Even so, their work inspired the establishment of national parks and conservation programs that, 150 years later, need effective tools to monitor and manage biodiversity on various scales as parks face threats due to urbanization, invasive species and climate change.

For that, quantitative biodiversity models like the ones being developed in Zipkin’s lab will help land managers and scientists predict the future of biodiversity at parks across the United States, adding to a growing wave of scientifically informed, ecological management.

“Science is often conducted at small scales—one wetland at a time—but management is large and often involves strategies or policy at large scales such as parks, entire park systems and even continents,” Wright explained. “In this paper, we developed statistical methods to reconcile this issue and integrate the scales of science and management, which can help protect biodiversity.”

By: Val Osowski

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