William & Mary

Threats to endangered species more than doubled in past 40 years, study finds

  • An endangered Columbia Basin Pygmy rabbit stands in the snow.
    Threat to habitat:  The Columbia Basin pygmy rabbit (Brachylagus idahoensis), the smallest species of rabbit in North America, was emergency listed as endangered in 2001 and remains listed today. According to the U.S. Fish and Wildlife Service, large-scale habitat loss played a primary role in the long-term decline of the species.  Photo by U.S. Fish and Wildlife Service
  • The research team of undergraduate students from William & Mary and Millersville University poses for a group photo on a rooftop in Washington, D.C.
    It’s a group effort:  The team of undergraduate researchers and co-authors pictured in D.C. (from left to right): Alexander Sandercock, Kayli Thomas, Delaney Costante, Isabel Ritrovato ’18, Jessica Evans ’17, Tyler Treakle ’18, Ann Marie Rydberg ’18, Courtney Check ’19 and Garrett Stewart ’18.  Photo courtesy Matthias Leu
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The year was 1973, three days after Christmas. President Richard Nixon’s approval ratings were bottoming out. The Watergate scandal was intensifying and Nixon had just professed to the nation he was “not a crook.” In the midst of political turmoil, he made a decision that would affect millions of lives for decades to come. He signed the Endangered Species Act into law.

“This legislation provides the Federal Government with needed authority to protect an irreplaceable part of our national heritage — threatened wildlife,” Nixon said in a statement. “America will be more beautiful in the years ahead, thanks to the measure that I have the pleasure of signing into law today.”

The primary goal of the legislation was to protect animal and plant life from extinction. To do so, the government tasked the U.S. Fish and Wildlife Service and the National Marine Fisheries Service with listing endangered species and recording threats to their survival.

“The Endangered Species Act is unique,” said Matthias Leu, associate professor of biology and chair of data science at William & Mary. “We were actually at the forefront of conservation in terms of this act. People forget that about Nixon. Despite his political issues, he was actually an environmentalist.”

For the past six years, Leu and a team of 11 undergraduate students have been data-mining ESA records to determine its efficacy and assess threats to domestic species over time. Their research, conducted in partnership with Millersville University, was recently published in Conservation Science and Practice, a journal of the Society for Conservation Biology. The paper enumerates threats to 1,549 species on the Endangered Species list from 1975 to 2017.

The research team was made up of undergrads from William & Mary and Millersville. In fact, all of Leu’s William & Mary co-authors were undergraduates at the time of submission: Courtney Check ‘19, Jessica Evans ‘17, Margaret Hollingsworth ‘18, Isabel Ritrovato ‘18, Ann Marie Rydberg ‘18 and Tyler Treakle ‘18.

“The publication of the paper is a reminder to me of how much I appreciate William & Mary’s emphasis on undergraduate research,” Evans said. “I did not realize how much creativity went into recognizing a knowledge gap, figuring out the multiple ways to collect information that could address this knowledge gap, coming up with reproducible, consistent methods for data collection, and understanding how to communicate the analysis of results.”

The team found that the number of threats per ESA listing decision increased more than twofold during that 42-year period. They also found that the number of native species impacted by habitat loss continues to increase. Threats due to invasive species and changes in the environment have increased exponentially in the past 30 years, as well.

“To our knowledge, this is the first evaluation of temporal changes in threat occurrence for U.S. species listed under the ESA as outlined in federal listing documents,” the paper states. “The increasing frequency of these threats over time point to the importance of federal protection for rare species.”

Since the passage of the ESA and its subsequent amendments, the number of U.S. species requiring federal protection has ballooned from 137 between 1967 and 1973 to 1,663 in 2019, with 43 species considered recovered during that period, the paper states.

The American bald eagle was one of the first species to be placed on the endangered list. The ESA regulations proved so successful that by 2007, the eagle population had recovered sufficiently to be removed from the list. Other success stories include the humpback whale, the Louisiana black bear, the Virginia northern flying squirrel and the Arctic peregrine falcon.

To analyze the species still included on the list, the researchers developed a giant database, scanning listing decision documents for 1,732 domestic species. They decided to divvy up the species based on student preference. For example, some students read documents for all 52 bird species on the list, others handled all 139 species of fish, yet others tackled all 40 reptile species, and so on.

“The vertebrates went first and then towards the end, the only species left were the ones that nobody wanted to look at, like the insects,” Leu said. “But we had to do them all, so somebody got the bugs.”

Ann Marie Rydberg decided she would analyze documents for flowering plants on the list. There were 910 plant species to analyze, so it required all hands on deck to finish the job.

“We read all the listing decisions and coded all the threats that we could,” Leu said.

The team eventually eliminated 183 species due to lack of information and/or errors in the listing decision. For the remaining 1,549 species, the team evaluated changes in the number of threats and specific threat occurrences over the past four decades.

Reading thousands of pages of documents was a challenge, but the real work came in deciphering what the documents actually said, Leu explained.

“The Fish and Wildlife Service is divided into eight regions and each region writes their own listing decision,” Leu said. “As far as we can tell, there was no coordination over terminology between regions, so the types of words they were using were all over the place. Then the language was changing over time, because we’re going back to the 70s, so we had geographic variation on top of the time variation. It was a nightmare.”

Ultimately, the team determined there were six overarching threat categories: habitat modification, overutilization, pollution, species–species interaction (aka invasive species), demographic stochasticity (aka inbreeding) and environmental stochasticity (aka environmental change, like erosion).

“Our major finding was that species are now listed with more threats, substantially more threats,” Leu said. “That’s going to make it harder to remove species from the list, because the threats are increasing.”

The team found habitat loss was, and continues to be, the top threat over time. As a result, most endangered species are found, at least in part, on private lands, the paper states. Leu asserts that more efforts are needed to work with private landowners to conserve species in the United States.

“What’s really scary is we have invested millions of dollars to save habitat, but there is no decrease in that threat trend. In fact, it’s slightly increasing,” Leu said. “It’s private landowners that own the really productive, high biodiversity land. The government needs incentives to engage private landowners in conservation strategies, because the federal government simply does not own enough land to protect all the species. That’s the depressing part. Recovery is going to have to happen one backyard at a time. “  

Leu says his research team is now collaborating with the D.C.-based conservation organization Defenders of Wildlife. The advocacy group is using the team’s data to craft legislation to protect threatened species.

“They are better situated and trained to take science to the Hill,” Leu said. “I don’t really see that as our role, but we’re glad they’re promoting our paper. It’s a nice translation from science into potential policy, because what our data show is we need to maintain existing government policy. We have empirical evidence showing it works.”