Habitat is king. That’s a central tenet of many campaigns to save species. The loss of habitat—whether to farming, logging or pavement—is frequently named as a chief culprit for the decline of species. That’s true for everything from salmon swimming in dammed rivers to migratory birds stranded on drained marshlands.
That insight has made habitat protections a rallying cry for conservationists trying to staunch the worldwide decline in biodiversity. Most notably the United Nations has mounted a campaign with the slogan “30 by 30” to protect 30% of the worlds land and oceans by 2030.
But there is surprisingly little evidence on a global scale across the animal kingdoms that wildlife reserves work— until now. Scientists scrutinizing the fate of more than 1,000 vertebrate species around the world have found that populations inside protected areas such as national parks or wildlife refuges decline five times more slowly than populations living elsewhere.
“Protected areas take us from a situation in which biodiversity is not-so-slowly ebbing away, to one where populations are at least close to stable,” said Luke Frishkoff, a biologist at the University of Texas at Arlington who took part in the research
While some might think such work is just stating the obvious, the work by Frishkoff and fellow scientists at the Smithsonian Institution, the Zoological Society of London and a handful of universities puts the habitat-centric view to the scientific test. And it uncovers intriguing differences depending on the type of animal.
To quantify the potential effect of habitat, the researchers turned to two databases that contained research tracking the ups and downs of 2,239 populations representing 1,032 different vertebrate species, including amphibians, reptiles, mammals and birds. The scientists matched populations of similar species inside protected areas with ones outside protected areas. They also made sure to compare “in” and “out” groups living in similar surroundings, to avoid being misled by differences in external factors such as elevation or the number of people living nearby.
The results revealed a stark difference. Overall, species populations shrank by 1.8% every year outside protected areas, compared to .4% on the inside, the scientists reported Sept. 27 in Nature.
If that rate held steady, it means animals without protected habitat could see their populations halved in 40 years, compared to 170 years for ones living behind these protections, noted Frishkoff. While that’s not the same thing as seeing populations grow, the slower rate of decline can “buy us much-needed time to figure out how to reverse the biodiversity crisis,” he said.
Not all creatures saw the same benefits. Some of the hardest-hit species gained the most. Overall, birds saw the biggest gains, with a 1.7% decline in unprotected places versus .3% – more than five times less. Amphibians are declining by a staggering 7.5% each year without protections, compared with a still-grim 2.6% annual decline.
“Amphibians typically have fairly small home ranges, and they’re also really sensitive to small changes in the environment,” said Jessica Deichmann, an ecologist with the Liz Claiborne & Art Ortenberg Foundation who took part in the study. “So, with amphibians living within protected areas, you’re really able to protect more of the habitat that they’re utilizing than you are with, say, a mammal that has a really large home range.”
In fact protected areas overall delivered fewer benefits to mammals and reptiles, at least when it comes to overall population changes. The advantages of refuges were small enough that they weren’t statistically significant.
While the research adds heft to calls for habitat protections, it also shows that simply setting aside land isn’t always enough. The data analysis showed that when habitat was lost on land surrounding protected areas, it diminished the benefits for amphibians dwelling in the refuges. Reptiles and amphibians in the tropics, meanwhile, proved especially sensitive to rising temperatures courtesy of climate change regardless of whether they were in protected areas. That is likely because these creatures are cold-blooded, making them less able to maintain safe body temperatures when their surroundings heat up.
Then there is the political factor. Protected areas performed better in countries ranked by as having more effective governments that maintain the rule of law and aren’t wracked by violence or corruption. The findings underscore that putting lines on a map doesn’t necessarily translate to protections.
“Countries can comply with 30 by 30 by creating ‘paper parks’ [parks that exist on maps but are largely ineffective],” Deichmann said. “But that will not achieve the desired outcomes of 30 by 30.
In fact, the benefits to species from living in well-run countries was roughly equal to the benefit of living inside a protected area, the scientists found. One more reason to work for democratic governments and the rule of law.
Nowakowski, et. al. “Protected areas slow declines unevenly across the tetrapod tree of life.” Nature. Sept. 27, 2023.
Image: Hourglass tree frog by Brian Gratwicke