Review written by Natalie Wong (2025, EEB)
The term “protected area” in the context of wildlife preservation calls to mind an idyllic haven untouched by civilization, where all organisms have the resources they need to thrive. The expectation is that animals–particularly those facing endangerment or extinction–will be kept safe from the humans who contribute to the rapid dwindling of their populations through laws put in place by humans. This paradoxical involvement of people is precisely where issues arise.
The reality is that protected areas, synonymous with “parks” in the conservation field, are subject to a multitude of bureaucratic decisions that undermine their purpose as safe zones for threatened species. Alterations in the laws governing parks can lead to relaxing limitations on how or by whom a park is used, decreasing its area, or stripping legal protections altogether . The park may also undergo land-use change, which covers the ways that humans take advantage of the environment for their own economic, cultural, and agricultural endeavors, thus modifying the quality and function of natural systems . Examples of this concept include constructing buildings in previously wooded areas and converting fields to farmland for cash crops.
With eased legal protections and increased changes in land use, and more than 7,400 terrestrial vertebrate species at some degree of risk, improving conservation tactics is of utmost priority. In 2019, Dr. Yiwen Zeng, Dr. Christopher Crawford, and Dr. David Wilcove of Princeton University, along with Dr. Rebecca Senior of Durham University, combined their expertise in public policy and ecology to take up this challenge. They sought to gain a nuanced understanding of where vulnerable species currently reside and when it would be appropriate to create new parks as opposed to strengthening existing ones. Four main questions focused their efforts: identifying species that were a) absent from parks and consequently lacking formal legal protections, b) “protected” in parks with weakened laws, c) jeopardized by land-use change prospects, and d) in a position to benefit from a particular intervention.
The team, led by Zeng, selected 4,946 mammals, amphibians, and birds from the International Union for Conservation of Nature (IUCN) Red List of Threatened Species for their study population. They chose only those that were dependent on ecosystems in the wild that had been subjected to human interference and seemed likely to benefit from potential interventions. From there, the researchers created an optimized map of the total amount of land available to each species. When habitats fell within protected areas, records and projections were utilized to determine if the parks had undergone or were likely to experience legal protection cuts and/or cropland and urban expansion (two forms of land-use change).
Zeng et al. ultimately came to a number of striking conclusions about species distribution. As a starting point, they affirmed that species that lacked substantial remaining habitat (which the team defined as less than 2,000 square kilometers) faced a much higher risk of extinction than species with larger amounts of suitable land area left. This finding can be understood with the idea that random events have a more pronounced effect on smaller populations with narrow ranges than on larger, widely-dispersed groups .
Consider, for example, a critically endangered animal included in the study: the Javan rhino, one of only five species of rhinoceroses left across all of South Asia and Africa . Due primarily to poaching, they now number around 70 individuals and are confined exclusively to Ujung Kulon National Park of Java, Indonesia . Furthermore, despite their protected status, they remain in a precarious position since the park is highly susceptible to tsunamis and volcanic eruption . If either one of these catastrophes were to impact where the rhino population is concentrated, the entire species could be decimated at once. This outcome would be unlikely, however, if the rhinos were instead spread out over a bigger area or if there were so many of them that the probability of at least a few surviving would be high.
Aside from chance occurrences, land-use change can similarly exacerbate harm for species that are already extremely restricted. Indeed, Javan rhinoceros territory is currently being threatened by the encroachment of economic development on the outskirts of the park, a phenomenon that will result in degradation of precious natural resources and further habitat shrinkage .
The following data illustrate the grave reality of the relationship between species’ range sizes and how well they are safeguarded on a broader scale. Nearly 30%, or 1,463 of the 4,946 species analyzed, had less than 10% of their remaining habitat legally protected in parks. These included animals spanning the full range of IUCN classifications from Least Concern to Critically Endangered, although the majority fell into the intermediate categories of Near-Threatened, Vulnerable, or Endangered. More concerningly, a greater proportion of species labeled as Vulnerable (31%), Endangered (31%), or Critically Endangered (32%) were altogether absent from parks compared to their counterparts in the Least Concern designation (25%). Even if species were mostly contained within parks, rollbacks on legal protections proved to be a pervasive threat. Over half of the leftover habitat for 182 species was located in parks that had already experienced one or more regressive policy changes, and on the whole, as habitat area decreased, the proportion of it affected by such instances grew, a trend that affected more vulnerable species to a greater extent.
These numbers do not even account for 42 species which had over 90% of their remaining habitats located in parks that hadn’t yet undergone legal or land-use change, but are very likely to in the future. By analyzing established models of cropland and urban expansion, the researchers determined that these species would lose more than 50% of their habitat by 2050, no matter whether the degree of land-use change regulation in the hypothetical scenarios was strong, medium, limited, or implemented in conjunction with continued fossil fuel development. It is also important to note that although stripped legal protections do not always correlate directly with species population decline, the fact that safeguards are being taken away to begin with indicates that parks cannot be entrusted with providing refuge to so many species that are almost completely dependent on them. Not even reversing detrimental policies can suffice if it fails to translate to real-world ecological restoration.
This is not, however, where the story ends; fortunately, the data also reveal the potential for directed remedial measures. For example, enlarging and bolstering park networks across 1% of the earth’s total terrestrial area has the potential to save 1,191 species. 816 of the species were identified as standing to benefit greatly from the creation of new parks, given that they do not have access to much land within or outside of current protected areas. The fates of the other 375 species were deemed to rest instead on restoring habitat and improving management in existing parks because of their vulnerability to legal and land-use changes. Nonetheless, with these endeavors comes another hurtle: the financial bandwidth of countries to support them. The hotspots with immense species diversity that have been suggested as intervention targets are located in less affluent countries such as Colombia, Peru, Madagascar, and the Philippines. Zeng et al. propose that funds should be diverted from wealthier countries to mitigate economic hardship from domestic implementation, though this is difficult in practice.
Another drawback of the regional approach is navigating how to execute plans in partnership with citizens and local governments. The authors emphasize that policy leaders must consider land rights, inadvertent pressures placed on other parks by focusing on just certain ones, overlapping aims of community-managed lands, and spaces open to both human use and species protection prior to diving headfirst into damage control. These steps, in addition to examining the net benefits of alternative solutions, are prime topics for further study.
Above all, the team’s research holds incredible promise for conservation and restoration moving forward, offering comprehensive mapping and actionable solutions to address one of the world’s most pressing issues.
The original article discussed here was published in Science Advances on June 2, 2023. Please follow this link to view the full version.
 Conservation International. How Well Protected Are Protected Areas?. Retrieved September 16, 2023, from https://www.conservation.org/projects/paddd-protected-area-downgrading-downsizing-and-degazettement
 United States Environmental Protection Agency. What are the trends in land use and their effects on human health and the environment?. Retrieved September 16, 2023, from https://www.epa.gov/report-environment/land-use
 Staude, I.R., Navarro, L.M., Pereira H.M. (2019). Range size predicts the risk of local extinction from habitat loss. Global Ecology and Biogeography, 29(1), 16. https://doi.org/10.1111/geb.13003
 World Wildlife Fund. Javan Rhino Facts. Retrieved September 26, 2023, from https://www.worldwildlife.org/species/javan-rhino