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The Endangered Endangered Species Act: the Shortcomings of Rebounding Populations

Written by Skylar Walters '26

Edited by Megan List '24

Over the course of its almost-forty year history, the Endangered Species Act (ESA) has prevented an estimated 1,700 species from going extinct– over 99% of the species it protects. It’s a glowing standard for conservation legislation worldwide, a success story for the world of biodiversity.

However, there’s a gaping hole in the power of the ESA. While it’s been enormously successful in preventing extinction, it has had little success in restoring populations.

Of the thousands of species to have been listed by the ESA since its creation, just 54 of them have had sufficient population growth to have been removed from the list. As ever-increasing numbers of organisms face die-offs, protecting biodiversity, and restoring it,is critical.

A recent study from Columbia’s Department of Ecology, Evolution, and Environmental Biology, in association with Princeton University, examines the mechanisms underlying this flaw within the ESA. The group analyzed trends in population size, funding, and wait time between petition to endangerment listing from 1992 to 2020, comparing these results to prior studies that compared similar data between 1985 and 1993. The researchers stated:

"We find that small population sizes at time of listing, coupled with delayed protection and insufficient funding, continue to undermine one of the world's strongest laws for protecting biodiversity."

In the 1993 study, researchers found that, on average, vertebrate species gained protections when their population sizes reached around 1075 individuals, while invertebrates gained protection at 999. Plants averaged at just 120 organisms. The 2022 study conducted a similar analysis, determining that population sizes at the time of listing have not changed significantly in the past 30 years.

When organism populations fall below a certain point, they become far more vulnerable to threats, such as environmental disasters and disease, which makes it difficult to bounce back to normal levels. Additionally, these small population sizes can lead to inbreeding, lowering the overall genetic diversity of the species. These population sizes at time of listing reflect a grim story: organisms are being protected too late, lacking the genetic diversity, resilience, and security that come with slightly larger populations.

“Our analysis of trends in the protection of imperiled species under the US Endangered Species Act warrants a limited amount of optimism and a larger amount of pessimism: Most species are not receiving protection until they have reached dangerously low population sizes,” they state.

Likewise, the wait time between petitioning for a species to be listed and the actual listing has remained constant, at roughly 3-9 years. When dealing with such small population sizes, time is critical: more time waiting for protection means more time to be struck by disease, natural disasters, or slowing birth rates.

If the population sizes and time for listing haven’t changed dramatically since the list’s advent, what has?

The answer lies in funding. Since 2010, funding allocations toward the endangered species act have steadily been decreasing, meanwhile the number of species listed has increased three-fold. As a result, the funding per species is now roughly half of the funding per species in 1985, slowing conservation efforts and research. This lack of funding plays into the other systemic issues as well: a lack of funding means a lack of staffing, which contributes to the extended waiting periods and population decrease.

This comes at a time when economic and political values and environmental values are at a crossroads: major policies, such as the Clean Air Act, are losing legislative power, while large governing bodies, like the UN, are reassessing conservation recommendations and projects.

The 1970s were characterized by a zeitgeist of conservation efforts, with the passage of the Clean Air Act, the Clean Water Act, the creation of the Environmental Protection Agency, and the advent of the Endangered Species Act. As air and water pollution affected poor, nonwhite communities, the fight for conservation became intertwined with civil rights, labor, and environmental justice. Meanwhile mass exodus to the suburbs highlighted the contrast in quality of life and natural resources outside of urban areas. These societal developments fostered a sense of environmental activism that hallmarked the era.

This same sense of conservation motivation still lingers in some ways, but the focus has largely shifted to more sweeping concepts, such as climate change, that are harder to directly relate to and quantify.

This December, the United Nations Convention on Biological Diversity is meeting to discuss the conservation of biodiversity and sustainability with the goal of creating conservation policy guidelines and agreements for the next decade. With the ESA’s international influence, reforming policy centered around these lessons on small populations, classification speed, and funding can allow the committee to create more effective policy that can protect endangered species– and the Endangered Species Act.



1. Greenwald N, Suckling KF, Hartl B, A. Mehrhoff L. Extinction and the U.S. Endangered Species Act. PeerJ. 2019 Apr 22;7:e6803.

2. Eberhard EK, Wilcove DS, Dobson AP. Too few, too late: U.S. Endangered Species Act undermined by inaction and inadequate funding. Rozylowicz L, editor. PLoS ONE. 2022 Oct 12;17(10):e0275322.

3. Wilcove DS, McMillan M, Winston KC. What Exactly Is an Endangered Species? An Analysis of the U.S. Endangered Species List: 1985-1991. Conservation Biology. 1993 Mar;7(1):87–93.

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