How Are Species Chosen for Protection? Conservation Criteria Explained

Not every endangered species receives the same level of attention or protection. With millions of species on Earth and limited conservation resources, scientists and policymakers have to make difficult choices about which species to prioritize. So how exactly do they decide? The answer lies in a combination of scientific criteria, strategic area management, and hard-learned lessons from decades of conservation work. Understanding these selection criteria is essential for anyone interested in how we protect life on this planet.

IUCN criteria for species protection 🔗

The most widely recognized framework for assessing which species need protection comes from the International Union for Conservation of Nature (IUCN) and its Red List of Threatened Species. The IUCN Red List divides species into nine categories: Not Evaluated, Data Deficient, Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild, and Extinct. Three of these categories – Vulnerable, Endangered, and Critically Endangered – fall under the umbrella term “threatened.”

The IUCN system relies on five quantitative criteria to evaluate a species’ extinction risk. These criteria focus on measurable factors that, when combined, paint a detailed picture of how much trouble a species is really in.

Population decline 🔗

One of the primary indicators is the rate at which a species’ numbers are falling. A species experiencing roughly a 90 percent population decline over ten years or three generations would typically be classified as Critically Endangered. A 50 percent decline over the same period would place a species in the Endangered category, while a 30 percent decline corresponds to Vulnerable status. These thresholds give scientists a standardized way to compare the urgency of different species’ situations.

Geographic range 🔗

Species are assessed using criteria that include area of geographic distribution and degree of population and distribution fragmentation. A species that occupies a very small area, or one whose range is shrinking rapidly, faces a higher risk of extinction. Geographic range matters because a species confined to a tiny patch of habitat is far more vulnerable to a single catastrophic event – a wildfire, a disease outbreak, or a natural disaster – than one spread across a continent.

Small population size 🔗

Species with very few remaining individuals are inherently at greater risk. Small populations face genetic bottlenecks, inbreeding depression, and reduced ability to adapt to environmental change. The IUCN criteria account for this by evaluating both the current population size and whether numbers are continuing to decline. It is important to note that a species cannot be classified using one criterion alone – scientists performing the assessment must consider multiple factors together.

Quantitative analysis of extinction probability 🔗

The fifth IUCN criterion involves statistical modelling that calculates the probability of a species going extinct within a defined timeframe. This brings mathematical rigour to the process, allowing researchers to project population viability under different scenarios. As of recent updates, over 172,600 species have been assessed for the IUCN Red List , making it the most comprehensive global inventory of species conservation status.

Zoning and protected area management 🔗

Identifying at-risk species is only the first step. The next challenge is protecting the habitats where these species live. This is where zoning within protected areas becomes critical.

What is conservation zoning? 🔗

Protected area zoning is a management strategy used to define and delimit land units for specific purposes, such as critical areas for conservation and areas for recreation activities. Rather than treating an entire national park or reserve as a single uniform block, zoning breaks it into different sections, each with its own set of rules and management objectives.

Protected areas often use zoning schemes to balance biodiversity conservation and sustainable human use, typically dividing the area into fully protected zones and others that permit varying levels of activity. This approach follows guidelines set by organizations like UNESCO and the IUCN.

Types of zones in protected areas 🔗

A typical zoning system includes three main levels. Core zones are strictly protected areas where human activity is severely limited. These zones shelter the most sensitive habitats and species. Buffer zones surround the core, providing a transition area where limited activities like research and low-impact ecotourism may be allowed. Transition or use zones are areas where sustainable human activities – farming, fishing, or settlement – are permitted under specific regulations.

A well-studied example of this approach comes from China’s Wolong Nature Reserve, home to giant pandas. Wolong has been zoned into three areas: a core area that strictly limits human activity, a buffer zone of limited access, and an experimental area where homes, businesses, and roads are present. Research from Michigan State University found that this zoning is helping protect some prime panda habitat, though it also revealed critical weaknesses where certain high-quality habitats fell outside the most protected zones.

The Great Barrier Reef model 🔗

Marine protected areas use zoning too. In multi-zone marine protected areas, the way zoning is built is a central component of the management plan, and its quality is a condition for the protected area’s success. The Great Barrier Reef Marine Park in Australia is widely regarded as a benchmark. Its re-zoning initiative was co-designed with local stakeholders, producing a plan that secured high levels of protection in ecologically important zones while still allowing sustainable use in other areas.

Challenges in protected area selection 🔗

Creating a protected area on paper is one thing. Making it work in practice is another. Several factors determine whether a protected area actually delivers conservation outcomes.

Habitat size and the SLOSS debate 🔗

Large protected areas contain greater habitat diversity than small ones, meaning they can accommodate more species, a wider range of ecosystem processes, and viable populations of large species that range over large areas and live at low densities. This principle – rooted in island biogeography theory – has led to one of conservation biology’s most enduring questions: is it better to create a Single Large Or Several Small reserves (the SLOSS debate)?

Habitat fragmentation divides large populations into more vulnerable subpopulations, leads to undesirable edge effects, creates barriers to dispersal, and provides entry points for invasive species. At the same time, there is growing evidence that even small protected areas, if well-connected, can maintain viable wildlife populations.

Species home ranges 🔗

Different species need vastly different amounts of space. A territorial bird might thrive in a few hundred hectares, while a large carnivore like a tiger or a wolf may need thousands of square kilometres. If home range areas are underestimated, the resulting protected areas may be insufficient for population survival and reproduction. This is especially problematic for large-bodied species that roam widely.

To effectively reduce fishing-related mortality in marine environments, the entire home range of individuals must be located within a fully protected area. This same principle applies on land – if an animal regularly leaves the protected area to forage or breed, it remains exposed to threats like poaching, road traffic, or habitat degradation.

Habitat fragmentation 🔗

Habitat fragmentation limits movement, dispersal, and colonization of species, restricts species’ access to resources, reduces population sizes, and supports species invasion through disturbed habitat. Even a well-designed reserve can fail if the surrounding landscape is heavily fragmented. Fragmentation is expected to worsen, as approximately 25 million kilometres of new paved roads are projected globally by 2050. This makes ecological corridors – strips of habitat that connect separate protected areas – increasingly important for conservation planning.

Political and economic constraints 🔗

Conservation decisions don’t happen in a vacuum. Protected areas must compete with agriculture, mining, urban development, and other land uses for space. Management costs of multi-zone protected areas are predicted to increase compared to single fully protected areas due to more complex enforcement. Limited budgets, weak governance, and conflicting stakeholder interests can all undermine even the best conservation plans.

Examples of successful species protection efforts 🔗

Despite these challenges, well-applied protection criteria and management strategies have produced remarkable results. Here are some standout examples.

Bald eagle (United States) 🔗

Few conservation stories are as iconic as the bald eagle’s recovery. Bald eagle numbers have rebounded to more than 14,000 breeding pairs today, thanks to protections under the Endangered Species Act, captive breeding programmes, habitat protection, and a ban on the pesticide DDT. By 2021, the bald eagle population had climbed to an estimated 316,700 individuals. The species was removed from the endangered list in 2007 – a powerful demonstration of what targeted legislation and public commitment can achieve.

Humpback whale (global) 🔗

Commercial whaling nearly drove humpback whales to extinction, reducing their population from around 125,000 individuals to just 1,200 in 1966. International protections – including the moratorium on commercial whaling by the International Whaling Commission, the Endangered Species Act, and the Marine Mammal Protection Act – have helped populations recover dramatically to more than 21,000 today. Humpbacks have almost returned to their pre-whaling numbers , though six of the thirteen great whale species remain endangered or vulnerable.

Mountain gorilla (Central Africa) 🔗

Sustained conservation efforts in the Virunga Massif in East Africa have seen mountain gorilla numbers rise from 480 in 2010 to 604 in 2016, bringing the total worldwide to over 1,000. Gorilla numbers have roughly doubled over the past thirty years thanks to increased conservation, restoration, and animal health measures. Protection of the Virunga Massif, combined with community engagement and tourism revenue, has been central to this recovery – though threats like insecurity, climate change, and disease persist.

Arabian oryx (Middle East) 🔗

Reintroduction efforts in several countries, coupled with breeding programmes and protection in private collections, have helped Arabian oryx numbers recover significantly. Once extinct in the wild, the Arabian oryx is now classified as Vulnerable by the IUCN, with around 1,220 individuals in the wild and an estimated 6,000 to 7,000 in captivity. Its story demonstrates that even species driven to extinction in their natural habitats can be brought back through captive breeding and coordinated reintroduction programmes.

Black-footed ferret (United States) 🔗

By 1987, only 18 black-footed ferrets were known to still exist. These animals were placed into a captive breeding programme, and the National Park Service began reintroducing ferrets to Badlands National Park in 1994. Today, thanks to decades of collaborative work involving multiple government agencies, approximately 1,000 of these ferrets live in the wild across several US states and Mexico.

What ties it all together 🔗

The process of selecting species for protection is not a single decision – it’s a chain of interconnected choices. It starts with the IUCN’s quantitative criteria, which identify species at the greatest risk. It extends to the design and management of protected areas, where zoning helps balance conservation with human needs. And it runs up against real-world challenges – from the size of an animal’s home range to the political willingness to set land aside.

The success stories, from bald eagles to mountain gorillas, prove that when scientific criteria guide the process and adequate resources follow, species can recover from the very edge of extinction. But they also underscore a harder truth: protection criteria mean nothing without enforcement, funding, and long-term commitment.

What do you think? Should conservation resources be focused primarily on the most critically endangered species, or is there a stronger case for investing in ecosystem-wide protection that benefits many species at once? And in a world of limited budgets, how should we weigh the scientific urgency of a species’ decline against the practical cost of saving it?

References

1. https://www.iucnredlist.org/
2. https://iucn.org/resources/conservation-tool/iucn-red-list-threatened-species
3. https://www.canr.msu.edu/news/Conservation_zoning
4. https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.969234/full
5. https://bio.libretexts.org/Bookshelves/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/13:_The_Importance_of_Protected_Areas/13.05:_Designing_Protected_Areas
6. https://www.endangered.org/12-conservation-success-stories-for-endangered-species-day/
7. https://www.unep.org/news-and-stories/story/back-brink-six-species-saved-ecosystem-restoration
8. https://www.iucnredlist.org/resources/categories-and-criteria