Why Are We Ranking Global Biodiversity Threats?

Research consistently shows that humans are driving unprecedented numbers of species into extinction. Scientists have generally given five key reasons for this: habitat destruction, “overexploitation” (e.g., poaching), climate change, pollution, and “biological invasions” (in other words, harms caused by introducing new species to a given region). 

These five factors are considered major threats to global biodiversity. Some international organizations have started ranking these threats as a way to help guide conservation priorities. However, each agency has its own way of measuring the threats, leading to different rankings. The authors of this paper argue that the lack of clarity makes it difficult to fully understand the problem and to develop and prioritize conservation solutions.

Throughout this opinion paper, the authors argue that we shouldn’t be focusing on ranking threats to biodiversity, as it may end up pointing us in the wrong direction. They give several reasons why this is the case:

Threats Depend On Context

Different locations and species are impacted in unique ways by a variety of threats. This means that it is difficult to apply a standard formula to all situations. For example, the authors claim that pollution is more of a threat in Europe than it is in the tropics, where habitat loss and overexploitation are common drivers of extinctions.

Threats Impact Animals Differently

When studying biodiversity threats, it’s important to consider different types of animals. For example, we shouldn’t lump marine animals and land animals together. Similarly, birds and mammals may be impacted by different threats than amphibians and reptiles. The authors even point out how size makes a difference — large mammals are often the most impacted by overexploitation, while small mammals may be more susceptible to pollution and habitat destruction.

Threat Rankings May Be Biased

As with many other aspects of research, most studies that inform threat rankings are based in high-income countries and focus on a small percentage of animal and plant species. Because representation is not equal, this may lead to bias in how conservation decisions and funds are allocated. Unfortunately, it also means that many places and species around the world could be overlooked despite facing major threats.

Threat Rankings Must Consider Time

In order to be effective, the authors argue that rankings must capture the impact of time relative to threats. For example, they point out that climate change is more likely to pose a major threat in the future, while other threats were more of a problem historically. The speed at which threats affect species is also a factor. While so-called “invasive” species may cause native species to decline quickly, habitat loss often takes longer to have a significant impact on species’ populations. However, just because a threat takes longer to take effect doesn’t mean it’s any less of a problem. 

Threat Rankings Use Different Methodologies

Measuring threats depends on having reliable metrics. However, the authors claim that necessary data is not always available, and metrics vary from one organization to the next. In general, many threat rankings depend on species-level data, but the authors say it’s important to consider other types of data (ecosystem and population-level data, for example). Likewise, threat rankings may not consider that a single threat has many different factors and outcomes. 

While ranking threats to biodiversity may seem like an issue for the conservation community, it’s important to our movement because the data are often used to secure funding and support for different conservation initiatives. The authors fear that the current way of ranking threats is too simplistic and may be confusing policymakers and the public. Moving forward, they suggest doing away with the system and instead educating people about all threats, their impacts, and how they interact with one another. By providing a fuller picture of different conservation scenarios with a variety of metrics, threats, solutions, and outcomes, we can encourage leaders to make more nuanced decisions to benefit the world’s vulnerable animals.