Stuart Pimm and John Gittleman tell us about their team’s effort to assess the successes and failures of the conservation enterprise in in Proceedings of the Royal Society B. Future success in conservation will depend on clearly defined metrics to measure what works and what does not. Such a recommendation resonates strongly with the work pioneered by Professor Dame Georgina Mace.
The title of this blog post is basically the core argument of our in Proceedings of the Royal Society B. We push back against the idea that we’re in some total, uncontrollable collapse of biodiversity where nothing is working. Instead, we make a more grounded claim: biodiversity loss is real and serious, but conservation efforts are having measurable, meaningful impacts—they’re just not happening at the scale or clarity needed to fully solve the problem.
First, our paper makes it clear that biodiversity is declining, and in some cases, rapidly. Our documents that species are going extinct globally at rates far higher than natural background levels—on the order of hundreds to thousands of times higher. Habitat loss is the main driver, especially in tropical forests and other biodiversity hotspots where many endemic species are concentrated. On top of that, there are additional pressures like invasive species, overexploitation, climate change, and pollution. So there’s no denial here—the situation is bad.
Where our paper differs from more alarmist takes is in how it interprets the data. It argues that broad claims like “the sixth mass extinction” or “total ecosystem collapse” are often oversimplified or exaggerated. The data we actually have is more complex. Different species, ecosystems, and regions show very different trends. Some populations are crashing, others are stable, and some are even increasing, thanks to conservation efforts. So instead of a single global story of decline, it’s more accurate to think of biodiversity as a patchwork of outcomes.
That’s where conservation comes in. We show that conservation actions are, in many cases, working. There’s strong evidence that conservation has prevented some extinctions. Without these efforts, extinction rates would have been significantly higher. In other words, things would be worse were it not for conservation efforts.
Beyond just preventing extinction, conservation has also helped recover populations. Protected areas, removal of invasive species, species reintroductions, and targeted management strategies have all contributed to positive outcomes. A large share of conservation interventions either improve biodiversity or at least slow its decline. It’s not perfect, and not every project succeeds, but the overall trend is clearly positive.
Protected areas are among the most important tools in conservation, and our paper devotes considerable attention to them. Globally, the amount of land and ocean under protection has increased a lot over the past few decades. These areas generally reduce habitat destruction compared to unprotected areas. So they’re not just symbolic—they have real effects.
That said, they’re not optimally placed. Many protected areas are in remote, less economically valuable regions—like deserts, mountains, or polar areas—rather than in biodiversity-rich regions that are under the most pressure. This creates a mismatch between where protection exists and where it’s most needed. Still, even with that bias, protected areas do tend to include many species with small geographic ranges, which are the ones most at risk of extinction. So they’re better aligned than some might think.
Another key point is that population trends are highly variable. Some species, like certain marine mammals and sea turtles, are recovering due to conservation efforts. Others, like many shark species, are still declining significantly. Even within the same species, trends can differ by region. This variability makes it difficult to summarise biodiversity change with a single number or statistic, which is something our paper strongly criticises.
The paper is particularly sceptical of large, simplified metrics like global “percentage declines” in wildlife populations. These kinds of numbers can be misleading because they average across very different systems and data quality levels. They make for strong headlines but don’t necessarily reflect reality in a useful way. As we argue in another , relying on these oversimplifications can distort understanding and even harm conservation by directing attention away from measurable, actionable problems.
A major theme running through the paper is the lack of clear, quantitative targets. Global frameworks like the Kunming–Montreal Biodiversity Framework set ambitious goals—like protecting 30% of land and ocean by 2030—but many of the targets are vague or not easily measurable. That makes it hard to track progress or hold anyone accountable.
Our paper argues that conservation needs better metrics—things like tracking changes in species’ conservation status, monitoring population sizes, and measuring habitat loss and recovery in consistent ways. Without these data, it’s difficult to know what’s working, what isn’t, and so where to invest resources.
There are also major gaps in knowledge. For example, ecosystem restoration is a big focus globally, but it’s not always clear how effective it is for biodiversity. Planting trees, for instance, doesn’t necessarily restore a functioning ecosystem—especially if those trees are non-native or planted as monocultures. Similarly, marine ecosystems are harder to monitor than terrestrial ones, so we have less reliable data on changes in ocean biodiversity.
The role of Indigenous peoples and local communities is another area where the evidence is still developing. There’s growing recognition that involving local communities can improve conservation outcomes, but the data are not always consistent, and the best approaches are still being worked out.
In the end, our paper’s main takeaway is pragmatic. Conservation is not a failure—it’s actually achieving real results. But those results are uneven, sometimes inefficient, and often poorly tracked. The biggest limitation isn’t a lack of tools or knowledge about what works; it’s a lack of clear goals, consistent measurement, and transparency.
So instead of framing biodiversity as a hopeless crisis, we suggest a more useful approach: focus on measurable outcomes, scale up proven strategies, fix gaps in data, and be honest about both successes and failures. Conservation works—but it needs to be sharper, more accountable, and more data-driven to actually meet global biodiversity goals.
About the authors
holds the Doris Duke Chair of Conservation at Duke University in North Carolina, USA.
was the founding dean of the Odum School of Ecology, in Georgia, USA.
Both are long-time friends and colleagues of the late Dame Georgina Mace and are delighted to be able to contribute this essay in her honour.
Read the paper: ''.
Proceedings B is the Royal Society's flagship biological research journal, dedicated to the fast publication and worldwide dissemination of high-quality research. For more information and details of how to submit, please .
Image: Georgina Mace. Credit: Jussi Puikkonen / KNAW, via Wikimedia Commons (CC BY 2.0).
