Declining primate numbers are threatening Brazil’s Atlantic Forest

We tend to think of debt as purely financial, but we can also reap what we sow in the natural world through what is known as extinction debt. This concept refers to changes in the past that affect a species’ survival in the future.

Ecosystems often undergo profound and dramatic changes, but their effects are not always obvious to the naked eye. These changes are increasingly caused or triggered by humans.

In many cases, affected species may not actually disappear for several decades or even centuries: individuals survive — but under ecological conditions that do not allow them to maintain genetically viable populations. This often occurs with plant and animal species with long life cycles, such as certain tree species.

Some redwood or yew populations may therefore survive with the bare ecological minimum for long periods, but this does not mean that their existence is assured in the long term. This delayed result is the “debt” of extinction.

Such situations can occur in any ecosystem in the world, including tropical and subtropical forests. In fact, several studies have shown...