Human activity has impacted every habitat on our planet and severely damaged global biodiversity, the variety of living organisms that we find on Earth. A peculiar fact is that while we have witnessed a worldwide loss of plants and animals, at a local level things are not as clear cut.

To better understand what is happening to local biodiversity, a team of researchers used a large dataset gathered from 239 different studies. What became clear is that there have been widespread changes in the composition of species that live in a particular location, but the number of individuals varies wildly. In some places, there has been an increase, in other places populations are in decline, while others have kept the same number over time.

In general, while average biodiversity has been reduced, the size of the change, along with whether it’s a loss or a gain, is very much dependent on the geographical location of a particular habitat. These findings were reported in this week’s issue of the journal Science.

The team saw that the most dramatic changes were happening in the oceans, particularly in tropical ones. The maximum rate of species turnover in marine habitats was double that observed for land habitats. The findings shed light on where conservation efforts need to be focused most urgently. According to the study, key areas to focus on include the aforementioned tropical oceans as well as marine habitats in the western Atlantic Ocean and the waters of northwest Australia.

However, that doesn't mean we shouldn't focus on other environments too. The team argues that conservation approaches should be different in places less affected by species turnover, like temperate broadleaf and conifer forests. These areas might be better served by proactive measures to help maintain their current biodiversity.

While the reorganization of species might not seem as worrying as a clean-cut loss, the researchers point out that it can nevertheless have severe consequences for a healthy ecosystem. The team achieved this by employing the BioTIME database, the largest collection of biodiversity time series data to date.

The next step for this research is to focus on understanding why different communities are affected differently by the factors driving biodiversity changes. It would be interesting to find out whether certain habitats are less exposed to threats or whether they are simply less vulnerable to the dangers they face.