Relational Thinking

Getting hit from all sides: Anthropogenic threats gang up on biodiversity

In this blog post Diana Bowler, Laetitia Navarro & Amanda Bates discuss the story of their research ‘Mapping human pressures on biodiversity across the planet uncovers anthropogenic threat complexes’ out today!

You can also read the authors’ plain language summary here.

The sChange working group in Feb 2016, at iDiv, Leipzig.

The story of this paper began way back in February 2016 during the second sChange workshop at the German Centre for Integrative Biodiversity Research in Leipzig. sChange was focused on understanding the patterns of biodiversity change across the world, mainly using the BioTIME database of standardized time-series. From the outset, there were a few defined focus points of the working group. First, the question of spatial scale – how do we square the observed differences between local and global biodiversity patterns of change vs loss (leading to this paper). And second, questions about the biogeography of change across realms and biomes (leading to this paper).

Nonetheless, especially for some of us, our thoughts kept returning to questions about the underlying anthropogenic drivers. Patterns of biodiversity change are varied and complex – dynamic in time and space, with distinct signals between different taxa. How could we better understand the drivers of this variation? Would the data even allow us to quantify drivers in a shared framework for both the terrestrial and marine realms? And should we be thinking beyond the “big five” classification of habitat change, overexploitation, climate change, pollution and invasive alien species?

The impact of an environmental change on species’ population usually boils down to two factors: (1) how much the environment changes (‘exposure’) and (2) whether the species is sensitive to the change (‘sensitivity’). The latter depends on species’ tolerances and niches – hence, it will be taxa-specific. By contrast, the former mostly depends on where a species lives. We realized that to better understand the patterns of biodiversity change, a key step is to develop understanding of the exposure to anthropogenic drivers of change.

We do already have maps of human activities and derived impacts, including the human footprint for the terrestrial realm and cumulative threats for the marine realm.  However, we were especially propelled by the challenge to examine anthropogenic environmental change across the whole surface of the planet, and to go beyond a cumulative analysis of human pressure. Too often marine and terrestrial ecologists shuffle into different rooms. We also were interested in how different drivers tend to group with each other and thus jointly act on communities. Simultaneous exposure to different drivers provides opportunities for interactive effects (synergistic or antagonistic) to emerge.

Based on our analysis of 16 different types of environmental changes at the global-scale, we found that the intensities of many drivers do tend to be correlated – especially on land, probably due to the varied needs and impacts of local human populations. We came up with the concept of the ‘Anthropogenic Threat Complex’. The ATCs represent the most typical combinations of drivers. For instance, some regions are exposed to high climate change but low pollution and habitat change while other regions are hit by everything. We mapped 11 of these across the entire surface of the world – each with different combinations of environmental changes, and hence with likely differing implications for biodiversity.

This type of paper can be a struggle to publish. Some reviewers raised concerns about the invasive alien species layer as we only had a proxy, but since this was just one of our layers, our key results are independent of any one data layer. Some reviewers also questioned the value of our maps – but at the same time, many others were fascinated by the cool maps we produced. Check out the paper. We are really excited to see what our approach inspires!

A big concern remains that we are always biased by data availability. Human actions that we cannot examine because of insufficient mapped data, we are more likely to think of as insignificant due to lack of evidence on their impact. Since the first workshop, we ourselves are on the lookout for new datasets, with higher resolution, or on “new” drivers (ocean plastic pollution, we’re looking at you). Global datasets, e.g., from remote-sensing, are becoming more detailed and varied, and ecologists of the future will be able to perform much deeper analyses of the environmental changes affecting biodiversity. We are rather jealous of these future scientists.

Apart from a paper that has made us proud, a plus coming out of this project was getting to know some amazing people and making some new science friends. Here’s hoping for further collaboration. Watch this space!