Yesterday, Georgina Mace gave a seminar in the Faculty of Life Sciences at the University of Manchester. Of course, I was at the front row (well, almost), as I have only just started at Manchester and I was employed to reinforce ecology and environmental sciences in the Faculty. I have seen Georgina Mace speak before, and today she spoke about biodiversity, and specifically, the decline of it.
In her talk, she highlighted trends in the decline of plants, birds, mammals, reptiles, fish, and amphibians, mainly as a result of habitat destruction. She spoke about mechanisms of these organisms to cope with disturbances; some species just cope with changing circumstances, some move away to new habitats, and some (or, rather a lot, as evidenced by the graphs in her presentation) go extinct. At the end of her talk, she spoke about why biodiversity is important for humans. First of all, humans value biodiversity because of its intrinsic value – we simply want to know that there are elephants in Africa, or panda bears in China (although personally, I couldn’t care less about panda bears). Second, we want to conserve species because we want to preserve the genetic library of life, and all the information about its evolution that is locked up in genes. And finally, we want to conserve biodiversity because it provides ecosystem services that are directly beneficial for humans, although the science underpinning this relationship is still thin on the ground.
Wait – did you notice anything? The above is all about aboveground organisms, whereas in her talk, Georgina also highlighted that we only know of, and have characterised, a small fraction of all existing species, and that many of those unknown species actually live below the soil surface. Yet, almost nothing is known about their distribution, their variation in time, and how they respond to human-induced disturbances.
I think this can be explained by the fact that research involving soil organisms tends to focus on their function, rather than their distribution. Many studies have linked soil biodiversity – whether this is actually the number of species or taxa present, or the functional diversity of the organisms – to ecosystem functioning, particularly carbon and nitrogen cycling. A good overview of this is given in the paper by Uffe Nielsen and co-authors, who did a meta-analysis in which they linked species richness of soil organisms to C cycling. They concluded that positive relationships were predominantly found in experiments with very low numbers of species. However, the functional composition of soil communities has been frequently linked to processes of C and N cycling. For example, my own work has shown that soil food webs that dominated by fungi and fungal-feeding organisms, rather than by bacteria and bacterial-feeding organisms, have lower N losses, and are more resistant to the devastating effects of climate change.
In her talk, Georgina highlighted that this link with ecosystem processes, which underpin provisioning and regulating ecosystem services, is one of the reasons why we want to conserve species. But, if for soil organisms there is so much evidence that they govern ecosystem processes, why do we not know more about their distribution?
Well, probably because it is so difficult to study them. Imagine that when you take one small soil sample of about 50 grams, extracting all the organisms and identifying them can easily take one person a month. And then you only know what is present in a tiny little spot of the globe, for example underneath one plant – it might be completely different under the next plant, as was shown by Martijn Bezemer and co-authors (note that these different soil food webs still performed pretty much the same functions!).
People are now beginning to realize that before we can actually use our knowledge about how soil organisms influence ecosystem processes to optimize the delivery of ecosystem services, we have to know what their distribution is, how their populations vary in time, and how they respond to human disturbances (although we now know actually quite a lot about how human activities affect soil organisms, and it is not positive!). One fantastic recent attempt is the European Atlas of Soil Biodiversity, although still, no information is present about how populations of soil organisms vary in time.
Fortunately, this is exactly what the Global Soil Biodiversity Initiative aims to do: increase awareness of the importance of soil biodiversity – both of the general public, and of policy makers. And hopefully, there will be a Global Atlas of Soil Biodiversity soon, information on population trends of soil organisms, a red list of threatened species, and a small photo of a soil organism in Georgina Mace’s next talk (and they can be cute – see the photo below from the BBC website)!