Shouldn’t we know by now if biodiversity is increasing or decreasing?

Biodiversity is the variety of species of living organisms of an ecosystem. Biodiversity is thought to boost ecosystem productivity where each species, no matter what shape, size, how rare or abundant they are have a role to play in their ecosystem.

Whether or not biodiversity is increasing or decreasing depends on the timescale in which you are looking as well as the spatial scale (e.g. local, regional, global). This makes it difficult to truly assess whether we have more, less or the same number of species. We based our discussion on: Dornelas et al., 2014, Vellend, et al., 2013, Brooks, et al., 2006, Hooper, et al., 2012 and McGill, et al., 2015.

We analysed the paper by Dornelas et al., 2014 which covered 35,613 species in their study. Although we decided with our critically thinking minds that when you initially read this figure of over 35,000 species it does not seem like that many relative to the 8.7 million eukaryote species there might be on Planet Earth!  However, when put in perspective, we decided that the study does have value. It includes data from more species than a lot of studies to date have managed to compile and realistically you don’t need every single species to draw valuable conclusions. Overall, we thought that it would have been more precise if Dornelas et al. 2014 had just focused on marine studies than to try to include terrestrial species as well, as we weren’t sure how comparable the marine and terrestrial data sets were in these analyses.

A concern of ours was that large geographic regions of the world absent due to data collection bias. This moved us on to discussing the repercussions of sampling biases. In the Vellend paper and Dornelas’ date came mostly from temperate, well developed areas where active ecosystem management has occurred for a number of years as shown in the following two maps.

The first map is from Vellend et al. 2013 and the second from Dornelas et al. 2014 paper showing the areas where spatial gaps in biodiversity data occur. Seeing these gaps made us think about where biodiversity research occurs globally and how certain regions are probably under represented in the ecology literature, such as for example Sub-Saharan Africa. We also pondered how the spatial biases with climate data are similar to those in ecology (third map), and how the same regions of the world are often understudied in a variety of different fields.

Although the results from the underrepresented areas seem to be consistent with the patterns found in well-studied parts of the world.  We were unconvinced that we definitively know what biodiversity changes at local scales might be across the planet as a whole without data from the regions with the fewest studies due to the vastly different ecosystems found in these locations.

An overarching problem in these global analyses is that, even analyses that are as holistic as these, have a bias of data collection in terms of what taxa were sampled. Microorganisms make up the vast majority of the species on earth, yet they are vastly underrepresented in the ecological literature because generally there is less interest in studying them (sorry microbes!). We agreed that we are very appreciative of the folks who go out to study microbial biodiversity out in the real world!  Thanks you guys!

The reduced emphasis on microbial ecology is likely because it is time consuming research, where species identification is very tricky and with many species that carry out the same or similar functions within an ecosystem. For example, if you removed a microbe from a system, it is likely that another will fill the niche and there will be no change in the overall ecosystem function. On the other hand, if you altered the top of a trophic pyramid by removing an apex predator the cascade of effects would be more noticeable. We discussed the concept of functional redundancy (which you can read more about here) and that it could be used to disperse conservation resources based on the usefulness of a species within an ecosystem.

To summarise, many scientists have attempted to track biodiversity increase and decrease and many of them come to different conclusions depending on the scale at which they conduct their study, as shown in the following graph. We agreed that an important thing to take away from this discussion is something highlighted in the Dornelas paper; it is important to think about biodiversity change, and it is not necessarily the increases or decreases that we should care about, but the effect that biotic homogenisation could have on our world.

Biodiversity Change across scales

Hypothesized species richness changes across scales (Myers-Smith et al. unpublished).

Are biodiversity changes the same across different scales or do we see different patterns depending on which scale we look at? (Figure from Isla’s Conservation Science Lecture on Biodiversity Changes)

By Hannah


One thought on “Shouldn’t we know by now if biodiversity is increasing or decreasing?

  1. Pingback: Good teaching – student and teacher perspectives from the Conservation Science course – Teaching Matters blog

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