How Well Do Biodiversity Experiments Represent The Real World?
The results of biodiversity–ecosystem functioning experiments are realistic (2020) Jochum et al., Nature Ecology and Evolution, https://doi.org/10.1038/s41559-020-1280-9
Testing how different measures of biodiversity contribute to important ecosystem functions, like carbon cycling or tree decomposition, are crucial to our understanding of how the loss of species will impact both local and global ecosystems. Yet these studies are hard to undertake in the real world, since species come and go all the time, and constantly accounting for important environmental factors like temperature or sunshine can be near impossible. It makes understanding exactly what is driving those important ecosystem functions difficult.
To get around this, researchers often set up more controlled experiments, filled with different plots containing random assemblages of species often found in the wild. Since there are different communities in each plot, but each is subject to similar environmental conditions, they can examine the different levels of ecosystem functioning within the different plots and start to understand the differences. But since they’re taking random species of plants, is this even useful as an indicator of what’s going on in the ‘real world’? That’s what today’s researchers tested.
What They Did
The authors looked at two long-term grassland experiments, one based in Jena Germany, the other in Cedar Creek, USA. They compared different metrics of biodiversity (like species richness and taxonomic diversity) of the plots to similar areas in the nearby region. They used these comparisons to determine which of the plots in the controlled experiments were ‘realistic’.
Additionally, they compared whether the relationships between the biodiversity of the controlled plots and some of the key ecosystem functions remained the same when the unrealistic plots were removed from the analysis.
Did You Know: The Cedar Creek Experiment
The Cedar Creek experiment mentioned here is actually a smaller experiment taking place at the Cedar Creek Ecosystem Science Reserve. The Reserve has been a massive undertaking, first established in 1942 by the university of Minnesota. It includes literally thousands of long-term experimental plots set up by different researchers, and has contributed an immeasurable amount to our understanding of plant community ecology.
What They Found
The experimental plots showed a wider variety of communities than the real-world plots, but nestled within that variety were a large number of communities very similar to the real-world plots. Experimental plots tended to be much more similar to the real-world plots when they were not weeded, suggesting that human interference could create key differences between the two, as opposed to surrounding environmental conditions.
The researchers classed 28% and 77% of the Jena and Cedar Creek experiments as realistic, respectively. The relationships between biodiversity and ecosystem functioning remained relatively similar when removing the 23% of unrealistic Cedar Creek plots from analysis, however there was some variation in the relationship when removing the unrealistic plots from the German analysis (though many relationships remained similar).
The scope of this paper is massive, but it’s important to remember that the scale of these experiments were fairly local, and only dealt with one habitat type. That’s not to downplay the results, since this sort of experiment can of course be scaled up and repeated in other ecosystems. However a lot of the communities studied here both in the real-world and the experiments were quite species poor, so it would be interesting to see how similar research coped with more diverse ecosystems.
This research is tremendously encouraging (and probably let some researchers breathe a sigh of relief), as it validates the work that both the Cedar Creek and Jena teams have been doing to decades now. And whilst only a subset of their plots might be ‘realistic’, those unrealistic plots still tell us a great deal about potential future scenarios that could come about as a result of climate change or species migrations. Even knowing which plots are realistic will probably be very helpful for experiments going forward.
Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology who is not fan of botany but concedes that it must have place somewhere in science. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.