A new paper published earlier this month on 15 May in Science Advances demonstrates the potential cascade of co-extinction in networks of plant species and pollinators in Europe (1). The authors suggest that whereas geographic location best predicts the probability of a particular plant species being driven to extinction by climate change, the local is is the network of interactions is the best predictor of subsequent coextinctions.
As the authors write, “Extinctions induced by climate change may trigger coextinction cascades — groups of species disappearing as a consequence of the extinction of species they depend on — thus driving many more species to extinction”.
In other words, extinctions beget more extinctions owing to the mutual dependencies of plant species. So it would seem codependencies, although essential for the incredible diversity of life on Earth, worsen the already detrimental effects of climate change.
To come to this conclusion, the researchers from Switzerland, Spain, Chile, and the UK quantified just how much climate change affects species when mutual dependencies are considered. They examined the networks of flowering plants and pollinators throughout various parts of Europe – seven distinct regions.
The study used data on seven European pollinator networks from the web-of-life dataset, a European Research Council-funded initiative set up by lead author Prof Jordi Bascompte of the University of Zurich. The project aims to map the global network of species interactions in order to better understand the interactions between plants and their insect pollinators, as well as the collapse of these fragile networks following global changes. The network can be used to simulate the network’s collapse and evaluate the rate of coextinctions of the species as they are gradually left without resources.
An example given by the authors is the sage-leaved rock rose, part of a network in southern Spain. The rose has a 52 percent predicted probability of extinction caused by climate change in 2080. If this happens, the small carpenter bee — one of its pollinators — will also be at risk of co-extinction. But the small carpenter bee also pollinates the myrtle. So, as a consequence, the myrtle will also be faced with the threat of extinction.
These knock-on effects seem to pose a particularly large threat in the Mediterranean. For instance, some species in Greece are 2–3 times more likely to become extinct by 2080 if mutual dependencies are considered.
One reason for this may be that the Mediterranean region is more strongly affected by climate change compared to the central and northern parts of Europe. In addition, species in southern Europe have a much narrower distribution range. And thus, more likely to face extinction, leaving many other species susceptible to the extinction cascade.
The higher probability of extinction — and subsequent coextinctions — pushes the network closer to the threshold of collapse. The authors also suggest, “Some species with a very low likelihood of climate-related extinction according to the traditional model are at high risk of extinction due to their dependencies.”
(1) Bascompte, J. et al. Mutualistic interactions reshuffle the effects of climate change on plants across the tree of life. Science Advances (2019). DOI: 10.1126/sciadv.aav2539