Rich and stable communities most vulnerable to change

16 08 2016

networkI’ve just read an interesting new study that was sent to me by the lead author, Giovanni Strona. Published the other day in Nature Communications, Strona & Lafferty’s article entitled Environmental change makes robust ecological networks fragile describes how ecological communities (≈ networks) become more susceptible to rapid environmental changes depending on how long they’ve had to evolve and develop under stable conditions.

Using the Avida Digital Evolution Platform (a free, open-source scientific software platform for doing virtual experiments with self-replicating and evolving computer programs), they programmed evolving host-parasite pairs in a virtual community to examine how co-extinction rate (i.e., extinctions arising in dependent species — in this case, parasites living off of hosts) varied as a function of the complexity of the interactions between species.

Starting from a single ancestor digital organism, the authors let evolve several artificial life communities for hundred thousands generation under different, stable environmental settings. Such communities included both free-living digital organisms and ‘parasite’ programs capable of stealing their hosts’ memory. Throughout generations, both hosts and parasites diversified, and their interactions became more complex.

oscillateThen they looked at how these communities would have responded to different scenarios of biodiversity loss. They found that when species go extinct consistently to their degree of adaptation to the ‘natural’ environmental conditions where they have evolved, their loss has a minimum effect on the overall community diversity. Any deviation from this pattern, however, can trigger extinction cascades, and lead eventually to community collapse.

Unfortunately, this is exactly what expected in the real world. Climate change and other human endeavours have modified natural systems so much to make species’ adaptation to past conditions not much help for present and future survival. Sharks are an emblematic example of this. Although they have not needed much evolutionary improvements over the last few million years, they are now struggling to survive in the Anthropocene’s pace and magnitude of change.

louseStrona and Lafferty explain why this happens, and show how this emergency could be ubiquitous in natural systems. By comparing the results of their artificial life simulations with several empirical host-parasite networks for different animal groups, they demonstrate that the basic rule permitting the evolution of complex systems (i.e., the tendency of consumers to rely and specialise on dependable resources) could have doomed many species to extinction. Resources that were largely available in the past are now becoming rarer, putting at risk all the species relying on them and so on. The systems that have been more stable during their past history, such as rain forests and coral reefs, are therefore those most at risk.

CJA Bradshaw

 


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