Understanding how ecosystems will respond to global change is an outstanding question. In a work published in Nature Communications (Environmental change makes robust ecological networks fragile), Strona and Lafferty show how new insights on this important topic can unexpectedly come from digital organisms, that is bacteria-like fragments of software code living, interacting and evolving within a computer simulation, feeding on computer memory and interacting with their digital environment (made up of numbers) by performing logical and mathematical operations.
Image - Illegal slash and burn practice in Madagascar, 2010 By Diorit - Own work, CC BY-SA 3.0,Wikimedia
Starting from a single ancestor digital organism, the authors let evolve several artificial life communities for hundred thousands generations 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.
The authors then investigated 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 have a minimum effect on the overall community diversity.
Any deviation from this pattern, however, may trigger extinction cascades, and lead, eventually, to community collapse.
Unfortunately, this is exactly what expected in the real world. Climate change and human activities have modified natural systems so deeply to make species' adaptation to past conditions not helpful for present and future survival. Sharks are an emblematic example of this. Although they have not needed much evolutionary improvements in the last million years, they are now struggling to survive the Age of Man.
Strona 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 which has permitted the evolution of complex systems, that is, the tendency of consumers to rely and specialize on dependable resources, may have doomed many species to extinction.
Resources that were largely available in the past are now becoming more and more rare, putting at risk all the species relying on them and so on. Sadly, the systems that have been more stable during their past history, such as rain-forests and coral-reefs, are those most at risk.
Environmental change makes robust ecological networks fragile - Giovanni Strona & Kevin D. Lafferty