Study identifies key species which act as warning signs of ecosystem collapse 

The Guardian 19th August 2016

The Earth’s biodiversity is under attack. We would need to travel back over 65 million years to find rates of species loss as high as we witness today. Extinction is – Jurassic Park science fiction aside – a one way street. An unbroken chain of genetic inheritance links every species back to the dawn of life some 3.8 billion years ago. Once a species becomes extinct it disappears from the universe forever. 

Conservation often focuses on the big, enigmatic animals - tigers, polar bears, whales. There are many reasons to want to save these species from extinction. But what about the vast majority of life that we barely notice? The bugs and grubs that can appear or vanish from ecosystems without any apparent impact.

It is generally expected that biodiversity increases resilience with more species being able to better withstand impacts. We can imagine decreasing biodiversity as popping out rivets from an aircraft. A few missing rivets here or there will not have any consequences. But continuing to remove them threatens a collapse in ecosystem functioning. Forests give way to desert. Coral reefs bleach and then die. 

New research that I was involved in argues that there may be a value of biodiversity that has typically been overlooked, but could be vitally important if we are to manage our impacts on ecosystems. Our study, published in the journal Ecology, shows that crucial information about the overall health or resilience of an ecosystem may be lurking in data about what could be considered to be inconsequential species. In fact, the presence or absence of some of the rarest species may be giving us important clues as to how near an ecosystem is to a potential collapse. 

Such rare species we call ecosystem canaries. Like canaries that coal miners used to check for poisonous gasses deep underground, ecosystem canaries are often the first species to disappear from a stressed ecosystem. Their vanishing can be linked to changes in the functioning of ecosystems, which can serve as a warning that a collapse is approaching. 

Our study involved researchers from the University of Southampton (UK), University of Nice (France), State Key Laboratory of Lake Science and Environment at Nanjing Institute of Geography and Limnology (China) and Aarhus Institute of Advanced Studies (Denmark). We used data collected from lakes in China that showed changes in the abundance of species from algae (diatom) and aquatic midges (chironomid) communities as they compete for resources under environmental pressures. From this data it was possible to identify three types of organism: slowly-replicating but strongly competitive ‘keystone’ species; weakly-competitive but fast-replicating ‘weedy’ species; and slowly-replicating and weakly-competitive ‘canary’ species.

Runoff of fertiliser from surrounding fields is a major environmental impact on these lake ecosystems. With increasing impacts, keystones initially prevail through competitive dominance over others, resulting in the early demise of canary species. With continuing degradation affecting all species, this leads to the eventual collapse of the keystone species as they are replaced by the weedy species. The loss of keystones tips the ecosystem into a critical transition – the point at which a system shifts into an alternate state which in lakes is dominated by smothering algae and absence of many plant and animal species. Moving a lake back to a clear water, high biodiversity state can be extremely difficult. It is always far better to avoid the collapse in the first place. 

Waiting to observe changes in the keystone species would not allow any intervention because the system would typically already be entrained into collapse. By searching for changes in the structure of populations that includes the ratio of keystone, weedy and canary species, we were able to detect a clear signal of an impending collapse many years, sometimes decades before the actual event. Time enough to put in place changes to farming and other practices.

The ecological theory underpinning this approach should apply to many other aquatic and terrestrial ecosystems. Given the extent and rapidity of human impacts there should not be any shortage of ecosystems to apply our findings to.