Researchers have looked into ‘ecosystem canaries’ - sensitive species that can offer early warnings of habitats or systems that come under threat before tipping points are reached and irreversible changes affect them.

According to researchers from the Potsdam Institute who last year warned that humanity had crossed four of nine planetary thresholds that would lock us onto a path of irreversible and large-scale change, the rate of extinction on the planet is about ten times sustainable levels, and we are sailing dangerously close to limits on forested landcover.

Now, research led by the University of Southampton suggest that, like canaries that coal miners used to check for poisonous gasses deep underground, 'ecosystem canaries' - species that are often the first to disappear from a stressed ecosystem - can be used to identify when a tipping point is approaching in an ecosystem. Southampton’s Dr James Dyke commented, "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.

"Our study shows that vital information about the overall health or resilience of an ecosystem may be lurking in data about what could be considered to be inconsequential species."

The research

To illustrate their theories about ‘ecosystem canaries’ the researchers studied three lakes in China, looking at changes in algae and midge numbers as they compete for resources under environmental pressures. From this data they identified 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.

As environmental degradation impacts on the ecosystem, 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 puts the ecosystem into a critical transition - the point at which a system tips into an alternate state which can be very hard to recover from.

The vulnerability of canary species suggests a role for this group as a sensitive indicator of environmental stresses, yet it is often assumed their presence or absence has no useful ecological information.

Professor Patrick Doncaster, from Biological Sciences at the University of Southampton and lead author of the study, explained "We identified an early warning signal of these changes in the relationship between compositional disorder, which is roughly equivalent to how jumbled up a community of species is, and biodiversity, which measured the total amount of species in a community. How these populations change over time reveals statistically significant signals of an approaching tipping point.

"We were able to detect a clear signal of an approaching tipping point in our selected Chinese lake ecosystems, through the analysis of multi-decadal data of fossilised diatoms and chironomids. In some cases we could detect an early warning signal up to three decades before the actual tipping point."

Dr Dyke added, ”Global environmental change presents a clear need for improved indicators of critical transitions. Our study demonstrates the potential role of changing species composition in the lead-up to ecosystem tipping points. To help ecosystem management, future research needs to develop models that can simulate critical transitions as a result of environmental factors.”

The researchers said there is potential to apply their new technique to many other habitats, to increase our understanding of how these sensitive species respond to human impacts such as overfishing, deforestation and climate change.