Researchers at Queen Mary University of London analyzed data from the BioTIME database and found species turnover in ecosystems has declined by a third since the mid-1970s. This challenges expectations that ecosystems would accelerate turnover in response to climate change and other pressures. Lead author Emmanuel Nwankwo described nature's self-repair mechanism as an engine grinding to a halt.
A new analysis published last month by Emmanuel Nwankwo and Axel Rossberg at Queen Mary University of London examined the BioTIME database, which compiles records from over half a million locations spanning more than 150 years. Covering diverse ecosystems from North American birds to seabed fish, the study measured species turnover—comings and goings over up to five-year periods—and detected a significant slowdown of one-third since the mid-1970s, coinciding with rapidly rising global temperatures. Rossberg noted, “We were very surprised at the discovery,” as many ecologists had anticipated increased turnover amid human impacts and climate change. Nwankwo added, “Nature functions like a self-repairing engine, constantly swapping out old parts for new ones. But we found this engine is now grinding to a halt.” Christopher Terry of the University of Oxford endorsed the findings, citing his own work on declining turnover in human-modified North American bird habitats. Ryan Chisholm of the National University of Singapore called the results “quite convincing.” However, Maria Dornelas, head of BioTIME’s leadership council, reported increases in turnover from long-term studies like the North Sea International Bottom Trawl Survey and the North American Breeding Bird Survey. She stated, “I am finding it difficult to reconcile the two findings.” Jacob O’Sullivan of Forest Research suggested discrepancies arise from differing time frames, affirming slowdown for short-term intrinsic turnover. Ecologists attribute the decline to habitat fragmentation, reducing opportunities for species replacement and connectivity. O’Sullivan noted turnover increases with regional species pools and landscape connectivity. This intrinsic turnover, distinct from responses to external pressures, is seen by some as a sign of ecosystem health, akin to natural cycles in predator-prey dynamics or fires. The findings revive debates on ecosystem stability, challenging older views like the rivet-popper hypothesis and Frederic Clements’ climax ecosystem concept, while Anne Magurran emphasized, “Species in ecosystems are not fixed entities, even without human-induced change.” Implications for conservation include rethinking efforts to halt change, with James Rosindell at Imperial College London arguing to accept natural turnover.
