QMUL Study Finds Species Turnover Is Slowing as the Planet Warms

Many ecologists have worked on the assumption that, as the planet heats up more rapidly, ecosystems ought to “move” more quickly as well.

The reasoning appears simple: as climate zones move, species are pushed from areas where they once survived, other species arrive, and local communities should reorganise at an ever-faster rate.

However, new research from Queen Mary University of London (QMUL) suggests that something much more unusual is happening.

After examining a vast collection of biodiversity surveys from terrestrial, freshwater and marine environments, spanning approximately the past century, the researchers discovered that local species turnover has not accelerated. Instead, it has slowed.

What the experts measured

The central concept is “turnover”: the rate at which the species list at a particular location changes through time.

Consider a section of seabed, a lake or a woodland survey site. High turnover means its cast of species changes rapidly; low turnover means the same species reappear year after year.

The researchers concentrated particularly on the years since the 1970s, a period in which the acceleration of global surface warming has been well documented.

They assessed turnover rates on either side of this acceleration, using short intervals of roughly 1 to 5 years, when rapidly changing environmental pressures would be expected to become apparent.

Yet the trend ran in the opposite direction: turnover decreased across highly varied ecosystems, from land-based birds to communities on the ocean floor.

Species turnover: an engine grinding to a halt

Dr. Emmanuel Nwankwo, the lead author of the study, described the finding with a metaphor that makes it more concrete:

“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.”

Put another way, ecosystems usually possess an inherent level of churn. Species appear and disappear even without dramatic environmental shifts, as competition, predators, prey, disease and random events continually alter the balance.

What makes the data surprising is that this underlying churn - this “self-repairing engine” - is declining precisely when many researchers expected it to speed up.

A big decline, not a tiny wobble

“We were surprised how strong the effect is. Turnover rates typically declined by one third,” said study co-author Axel Rossberg from QMUL.

A fall of one third is not minor statistical variation. It indicates that ecosystem behaviour may be changing widely, rather than reflecting a handful of isolated sites or an oddity in measurement.

One of the paper’s most notable elements is the authors’ interpretation of what turnover itself represents.

A widely held view is that ecosystems are primarily rearranged by external forces, including temperature, rainfall, land use and nutrient pollution.

These influences plainly matter. Nevertheless, the study proposes that many ecological communities are also shaped by powerful internal dynamics, even in the absence of outside pressure.

The authors connect this with the “Multiple Attractors” phase, a theoretical concept predicted by physicist Guy Bunin in 2017.

Rather than having a single stable or “best” community for a given place, a system can occupy several possible configurations.

Human impacts on species turnover

Through interactions such as competition, predation and mutualisms, species replace one another in a continual rock-paper-scissors-like process.

The researchers suggest that this internal churn may be a defining feature of ecosystems. They also argue that the evidence displays the pattern expected if “multiple attractors” behaviour occurs in the natural world rather than existing only in theory.

Why, then, would turnover decline? This is where the paper takes a more troubling direction.

If ecosystems naturally operate as revolving doors, slower turnover implies that those doors are becoming stuck. The researchers consider environmental degradation and reduced regional species pools the most likely explanation.

In a healthy ecosystem, the wider region generally contains a “bench” of potential arrivals: species able to establish themselves when conditions permit or when another species disappears.

However, when habitat loss, fragmentation, pollution, overexploitation and other human pressures diminish this regional pool, fewer species remain available to replace those that are lost.

Communities that cannot self-repair

This outcome does not necessarily indicate a peaceful, stable community. Rather, it can indicate one that is trapped, less capable of reorganising, less able to “self-repair”, and potentially less resilient.

“In other research we are seeing clear indications that human impacts cause the slowing of turnover. It is worrying,” Nwankwo said.

This is perhaps the easiest point to misread from a quick look at the headline. Little local community change might seem to imply that nature is remaining steady.

The authors say that interpretation is mistaken. Limited turnover may be a warning rather than a reassuring sign.

Where ecosystems depend on a continual supply of replacement species to respond to disturbance, declining turnover may show that they are losing the flexibility needed to withstand shocks.

Seen in this way, the slowdown resembles “depletion” more than “stability”.

Why this matters going forward

If the research is correct, it encourages scientists and conservation planners to approach climate change from a different perspective.

Warming may still be displacing species, but the pace at which local communities change could be constrained by a more fundamental factor: the condition of biodiversity across the surrounding region.

The future, therefore, may not simply involve increasingly rapid reshuffling. It may instead involve ecosystems becoming less dynamic because too few species remain to drive that reshuffling.

That represents a different warning signal - and, arguably, a more frightening one.