A species can look safe simply because it is numerous—but that headcount can miss the real danger. Its chances may depend on how differently its members move through space, and on the other species around them. Human impacts on biodiversity have prompted concerns about a potential mass extinction.

Yet, despite signals such as population declines and range contractions, the magnitude and trajectory of ongoing extinctions remain debated. Resolving these uncertainties requires theories that link what happens to local populations with how communities are arranged across space, and that can ultimately be checked against real data.

The study introduces a framework to measure how close each species is to being pushed out by competition in communities spread across different places. The central idea is like judging a shop’s resilience by more than the number of customers it has: the study also asks how much room is available, how species use that room, and how the surrounding community affects them.

The approach can be applied directly to real data without prior knowledge of species traits, population details, or pairwise interactions—information that is often unavailable in communities containing many species. To connect the framework with observations, the study uses a measure based on the fraction of space a species occupies divided by the locally available unoccupied space.

That adjustment matters because the same amount of space use means something different in a nearly full patch than in a patch with plenty of room. By giving more weight to space-limited patches, the measure rescales local space use to reflect the effort needed to establish in those places.

Comparison with forest data shows that species vulnerability cannot be fully predicted by abundance alone. Instead, vulnerability depends on how movement strategies, spatial distribution patterns, and total population size become entangled, placing each species within the wider community rather than judging it in isolation.

When species differ too much in their competitive standing, those with the lower standing may not survive long-term competition. The study measures vulnerability by asking how close a species is to the boundary beyond which it cannot survive, a boundary shaped by the competitive standing of all the other species.

A species on the surviving side of that boundary can persist, while one on the other side is predicted eventually to be outcompeted. The visual makes vulnerability a geometric gap to a survival boundary, then links that gap to abundance and to how unevenly species are spread across space.

The framework produces species-specific measures describing how varied a species’ movement strategies are and how strong its overall movement is. In the forest comparison, species that take advantage of openings and intermediate conditions show greater variation in movement strategies than species suited to shade.

The difference remains when the three groups are considered separately, consistent with the idea that canopy openings can create short-lived local dominance for species needing more light. The researchers then tested whether the framework could generalize to data it had not used to set its parameters.

They used one part of each forest plot to predict how much space each species occupied in the other part, and the predictions showed remarkable agreement with observations across all three datasets. There is an important limit: the vulnerability measure predicts the final outcome, but not how long different species take to reach it.

The study found that these times depend strongly on species-specific features, with some species settling faster than others, so short- and medium-term changes can still matter. The study finds that variety in movement strategies can protect a species from being pushed out, even when abundance alone looks similar.

That gives conservationists a way to judge risk from spatial population maps, without knowing every trait or interaction.