When species are subjected to changing environments, they can survive in their current location through genetic adaptation. However, this ability is not unlimited. In a study published in PNAS, biomathematician Jitka Polechová of the University of Vienna shows that, even when environmental change is only gradual, there is a tipping point beyond which adaptation can suddenly fail. When that happens, species’ ranges may shrink or populations may fragment into separate subpopulations.

Understanding the factors that determine the limits of adaptation is essential for predicting how species will respond to climate change and other environmental pressures. Until now, theoretical approaches have largely treated ecological and evolutionary processes separately. In nature, however, populations are shaped by the interplay of both. This new study explores the conditions under which populations are able to maintain sufficient genetic variation to adapt to changing environments, and the point at which this capacity breaks down.

A tipping point in adaptation

This study develops quantitative, testable predictions about the conditions under which populations can adapt and the limits of that adaptive capacity. The results show that the ability of species to adapt to changing conditions – and whether their ranges expand or collapse – depends above all on three measurable factors: the rate of environmental change, the extent of environmental variation across the species’ range, and the strength of genetic drift – the random fluctuations in the frequencies of genetic variants in small populations.

The study identifies how adaptation can fail abruptly. As environmental conditions change, the genetic composition of a population becomes less well matched to its surroundings. The size of a local population may then decline and therefore become more susceptible to genetic drift. As drift becomes stronger relative to selection, variants important for adaptation are more easily lost. This leads to genetic diversity declining and adaptation becoming more difficult, creating a self-reinforcing downward spiral. As genetic variance erodes and populations can no longer adapt to changing conditions, they collapse by contracting from the margins or fragmenting abruptly across the whole range.

Why genetic drift matters

A key factor here is the so-called neighbourhood size – the number of individuals within a local area who exchange genes. If the local gene pool is small, random shifts in the frequency of genetic variants – genetic drift – will have a strong effect. Greater genetic exchange between subpopulations can counteract this by introducing more variants and reducing the strength of genetic drift, thus preserving genetic variation. A larger neighbourhood size can therefore help populations continue to adapt and persist under ongoing environmental change.

Implications for conservation

The study provides a theoretical framework for conservation biology that yields concrete, testable predictions. It shows that even gradual environmental change can push populations past a tipping point, beyond which they may suddenly collapse.  It highlights the importance of maintaining gene flow — the exchange of genetic variants between populations — as a key conservation strategy. It identifies when measures that improve connectivity between populations may be particularly beneficial to keep populations above the critical threshold and preserve their adaptive potential.

About the study

This study develops a framework that brings together ecological processes, such as population growth and dispersal, and evolutionary mechanisms, such as selection and genetic drift (the random changes in the frequencies of genetic variants). Using analytical approaches and individual-based simulations, it examines how populations respond to environmental change across space and time, and derives quantitative, testable predictions about the limits to adaptation.  It shows that the interactions between ecological and evolutionary processes can profoundly change the outcomes predicted if each are viewed independently.

Summary

• Interactions between ecological and evolutionary processes can lead to a tipping point at which the adaptive capacity of a population breaks down.
• A critical threshold determines whether populations adapt, persist, or collapse.
• Greater genetic exchange between neighbouring populations can strengthen their adaptive capacity.
• Even gradual environmental change can cause species’ ranges to fragment abruptly.
• The study offers predictive insights with direct relevance for conservation.

About the University of Vienna:

At the University of Vienna, curiosity has been the core principle of academic life for more than 650 years. For over 650 years the University of Vienna has stood for education, research and innovation. Today, it is ranked among the top 100 and thus the top four per cent of all universities worldwide and is globally connected. With degree programmes covering over 180 disciplines, and more than 10,000 employees we are one of the largest academic institutions in Europe. Here, people from a broad spectrum of disciplines come together to carry out research at the highest level and develop solutions for current and future challenges. Its students and graduates develop reflected and sustainable solutions to complex challenges using innovative spirit and curiosity.

Original publication:

Polechová J. (2026) Evolution of Species‘ Range and Niche in Changing Environments. In PNAS.
DOI: 10.1073/pnas.2604510123