Monitoring species range changes in changing climate

As our planet undergoes significant changes due to climate change, habitats are altered, appearing, disappearing or changing in quality. Understanding the impact of these changes on the geographic distribution of species is of great importance. Shrinking ranges of protected species and ranges of harmful species such as pests and pathogens highlight the urgent need to accurately monitor range movements.

However, this task presents challenges as the available observation time is often short compared to the speed of underlying population processes, making it difficult to distinguish between directional changes and random fluctuations.

Faced with this challenge, Dr. Lorand Eydvos of the University and the Environmental Research Center in Budapest. A research team led by Beata Oborni has developed a new method to track range changes. The team aims to define the boundaries of ranges accurately and consistently to allow comparisons between different years, geographical locations and species.

The article has been published in the journal Ecology.

Accurately defining boundary contours is not a trivial task, as they often exhibit complex patterns. Occupied peninsulas are interspersed with unoccupied bays, and isolated occurrences mark the mainland. While traditional methods rely on external phenomena of a species, Oborni and his colleagues propose a different approach.

They suggest marking a threshold edge at the boundary between connected and fragmented phenomena called the „hull”. By marking the average position of the crust over time, the „linkage range,” the researchers provide a more statistically reliable method. This area has a high population density and exhibits small fluctuations, increasing the robustness of the approach.

Oborni and his colleagues investigated the mechanisms of pattern formation using transparent models. Unlike previous approaches based on common spatial statistical methods, their novel approach uses knowledge of the mechanisms that govern the appearance of these patterns: birth, spread, and death within populations. Through computer simulations the team explored connectivity limits of different species along environmental gradients (e.g. mountains).

Remarkably, they discovered that the crust exhibits a strong fractal structure with a dimension of 7/4. Further investigations by Beata Oborni and Daniel Zimmerman confirmed that this fractal structure is consistent regardless of whether the threshold is rapidly advancing or receding relative to the generation time. Notably, this pattern exhibited particular robustness at the retreating (rear) edge of species ranges.

These findings highlight the applicability of connectivity thresholding in tracking range changes in diverse geographic contexts, enabling a global perspective on these changes. For example, the method allows comparison of tree lines on different hills, even if they are of different species, using universal scaling laws.

The universal features revealed in this study find their explanation in percolation theory, a research field in statistical physics. This highlights the power of knowledge transfer between seemingly disparate scientific disciplines.

Insights gained from these studies deepen our understanding of the complex relationship between environmental changes and species distributions. As scientists continue to refine and validate this method, it has the potential to contribute to robust estimates of biodiversity changes and inform effective conservation strategies.