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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
For planning animal conservation measures, it is vital to know where endangered species live and how they interact. Leveraging this knowledge gained from tracking technology to understand how entire populations change, including long-term survival chances, is a long-standing open question in ecology. A major step toward an answer was now achieved by researchers from São Paulo State University (Brazil) and the Center for Advanced Systems Understanding (CASUS) at HZDR: They introduced a new theoretical framework that shows how individual animal movements and their home ranges shape population dynamics across space and time (Ecology Letters, DOI: https://doi.org/10.1111/ele.70269).
Despite decades of independent progress in population ecology and movement ecology, researchers have lacked a theoretical bridge between these two disciplines. “Ecologists have been trying to establish this link since the 1950s, when they started to characterize animal movement patterns,” says Dr. Ricardo Martinez-Garcia, head of the CASUS Young Investigator Group “Dynamics of Complex Living Systems” and senior author of the study. Classic population dynamics models, going back to Pierre François Verhulst’s work in 1838, describe how populations grow until they reach the limits imposed by available resources, such as food and space, but overlook the importance of animal movement in determining these saturation patterns. “In many cases, observed population sizes could not be explained with existing theoretical frameworks. We were confident that incorporating the movement behavior of individual animals we observe in tracking data could solve these discrepancies,” adds Martinez-Garcia.
Ecologists have long known that animals use their habitats non-uniformly and spend most of their lives within home ranges that are substantially smaller than the population range. In recent years, technological and methodological advances have provided unprecedented insight into how organisms move, including a more precise quantification of their home ranges. Central to this progress are statistical methods developed with key contributions from Prof. Justin M. Calabrese, co-author of the study and head of the Earth System Science department at CASUS. “A major innovation of our theory is that it allows the prediction of population dynamics to be based on the same animal movement model that is widely used to estimate home ranges from tracking data. This means that, under the hood, home-range estimation and population modeling can now be powered by the same engine, which gives our theory a stronger connection to data and leads to better-informed, real-world conservation recommendations,” says Calabrese.
Model incorporates interactions between more than two animals
A 2020 study led by Martinez-Garcia already linked individuals’ exact use of their home ranges, their so-called range-residency, to the frequency of interactions between two animals. It showed that encounter rates can deviate strongly from those predicted by classical models that oversimplify movement. The next logical step was moving from pairs to a larger number of animals. In this way, the theoretical framework would be able to account for demographic processes driven by cooperation, competition, reproduction and other animal interactions. But this change of scale in the study represented a significant challenge: “When we have an entire population of animals, each one will have its own movement behavior and the number of possible interactions becomes enormous very quickly,” says Rafael Menezes, a postdoctoral researcher at UNESP and former PhD student at Martinez-Garcia’s group.
The extended framework, named range-resident logistic model, manages this complexity elegantly by introducing a so-called crowding index that summarizes all relevant information about how movement shapes animal interactions. Menezes continues: “This coefficient, which can be readily calculated from animal tracking data, gives an indication of how animals in a population interact: are they avoiding each other, are they trying to spend more time close to each other, or are they somewhat indifferent?”
The direct comparison of the new and old models clearly indicates, as foreseen, a highly relevant impact of the movement data: Depending on the selected parameter conditions, population size predicted by the range-resident logistic model is sometimes twice, sometimes half the size of that predicted by the classical Verhulst equation. “A difference that can make a difference,” comments Martinez-Garcia. According to him, the new model is important when practical conservation questions are investigated, such as the impact of human infrastructure on the fate of wildlife populations. “One particular case we are currently working on is the question of what happens to a population when a new highway cuts through the animal’s habitat. Specifically, we are talking about Brazilian tapirs here. Only thanks to an accurate description of animal movements, we can quantify wildlife vehicle collisions and estimate viability of the tapir population.”
Brazilian scientist joins CASUS
Brazilian native Rafael Menezes is a postdoctoral researcher at the International Center for Theoretical Physics-South American Institute for Fundamental Research (ICTP-SAIFR), an international research center based at the Institute of Theoretical Physics of UNESP and supported by the São Paulo Research Foundation, FAPESP. Still a PhD student two years ago, Menezes was awarded competitive funding from the Brazilian federal agency CAPES to continue his doctoral research, supervised by Martinez-Garcia, in Görlitz. Menezes successfully defended his doctoral thesis at University of São Paulo’s Institute of Biosciences in early 2025.
Dr. Ricardo Martinez-Garcia | CASUS Young Investigator
Center for Advanced Systems Understanding (CASUS) at HZDR
email: r.martinez-garcia@hzdr.de
R. Menezes, J. M. Calabrese, W. F. Fagan, P. I. Prado, R. Martinez-Garcia: The Range-Resident Logistic Model: A New Framework to Formalise the Population-Dynamics Consequences of Range Residency, in Ecology Letters, 2025 (DOI: 10.1111/ele.70269)
Brazilian tapir (Tapirus terrestris) in the Pantanal
Source: Marco Zanferrari
Copyright: M. Zanferrari/Wikimedia Commons, CC BY-SA 2.0
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Brazilian tapir (Tapirus terrestris) in the Pantanal
Source: Marco Zanferrari
Copyright: M. Zanferrari/Wikimedia Commons, CC BY-SA 2.0
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