How a Desert Rodent Is Colonizing New Lands
Imagine a vast, arid landscape in Southern Russia, where the environment constantly shifts between desert and steppe. Here, a small, unassuming rodent—the midday gerbil—is undertaking an extraordinary journey. In recent years, this desert-dwelling species has been rapidly expanding its territory, colonizing new areas at an unprecedented rate. What drives this expansion? How do the pioneering gerbils differ from their relatives in established populations? And what can this natural experiment teach us about how species respond to environmental change?
Research conducted in the Kalmykia region of southern European Russia has revealed fascinating insights into these questions. As one scientist involved in the study notes, "We found that, during recent years, the species range has been rapidly expanding to the west, where gerbils have formed new colonies" 3 . This expansion provides a rare opportunity to observe ecological processes typically occurring over centuries in just a few short years, offering a real-time case study of how species navigate our rapidly changing world.
The story of the midday gerbil's expansion is inextricably linked to human-induced landscape transformations 1 3 . In Kalmykia, changes in land use and climate have triggered a process of desertification, converting steppe habitats back into desert environments that the gerbils prefer 8 .
These environmental shifts have created what scientists call a "natural experiment"—an unusual chance to observe range expansion as it happens rather than reconstructing it from historical data.
The gerbil expansion in Kalmykia represents what researchers term a "wave of colonization"—the leading edge of a species moving into new territory 3 .
Normally, species ranges change slowly, but human activities have dramatically accelerated these processes globally 1 . This phenomenon mirrors range expansions observed in other species. For instance, the striped field mouse has similarly expanded its range in southwestern Slovakia in recent years 6 . What makes the Kalmykia case particularly valuable is that researchers have been able to study the colonizing population in detail, comparing it with the source population the expansion originated from.
When researchers compared the colonizing gerbils with those from the source population, they discovered surprising differences. The colonists weren't just gerbils that happened to move to new territory—they had distinct characteristics that may contribute to their success as pioneers.
One of the most striking differences was in parasite load. Colonists were significantly less infested with fleas compared to gerbils from the source population 1 3 . Reduced parasite burden may give colonizing gerbils an advantage as they establish themselves in new territories.
To understand how gerbils colonize new areas, researchers designed a comprehensive study comparing the expanding western population with the stable eastern core population 1 3 8 . Here's how they uncovered the secrets of the gerbil expansion.
Scientists divided the study area into two main zones: the Western zone (area of expansion) and the Eastern zone (core population area) 8 . The Western zone had experienced a population collapse in 2017, with gerbils completely disappearing from the area, making it a clean slate for studying new colonization 8 .
Population collapse in Western zone
First colonists appear at two sites
Rapid expansion with multiple new colonies annually
Established colonizing population with several hundred individuals
Mid-April to mid-May
Mid-September to mid-October
| Tool/Method | Function | Significance |
|---|---|---|
| Shchipanov Live Traps 8 | Humane capture of gerbils | Allows researchers to study animals without harm |
| Animal ID Microchips 8 | Individual identification | Tracks movement, survival, and reproduction of specific gerbils |
| Tissue Sampling (toe clipping) 8 | Genetic analysis | Reveals genetic diversity and relationships between populations |
| Physical Measurements | Record size, weight, condition | Documents physical differences between populations |
| Parasite Inspection | Count flea infestations | Compares parasite loads between colonists and source population |
| Year | Colonization Status | Number of Colonies | Population Estimate |
|---|---|---|---|
| 2017 | Population collapse | 0 | 0 |
| Autumn 2019 | First colonists appear | 2 | Very low (founders only) |
| 2020-2021 | Rapid expansion | Multiple new colonies annually | Growing rapidly |
| 2022 | Established colonizing population | Numerous | Several hundred individuals |
Recent genetic research has added another layer to our understanding of the gerbil expansion. By analyzing mitochondrial DNA markers, scientists discovered that the colonizing population exhibits reduced genetic diversity compared to the core population—a classic signature of the founder effect 8 .
This occurs when a new population is established by a small number of individuals from a larger population, carrying only a fraction of the genetic diversity present in the source group 8 .
The genetic study also found evidence of allele surfing 8 —a phenomenon where genetic variants that are rare in the source population can increase in frequency at the expanding edge of a range simply by being carried along with the wave of expansion.
The midday gerbil's expansion offers more than just insight into a single species—it provides a model for understanding broader ecological patterns. Range expansions are becoming increasingly common worldwide as climate change and human landscape modifications create new opportunities for species to move into previously inaccessible territories 1 6 .
The gerbil case demonstrates that successful colonizing populations may share certain characteristics—youthful age structure, high reproductive rates, and possibly reduced parasite loads. These findings could help predict which species might successfully expand their ranges in response to environmental changes and what traits might make them successful colonists.
Interestingly, research on the striped field mouse's expansion in Slovakia showed similar ecological impacts, including reordering of species rank in native communities and negative effects on diversity when the expanding species reached a certain dominance threshold (25% in that case) 6 . This suggests that some patterns of range expansion may be consistent across different species and ecosystems.
The great gerbil expansion in Kalmykia continues, providing researchers with a front-row seat to observe ecological processes in real time. The pioneering gerbils—young, fertile, and relatively free of parasites—exemplify how species can respond to environmental changes.
Their story reminds us that our world is constantly in flux, with species continually adjusting their distributions in response to changing conditions. As one research team concluded, "The population on the wave of colonization does not experience the negative effects of low numbers, and the high reproductive rates in the colonist population account for its rapid growth and expansion" 1 .
As human activities continue to reshape landscapes and climate worldwide, understanding these patterns of range expansion becomes increasingly crucial—not just for ecologists, but for all of us interested in predicting how our living planet will respond to the changes ahead. The modest midday gerbil of Kalmykia, through its unassuming expansion, is helping science unravel these complex dynamics one burrow at a time.