The cautious pioneers - How animals spread out and their behavior changes in the process

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Red-backed voles were introduced to Ireland from central Europe in 1920 and have
Red-backed voles were introduced to Ireland from central Europe in 1920 and have been spreading across the island ever since. Animal behavior was studied at several study sites (black dots). Animals in the dispersal zone (orange) are more cautious and less active than animals in the established zone (green), but they also explore more extensively.
Invasive animal and plant species are affecting biodiversity worldwide. To better understand the specific dispersal processes during a biological invasion, researchers from the University of Potsdam and Trinity College Dublin studied an acute invasion. More than 100 years ago, red-backed voles, a Eurasian vole species, were accidentally introduced to the west coast of Ireland and have been spreading continuously ever since. Fringe populations emerge during the dispersal phase, with particular characteristics of individuals that differ from the long-established core populations. The results have now appeared in the Proceedings of the Royal Society and in the journal Current Zoology.

We were particularly interested in how willing individuals are to take risks when exploring their environment," summarizes Jana Eccard from the University of Potsdam. We expected to find particularly courageous pioneers in the marginal populations. The researchers used a risk test to examine more than 300 bank voles in six different Irish forest patches. In marginal populations along the current dispersal zone, however, the individuals are clearly more risk averse and less active compared to animals from core populations," explains the scientist. "A test maze set up in the forest, on the other hand, was studied more extensively in the fringe population than in the core populations." Dispersal into unknown terrain with unknown predators and unknown hiding places is very dangerous for mice, so that only those animals that are particularly cautious but eager to explore can successfully reproduce in the edge zone. Thus, a particularly cautious fringe population develops over many dispersal generations. Once a population is established, however, other traits such as competitive ability in turn lead to success, so that after a few generations courage and activity increase again.

The spatial structure of dispersing populations can be applied to many animal dispersal processes. The researchers’ work shows that the study of individual differences within a population contributes to the understanding of ecological processes such as biological invasions.

Figure : Red-backed voles were introduced to Ireland from Central Europe in 1920 and have since spread across the island. Animal behavior was studied at several study sites (black dots). Animals in the dispersal zone (orange) are more cautious and less active than animals in the established zone (green), but they also explore more extensively.

26-09-2023 / No. 097



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