The keys to the squirrel’s evolutionary success in the face of climate change have been identified

Squirrels form a diverse family of rodents. Nearly 300 species have been described, and they occur in every land environment on the planet, from tropical forests to hot and cold deserts. But why are there so many species? A study led by researchers from the Complutense University of Madrid and the Institute of Geosciences (UCM-CSIC) has examined the characteristics of squirrel species that contribute to their evolutionary success in the face of global climate change.

Their degree of ecological specialization —the capacity to inhabit many or few environments— is the most important factor in the evolutionary success of squirrels in the face of climate change, according to research led by the Complutense University of Madrid (UCM) and the Institute of Geosciences (UCM-CSIC).

“The most climate-restricted species, that is, those that are only present in a very specific environment, are more likely to become extinct due to destruction of their habitat,” explained Iris Menéndez, a researcher in the Department of Geodynamics, Stratigraphy and Palaeontology at the UCM and the first author of the article published in Mammal Review.

But precisely for the same reason, she added, they are more likely to generate new species: “As their habitat fragments due to climate change, their populations divide, and if they manage to survive long enough, continued isolation encourages speciation.”

However, species that are capable of inhabiting very different climates are less dependent on their environment and are less affected by climate change. Consequently, “these species survive longer, and can persist for millions of years without substantial change,” Menéndez indicated.

More evolution in mountainous and terrestrial habitats

This study, in which the University of Alcalá de Henares also participated, has demonstrated that species present in mountainous areas are also more likely to generate new species. During warm cycles, different populations may become isolated in the highlands, eventually becoming distinct species if the situation is sufficiently prolonged.

Other factors also affect the response of squirrels to environmental change. For example, all squirrels were originally arboreal but some lineages subsequently adapted to terrestrial habitats, enabling them to occupy new environments.

The Indo-Malayan region is the area with the highest number of squirrel species, inhabited by some 117 different species. However, analyses show that it is North American ground squirrels which have generated the most species in the shortest period of time. “North America hosts all the chipmunks, prairie dogs and marmots, which spread across the continent occupying its prairies. The explanation for this is that being terrestrial enabled them to exploit new resources and adapt to these new situations,” explained the UCM researcher.

Studying how climate changes have affected the evolution of squirrels sheds light on the possible consequences of present-day climate change. The study revealed that those squirrel species most specialized in one type of environment are also the most likely to become extinct.

In particular, for this group of small mammals, if climate change is combined with other factors such as deforestation, the consequences could be devastating. “That could herald the loss of much of the diversity of the squirrel family,” the author concluded.

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Universidad Complutense de Madrid