Life history traits, social organisation and the drivers of sociality in an invasive ground squirrel
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Date
2019-11-23
Authors
van der Marel, Anne Marie
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Abstract
Sociality evolves when the benefits outweigh the costs of interacting with conspecifics and can be influenced by genetic, phylogenetic, life history, or ecological constraints. Many groups are formed by natal philopatry with the environment constraining levels of sociality. For example, diurnal rodents living in harsh environments can be social to avoid the costs of predation. I used the invasive population of the Barbary ground squirrel (Atlantoxerus getulus) on the arid island of Fuerteventura, Spain, as my study system to explore this idea. Two Barbary ground squirrels were introduced to Fuerteventura in 1965. As they are invasive, I first questioned whether life history traits influenced their invasion success. Then, I used observational, experimental and genetic data to investigate whether they are social and whether predator avoidance is a selective pressure influencing their social patterns by studying their vigilance and alarm vocalisations. Barbary ground squirrels have large and frequent litters, and thus show potential for rapid population growth with a generation time of approximately one year, which may have contributed to their invasion success. They are social, as both males and females interact throughout the day, but they show sexual segregation of sleeping burrows. As group size increased, individual vigilance did not decrease, but collective vigilance did increase and they use alarm calls to warn group members of danger. Hence, they show partial collective detection of predators. The absence of a group-size effect can be explained since the squirrels synchronise their vigilance bouts. Thus, the constraints of living as a diurnal species in an arid environment and predation pressure are possible selective pressures explaining sociality in the invasive Barbary ground squirrel. This thesis advances our understanding of sociality in African ground squirrels, but also provides valuable insight into population growth and corresponding invasion success of an introduced species, as invasive species provide a unique framework to study evolution of sociality and population biology over a relatively short timeframe.
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Keywords
Sociality, Social organisation, Life history, Anti-predatory behaviour, Alarm-calling, Vigilance, Barbary ground squirrel, Invasive species