The role of chemical footprints for foraging and competitive interactions in ants
Sensory and Behavioural Biology
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Final Report Abstract
When walking, every insect involuntarily leaves tiny droplets of a waxy liquid behind. Their chemical composition is highly species-specific, such that other insects (and researchers) can determine the identity of the insect only based on these ‘chemical footprints’. Recent studies showed that ants respond to chemical cues of competing colonies. This is similar to ‘antipredator behaviour’, which is known for many animal taxa from insects to vertebrates. Here, prey organisms sense predator cues such as chemical footprints, urine, feces or (for spiders) silk, and adjust their behaviour so that they reduce the risk of encountering the predator. Likewise, ants may respond to cues of others to avoid fighting with superior competitors, but also to approach inferior colonies who might have discovered food sources that can be exploited (‘eavesdropping’). In this project, we therefore studied ant behaviour, in particular how ants respond to chemical cues (‘chemical footprints’) of their own colony and of competing colonies or species. It turned out that ants clearly respond to chemical footprints. However, these responses are way less clear-cut than initially expected: often, ants do not clearly avoid or approach a certain type of footprints. Rather, they modulate their own behaviour, for example by becoming less aggressive or more cautious, or by reducing their tendency to walk around in the search of food. A striking result of our studies was how variable this and other behaviours are. Firstly, footprint responses depend on experience. When ants learn that another ant species (which was unknown to them before) is aggressive, they will avoid their footprints. But they will ignore them if they encountered them without fights, or even approach their footprints if they associate the other ant to food. Thus, they are able to associate a living ant to a paper that carries nothing but their smell. This ability was unknown before and suggests that ants use a wide variety of chemical cues in their foraging range to optimise foraging efficiency while avoiding aggressive encounters. Furthermore, ant behaviour varies, even within species. This has long been known – also for other animals – , and has been termed ‘animal personality’. ‘Animal personality traits’ such as aggression, explorative behaviour, or foraging activity can vary consistently across individuals – in the case of ants, across different colonies. However, such traits were mostly conducted in the laboratory but rarely tested in the field, where strong environmental variation may cause too much noise to detect inter-individual differences. In large-scale field studies, we found that also in the field, ants show consistent fixed and plastic behavioural variation. Ant colonies differed consistently concerning their aggression, exploration and activity. At the same time, all these behaviours strongly varied over time (from June to September), and were also influenced by the current temperature. We found that different ant species show different levels of behavioural variation. Thus, behavioural differences between species do not concern average aggression or average exploration, but rather how these behaviours are influenced by the environment. Given that ants often compete via direct fights, such behaviours are crucial drivers of intraspecific and interspecific competition. Our finding that behaviours depend on the environment in species-specific ways suggests that in a fluctuating environment, competitive superiority shifts and none of the species is always dominant. This way, environmental fluctuation can promote species coexistence. Such dynamic dominance hierarchies may be a crucial mechanism of species coexistence in communities where niche differentiation is low or absent.
Publications
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Temporally consistent behavioural variation between wild ant colonies is robust to strong seasonal and thermal variation. Animal Behaviour, 196, 151-163.
Menges, Vanessa; Späth, Sophie & Menzel, Florian
