An analysis of the dynamics of resource sharing networks in ant colonies

Cooperation ties animals together into social groups that often demonstrate complex emergent behaviours. One striking example of this are social insect societies that emerge from extreme cooperative behaviour and have an important impact in many ecosystems. Colonies of most social insects construct and inhabit a single nest. However, colonies of some species have been found to spread across many different nests – known as polydomy. This strategy is thought to have evolved in response to several different drivers, such as increased foraging efficiency, avoiding nest-size limitations and territory defence. In this thesis, I present studies that investigated how polydomous colonies function and the reasons that some, but not all, ant species use polydomy as a strategy. I used a mathematical model to demonstrate that decentralization of the nest population can be advantageous under a variety of different conditions, which explains why polydomous species are so behaviourally and phylogenetically diverse. Using a longitudinal study of several years of data on a set of polydomous colonies I found that resource sharing networks become more static over a season and that while nest foundation occurs throughout the season, nest abandonment occurs at a much faster rate in the latter part of the season. Through sampling several polydomous colonies, I found that there is a correlation between relatedness of the inhabitants of different nests and the rate of resource sharing between the nests. The most likely mechanism for this is that nests that share resources become more closely related due to migration and brood transfer. Finally, using a resource manipulation study, I found that resource-sharing networks can adapt in response to change in the availability of food. Together these results demonstrate how ant colonies can use polydomy to their advantage and the various factors that are important in determining the dynamics of these complex societies

The effect of social information on the collective choices of ant colonies

© 2016 The Author. In collective decision making, groups collate social information to inform their decisions. Indeed, societies can gather more information than individuals - so social information can be more reliable than private information. Colonies of Temnothorax albipennis can estimate the average quality of fluctuating nest sites when the sharing of social information through recruitment is rare. However, collective decisions in T. albipennis are often reached with the use of recruitment. We use a new experimental setup to test how colonies react to fluctuating nest sites when they use recruitment to reach a decision. When recruitment is used, colonies consistently choose nest sites that fluctuate between being "good" and "poor" over constantly "mediocre" alternatives. Moreover, they do so even if the fluctuating option is only "good" for 25% of the time. The ants' preference for fluctuating nest sites appears to be due to tandem running. Even if a nest site is only briefly "good," scouts that experience it when it is "good" are likely to perform tandem runs to it. However, a constantly "mediocre" nest site is unlikely to ever provoke tandem runs. Consequently, the fluctuating nest sites attracted more tandem runs, even when they were only "good" for a short time. This led to quorum attainment in fluctuating nest sites rather than in constant "mediocre" nest sites. The results of this experiment demonstrate how sharing of social information through recruitment can change the outcome of collective decisions

Ant colony nest networks adapt to resource disruption

1. Animal social structure is shaped by environmental conditions, such as food availability. This is important as conditions are likely to change in the future and changes to social structure can have cascading ecological effects. Wood ants are a useful taxon for the study of the relationship between social structure and environmental conditions, as some populations form large nest networks and they are ecologically dominant in many northern hemisphere woodlands. Nest networks are formed when a colony inhabits more than one nest, known as polydomy. Polydomous colonies are composed of distinct sub-colonies that inhabit spatially distinct nests and that share resources with each other. 2. In this study, we performed a controlled experiment on 10 polydomous wood ant (Formica lugubris) colonies to test how changing the resource environment affects the social structure of a polydomous colony. We took network maps of all colonies for 5 years before the experiment to assess how the networks changes under natural conditions. After this period, we prevented ants from accessing an important food source for a year in five colonies and left the other five colonies undisturbed. 3. We found that preventing access to an important food source causes polydomous wood ant colony networks to fragment into smaller components and begin foraging on previously unused food sources. These changes were not associated with a reduction in the growth of populations inhabiting individual nests (sub-colonies), foundation of new nests or survival, when compared with control colonies. 4. Colony splitting likely occurred as the availability of food in each nest changed causing sub-colonies to change their inter-nest connections. Consequently, our results demonstrate that polydomous colonies can adjust to environmental changes by altering their social network.DATA AVAILABILITY STATEMENT: All data used in this paper are available from the OSF: https://doi.org/10.17605/OSF.IO/J4XHS (Burns, Franks, Parr, & Robinson, 2019).http://www.wileyonlinelibrary.com/journal/janehj2022Zoology and Entomolog