Does Environmental Predictability Affect Risk Mitigation Behaviours in Ants?

Social animals develop in environmental conditions which are always in flux. These changes
can be either predictable or unpredictable, and social insects must be prepared to adjust to
both. Resource distribution, and in particular, food availability is important in determining
many aspects of a social insect's life history and behaviour. Multiple strategies have evolved
within humans and/or the wider animal kingdom to minimise the risks of acquiring food in an
unpredictable environment. These include diversification/generalism, food storage,
nomadism/migration/relocation, and food exchange/polydomy. Due to the difficulty of
collecting direct information on food predictability and the strong influence of the
environment on food distribution we used environmental predictability as a proxy for food
predictability. By carrying out a meta-analysis of the model clade Formicidae, which displays
all four of these behaviours, we attempted to answer two questions:
1. When during the evolution of the ant taxa, have different risk-mitigation strategies
evolved?
2. Which of these behaviours are used under different levels of environmental
predictability?
In order to answer the first question we carried out an ancestral state reconstruction.
We found that the ancestral state for the Formicidae is a combination of both nomadism and
generalism strategies. We also found that the same combination was the most common
state throughout the evolutionary history of the Formicidae. Generalism and nomadism
behaviours are both found widespread throughout the phylogeny, while storage and
polydomy have evolved multiple times in more distinct groups. For answering the second
question we used temperature and precipitation to model environmental predictability using
Cowell’s indices. We then carried out a Bayesian categorical logistic regression on this
weather data. Our analysis informed us that as temperature constancy increases, nomadism
becomes more common with respect to a generalism. Conversely as precipitation constancy
and contingency increases, nomadism becomes less common with respect to generalism.