A recent paper by Sasaki and Pratt, published in Biology Letters last week, describes an elegant study that expands our understanding of ant decision-making. Their simple experimental design is shown in Figure 1 (taken from the paper):
The focus of their experiment was to determine if, when choosing which site to make a nest, ants shift the weights of attributes they consider as a result of previous experiences. Several past studies focusing on many different species have looked at the impact of weighting choices on decision-making, but this paper is, according to the authors, the first to document potential shifts in weighting multiple variables due to experiences. Specifically, Sasaki and Pratt looked at preferences for entrance size and light availability, because the ant species of interest, Temnothorax rugatulus, is known to prefer nests that have smaller entrance size and lower light availability.
What the researchers found was that when the ants were first exposed to only a standard (ideal) nest and another nest that varied in only one attribute (light or entrance size), the ants later exhibited a significant increase in preference for nest sites that were more desirable in that one attribute, but less desirable for the other. For example, the ants that were first made to choose between a standard nest and a nest with higher light availability consistently chose the standard, more ideal nest. Then, when presented with a choice between a nest that had a small entrance, but more light, and one that had less light, but a larger entrance, the ants chose the nest with more optimal light conditions at the expense of less ideal entrance size conditions. Revealingly, the ants that were first made to choose between a standard nest and one with a larger entrance size later chose the nest with the more optimal size conditions. Therefore, potentially due to the perception of rareness of one nest trait, the ants increased the weight of that trait when seeking out a new nest in the future. The results of this tight experiment seem to me to provide compelling evidence that ants somehow collectively use a decision-making process that incorporates past information to shift the weights of preference in later choices.
Perhaps the most interesting bit about the study is that the ants’ style of decision-making has also been documented in humans. As the authors note, past research has shown the influence of scarcity in social psychology, where people will more strongly seek out something that they perceive to be rare. Although the underlying mechanism used to incorporate scarcity into decisions may be different between ants and humans, it is interesting to consider that our mental processes may mirror those of the small creatures underfoot.
Sasaki, T. and S.C. Pratt. 2013. Ants learn to rely on more informative attributes during decision-making. Biology Letters 9: 20130667.