Male black carpenter ant - Camponotus pennsylvanicus
Image: Bruce Marlin
Ants adjust their social interactions to accommodate changes in population density, according to researchers at Penn State and Georgetown University. The findings suggest that ant colonies are capable of maintaining their sophisticated social organization despite potentially drastic changes in their environments.
"Ants are among the most ecologically successful groups in nature due to their complex social organization, particularly their division of labor, including food acquisition," said David Hughes, associate professor of entomology and biology. "The survival of ant colonies depends on their ability to maintain this organization. In our study, we saw remarkable resilience of ant colonies to changes in population density. This finding helps to explain ants' evolutionary success."
According to Hughes, changes in ant colony size and population density are natural occurrences. They can increase as the queen reproduces and the colony grows, and they can decrease when the colony decides to split into multiple nest sites.
"To minimize potentially adverse effects due to changes in density and to maintain social balance, ant colonies should try to actively manage the rates of their interactions," said Hughes." Until now, however, few studies have investigated these phenomena."
The researchers manipulated the population densities of three colonies of carpenter ants by quadrupling the sizes of their nest spaces. They placed the colonies inside wooden camera boxes fitted with infrared lights so they could film the ants under natural dark nesting conditions. The ants were able to leave the nests at any time to enter foraging areas.
The team manually identified the position in the nest of each ant at every point in time - equivalent to more than 6.9 million data points - to investigate whether the increased nest space influenced the spatial organization of the insects. The researchers found that the ants' positions relative to the others were similar regardless of the population density. When population density was lower, ants simply were separated farther in space from each other.
