Food supplementation alters caste allocation in a natural population of Pheidole flavens, a dimorphic leaf-litter dwelling ant
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Caste ratio theory predicts that polymorphic ant colonies should be able to alter the ratio of worker sizes in response to changing environmental demands. We selected a common dimorphic species, Pheidole flavens, for a field manipulation to test whether caste allocation will change in response to food supplementation. We collected, without replacement, control and treatment colonies from 1 m2 plots over a period of four months. Food was added to treatment plots every other day in either of two spatial presentations: clumped and split. Clumped food treatments received food in a single location in the center of the plot, while the split food treatments were spread throughout the plot area. To test how P. flavens responded to food supplementation, we compared the number of soldier pupae between control and treatment plots, as well as the ratio of adult soldiers to adult minor workers. We found a generalized increase in the number of soldier pupae produced within the treatment plots, which was not correlated with the duration of the treatment period. As the manipulation progressed, the ratio of soldiers to minor workers increased in the clumped food plots. The possible mechanisms for altered caste ratios include the absence of soldiers from their nests, increased frequency of interactions with competitors, and a change in the type of foods collected from the environment. The discovery that food resources can affect how ant colonies determine the ratio of sterile workers suggests that ants may change caste ratio in response to a number of environmental variables.
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