How wood-ants (Formica lugubris) exploit spatially dispersed regenerating sources of food
Three colonies of wood-ants Formica lugubris were taken from native Caledonian pinewoods and re-established in the laboratory. Experiments were conducted during which each of these colonies was provided with two discrete patches at which foragers could drink from filter papers saturated with aqueous solutions of sucrose; these patches were replenished continuously with the solutions. Three series of experiments were conducted in which the hypothesis tested was that the ants would distribute themselves between the patches according to the ideal free distribution. During the first series of experiments, the rate of supply of sucrose was manipulated by changing the concentrations of the solutions while maintaining equal rates of supply. Under each concentration ratio an equilibrium distribution was established. When the concentrations were equal, foragers distributed in a ratio of 1:1. When the concentrations were unequal the proportion of foragers at the richer patch was consistently less than the proportion of sucrose available there; ratios of sucrose of 1:2 and 1:4 were associated with equilibrium distributions of foragers in the ratios of approximately 1:1 and 1:2 respectively. In the second series of experiments, it was shown that these ratios were dependent on the overall rate of regeneration of the solutions; increases in the overall rate of regeneration were associated with increased proportional occupation of the richer patch. Throughout this experiment, the concentrations of the solutions were 7% w/v and 28% w/v and the rates of regeneration of the solutions at both patches were equal. Distributions were established at four different rates of regeneration. At the lowest rate of regeneration (0.2ml.h-1) the proportion of foragers at the richer patch was significantly lower than the ideal free prediction of 0.8. At the three higher rates of regeneration (0.4ml.h-1, 0.6ml.h-1 and 0.8ml.h-1) the proportion of foragers at the richer patch was significantly greater than the proportion of sucrose available there.