Antlion foraging: tracking prey across space and time

To capture their prey, larval antlions invest energy in building and maintaining conical pit traps in fine-particulate substrate. The resident antlions (Myrmeleon immaculatus) at Sleeping Bear Dunes National Lakeshore, Michigan, USA, seldom relocated their pits, and we wondered whether this site fidelity could be understood as an optimal (or near-optimal) response to observed spatial and temporal variation in prey availability. To determine this, we considered a large number of compound foraging strategies, each composed of the number of days over which the antlion evaluates foraging success at a site; the weighted-average foraging success during this interval, below which threshold the antlion moves to a new site; and the length of the random walk taken by the antlion to a new pit location. Using Monte Carlo simulation, we determined the expected net energy gain from each of these strategies by antlions rewarded according to the field data set. The overall highest gain strategy generally agreed with our a priori expectations for the observed pattern of patchiness in prey availability over space and time. Moreover, the corresponding optimal frequency of pit relocation, 1.65 moves over the observation period of ∼ 8 wk is in rough agreement with field observations. However, the gain surface was relatively flat: 60% of the investigated strategies yielded within 8% of the maximum gain. When costs of pit relocation were reduced, maximal gain strategies shifted to generate frequent movement, suggesting that the magnitude of such sampling costs may control the foraging strategy in environments with high spatiotemporal variability.