Antlion foraging: Tracking prey across space and time

To capture their prey, larval antlions invest energy in building and mainta ining conical pit traps in fine-particulate substrate. The resident antlion s (Myrmeleon immaculatus) at Sleeping Bear Dunes National Lakeshore, Michig an, USA, seldom relocated their pits, and we wondered whether this site fid elity could be understood as an optimal (or near-optimal) response to obser ved spatial and temporal variation in prey availability. To determine this, we considered a large number of compound foraging strategies, each compose d of the number of days over which the antlion evaluates foraging success a t 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 ran dom walk taken by the antlion to a new pit location. Using Monte Carlo simu lation, we determined the expected net energy gain from each of these strat egies by antlions rewarded according to the field data set. The overall hig hest gain strategy generally agreed with our a priori expectations for the observed pattern of patchiness in prey availability over space and time. Mo reover, the corresponding optimal frequency of pit relocation, 1.65 moves o ver the observation period of similar to 8 wk, is in rough agreement with f ield observations. However, the gain surface was relatively flat: 60% of th e investigated strategies yielded within 8% of the maximum gain. When costs of pit relocation were reduced, maximal gain strategies shifted to generat e frequent movement, suggesting that the magnitude of such sampling costs m ay control the foraging strategy in environments with high spatiotemporal v ariability.