Antlion Foraging: Tracking Prey across Space and Time

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. 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. by biological systems can be reduced to the need to gather resources, distributed across space and time, as efficiently as possible.Antlion larvae (Neuroptera: Myrmeliontidae), the focus of the present study, are generalist predators of arthropods that move along the soil surface. Larvae construct conical pits in the dry sandy or silty substrate and use them to capture prey. A large proportion of the antlion larval diet consists of ants, not because of any clear specialization or preference, but because ants are relatively abundant in the dry areas where antlions are found (Topoff 1977). Other prey frequently eaten by antlion larvae include spiders, beetles, isopods, flies, caterpillars, wasps, and mites (Turner 1915, Wheeler 1930, Heinrich and Heinrich 1984, Linton 1995.Prey are captured when they fall into the pit, are dragged under the sediment surface, and are digested externally. Digested prey fluids are then extracted from the prey and c...

Factors Influencing Site Abandonment and Site Selection in a Sit-and-Wait Predator: A Review of Pit-Building Antlion Larvae

“…The natural habitat of an individual antlion may greatly influence its ability to cope with a starvation period. It seems that antlions from a relatively prey-rich environment have a higher metabolic rate and starvation mortality and are more likely to relocate compared with antlions from a relatively prey-poor environment (Lucas, 1989a;Matsura and Murao, 1994;Crowley and Linton, 1999). Similar tendencies occur in spiders.…”

“…He therefore proposed shade as the major factor, since M. immaculatus, the subject of his research, inhabits shaded areas. Shade was also suggested as an important factor by Crowley and Linton (1999), who observed antlions tracking sources of shade or cover. However, there are many known species which inhabit open habitats and do not need shade, such as M. formicarius and M. bore (Matsura and Murao, 1994).…”

“…They showed that the daily relocation rate of M. formicarius is 3.3 times higher than that of H. micans, while M. bore almost never moves (also based on Matsura, 1987 (Rosenberg, 1987;Hauber, 1999). Crowley and Linton (1999) used a simulation model to explain several behavioral characteristics observed in the field, such as low rate of relocation. Their simulation results indicated that the most important factor depressing high relocation rate is the cost of moving, and that increasing the variance of prey availability resulted in an increase in the relocation rate, as suggested earlier.…”

“…According to the "marginal value theorem," a forager should quit a patch once its net energy gain equals the average rate of energy gain over all patches in the habitat (Charnov, 1976). A sitand-wait predator, however, usually does not deplete food resources significantly in its ambush site (Janetos, 1986;Crowley and Linton, 1999). Rather, an optimal sit-and-wait predator should relocate its ambush site when the benefit gained at a particular site falls below the environmental average gain.…”

“…In addition, differences in pit construction and reconstruction rates between field and lab experiments are also common (Heinrich and Heinrich, 1984;Griffiths, 1986;Lucas, 1989b;Crowley and Linton, 1999). Frequent relocations are rare in pit-building antlions, probably due to the high risk of intra-and interspecific predation and possibly due to the metabolic cost associated with relocation.…”