Pit relocation by antlion larvae: A simple model and laboratory test

Abstract

SummaryWe generated a computer model to analyse the effects of 'shadow' competition for sit-and-wait predators, particularly antlion larvae. The model used a simple foraging assessment rule to determine the quality of an antlion's location, and antlions relocated randomly in their habitat when a location proved to be of low quality. Shadow competition, or competition for food caused when one sit-and-wait predator intercepts moving prey before a second sit-and-wait predator is encountered, was incorporated into the model by restricting antlions to a bounded arena, and having prey for the antlions enter from the arena periphery. Antlions responded to shadow competition by relocating their pits to peripheral areas of their habitat. This peripheral accumulation of pits was most pronounced when antlion densities were high, and when prey availabilities were infermediate. An experimental test with the antlion Myrmeleon immaculatus supported the importance of shadow competition as a cause of observed pit distributions. Only the treatment which incorporated shadowing had pit distributions nearthe periphery, while the pit distributions in the control treatments did not differ from randomly generated distributions. We conclude that shadowing can influence sit-and-wait predator distributions when the prey distributions and movement patterns generate the conditions necessary for shadowing. But when prey availability is unpredictable, making assessment of patches difficult, or when prey do not originate in the periphery of the habitat, other factors, such as temperature or moisture, could be more important.

Antlion Foraging: Tracking Prey across Space and Time

“…Because antlion larvae sometimes move their pits as often as every 5 d in the few quantitative studies of their behavior in the field (Wilson 1974, Griffiths 1980b, Heinrich and Heinrich 1984, Linton 1995, we supposed that 3 d might provide a conservative estimate of the minimal time needed to evaluate a pit location. The model produced the frequent pit relocations and peripheral pit distributions generally consistent with the laboratory data that we subsequently obtained (Linton et al 1991). The model produced the frequent pit relocations and peripheral pit distributions generally consistent with the laboratory data that we subsequently obtained (Linton et al 1991).…”

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

“…Wilson (1974) suggested that 'shadow competition,' a type of exploitation competition, is the major factor influencing pit spatial arrangement, and consequently an antlion's decision when and where to relocate. Shadow competition occurs when one sit-and-wait predator can catch the moving prey before it encounters other predators (Linton et al, 1991), and this has also been documented in spiders . Wilson (1974) suggested that this type of competition should cause antlions to form a 'doughnut' configuration, i.e., the antlions occupy the periphery of their patch.…”

“…More recent studies suggest that at high population densities antlions should be distributed uniformly, while at low densities they should be distributed randomly (e.g., Matsura and Takano, 1989). Linton et al (1991) tested the hypothesis of 'shadow competition' and its influence on spacing and pit relocation. They used a model simulating a group of randomly distributed antlions, and prey items that moved and crossed the arena from random points along its edges in straight lines.…”

Substrate particle size-preference of wormlion Vermileo vermileo (Diptera: Vermileonidae) larvae and their interaction with antlions

“…This causes miniature landslides, which carry the prey back to the predator. Antlion larvae select sites for pit construction based on habitat suitability (Lucas, 1986;Farji-Brener et al, 2008), sand particle size (Allen & Croft, 1985;Loiterton & Magrath, 1996;Botz et al, 2003;Devetak et al, 2005;Matsura et al, 2005), prey availability (Griffiths, 1980;Sharf & Ovadia, 2006), level of disturbance (Gotelli, 1993) and abundance of conspecifics (Matsura & Takano, 1989;Linton et al, 1991).…”