The hidden spiral: systematic search and path integration in desert ants, Cataglyphis fortis

Abstract

The main navigational mechanism used by foraging desert ants of the genus Cataglyphis is path integration (dead reckoning). Any such egocentric system of navigation is prone to cumulative navigational errors.Hence, while homing Cataglyphis might have reset its path integration system and yet not arrived at the start of its foraging excursion, the nest entrance. Then it resorts to piloting or performs a systematic search for the nest. The search pattern consists of a system of loops of everincreasing size centred about the origin, i.e. the start of the search. Here we show that underlying the system of loops is a spiral search programme that gets transformed into the observed pattern of loops by the ant's idiosyncratic path-integration algorithm. The ant starts to follow a spiral course, then breaks off this course and walks towards the centre, i.e. to what its path-integration system has computed to be the origin of the search. This reset episode is followed by another spiral course, which is terminated by the next reset, and so forth. After each reset, the spiral gets wider, so that the whole pattern expands. Futhermore, every now and then the spiral might change its sign. Computer simulations based on these simple rules lead to search patterns of the kind actually recorded in Cataglyphis ants. These patterns ensure that those parts of the area in which the target (nest entrance) is most likely to be located are searched most heavily; in other words: the search density profile is adapted to the probability density function of the target.

Foray Search: An Effective Systematic Dispersal Strategy in Fragmented Landscapes

“…1). The same type of search strategy (which we will term "foray search") has been reported in many other animals, including other insects (Wehner and Srinivasan 1981;Hoffmann 1983;Mueller and Wehner 1994;Durier and Rivault 1999;A. Seymour, personal communication: Plebejus argus), mammals (Wiggett et al 1989;Christian 1993;Sun 1997;E.…”

“…In addition, foray search has at least two further important advantages, namely, that foray dispersers regularly return to their starting habitat patch and that the shape of the search pattern can be fine-tuned through evolution to a particular landscape. The first property enables foray dispersers to reorient themselves periodically (Mueller and Wehner 1994;Durier and Rivault 1999) and to postpone or abandon futile dispersal attempts (Christian 1993;Conradt et al 2000). It also enables them to replenish resources ) so that they need only to carry with them smaller, predeterminable quantities of resources during dispersal.…”

“…Two other systematic search strategies that have been suggested for dispersal are Archimedean spirals (Mueller and Wehner 1994;Zollner and Lima 1999) and dispersal along habitat corridors or landscape features (Vermeulen 1994;Irms 1995;Boudjemadi et al 1999;Tikka et al 2001; see also Bell 1991 for a review). While Archimedean spirals could In landscapes with clumped patch distribution, the higher patch density was, the larger was the difference between strategies Note: Model examines the influence of patch density, patch configuration, patch radius, perceptive range, cluster size, degree of clumpedness, and per-step mortality rate on the relative difference between foray search and random dispersal (positive estimates indicate higher mortality for foray searchers).…”

“…The model explained 50.9% of the total variance in difference between strategies. a p 0.05 in theory be very efficient at detecting new habitat patches (Zollner and Lima 1999), it is doubtful whether real animals have the navigational skills to implement them (for discussion, see Dusenberg 1992;Mueller and Wehner 1994;Zollner and Lima 1999). Systematic search along habitat corridors or along particular landscape features has been observed and could be very efficient in particular cases (Broekhuizen et al 1986;Vermeulen 1994;Tikka et al 2001).…”

Path integration in mammals

“…Without these cues, the animals continue their outward progression, in spite of the fact that the current state of their path integrator corresponds to the goal coordinates. During homing, when their path integrator indicates proximity to the nest, both species switch from a fairly linear homeward progression to circular movements in search of familiar cues near the nest entrance (Séguinot et al, 1993;Müller and Wehner, 1994).…”