Showing papers on "Ant colony published in 1998"

The Evolution of Agriculture in Ants

Abstract: Cultivation of fungi for food by fungus-growing ants (Attini: Formicidae) originated about 50 million years ago. The subsequent evolutionary history of this agricultural symbiosis was inferred from phylogenetic and population-genetic patterns of 553 cultivars isolated from gardens of "primitive" fungus-growing ants. These patterns indicate that fungus-growing ants succeeded at domesticating multiple cultivars, that the ants are capable of switching to novel cultivars, that single ant species farm a diversity of cultivars, and that cultivars are shared occasionally between distantly related ant species, probably by lateral transfer between ant colonies.

An Island Model Based Ant System with Lookahead for the Shortest Supersequence Problem

Abstract: In this paper we introduce an Ant Colony Optimisation (ACO) algorithm for the Shortest Common Supersequence (SCS) problem, which has applications in production system planning, mechanical engineering and molecular biology. The ACO algorithm is used to find good parameters for a heuristic for the SCS problem. An island model with several populations of ants is used for the ACO algorithm. Besides we introduce a lookahead function which makes the decisions of the ants dependent on the state arrived after the decision.

Ants, stem-borers, and fungal pathogens: experimental tests of a fitness advantage in Piper ant-plants

Abstract: This study tests experimentally the hypothesis that Pheidole bicornis ants increase the fitness of Piper ant-plants (Piperaceae) in Costa Rican forests. In two exper- iments with naturally occurring Piper ant-plants, -50 individuals were randomly selected and maintained either as controls (with ants) or as ant-exclusion plants (without ants) for 2 yr. Leaf replacement rates and seed production, as measures of relative plant vigor and reproductive potential, were significantly greater in control plants with intact ant colonies than in plants from which ant colonies were experimentally excluded by periodical treatment with dilute insecticide. A series of experiments was designed to assess the relative contribution of antiherbivore defense, nutrient procurement, and antipathogen defense as potential mutualistic functions of the ants. To assess the fitness effects of antiherbivore defense, leaf replacement rates and seed production were measured on plants to which artificial folivory was applied over a 2-yr period (33% of each leaf blade removed), and stem-boring weevil damage was monitored on plants with and without ants. Nutrient procurement by ants was estimated quantitatively, and net leaf production was monitored experimentally on control plants (with ants), on plants without ants, and on nutrient-enriched plants with ants (microquantities of fertilizer added to lower stem). Epiphyll loads, phylloplane spore densities, and disease incidence were compared on experimental plants with and without ant colonies. The results indicate that folivory, the classical parameter measured in ant-plant studies, was not related to differences in fitness in Piper ant-plants; instead, ant disruption of stem-borers and ant foraging on inflorescences to reduce fungal invasion were identified as probable mechanisms by which ants conferred an average fitness advantage of at least 60 and 10%, respectively, in the 2nd yr of the comparison. Although neither antifolivore defense nor nutrient pro- visioning by ants appeared to benefit Piper plants, they may contribute synergistically or may operate on temporal or spatial scales not included in the study. For example, nutrient provisioning may allow Piper ant-plant species to occupy and compete favorably in poor- soil habitats not evaluated in these experiments.

Application of the ant colony search algorithm to short-term generation scheduling problem of thermal units

Abstract: This paper presents a new cooperative agents approach, the ant colony search algorithm (ACSA), for solving a short-term generation scheduling problem of a thermal power system. One of the main goals of this paper is to investigate the applicability of an alternative intelligent search method in power system optimisation. The ACSA is derived from the theoretical biology on the topic of ant trail formation and foraging methods. In the ACSA, a set of co-operating agents called ants cooperate to find a good solution to the short-term generation scheduling problem of thermal units. The effectiveness of the proposed scheme has been demonstrated on the daily scheduling problem of a model power system and the results are compared with those obtained by a conventional scheduling method.

Ant colony optimisation for job shop scheduling

Abstract: A recent adaptive algorithm, named Ant System, is introduced and used to solve the problem of job shop scheduling. The algorithm was first introduced by Dorigo, Maniezzo and Colorni in 1991 and is derived from the foraging and recruiting behaviour observed in an ant colony. It can be applied to combinatorial optimisation problems. This paper outlines the algorithm’s implementation and performance when applied to job shop scheduling. The algorithm parameter settings seem to play a crucial role in its efficiency and determine the quality of solutions. In this paper we present some statistic analysis for parameter tuning and we compare the quality of obtained solutions for well-known benchmark problems in job shop scheduling.

Harvester Ants and Fire in a Desert Grassland: Ecological Responses of Pogonomyrmex rugosus (Hymenoptera: Formicidae) to Experimental Wildfires in Central New Mexico

Abstract: In this study, we measured rough harvester ant, Pogonomyrmex rugosus Emery, foraging activity, numbers and types of food items collected by foragers, ant foraging efficiency, and maximum foraging distances in a desert grassland site in central New Mexico before and after an experimental fire. We found that the ants exhibited no significant changes in any variable following the fire, with the exception of an increased number of insects being collected following the burn. Apparently, sufficient seed reserves remained after the fires to support ant foraging activity, and other insects killed in the fires were collected opportunistically by the ants. One year after the fire, all experimental ant colonies were alive and functioning normally. It appears that harvester ants are well-adapted behaviorally to cope with wildfires in the desert grassland of New Mexico.

Chemical mimicry in the root aphid parasitoid Paralipsis eikoae Yasumatsu (Hymenoptera: Aphidiidae) of the aphid-attending ant Lasius sakagamii Yamauchi & Hayashida (Hymenoptera: Formicidae)

Abstract: An aphidiid wasp, Paralipsis eikoae, was associated with both Lasius niger and L. sakagamii attending the wormwood root aphid Sappaphis piri. An L. sakagamii worker was observed carrying a winged female P. eikoae to its nest with its mandible, but it did not kill the wasp. Once accepted by the ants, the wasp often mounted and rubbed against the worker ants and sometimes teased them to regurgitate food to itself. No workers in the colony attacked the wasp. Conspecific foreign workers, however, viciously attacked the wasp when encountered. Gas chromatography-mass spectrometry analyses showed that the accepted wasp had complex cuticular hydrocarbons that were very similar to those of its host ants, whereas the winged wasps collected outside the ant nest showed only a series of n-alkanes. Additionally, the accepted wasp had a hydrocarbon profile closer to that of its host ants than to the conspecific foreign ants. We believe the wasp mimics ant cuticular hydrocarbons to integrate into the ant nest, acquiring the hydrocarbons by mounting and rubbing against the ants. In contrast, the cuticular hydrocarbons of the emerged wasp contained larval and pupal hydrocarbons of L. sakagamii that were also similar to those of L. niger. Both ant species rejected adult workers of the other species but accepted their larvae and pupae. We suggest that the emerged P. eikoae mimics the cuticular hydrocarbons of these Lasius larvae and pupae, which allows P. eikoae to be accepted by both L. sakagamii and L. niger.

Protection against herbivores of the myrmecophyte Leonardoxa africana (Baill.) Aubrèv. T3 by its principal ant inhabitant Aphomomyrmex afer Emery

Abstract: Leonardoxa africana T3 is a myrmecophyte, a plant with specialized structures (domatia) that shelter ants. Adult trees are essentially all occupied by the ant Aphomomyrmex afer. One tree possesses one ant colony. Ants tend homopterans inside the domatia. The plant provides ants with nest sites and food via production of extrafloral nectar and via honeydew produced by homopterans. Workers patrol the young leaves, although their nectaries are not yet functional. This study was conducted to investigate the nature of the relationship between the plant and its ants. In order to determine whether ants protect the plant against herbivorous insects, we placed microlepidopteran larvae on young leaves of several trees, and measured the time until discovery of the larvae by the workers. We then studied the responses of workers as a function of insect size. We showed that workers patrolled the young leaves of the majority of trees. There was, however, inter-colony variability in intensity of patrolling. Workers attacked every larva they found, killing and eating the smaller ones, and chasing larger ones off the young leaf. Most of the phytophagous insects attacking young leaves of L. africana T3 were inventoried in this study. We showed that the larvae of microlepidopterans, one of the most important herbivores of this species, form part of the diet of A. afer. The function of the stereotyped behaviour of ant patrolling on young leaves may be in part to obtain insect protein to complement carbohydrate-rich nectar and honeydew, and in part to protect the host and thus increase its production of resources for ants. Our study shows that ants protect the tree against herbivores, and that even if this protection is less pronounced and more variable than that demonstrated for their sister species L. africana sensu stricto and Petalomyrmex phylax, the association between L. africana T3 and A. afer is a mutualism.

Locating queen ant nests in the green ant, Oecophylla smaragdina (Hymenoptera, formicidae)

Abstract: Studies using Oecophylla smaragdina colonies to control cashew insect pests showed that the introduction of a partial ant colony was more permanent with a reproductive queen than without a queen. Thus, a technique to locate queens was needed. The nests of twelve established O. smaragdina colonies were examined. Each comprised many nests, but only one contained queens, and it commonly had multiple queens. The tree with queen ants had (1) the most ant trails connecting it to other trees included in the colony, and (2) more nests than the other trees in the colony. The nests with queen ants were near the top of the tree canopy and were of medium-size. Using these criteria, the average success rate of finding the queen nest in a colony was 95 %. The queens apparently stay in one nest from which eggs are distributed to the other nests in the colony.

The synchronization of recruitment-based activities in ants

Abstract: A simple model of recruitment-based foraging in ants illustrates the idea that synchronized patterns of activity can endow a colony with the ability to forage more efficiently when a minimal number of active individuals is required to establish and maintain food source exploitation. This model, which can be extended to other activities that involve recruitment, may help explain why bursts of synchronization have been observed in several species of ants.

Analysis of ant foraging algorithms

Abstract: We consider some models of ant foraging and recruitment behaviour that depend on each individual ant following a simple algorithm. Self-organisation enables the colony as a whole to establish a foraging strategy in the absence of any hierarchical control. In this paper we investigate how the effectiveness of such a foraging strategy depends on the persistence of the signals used by the individual ants and on the errors they make in following such signals. The use of inhibitory as well as excitatory signals is considered, and shown to be extremely effective in certain circumstances. This is interesting, as such signals have never been observed in real ant colonies. Such models are often investigated by simulation, but we approach them from the point of view of statistical mechanics. Looked at another way, which yields some insight, we approximate the stochastic process that models the system by a diffusion process with small diffusion parameter. This approach does not replace simulation, but supplements it. Its advantage is that it can elucidate the role of parameters more clearly and using much less computer time than simulation, but its disadvantage is that many simplifying assumptions must be made before the problem is amenable to analytic treatment.

Simulating multiple emergent phenomena exemplified in an ant colony (poster)

Abstract: Modeling the activity of an ant community based on the individual behavior of a single ant is a very modern approach, but until now the modeling has often been restricted to single phenomenon, e.g. foraging or recruiting. But these activities can not be seen independently from other necessary abilities. For example foraging, breeding, building a nest or defending a territory from enemies are all dependent on each other. In this paper we want to present a model of an ant community that unifies different activities during a complete life cycle of a colony. We present experiments with a simulated ant colony that exhibits concurrently - foraging and recruiting - storing energy and distributing it inside of the anthill - breeding and individual development - mass recruitment for defending the colony’s territory For modeling the behavior of an ant we use the SeSAm-architecture. This is a discrete, rule-based multi-agent simulation system that allows easy graphical modeling. Because of its simple structure and powerful graphical editors the large, unifying ant-model is easily accessible.

Temporal and spatial distribution of the rare, myrmecophagous Illidge's ant-blue butterfly, Acrodipsas illidgei (Lycaenidae)

Abstract: A survey of 591 branch sections containing arboreal ant colonies on 197 trees was undertaken over four consecutive seasons for the presence of immature Acrodipsas illidgei (Waterhouse and Lyell) in and adjacent to mangroves at Mary River Heads, Queensland, Australia. A. illidgei was found in 1.7% of ant colony sections sampled (ie 10 colony sections on five Avicennia marina (Forssk) trees). Despite the small number of immatures discovered, A. illidgei showed a strong tendency to occur in specific ant colonies over time. The host ant, Crematogaster sp. (laviceps group F. Smith) (Formicidae: Myrmicinae), was common and widespread within the survey area. The mean seasonal level of adult ant activity outside the nest positively correlated to mean seasonal ant brood levels within nests but were significantly linked only in spring and autumn. New information supports the hypothesis that ant colony odour selection by ovipositing female A. illidgei is the prime influence on this butterfly's localized distribution.

ANTS ’98 – From ant colonies to artificial antsc First International Workshop on Ant Colony Optimization

Abstract: ANTS '98, the First International Workshop on Ant Colony Optimization, was held in Brussels on the 14th to the 16th of October. The aim of the event was to bring together researchers and practitioners with a wide variety of interests, from biology to physics, engineering and computer science. The main topic considered was structured complex behaviors from the massive composition of simple communicating agents, in this case the lowly ant as the model.