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USC CSCI 534 - cs534FinalPaper-josh

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Explaining Invasive Ant Scenarios Using Emotion ModelingIntroductionRelated workMethodsUse of experiments in tuning the modelConclusionsReferencesExplaining Invasive Ant Scenarios Using EmotionModelingJoshua Wainer, Dusan Jan, and MinHee KwonIntroductionNative ant species play important roles in the stability of their ecosystems, acting as sources offood for many animals, natural predators for some, and facilitators in the life cycles of many plants. When native ant species are displaced or killed off by an invasive ant species such as Linepithema humile (Argentine ants), the latter rarely fills the same biological niches or assumesthe same ecological roles as the former. Subsequently, ecosystems that were once stable are usually made unstable by the arrival of an invasive ant species [7]. While the phenomenon of an invading species disrupting a local ecosystem is as old as biology itself, the exact mechanisms through which such upheaval takes place are rarely understood. However, recent research [2] has helped to explain the processes and interactions behind the successful invasions of L. humile into areas with Mediterranean climates, such as California. Because this area owes much of its economic success to its agriculture which in turn is dependent on the stability of local ecosystems, a proper understanding of the processes that drive invasive ant behaviors is critical. To this end, we will attempt to use a simple computational modelof emotions to synthesize both the local interactions among invasive and native ant species as well as the overall displacement of thelatter by the former. Related workThere are many papers that have dealt with interspecific ant interactions. Holway found that invasive Argentine ants exhibit fewer intraspecific conflicts than their native counterparts which leads to higher population densities, more foraging activity, and greater brood production, which presumably contribute to their successful invasions [8]. Later, he found while Argentine ants used chemical compounds as well as physical aggression when fighting with native ants, the key to their successes in fights lay in their numerical superiority. Furthermore, Argentine ants were unique in that they were both good fighters as well as good foragers, while most native ants had a negative correlation between the two traits [9]. Davidson had noted the same phenomenon in other invasive species and found that this could be attributed to factors such as using carbohydrates to replace nitrogen in their diets, the practices of polydomy and polygyny, and/or the formation of supercolonies [13]. Human and Gordon were the first to suggest importance in the Argentine ant’s ability to balance foraging success with fighting success [10], but their later work suggests that aggressive behavior does not correlate at all withforaging success among any ant species. Instead,it supports the idea that success at displacing other ant species was positively correlated with ahigh frequency of initiating interspecific interactions [2]. Additionally, there have been many papers that have attempted to recreate or mathematically model various behaviors of ants. Sumpter and Beekman showed that an ant’s response to a pheromone trail is nonlinear with respect to the amount of pheromone deposited and seems to suggest an activation threshold in ants for following a trail. Additionally, the amount of pheromone that ants laid on a trail directly correlated with the level of quality of the food source, and ants tended to follow a trail that had the most ants following it [11]. Chialvo and Millonas also studied the probabilities of ants moving in random directions as well as following a given pheromone trail and found thatthe empirically-determined probabilities enabled the formation of “well-defined” trails [14].Work has also been done that shows the validity of using emotions to drive the behavior of agents. Scheutz showed the validity of using emotions such as “anger” and “fear” as driving factors behind the actions of many agents [12] aswell as how displaying aggression is beneficial for social groups of agents[15].MethodsTo test whether an emotional model of ant behavior could synthesize the ants’ interspecific interactions and the overall result of an invasion by Argentine ants, we constructed a simulated environment in which two species of ants had their nests randomly placed within a 2D world. With all the ants of a given species starting at their nests, they began foraging for food at the same time. At random intervals, user-specified chunks of food would appear somewhere in the ants’ world. When the ants found food, they would try to take it back to their nest and store it,but if they had an interaction with another ant of a different species, there was a possibility that this would not happen. Operating under the assumption that a species of ant would either die out or be displaced in order to find food elsewhere when they gathered significantly less food than another species living in the same environment, we monitored how much food eachspecies gathered in a given simulation.Our simulation recreated both the behaviors common to all ants as well as the interspecific interactions found between various ant species. The behaviors equally prevalent in all species included randomly foraging, following a trail of pheromones to food, and returning with food to the nest. These behaviors were modeled as a set of states in every simulated ant, with foraging forfood set as a default behavior. If our simulated ants came across a pheromone trail laid by their own species, they would follow such a trail awayfrom their nests since it would be laid down withthe intention of leading ants to food [1]. Once theants found food, they would take it directly back to their nests while laying down a trail of pheromones for other ants of their own species tofollow. While the above behaviors occur without any communication at all among the ants, there is a specific set of behaviors that take place only when two or more ants interact with each other. Such behaviors include biting, lunging, running, and antennating (communicating through the touching of antennae), and can be grouped into three categories of behavior: aggressive, retreating, and neutral. These behaviors are found with varying degrees of frequency among different species of ants [2], though there are protocols of interaction that all ants seem to comply with: -


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