Understanding how Knowledge is exploited in Ant Algorithms

Centre for Intelligent Systems and their ApplicationsAnt algorithms were first written about in 1991 and since then they have been applied to many problems with great success. During these years the algorithms themselves have been modified for improved performance and also been influenced by research in other fields. Since the earliest Ant algorithms, heuristics and local search have been the primary knowledge sources. This thesis asks the question "how is knowledge used in Ant algorithms?" To answer this question three Ant algorithms are implemented. The first is the Graph based Ant System (GBAS), a theoretical model not yet implemented, and the others are two influential algorithms, the Ant System and Max-Min Ant System. A comparison is undertaken to show that the theoretical model empirically models what happens in the other two algorithms. Therefore, this chapter explores whether different pheromone matrices (representing the internal knowledge) have a significant effect on the behaviour of the algorithm. It is shown that only under extreme parameter settings does the behaviour of Ant System and Max-Min Ant System differ from that of GBAS. The thesis continues by investigating how inaccurate knowledge is used when it is the heuristic that is at fault. This study reveals that Ant algorithms are not good at dealing with this information, and if they do use a heuristic they must rely on it relating valid guidance. An additional benefit of this study is that it shows heuristics may offer more control over the exploration-exploitation trade-off than is afforded by other parameters. The second point where knowledge enters the algorithm is through the local search. The thesis looks at what happens to the performance of the Ant algorithms when a local search is used and how this affects the parameters of the algorithm. It is shown that the addition of a local search method does change the behaviour of the algorithm and that the strength of the method has a strong influence on how the parameters are chosen. The final study focuses on whether Ant algorithms are effective for driving a local search method. The thesis demonstrates that these algorithms are not as effective as some simpler fixed and variable neighbourhood search methods

How Collective Personality, Behavioral Plasticity, Information, and Fear Shape Collective Hunting in a Spider Society

The field of animal personality seeks to understand the potential adaptive value of temporally consistent inter-individual differences in behavior. Over the past several decades, this personality framework has helped behavioral ecologists better understand how social groups structure themselves behaviorally, and how intra-colony variation in personality can shape the emergent collective behavior of groups. While studies investigating how collective personalities interact with their environments and influence group survival are becoming more prevalent, research on this topic is still relatively scant. One important aspect of collective personality yet to be given attention is how group personality composition may influence a group’s response to invasion by a predator, or how the mere threat of predation can alter the collective behavioral phenotypes of groups. Given the near ubiquity of predation as a selective force in nature, it is important to incorporate both the direct and indirect effects of predators on collective behavior. This will lead to a better understanding about the environmental factors that shape the expression of group personality. This dissertation approaches these questions using three experiments. The first investigates how the behavioral distribution of colony constituents influences collective behavior in the context of colony defense. This study found that colonies of mixed personality composition exhibited twice as much defensive behavior as other compositions, and that bold compositions were displayed high degrees of behavioral flexibility relative to mixed and shy compositions. The second study observed how prolonged exposure to predators feeds back to determine the collective behavior of groups, and showed that colonies exposed to predators decreased overall collective aggressiveness by half, and eliminated the relationship between personality composition and aggressiveness. The last study investigated how groups prioritize information regarding predator presence when that information is possessed by the majority, or singleton immigrants that vary in leadership traits. This experiment found that groups operate under a “better-safe-than-sorry” strategy, and exhibit cautious collective behavior when any member of their group had been previously exposed to predators. Together, these experiments demonstrate that collective personality is a highly plastic and complex trait, that is determined by a combination if internal (group behavioral composition) and external (environmental risk) factors. Finally, I conclude this dissertation with a comprehensive review on the current state of collective personality research in insects and arachnids