Influence of intrinsic variation on foraging behaviour of adult female Australian fur seals

Phenotypic variation and individual experience can create behavioural and/or dietary variation within a population. This may reduce intra-specific competition, creating a buffer to environmental change. This study examined how intrinsic variation affects foraging behaviour of Australian fur seals. Foraging movements of 29 female Australian fur seals were recorded using FastLoc GPS and dive behaviour recorders. For each individual, body mass, flipper length and axis length were recorded, a tooth was sampled to determine age, and milk was collected for diet analysis. Clustering of fatty acid dietary analysis revealed 5 distinct groups in the population. Behaviour was described using 19 indices, which were then reduced to 7 principal components (>80% of the behavioural variation). Bayesian mixed effect models were developed to describe the relationship between these components and intrinsic variation. No association was found between diet and age or body shape; however, age had a negative relationship with component 1 (27% of variation). Older females spent less time at-sea and foraged nearer to the colony. Age had an effect on component 5 (7% of variation), which represented haul-outs and dive depth; older females made fewer visits to haul-out sites and dived deeper to the benthos. This suggests that as animals age they are able to utilise prior knowledge to exploit nearby foraging sites that younger animals are either unaware of, or have yet to gain the experience required to efficiently utilise. Mass had a negative effect on components representing the directedness of a foraging trip, suggesting heavier individuals were more likely to travel directly to a foraging site

Semantics of Agent Communication: An Introduction

Communication has been one of the salient issues in the research on concurrent and distributed systems. This holds no less for the research on multiagent systems. Over the last few years the study of agent communication, and in particular the semantics of agent communication, has attracted increased interest. The present paper provides an introduction to this area. Since agent communication builds upon concepts and techniques from concurrency theory , we start by giving a short historical overview that covers shared-variable concurrency, message-passing, rendezvous, concurrent constraint programming and agent communication. Standard approaches of agent communication identify three different layers: a content layer, message layer and communication layer. To this model we add an extra level, namely the layer of the multi-agent system. Subsequently, we discern three approaches in developing the semantics of programming languages: the axiomatic, operational and denotational approach. Additionally, we discuss semantic aspects of agent communication, including communication histories, compositionality, observable behaviour, failure sets and full abstractness. We illustrate these issues by means of the framework ACPL (Agent Communication Programming Language). Finally, we briefly consider the specification and verification of agent communication