Using Hidden Markov Models to characterise intermittent social behaviour in fish shoals

Nikolai W F Bode,Michael J Seitz

doi:10.1007/s00114-017-1534-9

Abstract

The movement of animals in groups is widespread in nature. Understanding this phenomenon presents an important problem in ecology with many applications that range from conservation to robotics. Underlying all group movements are interactions between individual animals and it is therefore crucial to understand the mechanisms of this social behaviour. To date, despite promising methodological developments, there are few applications to data of practical statistical techniques that inferentially investigate the extent and nature of social interactions in group movement. We address this gap by demonstrating the usefulness of a Hidden Markov Model approach to characterise individual-level social movement in published trajectory data on three-spined stickleback shoals (Gasterosteus aculeatus) and novel data on guppy shoals (Poecilia reticulata). With these models, we formally test for speed-mediated social interactions and verify that they are present. We further characterise this inferred social behaviour and find that despite the substantial shoal-level differences in movement dynamics between species, it is qualitatively similar in guppies and sticklebacks. It is intermittent, occurring in varying numbers of individuals at different time points. The speeds of interacting fish follow a bimodal distribution, indicating that they are either stationary or move at a preferred mean speed, and social fish with more social neighbours move at higher speeds, on average. Our findings and methodology present steps towards characterising social behaviour in animal groups.

Highlights

The movement of animals in groups is studied widely and is regarded to provide important insights for several areas of research
Our findings provide evidence for intermittent speedmediated social behaviour in guppies and sticklebacks
Our findings broadly confirmed our expectation of differences in the social movement between guppies and sticklebacks

Summary

Introduction

The movement of animals in groups is studied widely and is regarded to provide important insights for several areas of research. Studying the benefits individuals derive from moving in groups could highlight drivers for the evolution of sociality, understanding animal movement patterns is crucial for conservation, animal husbandry and pest. The current approaches for studying interaction mechanisms in moving animal groups can broadly be split into four. Theoretical models are used to establish what group-level dynamics emerge from hypothesised interaction mechanisms (Vicsek and Zafeiris 2012). Measurements from, or model fits to field or laboratory movement data are used to estimate the extent and nature of social interactions at the level of the entire group Similar approaches to the previous category are used to investigate social movement behaviour at the level of individuals We focussed on the fourth category and fit statistical models for individual movement to experimental data

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Results

Conclusion