Camouflage in a dynamic world

Abstract

This thesis concerns the effects of variable illumination on prey detection by predators. The environment plays a significant role in shaping the visibility of signals both to and from an organism. For example, against a static background movement is highly conspicuous, which favours staying still to optimise camouflage. However, backgrounds can also be highly dynamic, such as areas with wind-blown foliage or frequent changes in illumination. These dynamic features introduce visual noise which could serve to mask motion signals. Two forms of illumination change – the net-like underwater patterns known as caustics, and dappled forest light - are of particular interest because of their prevalence in the natural world. An experimental approach was taken: the gaming software, Unreal Engine 4, was used to simulate scenes containing each illuminant, and used to create interactive foraging tasks. Using model organisms from different taxa and environments – humans, birds and fish – I investigated the extent to which dynamic lighting influenced prey detection. When asked to capture moving prey items within the simulated terrestrial and aquatic scenes, human participants were significantly slower and more error-prone when viewing scenes with dynamic illumination. The presence of dynamic water caustics also significantly increased response times when searching for patterned prey items, particularly those with low contrast. In behavioural experiments with newly hatched domestic fowl chicks (Gallus gallus domesticus) and a wild-caught reef fish, the Picasso triggerfish (Rhinecanthus aculeatus, family: Balistidae), similar conclusions were drawn. Dynamic dapple, however produced, increased a chick’s latency to both fixate and peck the prey, while the presence of dynamic water caustics was shown to negatively affect prey detection and attack latency by triggerfish, an effect that should be most prominent in shallow water. Overall, I have identified a widespread factor
that can lessen the saliency of motion, and therefore shape many aspects of predator-prey interactions.

Date of Award	24 Mar 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Innes C Cuthill (Supervisor) & Nicholas E Scott-Samuel (Supervisor)