This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Matchette, Sam S Title: Camouflage in a dynamic world General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Camouflage in a dynamic world Samuel R. Matchette A dissertation submitted to the University of Bristol in accordance with the requirements for award of the degree of Doctor of Philosophy in the School of Psychological Science University of Bristol, UK November 2019 Supervisors: Prof. Nicholas Scott-Samuel and Prof. Innes Cuthill Words: 32,838 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 lessening the saliency of motion, a finding that is likely to shape many aspects of predator-prey interactions. i Acknowledgements I thank Nick Scott-Samuel and Innes Cuthill for their guidance and support throughout my PhD, as well as the other members (past and present) of the Camo Lab. I also thank Rhiannon Kearns for her patience and understanding throughout this endeavour. The Ph.D. was funded by a CASE studentship, supported by Engineering and Physical Sciences Research Council and QinetiQ, plc. ii Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University's Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate's own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. SIGNED: DATE: 21/11/2019 Published work and collaborations Three of the chapters contained in this thesis appear in published form elsewhere, and one is submitted for publication. In all cases, these papers/chapters were authored by me, with no more input from supervisors than would have been provided in any normal Ph.D. For the work on triggerfish in Chapter 7, Prof. Justin Marshall and Dr. Karen Cheney of the University of Queensland provided research facilities on Lizard Island (Great Barrier Reef) and invaluable advice on working with triggerfish. Chapter 1: Cuthill, I. C., Matchette, S. R., Scott-Samuel, N. E. Camouflage in a dynamic world. Current Opinion in Behavioral Science. 2019; 30:109-115 (doi.org/10.1016/j.cobeha.2019.07.007) Chapter 4: Matchette, S. R., Cuthill, I. C., Scott-Samuel, N. E. (2018). Concealment in a dynamic world: dappled light and caustics mask movement. Animal Behaviour. 2018; 143:51–57 (doi.org/10.1016/j.anbehav.2018.07.003) Chapter 6: Matchette, S. R., Cuthill, I. C., Scott-Samuel, N. E. Dappled light disrupts prey detection by masking movement. Animal Behaviour. 2019; 155:89-95 (doi.org/10.1016/j.anbehav.2019.07.006) Chapter 7: Matchette, S. R., Cuthill, I. C., Cheney, K. L., Marshall, N. J., Scott-Samuel, N. E. Underwater caustics disrupts prey detection by a reef fish. (under review at Proceedings of the Royal Society B: Biological Sciences) iii Table of contents CHAPTER 1. ................................................................................................................................................... 1 1.1 Camouflage, signal and noise ............................................................................................................. 1 1.2 A dynamic world ................................................................................................................................. 2 1.3 Organisms and their dynamic world ..................................................................................................... 6 1.4 Minimising the signal........................................................................................................................... 8 1.5 Increasing the noise .......................................................................................................................... 10 1.6 The role of attention .......................................................................................................................... 12 1.7 Thesis structure ................................................................................................................................ 13 CHAPTER 2. PILOT EXPERIMENTATION. ............................................................................................................. 14 2.2 Introduction ...................................................................................................................................... 14 2.3 Methods ........................................................................................................................................... 14 2.4 Results ............................................................................................................................................. 19 2.5 Discussion and methodological limitations ......................................................................................... 20 CHAPTER 3. COMMON METHODOLOGY. ............................................................................................................. 23 3.1 Creating natural scene simulations .................................................................................................... 23 3.2 Illuminant creation: dappled light ....................................................................................................... 25 3.3 Illuminant creation: water caustics ..................................................................................................... 26 CHAPTER 4. ASSESSING THE EFFECT OF DAPPLED LIGHT AND WATER CAUSTICS UPON PREY DETECTION AND CAPTURE: HUMANS. ...................................................................................................................................................... 29 4.1 Introduction ...................................................................................................................................... 30 4.2 Methods ........................................................................................................................................... 31 4.3 Results ............................................................................................................................................. 33 4.4 Discussion .......................................................................................................................................