Vision Science
Camouflage, such as the patterns on large cats like leopards, is nature’s form of disguise, enabling animals to blend in with surroundings. But how did this camouflage develop, why is some more detailed than others, and why do some cats such as tigers have stripes, while others such as leopards have rosette patterning? ‘We wanted to tackle the problem of cat coloration and explain it at different levels,’ Will Allen says of new research he has conducted as a graduate student at the University of Bristol. Allen is doing his PhD in Psychology, in vision science, and so is interested in the camouflage and coloration as visual signals. ‘Vision Science is especially relevant to stuff like camouflage,’ says Allen. ‘It’s interdisciplinary,’ says Allen, so the Bristol Vision Institute at the University is comprised of, ‘psychologists, biologists, and also engineers and computer scientists who all tackle the problem of vision and visual behaviours from their unique perspective.’

Mathematical model
Allen says that previous research had shown that pattern cats were more likely to be found in forest habitats. What the new research reveals is how differences in patterning have important implications. For example while cheetahs, jaguars and clouded leopards, had been classified together as simply patterned cats, Allen’s work shows that the irregularity and complexity of the patterning are driven by the cats’ habitats and behaviours. ‘We used a mathematical model to analyse the pattern from them. The mathematician Alan Turing first developed this class of mathematical models in the 1950s.’ They are called ‘reaction-diffusion’ equations. Allen and his advisers had a number of different observers manipulating the reaction-diffusion patterns until they found the best match to the cat pattern. ‘It’s a more rigorous way of classifying patterning than has been done before,’ says Allen.

Irregular patterns of hunters
They established a clear link between patterns and environment. It seems that cats in dense tropical rainforests have more complex patterns and more irregular patterns than those found in the open.  Equally cats who spend more time hunting in trees have more irregular and complex patterns than cats that hunt at night. ‘So, we can see that the detailed aspects of patterning evolve for a particular lifestyle for camouflage function.’