Countershading is one of the most common forms of colouration found throughout the animal kingdom. Predominantly presumed to enhance concealment through self-shadow concealment, there are several other mechanisms by which countershading can provide camouflage: enhanced background radiance matching or optical flattening. The majority of research to date has focused on the presence of this pattern in terrestrial animals. This thesis explores countershading in groups of aquatic species, and uses predictions of optimal countershading in cylindrical prey to determine the accuracy of survival benefits. 1. Anatomically accurate models of fish were used to predict optimal forms of countershading with regards to parameters affecting distribution of light: body shape, depth and colour of the substrate . . This is the first study to quantify predictions of countershading and compare to the observed patterns found in aquatic animals. Contrasts between the predictions and observed patterns suggest that countershading did not evolve for a single environment (i.e. one depth), but responds to multiple selective pressures. 2. I first test the effects of size on countershading, showing that increases in length and diameter have little effect on the contrast between dark to light gradient. I then move to qualitatively assess predicted countershading in marine predators, making associations between the behaviour and ecology of the species against the predictions for the function and occurance of countershading. Disparities between the predicted countershading and actual patterns, alongside the size and behaviours of the larger marine animals, suggests concealment via SSC or background matching is not essential. However, other functions of countershading such as protection from UVB are possible. 3. Using predictions of optimal countershading based on true measures of radiance, I investigate the effectiveness of optimal countershading for specific conditions against uniform and two-tone patterns, typically used in earlier countershading work. Patterns with optimised gradients performed significantly better than other patterns in all conditions of direct and diffuse lighting. This evidence shows countershading is inherently tied to the ambient light environment, and suggests that the gradation of pigment is more important to the survival than previously thought.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:690755 |
| Date | January 2014 |
| Creators | Sanghera, Nuvraj Simon Singh |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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