Camouflage and aposematism are two seemingly contrasting and mutually exclusive forms of anti-predator defence. With natural variation in predator experience and motivation to attack, however, defended prey may benefit from incorporating aspects of camouflage in order to reduce their predator encounter rate. One potential mechanism is distance-dependent signals, which take advantage of limitations in visual acuity to produce highly salient signals that are functionally camouflaged when viewed from a distance. Aposematic patterns often contain high contrast elements which have been suggested to increase the saliency of the signal. At greater viewing distances, however, the perception of pattern will change as different components dominate perceptual grouping mechanisms and adjacent patches of colour are summed to create a combined colour. Using computational modelling of ecologically relevant visual predators, laboratory experiments with human observers, and field experiments with bird predation, this thesis investigates distance-dependent signals in artificial prey and in two highly salient aposematic species: the cinnabar moth caterpillar (Tyria jacobaeae Erebidae). and the dyeing poison frog (Dendrobates tinctorius Dendrobatidae). Where the combined colour of a striped aposematic pattern matches that of the background, pattern-blending can create effective camouflage to distant observers, and lead to significant survival benefits. On more complex, visually textured, backgrounds, however, the homogenous colour produced by pattern-blending may not recreate the background, and a target will be easily detected. Indeed, pattern-blending may prevent an aposematic signal from being identified at the distance at which it is first detected. In this situation, optimal aposematic signalling appears to be produced from a balance between signal distinctiveness and recognition. Field experiments and visual modelling suggest that for both T. jacobaeae and D. tinctorius combining aposematism with camouflage, by exploiting distance-dependent effects, can be advantageous. Observer distance and its exploitation by specific colour patterns are likely to be underappreciated components of defensive colouration.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:702486 |
| Date | January 2016 |
| Creators | Barnett, James B. |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0158 seconds