Benjamin W Lindsey, and Jinzhong Fu

During foraging, animals often feed selectively and choose to pursue or ignore a prey item based on a specific set of pre-determined criteria (Shine and Sun, 2003). Lizards are no exception to this rule, and at present continue to gain popularity for their use as model organisms in ecological studies (Shafir and Roughgarden, 1998). Although chemoreception has been implicated in some species (Cooper, 2000; Kaufman et al., 1996), well developed visual systems remain essential for accurate prey recognition during foraging (Janzen et al., 1995). Attempts to isolate which discriminatory cues are correlated with prey selection are restricted to only a few recent studies (Kaufman et al., 1996; Diaz and Carrascal, 1993). As with other visual predators, the underlying assumption is that lizards should utilize a combination of fundamental visual cues including prey movement, color, size, and shape to discriminate between equally accessible prey items (Ibrahim and Huntingford, 1989).

Chameleons (family Chamaeleonidae) are excellent model systems for studying prey choice behavior for two reasons. First, they are unique for being the only terrestrial vertebrates that forage using monocular vision and independent lateral eye movement. Second, these animals possess lateral eye movement over a total range of 180° horizontally and 90° vertically (Haker et al., 2003). By switching between saccadic eye movements in the left and right eyes, these animals are able to detect prey in two separate visual fields (Pettigrew et al., 1999). This is of great benefit during prey choice experiments as prey can be introduced simultaneously into each visual field. This also provides advantages for sit-and-wait foragers such as chameleons, since they draw little attention to themselves by maintaining their head in a stationary position during prey detection.

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Lindsey and Fu, 2005 (58 KB)