The effect of size on the timing of visually mediated escape behaviour in staghorn sculpinLeptocottus armatus

Abstract

The effect of prey size on the timing of the startle response in the sculpin Leptocottus armatus was investigated. Escape responses were triggered visually by a looming image obtained using a computer-generated animation of an approaching black disk. The results showed that apparent looming threshold (T AL , i.e. the threshold at which the rate of change of the visual angle subtended by predator frontal profile onto the prey's eye triggers an escape response by the prey) decreased with increasing prey size. Distance travelled within a fixed time was unaffected by size. Theoretical considerations suggest that larger prey would need to travel a longer distance (and so they would need more time) in order to move their whole body outside the predator's approaching gape. Therefore, the scaling of T AL may be explained by taking into account both ultimate and proximate considerations that need not be mutually exclusive. At an ultimate level, lower T AL in larger fish may be explained in terms of offsetting the disadvantage of offering a larger volume to be intercepted by the predator. At a proximate level, T AL may be related to the fish's visual acuity, which is higher in larger fish.

Context‐dependent variability in the components of fish escape response: integrating locomotor performance and behavior

“…More recently, ALT was found to decrease (i.e., reaction distance increase) with prey size in staghorn sculpins (Paglianti and Domenici, 2006). Proximate and ultimate explanations were used to interpret these results.…”

“…Generally, results are in line with the prediction that reaction distance should increase with risk, because a higher speed and a larger predator should be perceived as a higher risk. Although the results can be interpreted using ultimate explanation, proximate explanations have also been considered related to visual acuity and neural processing (Dill, '74a;Anderson, '88;Paglianti and Domenici, 2006;Preuss et al, 2006). Nevertheless, as in other cases, here proximate and ultimate explanations can be considered as two non-conflicting aspects of the same phenomenon.…”

“…Proximate and ultimate explanations were used to interpret these results. Small individuals may take more risk than large ones because they have relatively higher energy requirements and because benefits of growing quickly decrease with increasing body size (Grant and Noakes, '87;Paglianti and Domenici, 2006). In line with this interpretation, large stickleback (Gasterosteus aculeatus), which are less affected by food deprivation than smaller three-spined stickleback, spent more time in refuges than smaller fish (Krause et al,'98).…”

“…In line with this interpretation, large stickleback (Gasterosteus aculeatus), which are less affected by food deprivation than smaller three-spined stickleback, spent more time in refuges than smaller fish (Krause et al,'98). In addition, because the speed attained within a fixed time from a standing start is size independent, large fish may be at higher risk of predation than small fish attacked by a predator of a given size (Paglianti and Domenici, 2006). This is because it takes longer for a large fish to get outside the projection of the predator's gape.…”

Effects of simulated underwater vehicle lighting on fish behavior

“…As an object or light approaches, the projected image on the observer's retina expands, a process referred to as visual looming (Schiff et al 1962), which frequently triggers avoidance behaviors in animals. In the ecological literature, this has been applied in the context of predator-prey interactions, and has been used to examine factors such as perception of predator size and prey-reactive distances (Domenici 2002, Paglianti & Domenici 2006. As a UV approaches, the lights from the vehicle will appear to loom to a fish, and as with trawls (Ryer 2008), may be interpreted by the fish as a threat, resulting in avoidance behavior.…”