| dc.description.abstract | For any prey animal, avoiding and fleeing from predators is one of the most important tasks in the key to survival. In order to avoid predation, a prey on detecting the predator must make appropriate decisions on how to respond to the threat. According to the optimal escape theory, initiation of escape should be a balance between the costs of staying (such as predation risk or death) and costs of fleeing (such as loss of feeding and reproductive opportunities and energy expenditure). Camouflage, particularly background matching, is also an important and widespread antipredator strategy, and it is commonly predicted that the likelihood of fleeing from a predator should depend on the level of camouflage of a prey animal. Moreover, most organisms encounter multiple predators rather than a single predator. Each predator possesses a different visual system and demonstrate various means of foraging and capture behaviour. Consequently, it becomes difficult for the prey to use the same antipredator strategy for multiple predators so prey species may evolve to form predator-specific responses as a counter strategy. Although a number of recent studies have considered the camouflage aspect in the common shore crab, research on how it works in combination with escape behaviour and whether it is affected by the type of predator remains unanswered. Although the association between camouflage strategies and escape behaviour has been researched in the past literature, many of these studies focus on the vertebrate taxa or do not directly measure camouflage and only few of them explore multiple predators. Within this thesis, I aim to address these gaps through a series of field-based experiments using background and predator treatments in the common shore crab (Carcinus maenas).
In chapter 2, I investigate the effects of camouflage on the escape response of shore crabs using mismatched backgrounds. Individuals were placed on the mismatched backgrounds and exposed to predator treatment and control of no predator treatment. The camouflage of crabs was measured in terms of brightness and colour difference using image analysis. Predator and background independently rather than their interaction had a significant influence on the escape behaviour. However, brightness and colour difference did not significantly affect their flight response. In addition, I also examined the effects of camouflage using substrate heterogeneity on the escape response of these crabs. Here, the camouflage based on brightness difference affected their escape behaviour on interaction with predator and substrate. Colour difference alone had a significant effect on the fleeing times and the interaction between predator and substrate was also found to be significant.
In chapter 3, I explore whether the escape responses of shore crabs are tailored to the type of predators using the same camouflage metrics. Here, predator and background when considered independently were found significant. Additionally, size of crabs was also significantly influencing the escape behaviour of crabs. Overall, this thesis indicates that camouflage influences the escape behaviour of prey species in complex heterogenous environments. Furthermore, it suggests that crabs and possibly other marine animals are capable of distinguishing between different predators and alter their escape responses based on the level of perceived threat. | en_GB |
