Effects of crab predation risk on behavioural and morphological traits of the periwinkle Littorina littorea.

Markus.Molis [ at ] awi.de


Most of the researches on behavioral ecology field have been focused on direct predation effect on prey species but very few studies dealt with the indirect risk effects of predators and found that risk effects (basically due to mere presence of predators) on prey population growth rates are seven times larger than the direct predation effect. Prey can detect their predators through different forms of chemical information and avoid them to reduce the predation risk. Risk of predation affects many aspects of prey´s life such as morphology, behavior, life history etc and prey need to adapt some defenses or modify some behavioral traits to reduce that predation risk. The effects of predation risk on trait changes (morphological, behavioral and life history) of Littorina littorea (L.) due to 24 hrs exposure to risk cues of predatory crabs, Carcinus maenas (L.) have been observed through this study. Not only the effects of constant 24 hrs crab exposure but also the effects of temporal variation in risk on periwinkle were tested. It was examined whether the 24 hrs constant presence of predatory crabs change the shell mass of periwinkle within three months. The shell mass accumulation of snails was determined by calculating their shell mess increment (%) for three months and found that snails with crabs had a tendency to accumulate more shell mass than the snails without crabs, though result was not significant but from this result we can make an assumption that L. littorea may change their shell morphology in presence of predators within a short time but further long term researches are needed to get a significant result. Prey can change their behavioral traits to reduce the predation risk by avoiding their predators or by reducing foraging activities such as feeding, mate searching etc and it has an impact on food consumption and reproduction. Animals have to trade-off the predation risk with different ways such as less foraging activity or more vigilance in high risk but more activity in low risk situation to get the required energy. Two different experiments were conducted to observe the (1) avoidance behavior and (2) egg production, feeding and mating behavior of snails due to 24 hrs constant exposure to crabs. Snails with crabs showed significantly more avoidance behavior (movement out of water) but less feeding and mating frequency (except egg production) than the snails without crabs. This study also investigated the effects of temporal variation of risk (very obvious in nature) on the basis of exposure time duration and exposure frequency of snails to risk cues and tested the two basic predictions of risk allocation hypothesis. The result of this study showed that snails significantly reduced their egg production, food consumption and mating frequency with the increasing of exposure time duration to crabs but in case of very frequent high risk they increased their foraging activity or reduced their anti-predator activities with the increasing of exposure frequency to risk cues as their sensory receptors used to detect the predation risk become fatigued and lose their sensitivity with the increasing of exposure frequency and these results supported the two predictions of risk allocation hypothesis. In order to better understand, more future efforts should be made to investigate the effects of temporal risk variation under natural field conditions and to compare the field result with the laboratory experiment results.

Item Type
Thesis (Master)
Publication Status
Eprint ID
Cite as
Tina, F. (2011): Effects of crab predation risk on behavioural and morphological traits of the periwinkle Littorina littorea. , Master thesis, University Bremen.

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