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To investigate how organisms respond to multiple cues, the responses of the crayfish Orconectes virilis to natural chemical stimuli presented both one at a time and in combinations were recorded in the laboratory. Following the introduction of predator (snapping turtle) odours, individuals decreased the rate of non-locomotory movements compared to control levels. The addition of food odour resulted in an increase in movement as well as postural changes. When both signals were presented simultaneously, the level of food-elicited movements was reduced and the extent of inhibition of food-related responses depended upon the relative intensity of the two types of input. The behavioural effect of predator odour introduction lasted about two hours. When alarm odour and food odour were presented simultaneously, movements were reduced even more strongly than with the predator odour-food odour combination. Presentation of two signals associated with danger (alarm and predator odours) resulted in a significantly greater reduction of food odour-induced movement than for either danger signal by itself.

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Clibanarius tricolor overlaps strongly in shell utilization with the other common species of intertidal hermit crabs found in the Florida Keys. Laboratory observations indicated C. tricolor can dominate Clibanarius antillensis in shell fights, while Calcinus tibicen dominates C. tricolor. In micro-areas of sympatry with C. antillensis, C. tricolor's shell fit is better and egg production parameters not affected when compared to adjacent areas where only C. tricolor occurs. Sympatry with Calcinus tibicen results in a poorer shell fit, a smaller shell size for a given size crab, a smaller mean size of crab, and a disruption of the relationship between clutch size and crab size:shell weight ratio. A strong effect of shell species on the probability of

No abstract