Filiform hairs located on the cerci of crickets are among the most sensitive sensors in the animal world and enable crickets to sense the faintest air movements generated by approaching predators. While the neurophysiological and biomechanical aspects of this sensory system have been studied independently for several decades, their integration into a coherent framework was wanting. In order to evaluate the hair canopy tuning to predator signals, we built a model of cercal population coding of oscillating air flows by the hundreds of hairs on the cerci of the sand cricket Gryllus bimaculatus (Insecta: Orthoptera). A complete survey of all hairs covering the cerci was done on intact cerci using scanning electronic microscopy. An additive population coding of sinusoid signals of varying frequencies and velocities taking into account hair directionality delivered the cercal canopy tuning curve. We show that the range of frequencies and velocities at which the cricket sensory system is best tuned corresponds to the values of signals produced by approaching predators. The relative frequencies of short (o0.5 Â 10 À3 m) and long hairs and their differing responses to oscillating air flows therefore enable crickets to detect predators in a time-frequency-intensity space both as far as possible and at close range. r

Feeding of the copepod Centropages typicus on the oligotrich ciliate Strombidium sulcaturn was studied in the laboratory under controlled, measured conditions of grid generated small scale turbulence. High levels of turbulence, F (kinetic energy dissipation rate) = 2.9 X 10-2 to 3 X 10-' cm2 s3, increased the clearance rate of C. typicus feeding on S. sulcatum by up to a factor of 4 in comparison to calm water values. At a level of turbulence of 4.4 cm2 s -~, we observed a drastic decrease in clearance rates to values equivalent to those in calm water. We suggest an explanation for the observed changes in predation rates with levels of turbulence. Video recorded observations of the behaviour of free swimming C. typicus conducted in calm conditions suggest that the copepod uses a cruising strategy to search and encounter S. sulcatum. In the presence of this cillate, C. typlcus increases the proportion of time spent swimming at a mean velocity of 3.5 mm S-': from 49.5'% in filtered seawater without ciliates to 79.5% in the presence of S. sulcatum (1 cell ml-l). Furthermore, a qualitative change of the swimming behaviour is triggered by the presence of the ciliate, resulting in an increased proportion of time spent slow swimming in a 'helical' mode. Our results suggest that high levels of small scale turbulence substantially increase predation rates of crunsing copepods.

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