The effects of copper on predator-prey interactions of fathead minnows (Pimephales promelas) and Daphnia pulex Public Deposited

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  • Total copper concentrations of 10 [mu]g/l to 100 [mu]g/l appeared to alter the predator-prey interactions of fathead minnows (Pimephales promelas) and Daphnia pulex. The effect of copper concentration on the total amounts of D. pulex consumed over a 12-h period varied with the density of prey stocked hourly in the aquaria. Four prey levels of 5, 10, 20 and 30 D. pulex per 20 l aquarium were used and control consumption rates ranged from 0.9% to 4.3% of dry minnow body weight. The functional consumption response to prey density shifted from an hyperbolic-Type II toward a sigmoidal-Type III shape and the predators became more efficient at obtaining prey at lower densities as copper concentration increased. Consumption was slightly depressed at intermediate levels of copper and prey density, it was greatly enhanced at high levels of both. Mechanistic components of the functional response, total time spent searching and average time spent in pursuit of a prey item, showed an opposite pattern of response. At intermediate levels of copper concentration and prey density the total time spent searching and average time spent in pursuit increased while capture success and prey consumption fell slightly relative to controls; at high levels of copper and prey the total searching time and average time spent in pursuit decreased while capture success and prey consumption increased. Significant (P < 0.05) increases were observed in predator reactive distance with increased copper dose and prey density held constant. An assay of prey activity levels showed at least a 50% reduction in gross swimming activity of D. pulex at all dose levels of copper. The effects of copper on the mechanistic components could not be used to predict the effect of copper on the functional response but indicated the shift in functional response was due to the differential susceptibility of predator and prey to copper and effects of copper on fish appetite.
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