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Diet choice of a predator in the wild: overabundance of prey and missed opportunities along the prey capture sequence
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Edité par CCSD ; Ecological Society of America -
International audience. Optimal diet theory (ODT) postulates that predators adjust their foraging decisions bycalculating a prey value from the potential biomass gain, handling time, prey vulnerability and encounterrate. Tests of ODT have however so far mainly been restricted to laboratory settings. By video surveillance,we gathered a large data set of more than 2000 field observations of crab spider (Misumena vatia)encounters with potential prey. We then tested whether the complex ODT or two simpler models (preyidentity and prey traits) best explain foraging decisions. Insect prey were killed with an average chance of3.5% when alighting on an inflorescence harboring a spider. Spiders refused to attack suitable prey in 46–79% of encounters when prey was in attack range, indicating an over-abundance of prey relative to theneeds of the spiders. Reduction of opportunities to capture prey along the prey capture sequence differedamong pollinator groups, with syrphids and solitary bees showing strong avoidance of spiders early in thesequence and bumblebees resisting the final strike. Simple prey traits explained foraging decisions betterthan ODT, which was not supported. In the absence of food limitation, optimality decisions may be lessstringent. The over-abundance of prey indicates that, in contrast to current theory, prey encounter rates arenot the most important factor driving predator foraging decisions. Our results are highly coherent withthose obtained in earlier field studies on patch leaving strategies and predator-prey encounters. Prey overabundanceand non-optimal predator behavior are apparently not uncommon in nature, and we highlightsome of the implications for predator-prey theory.
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