QUANTIFYING FOOD LIMITATION OF ARTHROPOD PREDATORS IN THE FIELD

A method for quantifying food limitation of arthropod predators in the field is presented and applied to species of ground beetles (Carabida e) and sheet-web spiders (Linyphiidae) from a cereal field. Food limit ation is expressed quantitatively as accumulated hunger (=starvation) by transforming 24-h food consumption at 20 degrees C of animals newly collected in the field into days of starvation at 20 degrees C. This is done by means of a reference curve relating 24-h food intake at 20 degrees C to starvation periods (days) at 20 degrees C. Such a referen ce curve was obtained for the carabid beetle Agonum dorsale in the lab oratory. For other species the reference curve was modified with speci es-specific data. The procedure makes it possible to compare the feedi ng conditions of different species populations that are part of the sa me community. Hunger levels in the field for females of A. dorsale wer e equivalent to c. 15 days of starvation in early spring, c. 5 days in June, increasing to c. 10 days in late summer. Two ground beetles occ urring during summer also showed increasing hunger levels from June to July, probably the result of a dry summer. Two spider species experie nced a hunger level in the range of 4-8 days of starvation.