Predator size and the suitability of a common prey

• Published in: Oecologia Vol. 109; no. 4; pp. 608 - 614
• Main Authors: Erikson, K.S, Morse, D.H. (Brown Univ., Providence, RI (USA). Dept. of Ecology and Evolutionary Biology)
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01.02.1997; Springer
• Subjects: Animal and plant ecology; Animal physiology; Animal, plant and microbial ecology; Animals; Autoecology; Average linear density; Biological and medical sciences; CANGREJO DE MAR; Community Ecology; CRABE; CRABS; DEPREDACION; DEPREDADORES; Flies; Foraging; Fundamental and applied biological sciences. Psychology; Instars; PREDATEUR; PREDATION; PREDATOR PREY RELATIONS; predator-prey relationships; PREDATORS; Protozoa. Invertebrata; RELACIONES PREDATOR PRESA; RELATION PREDATEUR PROIE; Relative profitability; Search time; Spiders; SYRPHIDAE; Thomisidae; Maximization; Profitability; Insecta; Predatory behavior; Araneida; Syrphidae; Energy balance; Arachnida; Partial; Food intake; Arthropoda; Body size; Thomisidae; Predation; Invertebrata; Diptera; Key words Crab spider; Predator mass; Syrphid fly; Partial prey consumption
• DOI: 10.1007/s004420050123
• ISSN: 0029-8549; 1432-1939

Although a predator's mass should influence the suitability of its prey, this subject has received little direct attention. We studied the capture and processing of an abundant syrphid fly Toxomerus marginatus (c. 4 mg) by 0.6- to 40-mg juvenile crab spiders Misumena vatia (Thomisidae) to determine how profitability, relative profitability (profitability/predator mass), overall gain in mass, and relative gain in mass differed with predator mass, and whether foraging changed concurrently. In multi-prey experiments, the smallest successful spiders (0.6-3.0 mg) extracted less mass from flies, and did so more slowly, than large spiders. This gain was proportionately similar to that of 10- to 40-mg spiders with access to many Toxomerus. However, many small spiders failed to capture flies. When we gave spiders only a single Toxomerus, the smallest ones again extracted mass more slowly than the large ones and increased in mass less than the large ones, but increased in mass proportionately more than large ones. Relative gain in mass from a single prey decreased with increasing spider mass. Spiders larger than 10 mg all extracted similar amounts of mass from a single Toxomerus at similar rates, but varied in time spent between captures. Thus, Toxomerus changes with spider mass from a large, hard-to-capture bonanza to a small, easy-to-capture item of low per capita value. However, Toxomerus is common enough that large spiders can capture it en masse, thereby compensating for its decline in per capita value.