Predator size and the suitability of a common prey

Area of Science:

• Ecology
• Predator-prey dynamics
• Arachnology

Background:

• Predator mass is expected to influence prey suitability, but this relationship is understudied.
• Crab spiders (Misumena vatia) provide a model to investigate how predator size affects foraging on abundant prey.

Purpose of the Study:

• To examine how prey profitability, mass gain, and foraging behavior change with predator mass in crab spiders.
• To determine if syrphid flies (Toxomerus marginatus) represent a size-dependent resource for juvenile crab spiders.

Main Methods:

• Studied capture and processing of Toxomerus marginatus by juvenile Misumena vatia (0.6–40 mg).
• Assessed mass extraction, processing time, and mass gain in single-prey and multi-prey experiments.
• Analyzed profitability and relative profitability in relation to predator mass.

Main Results:

• Smaller spiders (0.6–3.0 mg) extracted less mass and were slower, but achieved proportionally higher mass gain from single prey.
• Relative mass gain from a single prey decreased with increasing spider mass.
• Larger spiders (>10 mg) extracted similar mass from single prey at similar rates but varied in inter-capture intervals.
• Many small spiders failed to capture prey, while large spiders compensated for low per-capita value by capturing prey en masse.

Conclusions:

• Prey suitability shifts with predator size: large, difficult-to-capture prey for small spiders versus small, easy-to-capture prey of lower value for large spiders.
• Abundance of Toxomerus marginatus allows large spiders to compensate for reduced per-capita value through mass capture.
• Predator mass significantly influences foraging efficiency and prey selection strategies in crab spiders.