Variation in body size drives spatial and temporal variation in lobster-urchin interaction strength

Area of Science:

• Marine ecology
• Predator-prey dynamics
• Ecosystem engineering

Background:

• Predator-prey interaction strength is context-dependent and difficult to measure.
• General size-scaling relationships suggest predator size, prey size, and prey density influence interaction strength across taxa.

Purpose of the Study:

• To assess the accuracy of general size-scaling relationships in predicting specific predator-prey interactions.
• To quantify the size and density dependence of the functional response of California spiny lobsters (Panulirus interruptus) on purple sea urchins (Strongylocentrotus purpuratus).

Main Methods:

• Experimental mesocosm study quantifying lobster foraging on sea urchins.
• Analysis of size and density dependence of functional response.
• Comparison of experimental results with predictions from general size-scaling literature.

Main Results:

• Predator and prey body size significantly impacts interaction strength, especially at high prey densities.
• General size-scaling relationships failed to accurately predict the magnitude of lobster-urchin interactions, with predictions often an order of magnitude off.
• Body size, relative to prey density, explained up to 87% of spatio-temporal variation in interaction strength.

Conclusions:

• Species-specific estimates for interaction strength scaling are necessary for accurate predictions, rather than relying on general relationships.
• Understanding how changes in body size (due to factors like climate change) affect species interactions is critical for marine ecosystem management.
• Differences in size-frequency distributions can cause substantial variation in interaction strengths over small spatial and temporal scales.