PEELING OUT PREDATION INTENSITY: CAN REPAIR FREQUENCY BE A USEFUL PROXY TOWARDS UNDERSTANDING PREDATION?

Determining predation intensity in the fossil record is challenging, often because predators and prey are not found together. In addition, attack and kill frequencies in marine fossil populations cannot be determined easily, as kills often destroy the prey and prevent fossilization. Repair frequency, however, is easy to obtain, as many shelled organisms will bear evidence, a repair scar, of damage on their shell. Using repairs can be tricky as repairs represent failed attacks; repair frequency could increase because of an increase in attack (predation) intensity or a decrease in the predators’ success.

Modern work has shown a relationship between wave energy and repair frequency for the gastropod Chlorostoma funebralis, which are preyed upon by the crab Cancer productus near Bamfield, BC, Canada. Size distribution and foraging time of C. productus is limited by wave energy: wave exposed high-energy sites tend to exclude large, adult crabs because of the dangerous conditions. Smaller crabs use these settings to avoid intraspecific competition. In addition, crabs in these settings experience less foraging time. Conversely, wave sheltered low-energy setting crabs include larger adults, as foraging time is greater as suitable foraging water depths persist longer.

To determine whether repair frequency tracks attack frequency or predator success rate in this predator-prey system, a gradient of high- to low-energy localities were sampled for C. funebralis and their repair frequencies determined. If attack frequency drives repairs, then sheltered sites should have greater repair frequency due to the larger crabs and more foraging time. If success/failure drives repairs, then exposed sites should have greater repairs because smaller crabs would fail more frequently. Results indicate that the repair frequency of C. funebralis inversely tracks wave energy, such that low-energy localities have much greater repair frequencies than high-energy localities. Given the established relationship between repair frequency and wave energy, tethering experiments have been set up to confirm this result. If repair, attack, and kill frequencies of the tethering experiments show similar trends, these experiments may validate repair frequency as a proxy for predation intensity within paleoecological studies.