Reef Fish Predators Are Surprisingly Fair Hunters: New Analysis Shows Predation Spreads Evenly Across Prey

We challenged the common assumption that predators act independently: if one shark eats ten fish per day, do two sharks eat twenty? But on coral reefs, research by Adrian Stier and Wilson White reveals this simple math doesn't hold. When predators cluster on the same patch of reef, each individual becomes a less effective hunter.

We conducted experiments manipulating the density of predatory fish on coral reef patches. By controlling predator numbers and measuring how many prey each consumed, they could calculate what ecologists call the functional response: the relationship between prey availability and predation rate. Their focus was on how this relationship changed when multiple predators hunted the same area.

Our results showed clear predator interference. Per-capita predation rates declined as predator density increased. A single predator consumed prey at a higher rate than the same predator would achieve when hunting alongside others. Multiple predators together caught fewer total prey than you'd predict by multiplying single-predator rates.

Several mechanisms could explain this interference. Predators might compete directly for prey, with one predator's attack scaring away targets that another was stalking. They might waste time monitoring each other rather than hunting. Or prey might become more vigilant when multiple predators are present, making all hunters less successful.

This predator interference has important implications for reef dynamics. If predator effects don't simply add up, then models predicting reef community structure need to account for these non-linear effects. The interference could also stabilize predator-prey dynamics: as predator populations grow, per-capita hunting success declines, potentially preventing predators from driving prey populations to extinction.

The findings challenge simple assumptions about predation on reefs and highlight the complexity of multi-predator systems. Understanding these dynamics becomes increasingly important as reef communities shift under fishing pressure and climate change, altering the abundance and diversity of predators on reefs worldwide.

Citation

Stier, A. C.; White, J. W. (2014). Predator density and the functional responses of coral reef fish. Coral Reefs.

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