Understanding natural causes of density dependence is essential for identifying possible sources of population regulation. Field experiments on a model system of coral reef fishes showed that small juveniles of Chromis cyanea suffer heavy mortality that is spatially density-dependent only in the presence of two suites of predators: transient piscivores attacking from above, and reef-resident piscivores attacking from below. In the absence of either kind of predator, early mortality of Chromis is virtually density-independent. Because piscivores may have regulatory roles in this and similar marine systems, overfishing these predators may have ramifications for the remainder of the exploited community.
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