PREDATOR INSPECTION BEHAVIOR COVARIES WITH SCHOOLING TENDENCY AMONGSTWILD GUPPY, POECILIA-RETICULATA, POPULATIONS IN TRINIDAD

When fish inspect a predator they incur risk. One way of reducing the cost of inspection is to approach predators in groups large enough to benefit from the safety in numbers advantages of schooling. In a surve y of nine populations of guppies, Poecilia reticulata, in their native streams in Trinidad, we observed marked variation in schooling behavi our. Guppies from sites also inhabited by a major predator, the pike c ichlid, Crenicichla alta, devoted more time to schooling than those fr om less dangerous locations where the cyprinodont Rivulus hartii was p resent. We found a strong correlation between schooling tendency and t he group sizes adopted by guppies inspecting a realistic model predato r. Since guppies in dangerous localities approached a potential predat or in large groups it seems unlikely that many of these fish were caug ht in a Prisoner's Dilemma, Inspections by singleton fish were rare in high-risk locations but predominated in those populations where risk from fish predators was reduced.