Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 1792

George William Salt; Predation in an experimental protozoan population (Woodruffia-Paramecium). Ecological Monographs 37(2):113-144, 1967

Reprint

In File

Notes

1. A program of experimentation and observation has been conducted to study predator-prey relationships in protozoa. 2. The rationale has been that in protozoa, which have no sexes or larval stages and a constant number of offspring, the fundamentals of predation should be more evident than in higher animals with more complex behavior. 3. The predator used was Woodruffia metabolica, holotrichous ciliate, which is an obligate predator on Paramecium. The prey species was Paramecium aurelia. 4. Woodruffia exhibits a threshold response to prey density. If the prey density is below a threshold value, the predators encyst. Above the threshold density, variations in prey density have little effect on the behavior of the predator. 5. Searching rate is dependent on habitat complexity. It is lower in complex habitats largely because the rate of locomotion is less. 6. At most, Woodruffia spend only 20% of their time hunting. This occurs at low densities. The hunting time declines progressively with increases in density. 7. The number of Paramecium consumed for each new Woodruffia produced is inversely proportional to predator density. The number changes from fifteen at low densities to five or less at high densities. 8. There is little change in the rate of increase with changes in density. 9. Natural oscillation of Woodruffia and Paramecium numbers occur in closed culture dishes. This is due to the behavior of the Woodruffia. 10. Comparison of the findings on Woodruffia with commonly accepted generalizations and theories on predation provide additional support for some and suggest modification of others. 11. One of the most important modifications is that the response of a predator to changes in prey density may be a threshold response rather than a proportional one. 12. The finding on Woodruffia and evidence reported by others suggest that in most, perhaps all, naturally occuring predator-prey populations some mechanism exists which exempts a portion of the prey population from attack. Commonly this mechanism is a product of innate behavioral characteristics of the predator.