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Experimental studies on the role of dispersion and level of food supply in predator-prey relations were continued. They were conducted under controlled laboratory conditions using the phytophagous mite Eotetranychus sexmaculatus as prey, and the mite Typhlodromus occidentalis as predator. Results give additional support to earlier findings that more stable control of a population results when the environment is spatially more heterogeneous and there is a balance between the extent of heterogeneity and the amount of basic food. An excess of plant food at first generated large numbers of prey, and then an excess of predators which overexploited their prey and then starved. By using a complex spatial environment consisting of three grid-wire shelves in a cabinet, and a wide dispersion of the basic food material, the predator-prey interaction was continued for 490 days, and the end was brought about by a disturbing disease rather than by overexploitation on the part of the predatory mite. In contrast, trebling the quantity of basic food while maintaining other factors unchanged apparently created an imbalance between numbers of predators generated in the system and the hazards they faced in covering the areas to be searched—thus, they overexploited in each case at the end of the first prey population crash phase. These results also suggest the potential role of predation as a means of synchronizing cycle phase in some natural populations.
Huffaker et al. (Mon,) studied this question.