Space-Time Structure of the Environment and the Survival of Parasite-Host Systems

The role played by the space-time structure of the environment in the survival of the wasp (Nasonia vitripennis) parasite-fly (Musca domestica and Phaenicia sericata) host systems was studied in the laboratory using a special population cage which consisted of a group of interconnected cells. One 30-cell parasite-host system survived for longer than a year. Increasing the number of cells from 16 to 30 in the population cage, decreased the average density of parasites and hosts per cell, but increased the chances of survival of the system. The amplitude of the fluctuations of the parasite-host populations did not increase with time as proposed by Nicholson's theoretical models but was limited by intraspecific competition. The rapid rate of evolution which occurred was the most important aspect of the experimental parasite-host populations. Within eight generations in a 16-cell system, reproductive capacity of the parasite declined 40 per cent. In 20 generations in a 30-cell system, reproductive capacity of the parasite declined 68 per cent. Such important qualitative changes in the parasite and host populations influenced the population characteristics of the systems to some degree. This demonstrates the importance of considering qualitative changes in studies of population dynamics of all herbivore-plant, predator-prey, and parasite-host systems.