The influence of climatic factors on the demography of the terrestrial isopod Tracheoniscus rathkei Brandt

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Abstract
A field population of the isopod Tracheoniscus rathkei was monitored during 1971, 1972, and 1973. At the same time, laboratory data related to growth, reproduction, and survival were collected and combined to produce a simulation model. The model output was compared with the field data. In the laboratory, T. rathkei required humidities very near 100% relative humidity, day length had no effect on growth rates, and temperature altered rates of growth and survival and determined the periodicity of reproduction. In the field, T. rathkei exhibited a 2-year life cycle, breeding occurred in the spring and summer, and about 83% of the population bred once and 42% bred twice during each year. Juveniles grew throughout the fall, overwintered, reproduced at 1 year of age, continued to grow, overwintered a second time, reproduced again, and died. The simulation model mimicked this pattern with considerable precision. Both the field data and the simulated output suggested that the population expanded during 1971, 1972, and 1973. No mechanisms for population limitation were found.