Sheltering behavior of terrestrial isopods in grasslands

Abstract

Abstract. The hypotheses that the sheltering behavior of four species of terrestrial isopods varies in relation to differences in their morphological, physiological, and behavioral adaptations to the terrestrial environment were tested using artificial refugia together with independent estimates of density to derive an index of sheltering activity. (1) Porcellio scaber sheltered significantly more than Platyarthrus hoffmannseggi, Armadillidium vulgare, or Philoscia muscorum, which sheltered the least. (2) There was a decline in the sheltering index (SI) for all four species after the breeding season, continuing through to the autumn and remaining low throughout the winter. (3) Changes in the sheltering behavior of each species in relation to changes in environmental conditions were used to interpret known differences in the position and breadth of their resource utilization curves along a gradient of rabbit grazing intensity. (4) Porcellio scaber sheltered more where the soil was more calcareous, P. muscorum more under the shade of trees, and both P. muscorum and A. vulgare more in grazed than in ungrazed swards. (5) Sheltering behavior was found to be positively correlated to both rainfall and soil temperature the day before sampling for A. vulgare but negatively to rainfall for P. muscorum. There was a positive relationship between the SI for P. scaber and daily air temperature range. (6) Variations in the sheltering behavior of these four species of terrestrial isopod are discussed in the context of their foraging and digestive strategies and in relation to their morphological, physiological, and behavioral adaptations to the terrestrial environment.