Size-dependent survivorship in the web-building spiderAgelena limbata

Summary

Stage-specific mortality rates and mortality factors for the web-building spiderAgelena limbata, which is suggested to be food-limited, were studied, and the relationship between body size of spiders and survivorship for instar 3 to adults was examined. The mortality rate of the egg sac stage including eggs, deutova (prenymphal stage), and overwintering instar 1 nymphs was low. The low mortality of this stage was partly due to maternal care that reduced the mortality caused by predation and/or abiotic factors. From emergence of instar 1 nymphs from egg sacs to reproduction, the stagespecific mortality rates were almost constant, 32–47%, and the time-specific mortality rates were also constant. These results suggest a Deevey (1947) type II survivorship curve inA. limbata, in contrast to other reports on the wandering or burrowing spiders which suggested type III curves. Important mortality factors for nymphs and adults were parasitism by an ichneumonid wasp and predation by spiders. There were great variations in body size (carapace width) ofA. limbata in the field. Smaller individuals survived at a lower rate to the next stage than larger individuals. This tendency was clearer for the population living under poorer prey availability.A. limbata was unlikely to starve to death in the field because every stage ofA. limbata could survive starvation for a long time in the laboratory, 22–65 days on average. I suggest that the size-dependent survivorship of this spider is associated with vulnerability of smaller individuals to parasitism and predation.