RESOURCE CONSUMPTION VARIANCE WITHIN AND AMONG INDIVIDUALS - ON COLONIALITY IN SPIDERS

Several models for the economics of sociality demonstrate that the pro bability distribution of an individual's resource consumption could de pend on the size of its social group. When groups share food clumps di scovered by any member, expected resource consumption may increase or decline with group size, but the individual's resource consumption var iance will ordinarily decline as group size increases. Hence, the form ation and dissolution of social groups may represent risk-sensitive re sponses to foraging success. A series of field studies report greater mean prey consumption and decreased prey consumption variance as group size in colonial spiders increases. Several hypotheses attempt to exp lain this effect. Coloniality may promote acquisition of information c oncerning temporal variation in prey availability. Colony membership m ay permit individuals to steal food when the number of captured prey v aries spatially. Finally, coloniality can enhance food acquisition bec ause prey (that might otherwise escape) ricochet from one spider's web to another group member's web. Our purpose was to quantify each hypot hesis and ask if the resulting models predict reduced resource consump tion variance as group size increases. We model each mechanism and con clude that stealing prey is the simplest explanation for variance redu ction in spider colonies. We emphasize that variance among individuals need not provide a good estimate of the within-individual resource co nsumption variance, and it is the latter variance to which risk sensit ivity responds.