CASTE ALLOCATION IN LITTER PHEIDOLE - LESSONS FROM PLANT DEFENSE THEORY

The allocation to growth, defense and reproduction varies in social in sects within a species' life cycle and between species. A life cycle m odel (Oster and Wilson 1978) generally failed to predict caste allocat ion in small litter-nesting colonies of Neotropical Pheidole. Two of i ts assumptions were often invalid: food was unlikely to be limiting in four of five populations, and sexual biomass production accelerated, not decelerated, with colony size in three of five populations. One of five Pheidole populations studied had higher caste ratios (soldiers/w orkers) in reproductive colonies as predicted, and in no species did c aste functions conform to predictions. We also adapted three models fr om plant defense theory to study between-species patterns of caste all ocation. Among 12 litter Pheidole the amount of sterile biomass devote d to soldiers varied from 18 to 62%. Queen size, growth rate, and sold ier investment positively covaried. Only one model, the cost of replac ement hypothesis (McKey 1979), correctly predicted that species with c ostly female alates invest more in defense. The two hypotheses linking apparency to defense may also be valid if fast-growing colonies are m ore likely to attract the attention of predators.