A Test of the Principle of Allocation Using Two Sympatric Species of Cockroaches

The "principle of allocation" underlies much of current life history theory, but has never been critically tested. Although the cockroaches Periplaneta americana and P. brunnea are closely related and morphologically very similar, P. brunnea produces an ootheca nearly twice the mass of P. americana's. The principle of allocation predicts that P. brunnea should take longer to produce an ootheca, or that some other factor must be traded off. The principle was tested by comparing the mass budgets of Periplaneta americana and P. brunnea fed artificial diets under controlled conditions. Although dissections confirmed their morphological similarity, P. brunnea had a rate of dry biomass production of 11.2 mg/d, whereas that of P. americana was only 4.4 mg/d. The gross production efficiency of P. brunnea (38%) was also higher than that of P. americana (29%). These results challenge the generality of the principle of allocation. P. brunnea was much less resistant to starvation than P. americana. Although growth of the two species was similar on an adequate diet, P. brunnea grew faster but suffered higher mortality than P. americana on low—protein diets. The results suggest a view of organism design based on safety factors and adjustment to levels of key resources, as an alternative to a perspective of maximized production.