Capital and income breeding in two species of desert tortoise

Abstract

Evaluating resource acquisition and allocation schemes, such as capital and income breeding, can help identify limiting resources, delimit critical periods of resource availability, and improve conservation efforts. Female desert tortoises (Gopherus agassizii) and Central Asian tortoises (Testudo horsfieldii) rely upon accrued body reserves to produce eggs, providing evidence of capital breeding. Although both species use capital to reproduce, nutrient income seems to influence current reproductive allocations, suggesting that both species use a mixture of capital and income for reproduction. The desert tortoise, Gopherus agassizii, relaxes homeostasis, enabling it to store nutrients as they become available, and to reduce metabolic expenditures to conserve body nutrient reserves when environmental conditions are poor. Although relaxing homeostasis facilitates survival and reproduction, desert tortoises are vulnerable in particularly dry periods.