Growth, mortality, and longevity of the Egyptian tortoise Testudo kleinmanni Lortet, 1883

Abstract

Both demography and population regulation play an important role in the theory of sustainable exploitation and conservation of threatened taxa, such as terrestrial Chelonia. Here, we show and discuss some dynamic aspects of Testudo kleinmanni using modal progression analysis of length compositions. Although the Testudinata physiology is very different from that of fish, their growth model conforms to the Von Bertalanffy growth model. We observed a maximum of three age classes for both juveniles and females, and four classes for males. No appreciable between-sex differences were found in growth patterns, except for the diverse asymptotic length. Females should be subject to a strong sexual selection to quickly reach a large size in order to optimize lifetime reproductive output. The T. kleinmanni male size could be driven by predation escape and by easy accessibility to females, rather than by fighting for them. Thus, male reproductive success increases with the ability to fertilize females and female reproductive success increases with the ability to produce eggs, creating a large divergence in the context of selection between sexes. Different selective (synergetic or antagonistic) forces would appear to favor divergence in size between sexes. Additional properties found in the study regard the elevated mortality rate, probably also due to the human impact (poaching), and the relatively high longevity (26 and 22 years for females and males, respectively). Dynamics studies are useful for planning in situ activities of monitoring the population status, and could have a role in introducting programs and in control of reintroduced individuals during a restocking project.