Literaturdatenbank
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Kaddour, K. B. (2005). Ecology and life history traits of the moorish tortoise (testudo graeca graeca l., 1758) in an arid and overgrazed environment in western morocco: implications for conservation. Unpublished thesis , Universié Cadi Ayyad, Semlaia - Marrakech.
Added by: Admin (22 Feb 2009 11:56:22 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: Kaddour2005b View all bibliographic details  |
Categories: General Keywords: Habitat = habitat, Nordafrika = Northern Africa, Physiologie = physiology, Schildkröten = turtles + tortoises, Testudinidae, Testudo, Testudo graeca, Verhalten = ethology Creators: Kaddour Publisher: Universié Cadi Ayyad (Semlaia - Marrakech) |
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| Abstract |
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Testudinidae Wild populations of Testudo graeca graeca, the unique terrestrial tortoise in Morocco, are currently in regression following a combination of several climatic (e.g., drought) and anthropic (e.g., animal trade, destruction of the natural habitats, overgrazing.. etc.) factors. Data on the ecology and biodemography of this species occupy a central place in establishing of coherent management and conservation plans. The ecology and life history traits of a T. g. graeca population, living in an arid and overgrazed environment in the Central Jbilet mountains (western Morocco), were investigated between January 2000 and June 2004. We used a combination of varied and complementary methods. The population density of adults and sub-adult were estimated by Mark-recapture to 6 individuals/ha during the 2003 spring activity season. Dead animals collected during the study period indicated that mortality affects juveniles with more than 70%. The apparent population structure is characterized by a lack of 2 to 5 year old juvenile. Individual “catchabilty”showed that these later are weakly catchable and more than 60% of adults were captured only during three months suggesting that T. g. graeca populations can be strongly sensitive to illegal and repeated harvesting. Comparatively to terrestrial turtles, the population studied shows a “reverse”sexual size dimorphism (SSD) where females are larger than males. The sexual maturity is more precocious in males (7.1 ± 1.0 years) compared to females (9.3 ± 1.0 years) with no difference between their juvenile growth rates. The relatively delayed maturation in females is responsible of a longer juvenile growth period in females than in males and therefore a larger size at the adult stage. However, important inter-individual variations in growth and maturation patterns in both sexes were observed: more an individual growth faster, more its sexual maturity is reaches precociously, and then presents a lower size at maturity. Therefore, the age at sexual maturity in T. g. graeca seems to be determined mainly by juvenile growth rate. A shape sexual dimorphism (SSD) was also noted. Females have a carapace with important abdominal volume. On the other hand, males develop a carapace with large openings and a reduction of several plastrales plates allowing them a higher limb and tail mobility. These features are probably the result of a different selection context between male and female: importance of the selection for the fecundity in females and importance of the sexual selection in males. A comparative approach revealed that the SSD present more important geographical variation than of SSD. We finalized a new technique of behaviour automatic recording for T. g. graeca. Animals were equipped with acceleration loggers (Actitrac, IM Systems) glued on the shell. Thus, Activity budget during the main activity season (spring) was established. Our results showed that T. g. graeca presents a low bimodal daily activity with a sexual difference in favour of females. Time activity allocated to feeding was relatively more important in females than in males, but this time remains globally weak in both sexes (less than one hour/day). The yearly testosterone cycle in T. g. graeca males was established while achieving monthly blood samples on a total of 140 individuals. T. g. graeca males showed an original testosterone cycle with two peaks, one in summer and the other in winter. These two peaks correspond to the inactivity periods of the animal, and are then shifted in relation to the periods of expression of the sexual behaviours, concentrated in the spring and in autumn. Relationships between testosterone, activity budget and space occupation were studied in male Moorish tortoises by experimental manipulation of hormonal balances. The monitoring animal groups, during the spring activity phase, have received implants loaded either of testosterone, flutamide (antagonistic of testosterone) or no any of these products. The hormonal contrasts between experimental sets generated by the manipulation had no effect neither on the activity budget, nor on the space occupation of animals. These parameters seem only affected by the climatic constraints. Thus, testosterone had no apparent effect on the behaviours or if any effect exists, this would have an important temporal shifting, longer to our study period. Diet composition was determined by faecal analysis and compared to food availability resources. T. g. graeca seems to be a specialist herbivore. Only six main plant species represent 75% of plant matter identified in faeces and three among them were highly preferred whereas several other plant species, very common in the field, appeared to be actively avoided. The diet composition suggests that a strong competition may occur between domestic livestock and tortoises in overgrazed areas. However, T. g. graeca seems to concentrate his foraging effort under the Jujube thorny shrubs where the food resources are abundant and the impact of overgrazing is strongly reduced. These shrubs would insure other ecological functions for this ectothermic species, such protection against extreme conditions, thermoregulation sites, laying sites.. etc. Hence, conservation programs in favour of this species should take into account the protection of natural habitats of this herbivorous ecthothermic species, especially the thorny shrubs (Jujube and Acacia).
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