Ecological and Geographical Feeding Peculiarities of the Central Asian Tortoise (Agrionemys horsfieldii Gray, 1844) in Desert Landscapes

Abstract

In April 2002 – 2005, the feeding patterns of Agrionemys horsfieldii were studied in four different landscapes in Uzbekistan. At the four sites, with the combined area no less than 5 ha, 43 plant species from 17 families were recorded as forming the tortoise diet. The proportion of plant species and gill mushrooms consumed by the tortoise at these sites varied from 42 to 59% with highest feeding preferences was given to species from families Brassicaceae, Papaveraceae, Fabaceae, Poaceae. Some tortoises preferred species (Anisantha tectorum, Hypecoum parviflorum, Leptaleum filifolium) and these dominated in food in several communities while animals and other non-vegetable objects were rarely consumed (~2%). Spearman’s rank correlation between the level of availability of a plant species in landscapes and the proportion of its consumption by the tortoise was near to 0 in many cases and we are able to prove that the tortoise should be seen as a selective consumer (PSI = 0.22) rather than as a generalist. A number of species dominating in plant communities were not, or rarely, eaten and among these are plants containing alkaloids and ethers, as well as species with harsh fibers and thorny spikes. In each community there were three or five species constituting the base of the diet (63 – 81%) that sustained the population. The base part of the diet constituted the species which had both high availability in the community and a high index of electivity (Jacob’s index > 0.6). The tortoise’s habitat in arid and waterless desert landscapes requires high rates of water consumption which comes from its food: for this reason, tortoises prefer to eat species with high moisture content, even including some poisonous ones. However, it is quite possible that the consumption of poisonous plants also achieves antihelminthic prophylactics.