Lagarde, F., Bonnet, X., Corbin, J., Henen, B., Nagy, K., Mardonov, B. and Naulleau, G. (2003). Foraging behaviour and diet of an ectothermic herbivore: Testudo horsfieldi. Ecography 26:236-242.
Herbivorous vertebrates of arid regions are frequently faced with inadequate food quality, quantity or both. The time and energy devoted to foraging is vital to balancing their energy budgets. For desert ectotherms, a low metabolism should be advantageous, reducing their total energy requirement, but extreme ambient temperatures can strongly constrain these animals’ activity periods. We provide the first data on the activity budgets, foraging behaviour and diet of a highly abundant, desert dwelling, herbivorous ectotherm, the steppe tortoise Testudo horsfieldi. Extreme climatic conditions of Central Asia limit steppe tortoise’s activity to only three months per year. They remain inactive most of their ‘‘active season’’ (90%), and spend very little time foraging (_15 min per day). This suggests that steppe tortoises can satisfy their energy requirements with modest feeding efforts. Interestingly, steppe tortoises avoid feeding on grass species and feed mostly on plant species that are usually highly toxic to mammals. This result suggests that steppe tortoises and ungulates do not compete for food.
F. Lagarde (email@example.com ), X. Bonnet, J. Corbin
and G. Naulleau, Centre d ’Etudes Biologiques de Chize´
-CNRS, F- 79360 Villiers en Bois, France. – B. Henen, Dept
of Zoology, Biodi_ersity and Conser_ation Biology, Uni_. of
Western Cape, Bel_ille 7535, South Africa. – K. Nagy, Dept
of Organismic Biology, Ecology and E_olution, 621 Young
South Dri_e, Uni_. of California, Los Angeles, CA 90095-
USA. – B. Mardono_, Samarkand Di_. of the Academy of Sciences, 40 Djisakskaya St., Samarkand, 703032, Uzbekistan.
Excerpts from the article:
Later, from mid-April to mid-May, Papaveraceae, Koelpinia
and Brassicaceae tend to dominate the annual plant
community, and T. horsfieldi’s diet shifted towards those
plants. However, steppe tortoises avoided some potential
resources, particularly grass, abundant in the steppe plant
Drugs: foraging in haste?
Surprisingly, most of the plants consumed by T.horsfieldi have high contents of substances that are
notorious for their toxicity to herbivorous mammals. Papaver pavoninum contains alkaloids that can be poisonous to many mammals, and cases of intoxication have been documented in ungulates that consumed closely-related species (i.e. Papaver somniferum, Papaver rhoeas, Papaver nudicaule, Kingsbury 1964, Frohne and Pfander 1983, Cooper and Johnson 1984). Similarly, Koelpinia linearis contains several terpenoids, Koelpinin-A, B and C, all of which are potentially toxic for mammalian herbivores (Koul et al. 2000). Ceratocephalus, like other species of the closely related Ranunculus genus, produces and accumulates significant amounts of ranunculin, a potent poison, at least for mammals. Crushing the plant releases an enzyme that changes ranunculin, a glycoside, into protoanemonin, a highly irritant, yellow, volatile oil. This latter chemical is unstable and is transformed into the non-toxic anemonin or is volatilised upon drying. The average LD-50 is 10.9 g of fresh plant kg-1 for sheep that consume aboveground plant parts in the flower to early-seed stage. Sheep fed 7 g kg-1 of body weight may develop transient anorexic effects. An intake of 13.9 g kg-1 would usually be lethal (Nachman and Olsen 1983, Olsen et al. 1983). In Utah, 150 of 800 sheep that ingested ranunculin-containing buttercup died (Olsen et al. 1983, Cusick 1989). Such a diet that includes potentially toxic items has been documented in other chelonian species including Testudo hermanni and Eretmochelys imbricata (Meylan 1988, Longepierre and Grenot 1999). Such a diet has been interpreted in terms of anti-helminthic strategy (Satorhelyi and Sreter 1993, Longepierre and Grenot 1999). Female T. hermannii treated with vermifuge shift from a diet based on Ranunculaceae (with a high content of ranunculin) toward a diet based on Asteraceae (Longepierre and Grenot 1999), which lacks such compounds. Although steppe tortoises sometimes have a very high intestinal parasite loads (unpubl.), we can only speculate about the antiworm benefits of the plants consumed by the steppe tortoises.
Interestingly, steppe tortoises avoid feeding on grass
and feed mostly on plant species that are usually highly
toxic to mammals, suggesting a limited (if any) competition
for food between tortoises and wild or domestic ungulates.