Literaturdatenbank
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Avery, H. W. (1997). Challenges to a changing plant community: food selectivity and digestive performance of desert tortoises fed native vs. exotic forage plants. Proceedings: Conservation, Restoration, and Management of Tortoises and turtles - An International Conference.
Added by: Admin (17 Aug 2008 18:17:12 UTC) |
| Resource type: Journal Article BibTeX citation key: Avery1997 View all bibliographic details  |
Categories: General Keywords: Chelonia, Cheloniidae, Ernährung = nutrition, Gopherus, Gopherus agassizii, Habitat = habitat, invasive Arten = invasive species, Nordamerika = North America, Physiologie = physiology, Schildkröten = turtles + tortoises, Testudinidae Creators: Avery Collection: Proceedings: Conservation, Restoration, and Management of Tortoises and turtles - An International Conference |
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| Abstract |
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Gopherus agassizii Testudinidae The capacity of chelonians to grow, resist pathogens, and successfully reproduce depends upon their ability to acquire and process adequate amounts of foods that meet their nutritional requirements. The potential for nutritional constraints to affect herbivorous chelonians is magnified because many plant species are usually needed to meet all energy and nutrient requirements. Thus, nutritional constraints associated with food quality and abundance have important consequences for the management and conservation of herbivorous turtle and tortoise metapopulations inhabiting environments with modified plant communities. Exotic annual and perennial plants have become major components of arid plant communities within the geographic range of the desert tortoise, Gopherus agassizii. Some hypothesized effects of exotic plant introductions on desert tortoise nutrition include: (1) reduction in food choice due to decline in species diversity of forage plants, and (2) nutrient imbalances due to the consumption of lower quality forage plants that do not meet minimum nutritional requirements. The objectives of this study were to: (1) compare the nutrient content of native and exotic annuals known to be consumed by free-living desert tortoises, and (2) determine the food preferences of tortoises fed exotic versus native plant species. Fifteen desert tortoises were used in a selectivity trial in outdoor enclosures at The Living Desert, Palm Desert, California. The exotic annual species of filaree (Erodium cicutarium) and splitgrass (Schismus barbatus) were fed to one group of tortoises. The annual woody bottlewasher (Camissonia boothii) and the perennial shrub, wishbone bush (Mirabilis bigelovii) were fed to a second group of tortoises. A mix of all four plant species was provided to a third group of tortoises. Selectivity of forage plants was determined by measuring the consumption rates of each plant species by tortoises within morning feeding intervals. For tortoises fed the two exotic annuals there were significant preferences for Schismus over Erodium. For tortoises fed native plants, there was no difference in preference for Mirabilis versus Camissonia. Tortoises fed a mix of native and exotic plants preferred Schismus over all other native and exotic plants. This finding was in direct contrast to field studies indicating that wild desert tortoises prefer native plants over exotic plants. Nutrient contents for native and non-native plants were compared. Native plants were higher in crude protein than Schismus, but were similar to Erodium. Essential amino acids were greater in native plants versus non-native plants. Energy concentration was similar for all plants, and is not an adequate parameter for determining food quality. Dietary fiber, a nutritional challenge to all herbivorous vertebrates, was greater in exotic species than in native species. Schismus had a higher concentration of heavy metal ions than filaree or both native plant species. Data on the food selectivity, nutritional quality, and digestive performance of tortoises fed native versus exotic plants are used to assess the potential for maintaining viable metapopulations of desert tortoises in habitats characterized by high relative abundances of exotic plants.
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