Literaturdatenbank
Literaturdatenbank |
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Sadeghayobi, E. (2011). The gut passage time in the galapagos giant tortoise (chelonoidis nigra) and its role for seed dispersal. Unpublished thesis , Uppsala University, Uppsala.
Added by: Sarina Wunderlich (25 Jun 2011 12:41:59 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: Sadeghayobi2011 View all bibliographic details  |
Categories: General Keywords: Chelonoidis, Chelonoidis nigra, Ernährung = nutrition, Schildkröten = turtles + tortoises, Testudinidae Creators: Sadeghayobi Publisher: Uppsala University (Uppsala) |
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| Abstract |
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The native vegetation on the Galapagos Islands has for a long time been threatened by introduced plants and the most widespread plant on several of the islands, common guava (Psidium guajava), is also consumed by the Galapagos giant tortoises (Chelonoidis nigra) in large quantities. The role of the Galapagos giant tortoises as seed dispersers on the Galapagos Islands is poorly studied. This is why it is important to study the passage time through the digestive tract as part of the understanding of how far the tortoises are able to disperse seeds. Ingested pseudo- and natural seeds were used as markers to track the gut passage time. Nineteen tortoises were fed pseudoseeds of different size to investigate the variability of the different sizes in passage time through the gut. Some of the tortoises were in addition given a mix of artificial seeds with known specific gravities or natural seeds of papaya (Carica papaya), passion fruit (Passiflora edulis) and common guava. Different types of seeds were given in order to observe the difference of gut passage time of the different kinds. The tortoises were fed only once with two hundred pieces of each kind in a given mix. Fecal samples were collected, washed and the recovered seeds were counted. The nineteen tortoises were divided into four groups and each was studied in a time sequence. The first two groups were studied in the cooler season and the last two groups in the hot season. The nineteen tortoises were fed a total of 22 000 seeds and 86 % of these were recovered. The results show that the gut passage time was individual between the tortoises. Seeds were frequently recovered between the first and the last seed observation. The first seeds appeared in all individuals from 6 to 13 days after seed ingestion. The longest seed transit was observed after 33 days, which indicates that the chances that seeds get dropped far away from their original site are high. The tortoises spread ingested seeds in both small and high frequencies on both short and long distance. No clear conclusions on the difference of the pseudoseeds of various sizes could be drawn. No clear difference among and in between the fruit seeds and the pseudoseeds were found either, which makes the gut passage time of the pseudoseeds comparable to natural seeds. The gut passage times also varies between the tortoises studied at different time periods. The gut passage time is faster in the hot rainy season than in the cooler season, suggesting that e.g. temperature or hormone levels affect the gut passage time. Due to our results together with the knowledge of the movement pattern of the tortoises, it is suggested that Galapagos giant tortoises could have a strong role on the vegetation dynamics as seed dispersers on the Galapagos Islands.
Added by: Sarina Wunderlich |