Lieshout, S. van (1997) Food preference and food quality of Brent geese. Master's Thesis / Essay, Biology.
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Abstract
According to classical exploitation theory, the increase in primary productivity found over the successional gradient of the salt marsh of Schiermonnikoog should result in an increased grazing pressure. However field data obtained from the salt marsh showed the highest Brent geese grazing pressure at salt marsh areas with low primary productivity. The grazing pressure was relatively low in the more productive parts later in succession, We hypothesized that this could be due to plant species replacement along the successional gradient, with, in the course of succession, abundance of by the geese less preferred species. Therefore this study examined the relations between Brent geese and their food stock along the successional gradient with two major questions in mind. First, is there a correlation between observed grazing pressure distribution and abundance of by Brent geese preferred food plants? Second, can we explain Brent geese preference for plant species by means of aqualitative analysis of plant material? In order to answer the first question we investigated the diet of Brent geese at three different successional stages and their preference for plant species at these areas. We determined the availability of preferred and disfavoured plant species at the successional stages of different age and compared this with the observed grazing pressure distribution. Our data show that grazing pressure and abundance of preferred species are correlated, The relative abundance of preferred species is highest in the youngest areas. Brents are, in the course of succession, faced with vegetation composed of an increasing amount of disfavoured plant species. Diets however, changed only marginally, incorporating only I 5% disfavoured species in the oldest successional stage. An answer to the second question was sought by determining energy intake, soluble carbohydrates, crude protein, fibre, ash and in vitro digestibility of most plant species present at the salt marsh and comparing these with the observed preference. Three clearly defined plant species clusters were found. One cluster was formed by the monocots, Festuca rubra, PuccineIIia maritina, Juncus gerardi and Elymus sp which were all high in soluble carbohydrates and fibres. Triglochin maritina, in which the concentration protein was highest, formed a second cluster, and a third was composed of the dicots Plantago maritima, Spergularia maritina and Aster tripolium, highest in ash content. The percentages of carbohydrates of neutral preferred species was significantly higher than the carbohydrate content of disfavoured species, There was also a tendency that preferred plants were more easy to digest. We can conclude that the observed grazing pressure distribution correlates positively with the relative abundance of preferred forage. Data, however, indicate that it is difficult to link the observed food preference to one of the analysed food quality aspects. Future studies will have to provide more insight in the feeding strategies of Brent geese.
| Item Type: | Thesis (Master's Thesis / Essay) |
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| Degree programme: | Biology |
| Thesis type: | Master's Thesis / Essay |
| Language: | English |
| Date Deposited: | 15 Feb 2018 07:48 |
| Last Modified: | 15 Feb 2018 07:48 |
| URI: | https://fse.studenttheses.ub.rug.nl/id/eprint/10116 |
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