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BiodiversitätWildtiere |
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Suter Werner |
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| 3.05.1458 | Recolonization of a savanna ecosystem by ungulate herbivores after abandonment of ranching | The aim of this proposal is to investigate how ungulates recolonise a savanna ecosystem largely devoid of its native ungulate fauna, and how - as a consequence - the structure and function of a grazing ecosystem are restored. The study site at Mkwaja Ranch offers an excellent opportunity to carry out this work. The ranch was formerly one of the largest cattle raising businesses in Tanzania (13'000 head of cattle) but was closed down in the year 2000. To the south of the former ranch is the Saadani Game Reserve, which has a high animal biomass including at least 19 ungulate species. The entire area is now under protection in the form of the new Saadani National Park and wildlife are slowly recolonizing the former Mkwaja Ranch area. This study is based on the proposition that a savanna largely devoid of ungulate herbivores presents a difficult environment for recolonization by grazers, mainly because of the reduction in plant food quality that occurs in the absence of grazing. Populations of nutritionally demanding, mostly smaller grazers, can only become established where food resources have been altered by less demanding pioneer species (facilitation), or by fire. The study, intended for two doctoral students, is organised around three main research questions: A. What are the spatial and temporal patterns of ungulate recolonization of the former ranch area? This will be investigated by direct and indirect (dung and tracks) observations of wildlife and by characterization of their habitats. B. How do diet, habitat use and movement patterns of ungulates differ between the former ranch area and the game reserve, and how do they relate to differences between the landscapes in habitat structure and nutrient distribution? For selected ungulate species, detailed studies will be made of habitat use and diet (from epidermal fragments and stable isotopes in dung). In addition, the activity patterns and distribution of warthogs will be followed using GPS collars. C. How do increased grazing and browsing by recolonizing ungulates change vegetation structure, composition and quality on the former ranch area, and how do nutritionally more demanding species respond to these changes? Experimental plots will be set up with mowing treatments to simulate grazing. The nutrient balance due to herbivores' use of an intensively used grassland area will also be studied. |
2005 - 2007 |
