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Tropical wetlands maintain a high biodiversity and provide ecological services which are basis for millions of livelihoods. However, freshwater ecosystems are largely neglected in research and environmental policy. Today they are among the most threatened habitat types throughout the world with highest loss rates for natural inland wetlands in the tropics. The high dependency of local communities upon natural resources makes conservation management for wetlands in developing countries to a particular challenge.
This study investigated the different perspectives of conservation planning at Lake Alaotra, the largest wetland complex of Madagascar. First, the ecological state of Lake Alaotra was assessed to close knowledge gaps and to provide an adequate basis for ecosystem-based conservation measures. Second, I evaluated the community-led management of a small protected area in order to determine its potentials and weaknesses. Third, the local fishery, as the largest lake resource user group, was investigated to understand the drivers of overfishing.
By interlinking the results of the three perspectives of conservation planning – ecology, management and resource user – interrelations and trade-offs between the three dimensions were identified. The current ecological state of Lake Alaotra reveals that the anthropogenic disturbance is favoring the proliferation of invasive plant species and leading to the alteration of the water quality (e. g. hypoxia). Insights into the local management show that the community-based management contributes to the conservation of the natural flora and fauna. However, the small-scale conservation area suffers from isolation and illegal activities, while its management lacks recognition at community level. The fishery sector has grown dramatically although fish catches have fallen sharply. Species composition changes and low reproduction rates are reflecting the fishing pressure. A high population growth and lacking agricultural land force people to enter fishery and increases the human pressure on the lake.
Overall this study shows that the conservation of multiple-value ecosystems, such as tropical wetlands in developing countries, require site-specific multidimensional approaches that interlink ecological demands, resource user needs and the local sociocultural setting. This research demonstrates that: ongoing livelihood dynamics linked to the socio-economic conditions have to be considered to create more realistic management policies; strengthening resource users’ assets will help to decrease the human pressure on the already considerably altered ecosystem; capacity building for local management associations and the adoption of local ideas and management concepts is needed to enable the evolvement of an locally legitimated and tailored wetland conservation management.
Arthropod herbivores act as mediators for effects that cascade up and down the trophic chain. Therefore, herbivory plays an important role for driving ecosystem processes and influencing ecosystem structures and functions. Generally, ecosystem processes are mediated by interactions between organisms. The plant community composition is influenced by competitive interactions among plants, which is affected by herbivore species. Leaf area loss to insects can reduce tree growth, but alters material flows from canopies to forest soils. Therefore, the chemical quality of litter is changed (increases in nitrogen content) through enhanced nutrient cycling rates caused by herbivory.
Climate and microclimate can affect insect physiology and behaviour directly or indirectly through climate-induced changes of host plants. Temperature determines the geographical range, site and timing of activities, success of oviposition and hatching, and the duration of developmental stages of arthropod herbivores. The activity of poikilothermic insects increases with temperature, and therefore growth and consumption rates are enhanced. However, morphological and functional leaf traits that determine host plant palatability often mediate indirect environmental effects on herbivory. Leaf palatability is determined by leaf toughness, nutrients, and defence compounds. In warm environments, expected high rates of arthropod herbivory can then be suppressed by negative changes of leaf traits.
Microclimate gradients are found across the different strata of forest ecosystems. Abiotic factors change vertically between forest layers due to a micro-environmental gradient. Along the vertical gradient, microclimate is affected by the light regime, with increasing temperatures and decreasing humidity from understorey to upper canopies. Various organisms are distributed along the vertical forest gradient based on changes in environmental conditions and in the quality and quantity of available resources. Temperate deciduous forests reveal highly stratified arthropod communities with vertical and horizontal distribution patterns. Microclimatic requirements and the availability of food resources along the vertical forest gradient can reflect spatial distributions and preferences of arthropods.
This research study investigated arthropod herbivory on leaves of deciduous tree species along the vertical gradient of temperate forests. A field study with ten forests sites in Central Germany and an experimental study in greenhouses were conducted, addressing effects of microclimate and leaf traits on arthropod herbivory. Juvenile and adult individuals of Fagus sylvatica L. (European beech), the dominant deciduous tree species in Central Europe, were chosen as main research subjects. Furthermore, Acer pseudoplatanus L. (Sycamore maple) and Carpinus betulus L. (hornbeam), two frequent tree species in the forest understorey, were also surveyed.
Grazing animals alter natural processes by affecting ecosystems and at the same time fulfilling ecosystem functions, thus they are regarded as ecosystem engineers. Effects of grazing are mainly studied in managed systems, where grazing animals are restricted in their movement and thus limited to certain vegetation types. On the island of Asinara the grazing system is now, due to its history as agro-penitentiary, a natural grazing system with donkeys, horses, goats, mouflons and wild boars. This multitude of grazers poses a challenge for the Asinara National Park and its management. Therefore this dissertation takes an interdisciplinary approach to investigate grazing animals and their interrelations with different components of the island ecosystem to analyse their role on the island and evaluate their effects on the biodiversity. The composition and distribution patterns of the five grazing animal species have been investigated in the context of the land-cover types of the island ecosystem. In addition, the input on the vegetation through endozoochorous seed dispersal by donkeys and goats was analysed, and the impact of grazing animals on dung beetle assemblages was studied in three highly frequented vegetation units, taking into account the intensity of use by the grazing animals. The results derived from this work highlight the importance of studying grazing animals and their interrelations within an island ecosystem. Moreover, the insights given in this thesis concerning the interrelations of grazing animals with different components of the island should open up the view on grazers and their multifaceted effects on the biodiversity, thus leading to management implementations for a sound functioning of the island ecosystem as well as the conservation and maintenance of biodiversity.
The water hyacinth (Eichhornia crassipes) is one of the top ten most invasive aquatic plant species in the world. Due to its worldwide distribution, the plant has caused tremendous damage on ecosystems and human livelihoods alike. These negative impacts are especially problematic for developing countries such as Madagascar. Considering the weak economic situation of the country, using water hyacinth to generate economic profits remains the last option to manage the species. We investigated the use of water hyacinth at Lake Alaotra, the largest lake in the country. This lake and the surrounding area are of great ecological and economic relevance for Madagascar. However, the isolation of the region and poverty limit water hyacinth use only to alternatives suitable to the weak local infrastructure. The goal of this research is firstly to identify suitable water hyacinth use options according to the local conditions and to compare them with the locally used raw materials. The first part of this research identified drivers and barriers for using water hyacinth in the region according to the prevailing socioeconomic conditions. It identified especially the use of water hyacinth as raw material for fertilizers and handicrafts as suitable alternatives for Lake Alaotra. Within the second phase, water hyacinth handicrafts were produced and compared with the predominantly used traditional papyrus handicrafts regarding production path and related costs. It was found that assembling water hyacinth handicrafts was easier and faster and they could be sold at three times the sale prices of the traditional papyrus handicrafts. Within the last part, fertilizers based on water hyacinth (composts, green manure and ash) were locally produced and compared with the commonly used agricultural fertilizers NPK and cow dung. This was done by conducting a growth experiment with Chinese cabbage, a common fast-growing vegetable in the region. Additionally, the production and transportation costs of each type of fertilizer were also taken into account. The results showed high biomass gain of cabbage grown with water hyacinth composts which was also proved be cheaper than using NPK and cow dung. All in all, this research demonstrated the efficiency of water hyacinth use as compost and handicraft as a new source of income for the Alaotra region. However, the poverty and high vulnerability of the local population must be considered along the process for a successful implementation of water hyacinth use at Lake Alaotra. A participatory approach and by offering financial insurance to the farmers during the implementation phase could encourage them to test water hyacinth compost on their own fields. Due to the various external factors influencing the marketing of water hyacinth handicrafts, an intensive and sustained supervision should be provided to the craftswomen.
