7 search hits
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Exotic Species Invasion and Biodiversity in Bangladesh Forest Ecosystems
(2011)
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Mohammad Belal Uddin
- Both, biological invasion by exotic plant species and biodiversity including spatial patterns and drivers are two major issues in tropical forest ecosystems. This dissertation deals with these two issues in a tropical forest ecosystem in Bangladesh. Considering the first issue, it comprises two manuscripts: a systematic review and a field survey in Bangladesh forest ecosystem. The review was done based on a formalized literature search in order to summarize the approaches that were hitherto applied as well as to mark gaps in tropical invasion research. A considerable number of primary research papers focused on invasion by plants in tropical forests were reviewed. The results identified ample gaps of research. Adressing these gaps may generate promising future research to understand and mitigate this great challenge in different types of tropical forests. Then a case study was conducted to examine the invasiveness and invasibility characteristics in a forest ecosystem of Bangladesh. This study seeks to find out the characteristics of exotic species and relationships between native species richness, environmental variables, disturbances and exotic plant invasion in this ecosystem. Boosted Regression Trees and Detrended Correspondence Analysis are used to determine these relationships. Most exotics are trees followed by shrubs and herbs. Fabaceae and Asteraceae contribute a large proportion of exotic species. Most of them originated from other tropical areas. Native species richness was found to be the best predictor for the number and percentage of exotic species in the study area. However, a unimodal relationship was found. Multiple other factors also influence the success of exotic species. The number and the percentage of exotic species are positively correlated with frequency of disturbances and with soil attributes (phosphorus and bulk density) but negatively correlated with topography (elevation) and conservation patterns (protection). Considering the biodiversity issue, it encompases another two manuscripts based on a case study conducting a systematic field work in the same forest ecosystem of Bangladesh. They are the first spatially explicit analysis of drivers and patterns of biodiversity in this terrestrial ecosystem based on multivariate approaches, similarity analysis and variation partitioning. One manuscript assesses the relationships between landscape and habitat characteristics, conservation patterns, and plant diversity in this tropical forest ecosystem. This study analyses the effects of soils, topographic conditions, disturbances and nature protection on plant species richness and species composition. The results reveal that biodiversity patterns in the study area are positively correlated with protection and elevation. These patterns are, however, negatively correlated with disturbances. The other manuscript focuses on the stand characteristics and spatial patterns of biodiversity as they are rarely studied in the tropics in general and in Bangladesh in particular. Data on tree species are used as they are the most conspicuous element of these ecosystems. Tree species composition was recorded in a systematic plot design and diameter was measured at breast height for each individual tree. Distance-decay approach was applied to analyze the spatial pattern of biodiversity for the whole study area and two subsamples from Satchari National Park and Satchari Reserve Forest. Analyses showed that biomass increased significantly with protection status. Plots in the Reserve Forest were associated with higher species turnover than in the National Park. This dissertation identifyies, for the first time in a systematic approach, the major drivers for invasion and biodiversity pattern in a forested area in Bangladesh. In conclusion, both, biological invasion by exotic plant species as well as biodiversity are strongly related to the disturbance regime and nature protection.
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Structuring Descriptive Data of Organisms — Requirement Analysis and Information Models
(2007)
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Gregor Hagedorn
- Data that describe organisms in a structured form are indispensable not only for taxonomic and identification purposes, but also many phylogenetic, genetic, or ecological analyses. By analyzing existing information models and performing selected fundamental requirement analyses, the present work contributes to a broadening of the understanding of these forms of data. It falls into an interdisciplinary area between biology and information science. The term “descriptive data” is understood here in a broad sense: As descriptions of individuals, populations, or taxa, intended for various purposes (e. g., genetic, phylogenetic, diagnostic, taxonomic, or ecological), and covering a wide array of observation methods and data types (e. g., morphological, anatomical, genetic, physiological, molecular, or behavioral data). The position of descriptive data in the context of biodiversity framework concepts (covering, e. g., nomenclatural data, specimen collection data, or resource management) is discussed. A number of fundamental problems arise when modeling biological descriptive data. The ways in which existing data exchange formats, information models, and software applications address them are studied and future possible solutions are outlined. One such solution, the information model for the software “DiversityDescriptions (DeltaAccess)” is one of the results of this thesis and fully documented (Ch. 7). This entity relationship model fully supports the concepts of the traditional DELTA data exchange format (Description Language for Taxonomy; TDWG standard since 1986). If further improves on DELTA by introducing “modifiers” as a new terminology class, by introducing a more flexible system of handling statistical measures, by improving the handling of multilingual data sets, by supporting subset and filter features for concurrent collaborative editing (instead of supporting these for report-generation purposes alone), by supporting improved character attributes to create natural language descriptions from structured descriptions, and by adding metadata for a data set to improve the ability of data exchange without external documentation. In preparation of a future improved information model for descriptive data, the results of three requirement analyses are presented: a data-centric analysis of general concepts, a process-centric analysis of identification tools, and a high-level use case analysis. The first analysis (Ch. 4) is a structured inventory of fundamental approaches and problems involved in collecting and summarizing scientific descriptions of organisms. It is informed in part by current practices in information science, comparative data analysis, statistical, descriptive or phylogenetic software applications, and data exchange formats in biodiversity informatics. At the end three topics are discussed in particular detail (“Federation and modularization of terminology”, “Modifiers”, and “Secondary classification resulting in description scopes”). Except for phylogenetic analyses, identification is the most common usage of descriptive data. The second analysis (Ch. 5) therefore studies the processes, data structures, presentational and user interface requirements for printable and computer-aided identification tools (“keys”). Finally, a general use case analysis is performed with the goal of creating a framework of high-level use cases into which present as well as future requirements may be integrated (Ch. 6). All three requirement analyses are explorative and do not fulfill formal criteria of software engineering. They identify many requirements not addressed by the relational DiversityDescriptions model. Some of these could only be explored and await future solutions. For others solutions are proposed (some of which could already be incorporated into the design of SDD, an xml-based TDWG standard since 2005): The traditional data types are changed into an extensible character type model. The importance of data aggregation concepts was recognized to be fundamental. Complementary to data aggregation, the present and potentially future use of data inheritance along the lines of the taxonomic hierarchy is briefly studied. The concept of calculated characters could be addressed only insofar as the mapping between values can potentially be generalized. Character decomposition models are studied, but ultimately the traditional character concept, supplemented with a forest of ontologies for compositional and generalization concept hierarchies, is preferred as a more general concept. Both the traditional character subset and character applicability models can be integrated into concept hierarchies.
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Direct Amino Acid Uptake by Plants related to Grassland Diversity - methodological and ecological Investigations
(2009)
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Leopold Sauheitl
- Uptake of intact amino acids by plants has been identified as an alternative nitrogen (N) source for plants in a number of ecosystems and soil types. Up to now it is assumed that this uptake strategy is of particular relevance in ecosystems with low mineral N (Nmin) contents due to insignificant microbial activity or due to poorly developed soils. However, it has also been discussed that amino acid uptake might enable plants to lower intracspecific competition for mineral N and shortcut the microbial mineralization of organic N in systems were competition is exceptionally high. The positive effect of plant diversity on plant productivity is known to induce conditions of intense N competition and thus amino acid uptake might explain how plant communities enable higher productive with increasing diversity. However, the ecological importance of organic N uptake has also been questioned due to the high competitive power of microbes in soils of the temperate zone and due to a number of flaws in the commonly used method to proof and quantify direct amino acid uptake. In this, dual labelled (13C and 15N) amino acids are injected into the soil and direct tracer uptake is quantified via bulk isotope measurement of 13C and 15N enrichment in plant tissues, which recently has been challenged to exclusively reflect direct amino acid uptake. The first objective therefore was to identify and reduce methodological influences on the direct amino acid uptake by plants. Thus the effect of changed amino acid concentrations on amino acid uptake was investigated by application of different tracer amounts. Next, the accuracy and precision of commonly used bulk isotope measurements were compared to compound specific measurements with respect to the determination of direct amino acid uptake. It was shown that the use of high tracer amounts accompanied by high Nmin release reduces direct amino acid uptake via plant internal down regulation of amino acid transporters. This corroborates the importance of minimizing tracer amounts and suggests that plants can actively increase amino acid uptake when N availability in soil is low. Bulk measurements turned out to overestimate direct amino acid uptake by a factor of up to six, as they were not able to separate uptake of intact tracer molecules from uptake of tracer fragments or inorganic carbon. At the same time compound specific isotope measurements proofed to be an accurate and precise tool to demonstrate and quantify uptake of intact amino acids. Using these optimized methods, the importance of amino acid uptake for the N-nutrition of plants with respect to changing plant diversity was investigated. The uptake of amino acids and mineral N by plants as well as the competition between plants and microbes for amino acid N was investigated in grassland communities with 1 to 16 grassland species. Microbes were superior competitors for amino acid derived nitrogen, irrespective of plant diversity and took up 54% of the applied amino acid N in average within 24 h. In contrast, plants only incorporated 2.7% of the applied N and were thus less effective by a factor of 20 in short term N acquisition than microbes. In addition, plant mineral N uptake decreased with increasing plant diversity while uptake of intact amino acids increased. Thus the contribution of amino acid uptake to the overall plant N nutrition increased from 1.5 to 7.0% in which amino acid uptake was mainly controlled by plant N concentration shoot biomass and rooting density while mineral N uptake was controlled by microbial competition. In detail amino acid uptake increased with decreasing plant N concentration while mineral N uptake decreased with increasing microbial abundance and microbial N uptake. Thus, the boosted importance of amino acid uptake for plant N nutrition has to be seen as a reaction on increased N competition with increasing plant diversity. Additionally, plant diversity stimulated microbial diversity which was most likely due to the bottom up effect of increased root exudation and litter input caused by increasing N competition and plant productivity, respectively. While the microbial community was dominated by bacteria (54.7%) the abundance of litter and soil organic matter decomposing gram positive bacteria and fungi as well as protozoan abundance increased with increasing plant diversity. Protozoa are known to stimulate turnover of bacteria which was indicated by higher tracer incorporation of this microbial group and an overall increase of deaminase activity with increasing plant diversity. As higher microbial turnover is associated with increased loss of microbial N to plants, we have to expect higher N availability for plants in the long term. The positive feedback of a plant-induced higher microbial turnover rate on N availability in soil together with an increased amino acids uptake might therefore be an important model to explain the positive effect of plant diversity on plant productivity.
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Soil microbial community structure and function of agriculturally used Mollisols in the periurban area around Buenos Aires, Argentina, with emphasis on pesticide and heavy metal contamination
(2007)
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Thorsten Ullrich
- Buenos Aires, the capital of Argentina is surrounded by an agricultural green belt with fertile Mollisols, which provides the entire supply especially for vegetables of the city. The fast growing population is causing a decrease in the agriculturally available area on the one hand and also a higher demand for food on the other hand. Therefore, an intensification of agriculture and the maintenance of sustainable soil fertility are of essential importance. However, the population is increasingly concerned about an environmental contamination because of an enhanced application of pesticides and heavy metal containing fertilisers in the course of which organic management systems are getting increasing attention. The green belt is agriculturally used in manifold ways. Besides fallows and pastures, organic and conventional cultivations are conducted on open fields and under greenhouses, while also anthropogenically unaffected areas with soils representing a reference for natural soil condition still exist. The objectives of this dissertation were to examine whether inputs of pesticides and heavy metals cause soil pollution and whether the different land use systems lead to an alteration of soil microbial community structure and function. Additionally, it was investigated whether conventional cultivation leads to a soil quality deterioration and if a replacement by organic cultivation can improve this situation. With the aid of a field experiment it was also tested whether land use conversion from a fallow to typical management systems influences soil microbiology, why special emphasis was put on conventional as well as on organic cultivation and pesticide application. Exclusively in top soils of conventionally managed fields pesticides were quantified up to 34.2 µg/kg. The mean heavy metal concentrations did not differ significantly from natural background contents and between the diverse land use systems. A contamination hazard coming from pesticides and heavy metals was regarded as low and consequently, no risk potential for the ecosystems were expected. For the characterisation of the soil microbial community structure and function in soils of the different land use systems twenty phospholipid fatty acids and the following parameters were examined, respectively: enzyme activities (acid phosphatase, arylsulfatase, cellulase, dehydrogenase and urease), basal and substrate-induced respiration, soil microbial biomass, metabolic quotient, net nitrogen mineralisation, net nitrification and potential denitrification. Two principal component analyses were carried out, one for the structural and one for the functional parameters. For the first ones six microbial taxonomic groups were distinguished, while for the latter four principal components (microbial capacity, mineralisation activity, nitrogen transformation potential and metabolic activity) were extracted. With the aid of a subsequent discriminant analysis calculated by the functional data six independent land use groups could be differentiated. Nearly all soils of conventionally managed greenhouses as well as those of organically managed greenhouses and agricultural fields, pastures and the reference were allocated to the expected groups. Only soils of conventionally managed agricultural fields and fallows were combined into one group exhibiting high similarities between these two land use systems. All microbial taxonomic groups showed a reduction in biomass due to agricultural use, while a shift of relative contributions to the total biomass was hardly observable. A differentiation of the land use systems by a discriminant analysis calculated by the structural data was not possible. In the field experiment with the aid of two discriminant analyses calculated by both the data of the structural and the functional parameters it could clearly be distinguished between conventionally and organically managed as well as non-treated and fallow soils. However, a differentiation between soils of the same management with respect to different pesticide applications and varying application amounts was not possible. Finally, correlations between phospholipid fatty acid contents of all analysed microbial taxonomic groups and soil microbial functional parameters were found indicating close connections between soil microbial community structure and function. Hence, the microbial community composition on its own is of no indicator value for soil quality and has to be combined with functional properties. Recapitulatory, it can be concluded that the Mollisols of the green belt around Buenos Aires are not sensitive against intensive agricultural utilisation.
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Diversity and species composition of two different moth families (Lepidoptera: Arctiidae vs. Geometridae) along a successional gradient in the Ecuadorian Andes
(2005)
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Nadine Hilt
- The diversity of two very species-rich families of arctiid and geometrid moths was investigated in a montane area in the Andes in southern Ecuador (Reserva Biológica San Francisco, 3°58´ S, 79°5´ W) along a succession gradient ranging from a barely vegetated landslide area to mature forest understorey between 1,800 and 2,005 m above sea level. This study was part of a larger interdisciplinary project on diversity and functioning of a tropical mountain rainforest ecosystem. Moths were collected during three field periods in the years 2002 (March to April, October to November) and 2003 (August to October) at the 15 succession sites. Moths were manually sampled by attraction to weak light sources (2 x 15 W tubes: black light and super-actinic light) in a white gauze cylinder from 18:45 to 21:45 h. Data from this study (15 succession sites) were compared with data from six natural forest understorey sites sampled in the years 1999 and 2000 in the same region. A total of 9,211 arctiid moths representing 287 species, of which 135 belong to the tribe Phaegopterini, followed by Ctenuchini/Euchromiini (82), Lithosiinae (54), Pericopini (9), and Arctiini (7), as well as 23,720 geometrid moths representing 868 species were recorded at 21 sites. Large proportions of the samples (Arctiidae: 70.4% of species, 76.1% of individuals; Geometridae: 65% of species, 78.1% of individuals) were identified to species level. The study deals with patterns of alpha- and beta-diversity, ensemble structure, wing colouration and various other morphological traits of arctiid moths along the succession gradient. In addition, temporal dynamics of moth ensembles as well as the role of environmental factors such as temperature or habitat openness as predictors of faunal change at small spatial scales were investigated.
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How availability and quality of nectar and honeydew shape an Australian rainforest ant community
(2003)
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Nico Blüthgen
- Ant communities visiting nectar and honeydew sources were studied in a tropical lowland rainforest in North Queensland, Australia. The study focused on the hypothesis whether the distribution and composition of nectar and honeydew diets influence resource partitioning and competition in the ant community, and thus regulate community composition. Ants were the most common consumers on all extrafloral nectaries, while they constituted only a minority of floral visitors. In total, 43 ant species were observed to consume nectar from extrafloral nectaries (34 plant species) or from flowers (14 plant species), and wound sap exudates (three plant species). Six nectar-foraging ant species attended trophobionts (including at least 12 species of homopterans and two species of lycaenid caterpillars) for honeydew. Ant species showed a significant compartmentalisation of nectar use across plant species, although most ant species visited a broad spectrum of plants that strongly overlapped between different ants. Trophobioses were much more specialised at the study site, and some ant species attended certain trophobionts exclusively. On each plant individual, only a single ant colony was observed attending trophobionts. In contrast, simultaneous co-occurrences between different ant species foraging for nectar on the same plant individuals were common (observed in 23% of the surveys), although these proportions varied strongly across plant and ant species. The two most dominant ant species (Oecophylla smaragdina and Anonychomyrma gilberti) had mutually exclusive territories, and they were each associated with a significantly different assemblage of other ant species on nectar plants. This community pattern corresponds with the concept of ant mosaics that is based on dominance hierarchies. Honeydew and nectar sources varied substantially in carbohydrate and amino acid concentration and composition (HPLC analyses). There was a strong relationship between the composition of these resources and their use by ants, in particular by the dominant O. smaragdina. Among all 32 nectar and honeydew sources analysed, resources actually consumed by this ant were characterised by relatively similar amino acid profiles and higher total sugar concentration. The most common diets of O. smaragdina included two honeydew sources (Sextius ‘kurandae’ membracids on Entada phaseoloides and Caesalpinia traceyi legume lianas) and two extrafloral nectars (Flagellaria indica and Smilax cf. australis) that had the broadest spectrum of amino acids. Furthermore, these trophobioses on lianas showed a significantly higher per capita recruitment of this ant species (number of workers per individual homopteran) compared to trees. F. indica and S. cf. australis extrafloral nectaries were also commonly monopolised by O. smaragdina in a similar way as trophobioses; co-occurrences were significantly rarer than at other nectar sources. Field experiments on nectar preferences were performed using artificial sugar and amino acid solutions in pairwise comparisons. Preferences among sugars were largely concordant between ant species. For most ant species, sucrose was more attractive than any other sugar, and attractiveness increased with sugar concentration. Most ant species also preferred sugar solutions containing mixtures of amino acids over pure sugar solutions. However, choices between different single amino acids in sugar solutions varied substantially and significantly between species. Preferences between solutions were significantly reduced in the presence of competing ant species. Thus the experiments show that both variability in gustatory preferences, especially for amino acids, and conditional effects of competition may be important for resource selection and partitioning in nectar feeding ant communities. Stable carbon and nitrogen isotope composition was analysed for 50 ant species, and additionally for associated plants, homopterans and other arthropods from the study site. Nitrogen isotope ratios (d15N) of ants were not correlated with those of plant foliage from which the ants were collected. Instead, d15N may represent a powerful indicator of trophic position of omnivorous ants like in other foodweb studies, suggesting that members of the ant community spread out in a continuum between largely herbivorous species, feeding on nectar or honeydew, and predatory taxa. Variability between colonies of the same species was also pronounced. d15N values of O. smaragdina colonies from mature forests, where most of their nectar and honeydew sources are found, indicate lower trophic levels than isotope signatures of colonies from open secondary vegetation. This study demonstrates that the distribution and quality of honeydew and nectar sources have a strong structuring impact in diverse tropical ant communities. Amino acids were found to play a key role for ant species preferences and competition, and for nitrogen fluxes to colonies of the arboreal ant fauna.
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Diversity of geometrid moths in a montane rainforest in Ecuador
(2002)
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Gunnar Brehm
- The diversity of the very species-rich family of geometrid moths was investigated in a montane forest at the border of the Podocarpus National Park in southern Ecuador along an altitudinal gradient ranging from 1,040 m to 2,677 m above sea level. This study is part of a larger interdisciplinary project on diversity and functioning of a montane forest ecosystem. A total of 13,938 moths representing 1,010 species were sampled in light-traps at eleven elevational levels (two replicate sites each). Most species belonged to the subfamily Ennominae (500 sp.), followed by Larentiinae (391 sp.), Sterrhinae (58 sp.), Geometrinae (57 sp.), Oenochrominae (3 sp.), and Desmobatrinae (1 sp.). The study covers aspects of host-plant relationships, community structure, endemism, alpha-, beta-, and gamma-diversity. The role of different environmental factors as mechanisms for the diversity of the moths is discussed. Furthermore, methodological aspects of light-trap sampling, and selection of appropriate diversity measures and analytical tools are considered in this study.
