42 Biologie
- 42.00 Biologie: Allgemeines
- 42.01 Geschichte der Biologie
- 42.02 Philosophie und Theorie der Biologie
- 42.03 Methoden und Techniken der Biologie
- 42.04 Ausbildung, Beruf, Organisationen
- 42.05 Naturgeschichte
- 42.07 Biogeographie
- 42.10 Theoretische Biologie
- 42.11 Biomathematik, Biokybernetik
- 42.12 Biophysik
- 42.13 Molekularbiologie
- 42.14 Strahlenbiologie
- 42.15 Zellbiologie
- 42.17 Allgemeine Physiologie
- 42.18 Physiologie der Enzyme, Hormone, Sekrete
- 42.20 Genetik
- 42.21 Evolution
- 42.22 Exobiologie
- 42.23 Entwicklungsbiologie
- 42.25 Spezielle Biologie
- 42.30 Mikrobiologie
- 42.32 Virologie
- 42.35 Protistologie
- 42.36 Parasitologie
- 42.38 Botanik: Allgemeines
- 42.40 Pflanzencytologie, , Pflanzenhistologie, Pflanzenmorphologie
- 42.41 Pflanzenphysiologie
- 42.42 Fortpflanzung, Entwicklung
- 42.43 Pflanzengenetik
- 42.44 Pflanzengeographie, Pflanzenökologie, Pflanzensoziologie
- 42.45 Botanische Gärten, Herbarien
- 42.47 Spezielle Botanik: Allgemeines
- 42.48 Kryptogamen
- 42.49 Prokaryota
- 42.50 Phycophyta
- 42.51 Mycophyta, Lichenes
- 42.52 Bryophyta
- 42.53 Pteridophyta
- 42.54 Spermatophyta
- 42.55 Gymnospermae
- 42.56 Angiospermae
- 42.57 Monocotyledoneae
- 42.58 Dicotyledoneae
- 42.59 Botanik: Sonstiges
- 42.60 Zoologie: Allgemeines
- 42.61 Tiercytologie, Tierhistologie
- 42.62 Tiermorphologie, Tieranatomie
- 42.63 Tierphysiologie
- 42.64 Tiergenetik
- 42.65 Tiergeographie, Tierökologie
- 42.66 Ethologie
- 42.67 Fortpflanzung, Entwicklung
- 42.68 Tiergärten, Aquarien, Terrarien
- 42.69 Spezielle Zoologie: Allgemeines
- 42.70 Protozoa
- 42.71 Invertebrata: Allgemeines
- 42.72 Porifera, Coelenterata
- 42.73 Mollusca
- 42.74 Articulata
- 42.75 Insecta
- 42.76 Plathelminthes, Aschelminthes, Nemertini
- 42.78 Echinodermata
- 42.79 Invertebrata: Sonstiges
- 42.80 Vertebrata: Allgemeines
- 42.81 Pisces
- 42.82 Amphibia, Reptilia
- 42.83 Aves
- 42.84 Mammalia
- 42.86 Spezielle Zoologie: Sonstiges
- 42.88 Physische Anthropologie
- 42.89 Zoologie: Sonstiges
- 42.90 Ökologie: Allgemeines
- 42.91 Terrestrische Ökologie
- 42.92 Hydrobiologie
- 42.93 Limnologie
- 42.94 Meeresbiologie
- 42.97 Ökologie: Sonstiges
- 42.99 Biologie: Sonstiges
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Keywords
- Beta-Diversität (1)
- periphyton (1)
The stands surveyed are among the last closed canopy forests in Rwanda. Their exploration began in the early twentieth century and is still ongoing. Previous studies were mainly concerned with plant sociological issues and presented references to environmental factors in anecdotal form, at best using indirect ordination methods. The present study undertakes a classification of the vegetation with numerical methods and establishes quantitative relationships of the species’ distributional structure to environmental parameters using spatially explicit procedures. For this purpose, 94 samples were taken in 100 m² hexagonal plots. Of these, 70 samples are from Nyungwe, 14 are from Gishwati, and 10 are from Cyamudongo. Given the homogeneity of the terrain and vegetation, all vegetation types encountered, all types of stands, and all vegetation strata were included. The beta diversity is expressed by an average Bray-Curtis dissimilarity of 0.92, and in JOST’S (2007) numbers equivalents, 37.90 equally likely samples would be needed to represent the diversity encountered. Within the survey, 1198 species in 127 families were collected. Among the specimens are 6 local endemics and 40 Albertine Rift endemics. Resulting from UPGMA and FCM-NC, 20 to 40 plant communities were established depending on the level of resolution. It can be inferred by means of a Mantel correlogram that the mean zone of influence of a single vegetation stand, as sampled by a 100 m² plot in Nyungwe Forest, ranges between 0.016 and 3.42 km. Of the communities compiled using FCM-NC and UPGMA, 50% consist of individual samples. Beyond undersampling, natural small-scale discontinuities are reflected by this result. Partial db-RDA resulted in an explained variation of 9.60% and 14.41% for environmental and soil factors, respectively. Utilising variation partitioning analyses based on CCA and tb-RDA, between 21.70% and 37.80% of the variation in vegetation data could be explained. The spatially structured fraction of these parameters accounts for between 30.50% and 49.80% of the explained variation (100%). The purely environmental parameters account for a share of 10.30% to 16.30%, whereby the lower limit originates from the unimodal approach and has lost its statistical significance. The soil variables, also after partial analysis, account for a share of 19.00% to 35.70%. While the residual impact of the climatic parameters is hardly significant, the effect of the soil properties is prevalent. In general, the spatially structured fraction of the parameters is predominant here. While on the broad-scale climatic factors, the altitude a.s.l. and the geology are determining factors, some soil parameters and matrix components also show their impacts here. In the mid-range of the scale, it is the forest matrix, the soil types, and the geology that determine species distribution. While in the fine range of the scale, some unrecorded parameters seem to have an effect, there are also neutral processes that determine species composition.
Small headwater streams comprise most of the total channel length and catchment area in fluvial networks. They are tightly connected to their catchments and, thus, are highly vulnerable to changes in catchment hydrologic budgets and land use. Although these small, often fishless streams are of little economic interest, they are vital for the ecological and chemical state of larger water bodies. Although numerous studies investigate the impact of various anthropogenic stressors or altered catchment conditions, we lack an in-depth understanding of the natural conditions and processes in headwater streams. This natural state, however, largely affects how a headwater stream responds to anthropogenic or climatic changes. One of the major threats to aquatic ecosystems is the excessive anthropogenic input of nutrients leading to eutrophication. Nutrients exert a bottom-up effect in the food web, foremost affecting primary producers and their consumers, i.e. periphyton and benthic grazers in headwater streams. The periphyton-grazer link is the main path of autochthonous (in-stream) production into the stream food web and the strength of this link largely determines the effectiveness of this pathway. Therefore, this thesis aims at elucidating important biological processes with the explicit focus on periphyton-grazer interactions. I assessed different aspects of periphyton-grazer interactions using laboratory experiments to solve methodological problems, and using a field study to compare the benthic communities of three morphologically similar, phosphorus-limited, near-natural headwater streams. With the results of the laboratory experiments, I was able to show that periphyton RNA/DNA ratios can be used as proxy for periphyton growth rates in controlled experiments and that the fatty acid composition of grazing mayfly nymphs responds to changes in fatty acids provided by the diet after only two weeks. The use of the RNA/DNA ratio as a proxy for periphyton growth rate allows a comparison of these growth rates even in simple experimental set-ups and thereby permits the inclusion of this important process in ecotoxicological or ecological experiments. The observed fast turnover rates of fatty acids in consumer tissues show that even short-term changes in available primary producers can alter the fatty acid composition of primary consumers with important implications for the supply of higher trophic levels with physiologically important polyunsaturated fatty acids. With the results of the field study, I revealed gaps in the understanding of the linkages between catchment and in-stream phosphorus availability under near-natural conditions and demonstrated that seemingly comparable headwater streams had significantly different benthic communities. These differences most likely affect stream responses to environmental changes.
Estuaries are characterized by a longitudinal salinity gradient. This gradient is one of the main environmental factors responsible for the distribution of organisms. Distinguishing salinity zones is of crucial importance, e.g., for the development of tools for the assessment of ecological quality. The methods most often applied for classifying water according to salinity are the Venice System and the method of Bulger et al. (1993), both of which determine zone boundaries using species occurrences relative to mean salinity. However, although these methods were developed for homoiohaline waters, they have also been routinely applied to poikilohaline systems. I tested the applicability of both methods using salinity and macroinvertebrate data for the poikilohaline Elbe Estuary (Germany). My results showed that the mid-estuary distribution of macro-invertebrates is determined by variation in salinity rather than by mean salinity. Consequently, neither of the two methods is applicable for defining salinity zones in the Elbe Estuary. Cluster analysis combined with a significance test, by contrast, was a better tool for identifying the boundaries of salinity zones in poikilohaline systems.
In many estuaries, such as the Elbe Estuary, a maximum turbidity zone (MTZ) develops, where suspended matter accumulates owing to circulation processes. It is assumed that the MTZ is a stressful environment with an excess of organic matter, high deposition rates, large variations in salinity, and dredging activities. Under such harsh conditions, populations might remain below the carrying capacity, and it is assumed that competition is of little importance, as predicted by the stress gradient hypothesis. I tested whether competition for food is important in the MTZ of the Elbe Estuary using stable isotope analysis of the macroinvertebrate community. The isotopic niches of no two taxa within a feeding group overlapped, which indicated different resource use and the absence of competition. The main reasons for the lack of overlap of isotopic niches were differences in habitat, feeding behavior, and migration behavior.
The Elbe Estuary is nowadays highly industrialized and has long been subjected to a plethora of human-caused alterations. However, it is largely unknown what changes occurred in benthic communities in the last century. Hence, I considered taxonomic and functional aspects of macrobenthic invertebrates of the Elbe Estuary given in data from 1889 (most natural state), 1985 and 1986 (highly polluted state), and 2006 (recent state) to assess benthic community shifts. Beta-diversity analysis showed that taxonomic differences between the sampling dates were mainly due to species turnover, whereas functional differences were predominantly a result of functional nestedness. Species number (S), functional richness (FRic), and functional redundancy reached minimum values in 1985 and 1986 and were highest and rather similar in 1889 and 2006. The decline in FRic from 1889 to 1985/1986 was non-random, consistent with habitat filtering. FRic, functional beta diversity, and S data suggested that the state of the estuary from 1889 was almost re-established in 2006. However, the community in 1889 significantly differed from that in 2006 owing to species replacement. My results indicate that FRic and FR in 1889 could have promoted ecosystem resilience and stability.
