Biologische Hochschulschriften (Goethe-Universität)
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In over 100 genera of tropical angiosperms, one or more species possess specialised structures for housing ants. The longevity and intimacy of these associations has often facilitated an increasing specialisation of both the ants and the plants, leading to a number of highly specific and obligate symbioses. Early literature contained only few anecdotal reports of the ant genus Cladomyrma WHEELER inhabiting (unidentified) plants. This work presents the new findings on Cladomyrma and its host plants that accumulated over the last two decades. My studies of Cladomyrma reveal that there is a largely overlooked community of south-east Asian plant-ants and their associated plants. Currently the genus consists of at least 12 species. Cladomyrma has been thought to be restricted to the ever-wet part of the West Malesian floristic region, comprising the Malay Peninsula, Borneo, and Sumatra, but recent collections from Thailand and Vietnam indicate that species of the genus penetrate the seasonal tropical forests of Continental Asia. Cladomyrma inhabits 24 plant species belonging to a surprisingly extensive range of plant taxa: Callerya, Saraca, Spatholobus (Fabaceae), Crypteronia (Crypteroniaceae), Drypetes (Putranjivaceae), Ryparosa (Achariaceae), Strychnos (Loganiaceae), Neonauclea (Rubiaceae), Luvunga (Rutaceae) and Sphenodesme (Verbenaceae). In terms of taxonomic diversity on the genus and family level the range of hosts utilised by Cladomyrma is one of the broadest ever recorded for any live stem-nesting plant-ant lineage worldwide. This work provides a species-level overview of all Cladomyrma host plants known from Borneo, the Malay Peninsula and Sumatra, including descriptions of ant-housing structures (domatia), ant inhabitant identity, onset of colonisation during plant ontogeny, nest structure, occupancy rate, and considerations of results obtained from herbarium specimens. Both the regularity of ant association and the degree of morphological specialisation toward myrmecophytism are assessed. The behavioural traits of Cladomyrma are compatible with traits exhibited by other protective plant-ants. This work demonstrates that all species of Cladomyrma investigated (dianeae, maschwitzi, yongi, petalae) confer antiherbivore protection to young leaves of its host. The ants also attack and repell or kill herbivorous insect larvae encountered on young foliage. Cleaning behaviour appears to be a trait shared by all members of the genus, and the two species tested (maschwitzi, petalae) successfully removed termite eggs experimentally placed onto young leaves. Another trait common to all known species of the genus is that the ants preferentially patrol young shoots and leaves ('neophily'). These behavioural traits of Cladomyrma likely reduce stem damage and pathogenic infection of their host. The ants prune encroaching vegetation (tested in dianeae maschwitzi, petalae, yongi, observed in crypteroniae) and attack paper tape used to mark host plants (observed in andrei, dianeae, hobbyi, nudidorsalis, maschwitzi, yongi, petalae). If these traits combined translate into a better reproductive success of the hosts has yet to be verified. Evidence for lifetime fitness benefits is particularly difficult to quantify for the long-lived woody host plants of Cladomyrma. The predominant food source of Cladomyrma appears to be the honeydew of scale insects (Coccidae and Pseudococcidae) which the ants tend inside their nest cavities. Observations on scale insect acquisition by Cladomyrma foundress queens show that hemipteran trophobionts are not transported by the queens on their nuptial flight but they nevertheless arrive on the host plant independently of the ants. Entry into nest chambers is facilitated by small holes kept open by the foundress queen. Most Cladomyrma species have been recorded from only one or two (three) host plant species (andrei, crypteroniae, hobbyi, maschwitzi, nudidorsalis, scopulosa, yongi), but two species, Cladomyrma petalae and C. dianeae, are more catholic in their host usage; the first being a 'generalist' plant-ant colonising hosts across a broad taxonomic range, the second inhabiting several members of the genus Neonauclea. First results of host-choice experiments with C. petalae are presented and the potential mechanisms promoting host specificity are discussed. My studies of the Cladomyrma/plant associations indicate that codiversification and host shifts or host expansions, rather than cospeciation, shape the pattern of species interactions in this system. Finally, I propose a scenario in which three key traits of Cladomyrma –access to live stems, utilisation of indirect food rewards via trophobionts and 'neophily'– are hypothesised to favour niche differentiation and the acquisition of new hosts over evolutionary time.
There is increasing evidence that climate change will have a severe impact on species’ distributions by altering the climatic conditions within their present ranges. Especially species inhabiting stream ecosystems are expected to be strongly affected due to warming temperatures and changes in precipitation patterns. The aim of this thesis was to
investigate how distributions of aquatic insects, i.e., benthic stream macroinvertebrates would be impacted by warming climates. The methods comprised of an ensemble forecasting technique based on species distribution models (SDMs) and climate change scenarios of the Intergovernmental Panel on Climate Change of the year 2080. Future model projections were generated for a wide variety of species from a number of taxonomic orders for two spatial scales: a stream network within the lower mountain ranges of Germany, and the entire territory across Europe. In addition, the effect of the modelling technique on habitat suitability projections was investigated by modifying the choice of study area (continuous area vs. stream network) and the choice of predictors (standard vs. corrected set).
Projections of future habitat suitability showed that potential climate-change impacts would be dependent on species’ thermal preferences, and with a similar pattern for both spatial scales. Future habitat suitability was projected to remain for most or all of the modelled species, and species were projected to track their climatically suitable conditions by shifting uphill along the river continuum within the lower mountain ranges, and into a north-easterly direction across Europe. Cold-adapted headwater and high-latitude species were projected to lose suitable habitats, whereas gains would be expected for warm-adapted river and low-latitude species along the river continuum and across Europe, respectively. Additionally, habitat specialist species in terms of endemics of the Iberian Peninsula were identified as potential climate-change losers, highlighting their restricted habitat availability and therefore vulnerability to warming climates.
The main findings of this thesis underline the high susceptibility of stream macroinvertebrates to ongoing climate change, and give insights into patterns of possible consequences due to changes in species’ habitat suitability. Concerning the methodology, a clear recommendation can be given for future modelling approaches of stream macroinvertebrates by building models within a stream network and with a careful choice of environmental predictors, to reduce uncertainties and thus to improve model projections.
Understanding major causes of biodiversity and range dynamics requires research on evolutionary processes under consideration of environmental changes. In my thesis, I investigated the spatio-temporal evolution of the Neotropical tree genus Cedrela from the Meliaceae family by studying its genetic diversity, taxonomy, colonization history, climatic niche changes and dynamics of species distributions. My results show that climatic and geological changes are major drivers of biological diversification in Cedrela.
In almost all parts of the world the industrialisation grows continuously and thus, the chemical pollution of natural waters has become a major public concern. A major consequence and one of the key environmental problems we are facing today is the increasing contamination of freshwater systems with chemicals. The chemicals are detected in wastewater, surface (river) water, ground water and drinking water ubiquitously in natural waters and not only in industrialised areas. The main point sources for water pollution and the release of these synthetic organic substances of human origin, so called micropollutants (MPs), are wastewater treatment plants (WWTPs). These MPs such as pharmaceuticals, personal care products, disinfectant chemicals, chemicals used in the industry and in households, contraceptives, hormones, food additives, artificial sweeteners, pesticides, biocides, and many emerging contaminants are only incompletely removed by the existing conventional wastewater treatment technologies. The MPs end up in the water cycle and have adverse effects on wildlife aquatic ecosystems and human health even at very low concentrations. Therefore, advanced wastewater treatment (AWWT) technologies, such as ozonation, treatment with activated carbon, biofiltration, membrane bioreactors (MBRs) or exposure to ultraviolet light are investigated as options to upgrade conventional WWTPs. However, several studies show that especially the ozonation of wastewater generates diverse transformation products (TPs) with unknown properties. These TPs could be more toxic than the mother compound. Thus, a post-treatment after the ozonation process is required.
The present thesis was part of the BMBF-funded TransRisk project dealing with “the characterisation, communication, and minimisation of risks of emerging pollutants and pathogens in the water cycle”. One main objective was the investigation of conventional treated wastewater after a full-scale ozonation with four post-treatments (each non-aerated and aerated granular activated carbon (GAC) filtration and biofiltration) in comparison to a MBR treatment of raw (untreated) wastewater separately and in combination with an additional ozonation on a pilot WWTP. For this purpose, the wastewater samples were characterised with a comprehensive battery of in vitro and in vivo bioassays. The in vitro bioassays were performed to detect endocrine activities (such as (anti)estrogenic and (anti)androgenic activities), genotoxicity, and mutagenicity. The results showed a decreased estrogenic activity due to the conventional wastewater treatment as well as the ozonation, but a distinct increase of the anti-estrogenic activity and the mutagenicity in the ozonated wastewater, possibly caused by new formed TPs, that were reduced after the post-treatments whereas the GAC filtration performed better than the biofiltration. The in vivo bioassays included for example the impact of the wastewater on mortality, reproduction, development, and energy reserves of the test organisms. The in vivo on-site tests with the mudsnail Potamopyrgus antipodarum and with the amphipod Gammarus fossarum indicated a major impact of conventional treated wastewater, ozonated wastewater, and MBR treated wastewater. The flow channel experiments in the laboratory with Gammarus pulex pointed to a serious impact of an estrogenic effluent on life-history traits of the amphipod. Finally, an ozonation of the wastewater with subsequent GAC filtration represented the most promising option. In addition, chemical analyses of 40 selected MPs, so called tracer substances, performed in parallel to the in vitro and in vivo bioassays underlined this assumption.
A second main objective was the optimisation of the preparation of water and wastewater samples for ecotoxicological in vitro bioassays because common sample preparation techniques are predominantly adapted for chemical analyses. Therefore, the impact of sample filtration, long-term acidification with following neutralisation as well as the enrichment with solid phase extraction (SPE) in combination with short-term acidification were investigated using amongst others raw (untreated) wastewater, hospital wastewater, conventional treated and ozonated wastewater, surface water, and ground water. Overall, eleven in vitro bioassays were performed for the detection of endocrine activities, genotoxicity, and mutagenicity. The results show that sample filtration and acidification/neutralisation significantly affected the outcome of the bioassays especially the anti-estrogenic activity and the mutagenicity whereas the sample filtration had a minor impact than the acidification. Thus, the testing of untreated (waste)water samples is advisable because the sample is minimally processed. Furthermore, the SPE extracts showed in parts high cytotoxic effects whereby no conclusions on the results of the bioassays were possible. However, the enrichment of endocrine activity and mutagenicity was predominantly effective but depended on the used SPE cartridge and the pH value of the (waste)water samples. Based on the results the use of a Telos C18/ENV cartridge and an acidified sample is recommendable. In the end, there is a need to optimise the sample preparation for in vitro bioassays to reach their maximum outcome for the best possible assessment of the water quality.
Invasive non-native species are key components of human-induced global environmen-tal change and lead to a loss of biodiversity, alterations of species interactions and changes of ecosystem services. Freshwater ecosystems in particular are strongly affect-ed by biological invasions, since they are spatially restricted environments and often already heavily impacted by anthropogenic activities. Recent human-induced species invasions are often characterized by long-distance dispersal, with many species having extended their native distribution range within a very short time frame. However, a long term view into the past shows that biological invasions are common phenomena in nature—representing the arrival of a species into a location in which it did not originally evolve—as a result of climatic changes, geotectonic activity or other natural events. Once a species arrives in a new habitat, it may experience an array of novel selection pressures resulting from abiotic and biotic environmental factors and simultaneously act as a novel selective agent on the native fauna. Consequences of species invasions are manifold. My thesis, which combines seven studies on different aspects of biological invasions, aims to explore the influence of abiotic stressors and biotic interactions during species introductions and range expansions, as well as the consequences of biological invasions on evolutionary and ecosystem processes.
The first part of my thesis examines human-induced biological invasions, dealing with basic ecological characteristics of invaded ecosystems, novel predator-prey interactions, functional consequences of species invasions and certain behavioral traits that may contribute to the invasiveness of some species. The second part of my thesis examined distribution patterns and phenotypic trait divergence in species that historically invaded new geographical areas. I investigated variation of abiotic and biotic selection factors along a stream gradient as well as ecological and evolutionary consequences of species invasions to extreme habitats. The results highlight the importance of simultaneously considering processes involved in natural invasions and during human-induced invasions to understand the success of invading species.
We often lack detailed information on the impacts of historical biological inva-sions. Also, we are currently lacking crucial knowledge about the time scales during which different mechanisms (behavioral flexibility, plastic phenotypic changes, and ge-netic adaptation) play a role during biological invasions and affect species exchange and establishment. Comparative analyses of historical, natural invasion and recent (man-made) invasions can provide insights into the relative importance of the processes governing adaptation to abiotic stressors and selection resulting from biotic interactions. Beyond their negative effects, the establishment of invasive species and the subsequent range expansion represent “natural experiments” to investigate fundamental questions in ecology and evolution. My comparison of natural and human-induced biological invasions revealed that in many cases preadaptation to altered abiotic conditions plays a key role during early stages of invasions and range expansions. Considering the evolutionary history of invasive species and the evolutionary history of the recipient native fauna might therefore help predict the consequences of biological invasions for the ecosystem under consideration and the future success of the invading species. This knowledge can also be implemented when formulating conservation strategies, including methods to mitigate and manage human-induced biological invasions.
In der vorliegenden Arbeit konzentrierte ich mich auf mediterrane wirbellose Tierarten, welche sich als Konsequenz ihrer Lebensweise nur schlecht ausbreiten können. Nichtsdestotrotz haben es Süßwasserkrabben der Gattung Potamon und Landschnecken der Gattung Tudorella geschafft, große Gebiete zu besiedeln, die heute durch das Mittelmeer getrennt sind. Für beide Gruppen wurde spekuliert, dass Menschen an ihrer Ausbreitung beteiligt waren. Es war mein Ziel die biogeographischen Muster dieser beiden Gattungen zu analysieren und abzuschätzen, ob Menschen tatsächlich Vektoren ihrer Ausbreitung waren. Meine Analysen fanden auf drei Ebenen statt: Taxonomie, Gattung und Art.
Antagonistic and mutualistic species interactions provide important ecosystem functions affecting plant population dynamics and distribution. Many of these functions are important for the regeneration of plants, either by limiting or facilitating successful transition between life stages. Interactions can occur across the whole geographical range of a species and thereby encompass different environmental gradients, such as changes in temperature or water availability. Understanding the joint effects of species interactions and environmental factors on the regeneration of plants is key for understanding plant population dynamics under global change and could provide important recommendations for managing and conservation efforts.
My thesis aimed at advancing the knowledge of how species interactions depend on environmental conditions and jointly affect plant recruitment along the elevational distribution of plants. This thesis includes three chapters in which I studied the effects of animal seed deposition, seed predation, mycorrhizal and pathogenic fungi occurrences as well as abiotic and biotic environmental factors on the recruitment of Swiss stone pine (Pinus cembra). I conducted fieldwork in the Swiss Alps across the entire elevational distribution of the pine (1850 – 2250 m a.s.l). Over a period of three years, I recorded animal seed deposition by spotted nutcrackers (Nucifraga caryocatactes) and conducted seed translocation experiments. Further, I assessed fungal communities using DNA metabarcoding. I measured abiotic environmental factors such as temperature, water and light availability, pH, as well as biotic environmental factors such as distance to conspecific adults and ground vegetation cover. In my thesis, I used a broad range of community ecology approaches, from seed dispersal ecology to experimental plant ecology and microbial ecology.
First, I investigated the effects of environmental factors on four recruitment processes (i.e. seed deposition, seed predation, seed germination, seedling survival) of Swiss stone pine. Further, I aimed at identifying the most important recruitment processes potentially limiting pine regeneration across its elevational range. To investigate pine recruitment, I firstly tested how seed deposition, seed predation, seed germination and seedling survival were affected by the microhabitat characteristics ultimately determining where a seed arrives in the environment (i.e. canopy cover & ground vegetation cover). Secondly, I applied a sensitivity analysis to investigate which of the four recruitment processes poses limitation to the pines’ regeneration across its range. My results reveal that the importance of particular recruitment processes varies along the pines’ elevational range. I found that at the lower range margin and the distribution centre seed germination and seedling survival were the main limiting factors, whereas animal-mediated seed dispersal became especially important at the upper range margin. My study contributes to the field with a new approach for disentangling the relative importance of recruitment processes across environmental gradients and thereby could help to project how plant recruitment might respond to future changes in environmental conditions.
The second aim of my study was to investigate how abiotic and biotic environmental factors affect the occurrence of Swiss stone pine-associated pathogenic and mutualistic fungi by combining field measurements of environmental factors with a DNA metabarcoding approach. I identified potentially important fungal interaction partners of the pine and determined drivers shaping their occurrences. My results reveal that generalist fungi were not affected by abiotic and biotic environmental factors. However, specialist pathogens showed patterns according to the Janzen-Connell framework (i.e. accumulation of pathogen close to adult plants). Interestingly, I found evidence for an “inverse” Janzen-Connell effect, i.e. high abundance of a specialist mutualist close to adult plants, potentially mitigating effects of soil pathogens close to parent trees. Further, I found that pine-associated fungi are distributed widely within and beyond the range of their host plant, adding knowledge on how mutualisms and antagonisms might be affected when plants move their distributional range upwards.
Finally, I investigated how known and unknown plant-associated fungi affect the regeneration of Swiss stone pine in an environmental context. My results suggest that seedling establishment was most strongly affected by abiotic environmental factors, such as light availability and maximum summer temperature. Further, the results indicate that seedling survival was affected by biotic environmental factors, i.e. fungal agents, with high abundances of a known fungal pathogen co-occurring with low seedling survival rates. My results also reveal that known mycorrhizal partners as well as a large number of unknown fungal operational taxonomic units (OTUs) were associated with the survival of seedlings. My findings highlight the importance of plant-fungal interactions for plant recruitment and offer a feasible approach for the identification of hidden plant-fungal associations in highly complex DNA metabarcoding datasets. This approach offers a valuable tool for investigating plant-microbe interactions, ultimately helping to understand plant population dynamics.
My dissertation adds to a deeper understanding on the linkage between plant regeneration and species interactions, especially on how plant-animal and plant-fungal interactions in concert with environmental factors shape plant recruitment. My study reveals the importance of animal-mediated seed dispersal and fungal pathogens in plant recruitment with consequences for potential range shifts of plant species. My thesis has important implications for conservation and management efforts by informing on key species interactions under environmental change.
Long-distance seed dispersal is a crucial process allowing the dispersal of fleshy-fruited tree species among forest fragments. In particular, large frugivorous bird species have a high potential to provide inter-patch and long-distance seed transport, both important for maintaining fundamental genetic and demographic processes of plant populations in isolated forest fragments. In the face of increasing worldwide forest fragmentation, the investigation of long-distance seed dispersal and the factors influencing seed dispersal processes has recently become a central issue in ecology. In my thesis, I studied the movement behaviour and the seed dispersal patterns of the trumpeter hornbill (Bycanistes bucinator), a large obligate frugivorous bird, in KwaZulu-Natal, South Africa. I investigated (i) the potential of trumpeter hornbills to provide long-distance seed dispersal within different landscape structures, (ii) seasonal variations in ranging behaviour of this species, and (iii) the potential of this species to enhance the functional connectivity of a fragmented landscape. I used highresolution GPS-data loggers to record temporally and spatially fine-scaled movement data of trumpeter hornbills within both continuous forests and fragmented agricultural landscapes during the breeding- and the non-breeding season. First, combining these data with data on seed-retention times, I calculated seed dispersal kernels, able to distinguish between seed dispersal kernels from the continuous forests and those from the fragmented agricultural landscapes. The seed dispersal distributions showed a generally high ability of trumpeter hornbills to generate seed transport over a distance of more than 100 m and for potential dispersal distances of up to 14.5 km. Seed dispersal distributions were considerably different between the two landscape types, with a bimodal distribution showing larger dispersal distances for fragmented agricultural landscapes and a unimodal one for continuous forests. My results showed that the landscape structure strongly influenced the movement behaviour of trumpeter hornbills, and this variation in behaviour is likely reflected in the shape of the seed dispersal distributions. Second, for each individual bird I calculated daily ranges and investigated differences in daily ranging behaviour and in the process of range expansion comparatively between the breeding- and the non-breeding season. I considered differences in habitat use and possible consequences resulting for seed dispersal function during different seasons. I found that within the breeding season multi-day ranges were built from strongly overlapping and nearly stationary daily ranges which were almost completely restricted to continuous forest. In the non-breeding season, however, birds assembled multi-day ranges by shifting their range site to a generally different area, frequently utilizing the fragmented agricultural landscape. Thereby, several small daily ranges and few large daily ranges composed larger multi-day ranges within the non-breeding season. Seasonal differences in ranging behaviour and range assembly processes resulted in important consequences for seed dispersal function, with short distances and less spatial variation during the breeding season and more inter-patch dispersal across the fragmented landscape during the non-breeding season. Last, I used a projection of simulated seed dispersal events on a high-resolution habitat map to assess the extent to which trumpeter hornbills potentially facilitate functional connectivity between plant populations of isolated forest fragments. About 7% of dispersal events resulted in potential between-patch dispersal and trumpeter hornbills connected a network of about 100 forest patches with an overall extent of about 50 km. Trumpeter hornbills increased the potential of functional connectivity of the landscape more than twofold and seed dispersal pathways revealed certain forest patches as important stepping-stones for seed dispersal among forest fragments. Overall, my study highlights the overriding role that large frugivorous bird species, like trumpeter hornbills, play in seed dispersal in fragmented landscapes. In addition, it shows the importance of fine-scaled movement data combined with high-resolution habitat data and consideration of different landscape structures and seasonality for a comprehensive understanding of seed dispersal function.
Fungi are an important component of every ecosystem but hardly considered in biodiversity monitoring projects. This thesis aims at characterizing fungal diversity, with an emphasis on epigeous fungi, encompassing different biogeographic zones and points in time. A main sampling area was established in the Taunus mountain range in Germany, which was sampled monthly over three years.
For testing species richness on spatial scale, the Taunus transect was compared with four other areas, which were assessed with lower sampling effort. One of these areas was Bulau in Germany, in which four excursions were made. Furthermore, two sampling events were performed in Somiedo in Spain and one sampling event in Kleinwalsertal in Austria. Already existing data of a two-year monitoring project in Panama next to the river Majagua were additionally used for comparison.
All these areas were investigated with a standardized sampling protocol focusing on macroscopically evident fungi and vascular plants using a time-restricted transect design. The transects consisted of strips, which were 500 m long and about 20 m broad, and were sampled for 2 hours at each single sampling event....