Institut für Ökologie, Evolution und Diversität
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Im Rahmen dieser Dissertation wurden unterschiedliche Aspekte der Verbreitung der Vertreter des Pseudoterranova decipiens Komplexes betrachtet und Fragestellungen zur Ökologie und Humanpathogenität der Parasiten bearbeitet. Sie basiert auf drei (ISI-) Fachartikeln, in denen die Nutzung von Fischparasitengemeinschaften als ökologische Indikatoren für entlegene Ökosysteme des Südpolarmeeres (I), die Modellierung geeigneter Verbreitungsgebiete für Arten mit geringen Vorkommensdaten am Beispiel des P. decipiens Komplexes (II) und das Vorkommen potentiell humanpathogener P. bulbosa in unterschiedlichen Mikrohabitaten in Atlantischem Kabeljau (III) thematisiert wurde.
Die Parasitengemeinschaften der in Studie I untersuchten, nahverwandten Antarktisdorsche (Nototheniinae) Nototheniops larseni (n=40), N. nudifrons (n=40) und Lepidonotothen squamifrons (n=49) unterschieden sich hauptsächlich hinsichtlich seltener Parasitenarten. Pseudoterranova decipiens E zählte zu den häufigsten Parasiten der drei betrachteten Wirtsarten. Die Analyse der Wirtsspektren der auf Artebene bestimmten Parasiten zeigte eine geringe Spezifität antarktischer Fischparasiten im Larven- (z.B. Pseudoterranova decipiens E) und Adultstadium (z.B. Elytrophalloides oatesi). Für eine Nutzung als Bioindikatoren ergibt sich die Empfehlung, nicht auf einzelne Parasitenarten, sondern die Zusammensetzung von Parasitenfaunen zurückzugreifen und Parameter wie Abundanz oder Intensität zu berücksichtigen. Vergleiche mit Literaturdaten legten nahe, dass ein Studiendesign, das den periodischen Vergleich der Parasitierungsmuster von Nototheniinae ermöglichen soll, Standorteffekte berücksichtigen sollte. Da es sich bei der Probennahme demersaler Fische um ein aufwändiges und einschneidendes Verfahren handelt, sollten alternative Samplingmethoden vorangetrieben und eine Datenbasis dafür geschaffen werden.
Um die Belastung von Speisefischen mit potentiell humanpathogenen Parasiten in bestimmten Fanggebieten abzuschätzen, kann anhand von Vorkommens- und Umweltdaten mittels statistischer Modelle die Habitateignung für den Parasiten bestimmt werden. Eine Voraussetzung für eine verlässliche Modellierung bilden die Wahl eines geeigneten Algorithmus und die Qualität der Eingangsdaten. Für die Modellierung geeigneter Verbreitungsgebiete für die sechs Arten des P. decipiens Komplexes wurde im Rahmen von Studie II erstmalig ein biotischer Deskriptor herangezogen. Dem Ansatz lag die Annahme zugrunde, dass das Vorkommen geeigneter Endwirte der entscheidende, limitierende Faktor für die Verbreitung eines Parasiten ist, da nur so der Lebenszyklus geschlossen werden kann. Als Hypothesentest dienten Vergleiche der ökologischen Nischen von Parasiten und ihren spezifischen Endwirten im Nischenraum. Anhand der Endwirtdistanz wurde eine Verbesserung der Modellierungsergebnisse mit MaxEnt, gegenüber der ausschließlich auf abiotischen Prädiktoren basierenden Modellierung, für alle Pseudoterranova Arten, insbesondere jene mit einer geringen Anzahl Fundpunkte, erzielt. Grundsätzlich ist der Ansatz auf marine Parasitenarten, deren spezifische Endwirte verlässliche Vorkommensdaten aufweisen, übertragbar. Die Methode stellt jedoch keinen Ersatz für die Erhebung von Vorkommensdaten dar, weshalb die genetische Bestimmung schwer zu identifizierender Taxa sowie die Angabe von Metadaten in jeder parasitologischen Studie obligatorisch sein sollten.
Die Verteilung potentiell humanpathogener Parasitenstadien in für den menschlichen Verzehr vorgesehenen Fischen kann ein entscheidender Faktor für die Übertragung sein. Im Rahmen von Studie III wurde mit dem Referenztranskriptom von P. bulbosa das erste Transkriptom für eine Art den P. decipiens Komplexes erstellt. Anhand einer differentiellen Genexpressionsanalyse wurde untersucht, was die Verteilung der Parasiten auf unterschiedliche Mikrohabitate beeinflusst haben könnte. Dabei wurden siebzig differentiell exprimierte Gene identifiziert, die in aus Leber (32 Gene) und Viscera (38 Gene) von Atlantischem Kabeljau (Gadus morhua) isolierten Proben von P. bulbosa hochreguliert waren. Eine Erklärung für diesen subtilen Unterschied könnte ein Dauerstadium der P. bulbosa Larven zum Zeitpunkt der Probennahmen sein. Ob sich bestimmte Mikrohabitate innerhalb des Wirtes begünstigend auf den Parasiten auswirken, muss mit Hilfe experimenteller Studien gezeigt werden. Erste in Studie III erhobene Daten zum allergenen Potential von P. bulbosa sollten in serologischen Studien getestet werden. Als Grundlage für die Bewertung des pathogenen Potentials von P. bulbosa, sowie der weiteren Arten des P. decipiens Komplexes, sollten in experimentellen Studien NGS-Daten erhoben werden.
Im Rahmen dieser Dissertation wurde in drei methodisch unterschiedlichen Studien ein Bedarf besserer Referenzdaten aufgezeigt. Bestreben diese Datenlücken zu schließen, um das Potential der Methoden besser ausschöpfen zu können, müssen zukünftig noch weiter verstärkt werden.
In the light of emerging resistances against common drugs, new drug leads are required. In the past natural sources have been more yielding in this respect than synthetic strategies. Fungi synthesize many natural products with biological activities and pharmacological relevance. However, only a fraction of the estimated fungal diversity has been evaluated for biological activity, and much of the Fungi’s natural chemical diversity awaits discovery. Especially promising in this context are lichenized fungi. Lichens are well known for their particularly rich and characteristic secondary chemistry which allows them to withstand intense UV radiation, protects them against herbivory, and prevents them from being overgrown. The slow growth rates of lichens and difficulties and infeasibility of large scale cultivations in the laboratory render lichens inaccessible for applied purposes. These experimental challenges have led to a poor understanding of the molecular mechanisms underlying the biosynthesis of characteristic lichen secondary metabolites. The recent development of improved sequencing techniques has enabled new strategies to address multi-species assemblages directly through metagenome sequencing and survey their biosynthetic potential through genome mining. However, whole genome sequencing of entire lichen thalli to metagenomically assess the lichen-forming fungus without the need of cultivation has not been evaluated for lichens before. This approach will enable the reconstruction of fungal genomes from mixed DNA from lichen thalli and allow the exploration of biosynthetic gene content.
My thesis was conducted in two parts: a methodological evaluation of a metagenomic strategy to reconstruct genomes and gene sets of lichen-forming fungi, and the exploration of biosynthetic gene content with the help of comparative genomics and phylogenetics. For the first part, I evaluated the quality of metagenome-derived genome assemblies and gene sets by direct comparison to culture-derived reference assemblies and gene sets of the same species. I showed that metagenome-derived fungal assemblies are comparable to culture-derived references genomes and have a similar total genome size and fungal genome completeness. The quality of assemblies was affected strongly by the choice of assembler, but not by the method of taxonomic assignment or inference of non-mycobiont DNA sequences. The fungal gene space is well covered in metagenome-derived and culture-derived fungal gene sets and overlaps to 88-90 %. Finally, the metagenome-derived assemblies reliably recover gene families of secondary metabolism. This shows the suitability of metagenomically derived genomes for mining biosynthetic genes, and potentially also other gene families. Overall, the method validation showed a high similarity between metagenome- and culture-derived genome assemblies.
For the second part of my thesis, I explored the biosynthetic gene content in two different systems: Between two sister-species with different ecological requirements but similar chemical profile, and between two species which are metabolite-rich and economically relevant in the perfume industry. I compared the diversity of biosynthetic gene clusters between the species and in the broader context of other lichenized and non-lichenized fungi. Overall, the whole genome mining revealed a large number of uncharacterised secondary metabolite gene clusters in fifteen genomes of lichen-forming fungi compared to other fungal classes. Their number highly outweighs the number of known synthesized metabolites and highlights the hidden biosynthetic potential in lichen-forming fungi. Many biosynthetic gene clusters in the ecological distinct sister-species showed a high homology in accordance with the high synteny in gene content and order in both genomes. These clusters represent ideal candidates for secondary metabolites synthesized by both species, while the remaining clusters may encode for metabolites relevant for the different ecological requirements of both species. The metabolite-rich species used in the perfume industry showed a particularly high number of biosynthetic gene clusters. An in-depth characterization of architecture and gene content of homologous gene clusters together with hints from phylogenetic relatedness to functional characterized metabolites provides promising insights into the biosynthetic gene content of these lichen-forming fungi.
In conclusion, I showed that metagenome sequencing of natural lichen thalli is a feasible approach to reconstruct the fungal mycobiont genome of lichens and circumvent time-consuming and in some cases impossible cultivation of individuals. The genome mining for secondary metabolite gene clusters in lichen-forming fungi revealed a high biosynthetic potential for the discovery of new natural products. One of the focal species, Evernia prunastri, contained the highest ever reported number (80) of biosynthetic clusters in lichenized fungi. The comprehensive cluster characterizations through annotation, comparative mapping and phylogenetics provide first valuable hints for linking metabolites to genes in these lichen-forming fungi. My results pave the way for biotechnological strategies to unlock the vast richness of natural products from lichens for applied purposes.
Panama is a megadiverse country that together with Costa Rica constitutes Lower Central America (LCA). Western Panama's Cordillera Central accounts for the eastern part of the LCA highlands shared between these countries. The aim of the present study is to compile the most complete and updated picture possible of the taxonomy, diversity, and distribution of reptiles that occur from 500 m asl upwards along the Talamanca and Tabasará ranges. These two continuous mountain ridges account for the western two-thirds of the Cordillera Central between the Costa Rican border and 81°W Including specimens collected four own research travels, I morphologically examined more than 1800 specimens, analyzed 16S and/or COI barcodes of 300 specimens, and performed a thorough search in literature and databases to obtain locality records for specimens and species occurrences. My complete occurrence dataset comprises 14620 georeferenced occurrence records in three quality categories. Conceivable occurrences of species not yet documented from a given area are evaluated on the basis of existing data either as "plausible" or "possible". I provide all datasets which I generated for this study in Appendices. The previously published descriptions of Dactyloa ginaelisae Lotzkat, Hertz, Bienentreu & Köhler 2013, Norops benedikti (Lotzkat, Bienentreu, Hertz & Köhler 2011), Sibon perissostichon Köhler, Lotzkat & Hertz 2010, and Sibon noalamina Lotzkat, Hertz & Köhler 2012 are included in the present work. In the course of integrative taxonomic analyses, I classify 15 genealogical lineages revealed by DNA barcoding within 7 anole species as Deep Conspecific Lineages (DCLs) because they lack consistent morphological differences to their nominal conspecifics. I provisionally classify 18 mitochondrial lineages found within six other anole species as Unconfirmed Genealogical Lineages (UGLs) pending adequate analyses of their morphological variation. I regard the two additional UGLs Celestus sp. and Geophis sp. and the two Confirmed Genealogical Lineages (CGLs) Lepidoblepharis sp. 1 and 2 to represent undescribed species. My taxonomic analyses yield the hitherto most comprehensive survey of the variability exhibited by dozens of reptile species in western Panama. The 16S and/or COI barcodes I provide represent 65 species recognized herein and constitute the first DNA barcode reference library for LCA reptiles. The reptile fauna of Panama comprises 265 species, including the four UGLs and CGLs mentioned above and characterized for the first time in this study, as well as Dendrophidion crybelum Cadle 2012 whose presence in the country I consider plausible. My occurrence dataset reveals that 160 of these species have been documented to occur in my study area. Adding the 20 species whose occurrence therein I consider plausible, I report the total species richness of the Talamanca and Tabasará ranges as comprising 180 species representing 81 genera in 25 families. With 178.8 species per 10 000 km2, the relative species richness of the area is extremely high even in a tropical context. In view of their overall documented distribution, I regard the presence of 27 additional species in my study area as possible. For the 180 species occurring in my study area I provide standardized species accounts that, together with the taxonomic results, for the first time permit the doubtless identification of all 180 species, and illustrate 168 of these with color photographs. Concerning biogeography, my georeferenced dataset yields noteworthy distribution extensions for many species. Moreover, I present the hitherto most comprehensive, detailed, and reproducible assessments of the distribution patterns, historical origins, and conservation as well as of the occurrence among physiographic regions, climatic and altitudinal belts, political subdivisions, and protected areas, for my study area's reptile fauna. With 65 species, more than a third of the fauna is endemic to LCA. Among these, 42 Talamancan highland endemics are restricted to the LCA highlands, in the case of 16 small-scale highland endemics with documented ranges spanning less than 100 km. I assess many of these endemics as endangered. The fact that several of these species do not occur in any protected area renders the establishment of additional conservation areas necessary, especially in the central Serranía de Tabasará. Distributional range boundaries shared among different clades of highland anoles indicate physiographic and climatic barriers that may have effected in situ speciation within these lineages. As the largest study on Panamanian reptile diversity assembled to date, the present dissertation considerably increases our knowledge on the reptiles along the Cordillera Central and beyond, and thus constitutes a solid basis for future studies.
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.
Adaptive Radiation und Zoogeographie anisakider Nematoden verschiedener Klimazonen und Ozeane
(2013)
Anisakide Nematoden sind Parasiten aquatischer Organismen und weltweit in marinen Habitaten verbreitet. Ihre Übertragungswege sind tief im marinen Nahrungsnetz verwurzelt und schließen ein breites Spektrum pelagisch/benthischer Invertebraten (z.B. Cephalopoda, Gastropoda, Crustacea, Polychaeta) und Vertebraten (z.B. Teleostei, Elasmobranchia, Cetacea, Pinnipedia, Aves) als Zwischen- bzw. Endwirte ein. Aufgrund der hohen Befallszahlen u.a. in der Muskulatur und Viszera kommerziell intensiv genutzter Fischarten (z.B. Clupea harengus, Gadus morhua, Salmo salar) sowie ihrer Rolle als Auslöser der menschlichen Anisakiasis nehmen die Vertreter der Gattung Anisakis unter den anisakiden Nematoden eine Sonderstellung ein. Anhand der verbesserten Diagnostik und der Etablierung sowie Weiterentwicklung molekularbiologischer Methoden ist es in den letzten zwei Dekaden gelungen, die bestehende Taxonomie und Systematik der Gattung Anisakis zu erweitern bzw. zu revidieren. Aktuelle molekulare Analysen weisen auf die Existenz von insgesamt neun distinkten Arten hin, welche eine hohe genetische Heterogenität und Wirtsspezifität aufweisen, äußerlich jedoch nahezu identisch sind (sog. kryptische Arten). Trotz kontinuierlicher Forschung auf dem Gebiet ist das Wissen über die Biologie von Anisakis immer noch unzureichend.
Die vorliegende Dissertation ist in kumulativer Form verfasst und umfasst drei (ISI-) Einzelpublikationen. Die Zielsetzung der durchgeführten Studien bestand unter anderem darin, unter Verwendung molekularbiologischer und computergestützter Analyseverfahren, Fragestellungen zur Zoogeographie, (Co-)Phylogenie, Artdiagnostik, Lebenszyklus-Ökologie sowie des bioindikatorischen Potentials dieser Gattung zu bearbeiten und bestehende Wissenslücken zu schließen.
Die Verbreitung von Anisakis, welche bisher ausschließlich anhand von biogeographischen Einzelnachweisen abgeschätzt wurde, konnte durch den angewandten Modellierungsansatz erstmalig interpoliert und in Kartenform vergleichend dargestellt werden. Dabei wurde gezeigt, dass die Verbreitung von Anisakis spp. in den Ozeanen und Klimazonen nicht gleichmäßig ist. Die Analysen deuten auf die Existenz spezies-spezifischer horizontaler und vertikaler Verbreitungsmuster hin, welche neben abiotischen Faktoren durch die Verbreitung und Abundanz der jeweiligen Zwischen- und Endwirte sowie deren Tiefenverteilung und Nahrungspräferenzen geprägt sind.
Durch die umfangreiche Zusammenstellung und anschließende Kategorisierung der (mit molekularen Methoden) geführten Zwischenwirtsnachweise konnten indirekte Rückschlüsse über die vertikale Verbreitung von Anisakis spp. entlang der Tiefenhabitate gezogen werden.
Während Anisakis auf Gattungsebene in der gesamten Wassersäule entlang verschiedener Tiefenhabitate abundant ist, wurde für die stenoxene Art Anisakis paggiae ein meso-/bathypelagisch orientierter Lebenszyklus postuliert. Durch den Einbezug eines breiten Spektrums (paratenischer) Zwischen- und Transportwirte aus unterschiedlichen trophischen Ebenen werden Transmissionslücken im Lebenszyklus der Gattung weitestgehend minimiert und der Transmissionserfolg auf den Endwirt, und damit die Wahrscheinlichkeit einer erfolgreichen Reproduktion, erhöht. Ausgeprägte Wirtspräferenzen sowie phylogenetische Analysen des ribosomalen ITS-Markers stützen eine Theorie zur co-evolutiven Anpassung der Parasiten an ihre Endwirte. Anisakis eignet sich daher unter Einschränkungen als Bioindikator für die vertikale und horizontale Verbreitung und Abundanz der Endwirte und lässt Rückschlüsse auf trophische Interaktionen im Nahrungsnetz zu. Durch die weitere Beprobung von Zwischenwirten aus verschiedenen trophischen Ebenen in zukünftigen Studien, kann eine genauere Bewertung potentiell abweichender Lebenszyklus-Strategien gewährleistet werden. Insbesondere ist die Datenlage zur Prävalenz und Abundanz anisakider Nematoden in Cephalopoda und Crustacea noch unzureichend. Die Probennahme sollte dabei unter besonderer Berücksichtigung bislang wenig oder unbeprobter geographischer Regionen, Tiefenhabitate und Wirtsarten durchgeführt werden.
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.
The environmental impact of climate change is meanwhile not only discussed in the scientific community but also in the general public. However, little is known about the interaction between climate change and pollutants like pesticides. A combination of multiple stressors (e.g. temperature, pollutants, predators) may lead to severe alterations for organisms such as changes in time of reproduction, reproductive success and growth performance, mortality and geographic distribution. The questions if aquatic organisms tend to react more sensitive towards incidents under climate change conditions remains. Therefore, within the present thesis the aquatic ecotoxicological profile of the fungicide pyrimethanil, as an exemplarily anthropogenic used contaminant, was examined.
A large test battery of ecotoxicological standard tests and supplement bioassays with non-model species was conducted to investigate if species-specific or life stage-specific differences occur or if temperature alteration may change the impact of the fungicide. Two of the most sensitive species (Chironomus riparius and Daphnia magna) were used to investigate the acute and chronic thermal dependence of pyrimethanil effects. The results clearly depict that the ecotoxicity of pyrimethanil at optimal thermal conditions did not depend on the trophic level, but was species-specific. With regard to EC10 values the acute pyrimethanil toxicity on C. riparius increased with higher temperature (6.78 mg L-1 at 14°C and 3.06 mg L-1 at 26°C). The chronic response of D. magna to the NOEC (no observed effect concentration) of the fungicide (0.5 mg L-1) was examined in an experiment which lasted for several generations under three simulated near-natural temperature regimes (‘cold year, today’ (11 to 22.7°C), ‘warm year, today’ (14 to 25.2°C) and ‘warm year, 2080’ (16.5 to 28.1°C)). A pyrimethanil-induced mortality increase was buffered by the strongly related increase of the general reproductive capacity, while population growth was stronger influenced by temperature than by the fungicide. At a further pyrimethanil concentration (LOEC – lowest observed effect concentration: 1 mg L-1), a second generation could not be established by D. magna under all thermal regimes.
Besides daphnids, the midge C. riparius was used for a second multigeneration study. In a bifactorial test design it was tested if climate change conditions alter or affect the impact of a low fungicide concentration on life history and genetic diversity. The NOAEC/2 (half of the no observed adverse effect concentration derived from a standard toxicity test) was used as a low pyrimethanil concentration to which laboratory populations of the midges were chronically exposed under the mentioned temperature scenarios. During the 140-day-multigeneration study, survival, emergence, reproduction, population growth, and genetic diversity of C. riparius were analyzed. The results reveal that high temperatures and pyrimethanil act synergistically on life history parameters of C. riparius. In simulated present-day scenarios, a NOAEC/2 of pyrimethanil provoked only slight to moderate beneficial or adverse effects. In contrast, an exposure to a NOAEC/2 concentration of pyrimethanil at a thermal situation likely for a summer under the future expactations uncovered adverse effects on mortality and population growth rate. In addition, genetic diversity was considerably reduced by pyrimethanil in the ‘warm year, 2080’ scenario, but only slightly under current climatic conditions. The multigeneration studies under near-natural thermal conditions indicate that not only the impact of climate change, but also low concentrations of pesticides may pose a reasonable risk for aquatic invertebrates in the future. This clearly shows that thermal and multigenerational effects should be considered when appraising the ecotoxicity of pesticides and assessing their future risk for the environment.
In addition to temperature further multiple abiotic and biotic stressors alterate pollutant effects. Moreover, to better discriminate and understand the intrinsic and environmental correlates of changing aquatic ecosystems, it was experimentally unraveled how the effects of a low-dose of pyrimethanil on daphnids becomes modified by different temperatures (15°C, 20°C, 25°C) and in the presence/ absence of predator kairomones of Chaoborus flavicans larvae. The usage of a fractional multifactorial test design provided the possibility to investigate the individual growth, reproduction and population growth rate of Daphnia pulex via different exposure routes to the fungicide pyrimethanil at an environmentally relevant concentration (0.05 mg L-1) - either directly (via the water phase), indirectly (via algae food), dually (via water and food) or for multiple generations (fungicide treated source population).
The number of neonates increased with increasing temperatures. At a temperature of 25°C no significant differences between the individual treatment groups were observed although the growth was overall inhibited due to pyrimethanil. Besides, at 15 and 20°C it is obvious that daphnids which were fed with contaminated algae had the lowest reproduction and growth rate. The obtained results clearly demonstrate that multiple stress factors can modify the response of daphnids to pollutants. The exposure routes of the contaminant are of minor importance, while temperature and the presence of a predator are the dominant factors impacting the reproduction of D. pulex. It can be concluded that low concentrations of pyrimethanil may disturb the zooplankton community at suboptimal temperature conditions, but the effects will become masked if chaoborid larvae are present. Therefore it seems necessary to observe prospectively if the combination of several stress factors like pesticide exposure and suboptimal temperature may influence the life history and sensitivity of several aquatic invertebrates differently.
Besides standard test organisms it is inevitable to conduct test with aquatic invertebrate which are not yet considered regularly in ecotoxicological experiments. For example molluscs represent one of the largest phyla of macroinvertebrates with more than 100.000 species, being ecologically and economically important. Therefore, within the present study embryo, juvenile, half- and full-life cycle toxicity tests with the snail Physella acuta were performed to investigate the impact of pollutants on various life stages. Different concentrations of pyrimethanil (0.06-0.5 or 1.0 mg L-1) assessed at three temperatures (15°C, 20°C, 25°C) revealed that pyrimethanil caused concentration-dependent effects independent of temperature. Interestingly, the ecotoxicity of pyrimethanil was higher at lower temperature for the embryo hatching and F1 reproduction, but its ecotoxicity for the growth of juveniles and the F0 reproduction increased with increasing temperature. More specifically, it could have been observed that especially during the reproduction test high mortality rates occurred at the highest concentration of 1 mg L-1 at all temperatures. Due to high mortality rates no snails were available for the F1 at the highest concentrations (0.5 and 1.0 mg L-1). Compared to the F0, overall more egg masses were produced in the F1, being all fertile and no mortality occurred. For the F1-generation the strongest pyrimethanil effects were detected at 15°C. A comparison of effect concentrations between both generations showed that the F1 is more sensitive than the F0.
These results indicate that an exposure over more than one generation may give a better overview of the impact of xenobiotics. With the establishment of an embryo and reproduction test under different temperatures and various concentrations of pyrimethanil with P. acuta we could successfully show that molluscs can respond more sensitive than model organisms and that both, chemical and thermal stressor strongly influence the behaviour of the pulmonates. It can be concluded that the high susceptibility for the fungicide observed in gastropods clearly demonstrates the complexity of pesticide-temperature interactions and the challenge to draw conclusions for the ecotoxicological risk assessment of pesticides under the impact of global climate change.
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.
Savannas are the most important timber and non-timber forest products (NTFPs) providing ecosystems in West Africa. They have been shaped by traditional human land-use (i.e. agriculture, grazing, and harvesting) for thousands of years. In the last decades, land-use has drastically changed due to the rapid population growth and the growing production of cash-crop in West Africa and this process is still continuing. The percentage of land intensively used for agriculture has increased, while the length of fallow periods has decreased. Such changes have enormous ecological, economic, and social consequences. In the context of land-use changes, there is an urgent need to better understand and evaluate the impact of land-use on savannas. Such an understanding provides insights on appropriate management activities that ensure the maintenance of savannas and guarantee the availability of savanna products for subsistence and commercial use of rural West African people.
The major objective of the present thesis was to study the impact of land-use on savanna vegetation and diversity as well as on populations of two important NTFP-providing tree species in a semi-arid area in West Africa. The study area was located in the south-eastern part of Burkina Faso and comprised the protected W National Park and its adjacent communal area.
In the first study (chapter 2), I investigated in cooperation with a colleague from Burkina Faso (Blandine Nacoulma) the impact of land-use on the savanna vegetation. We analyzed which environmental factors determine the occurrence of the vegetation types and investigated the effect of land-use on vegetation structure and the occurrence of life forms and highly valued tree species. Furthermore, we tested whether land-use has an impact on plant diversity pattern and if this impact differed between the vegetation types and layers (woody and herb layer). Vegetation relevés were performed and the vegetation and plant diversity of the protected W National Park were compared with those of its surrounding communal area. Our results reveal five vegetation types occurring in both areas. Elevation and physical soil characteristics and thus soil water availability for plants played the most important role for the occurrence of the vegetation types. The influence of land-use on plant diversity differed between the five vegetation types and the two layers. The impact was highest on the vegetation types with the most favorable soil conditions for cultivation and lowest on rocky habitats with poor soils. While the diversity of the woody layer was increased under human land-use, the diversity of the herb layer was diminished. Overall, as land-use effects were not only negative, our findings suggest that land-use does not automatically lead to a loss of plant species and to a degradation of savanna habitats. We conclude that both protected and communal areas are of great importance for the conservation of savanna vegetation and diversity. Our study highlights furthermore the importance of different management strategies for each vegetation type.
In the following two studies (chapter 3 and 4), the impact of land-use - and in particular of harvesting - on populations of Adansonia digitata L., the baobab tree, and Anogeissus leiocarpa (DC.) Guill. & Perr. was examined. These two tree species were chosen as they provide several NTFPs for the local population and as they show different levels of human protection and opposed life histories. Thus, they may react differently to land-use. Stands of the protected W National Park were compared with those of its surrounding communal area (in fallows, croplands, and villages). I applied dendrometric methods to study the population structures and combined it with rates and patterns of NTFP-harvesting (debarking and chopping/pruning). Furthermore, the impact of land-use and harvesting on the fruit production of A. digitata and on the sprouting ability of A. leiocarpa were studied. The inverse J-shaped size class distribution curve indicates that the stands of A. digitata were in a healthy state in the park, while the low number of smaller size classes in fallows, croplands, and villages may give evidence of an ageing population. However, a high number of seedlings were recorded in villages. The stands of A. leiocarpa were also in healthy states in the park and likewise in fallows. In contrast, the absence of saplings gives evidence of a declining population in croplands. Both species were strongly harvested by local people and harvesting was tree size-specific. Pruning in interaction with tree-size had a significant impact on fruit production of A. digitata. While smaller trees were more vulnerable to pruning, bigger trees benefited from slight-pruning. A. leiocarpa had a great ability to respond to chopping by sprouting. The sprouting ability increased even with higher chopping intensity. Results suggest that despite the intense harvesting and the land-use impact, populations of both species are still well preserved. While A. digitata can withstand the harvesting and land-use pressure by its longevity, extremely low adult mortality rates, and particularly due to positive human influences, A. leiocarpa is able to withstand the use pressure by its fast growing, high recruitment, and high sprouting ability. I conclude that a none protected tree species (A. leiocarpa) might not necessarily be at higher risk to the harvesting and land-use impact than a protected tree species (A. digitata) as the adverse impact of harvesting and land-use can be compensated by its specific life history.
Important additional information to such ecological findings can be provided by local people. Learning from traditional knowledge and management systems of local people will help to produce culturally and ecologically reasonable conservation and management strategies. Thus, I investigated local uses and management strategies of A. digitata and A. leiocarpa in the last two studies (chapter 5 and 6). Quantitative ethnobotanical surveys among the Gulimanceba people were conducted in the communal area in order to document uses of the different plant parts, harvesting modes, perceptions about the population status, and conservation status of both species. Hereby, differences in knowledge between gender, generations, and people from different villages were tested. Interviews reveal that both species are harvested for multipurpose and emphasize the high importance of both species for local people. Especially the leaves and fruits of A. digitata add valuable minerals and vitamins to the otherwise micronutrient-“poor” staple crops of the Gulimanceba people. In comparison with other studies in West Africa, it has turned out that people in this area could benefit even more from A. leiocarpa, e.g. for dyeing of clothes, for treatment of malaria and skin problems. Local knowledge did not differ between genders and generations, while it slightly differed between people from different villages. The lack of age differences suggests that the traditional knowledge about these two species is passed on from one generation to another. Differences between people from different villages might be explained by influences from the neighboring countries Niger and Benin. Current local harvesting modes and management strategies of both species resulted in sustainable use. However, ongoing land-use intensifications require adapted harvesting and management techniques to guarantee the persistence of these economically important species. These results provide, in combination with the ecological findings (chapter 3 and 4), appropriate management recommendations for A. digitata and A. leiocarpa that are reliable under currently practiced management strategies.