Institut für Integrierte Naturwissenschaften, Abt. Biologie
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Invasive crayfish are a serious threat and ecosystem engineers that compete with native species for shelter and food resources, show combative interactions against native species, and negatively affect species diversity. In this work, I used two North American invasive crayfish species that have successfully spread across Europe spinycheek crayfish (Faxonius limosus) and signal crayfish (Pacifastacus leniusculus) as models to assess their potential Impacts on native benthic fish, stone loach (Barbatula barbatula) and bullhead (Cottus gobio), which are among the most common benthic fish in Europe. I have investigated the competition for shelter and agonistic interactions between these invasive crayfish species and the native benthic fish species under laboratory conditions have employed a multi-object tracking algorithm to monitor and visualize the fish's and crayfish's activity inside the experimental tank. Spinycheek and signal crayfish successfully displaced both benthic fish species from their shelter. Both crayfish species attected the behaviour of stone loach, reducing its activity and increasing its hiding outside the shelter. Although bullheads did not reduce shelter use, they displayed similar behavioural changes, if less intense, In addition, I demonstrated remarkable aggressive interactions by both crayfish species against stone loaches and bullheads. Further investigations were performed to assess how variations in crayfish density influence the structure of invertebrate communities. I conducted comparative analyses of community composition across nine stream sites with varying densities of signal crayfish in Wied Stream, Germany. These findings revealed a correlation between crayfish density and diversity and evenness of invertebrates, suggesting that signal crayfish pose a substantial threat to Invertebrate biodiversity
In conclusion, this thesis reveals that these invasive crayfish species not only compete with native biota for essential resources but also fundamentally alter the ecological dynamics of freshwater habitats. This thesis emphasises the urgent need to manage and mitigate the potential consequences of crayfish invasion and to preserve native aquatic ecosystems.
Population genetics investigates genetic diversity and its changes within and between populations over space and time. Genetic diversity is important for fitness, adaptive capacity, and the survival of populations and is influenced by several factors, such as mutation, selection, genetic drift and gene flow. Copper butterflies (Lycaena) are suitable for analysing structures influencing population connectivity as they potentially form more or less closed populations. However, very little is known about their genetic diversity and what influences it. Therefore, this thesis (1) provides newly developed microsatellite markers and uses genetic markers (2) to investigate genetic diversity across four different Lycaena species in the European Alps and to determine (3) which geographic and species specific factors influence population structure, (4) which large- and small-scale structures impact the population structure, (5) how natural and anthropogenic structures influence the population structure within an Alpine valley, and (6) whether and how genetic diversity changes over time. It was shown that the postglacial relict species L. helle has a relatively high genetic diversity compared to the other three species investigated. This suggests that L. helle is still able to adapt to environmental changes. Low genetic diversity was found in L. tityrus subalpinus, although high gene flow was found within one population of this species. High mountain ridges and large river valleys can act as dispersal barriers for Copper butterflies and thus have an impact on population structures. Here, dispersal ability as a species-specific factor also plays an important role, as some barriers are less likely to affect the population structure in the more mobile species L. virgaureae. Furthermore, forests, ravines and roads, but not small rivers, represent dispersal barriers for L. tityrus subalpinus within an Alpine valley. Finally, over ten years, the genetic diversity of L. hippothoe eurydame has decreased, whereas that of L. helle has remained stable. Against the backdrop of increasing global changes, it is important to understand the genomic underpinning of population structure and adaptation as well as to investigate and monitor whether populations are able to adapt to changing environmental conditions.
Coat color and pattern are a distinguished feature in mammalian carnivores, shaped by climatic cycles and habitat type. It can be expressed in various ways, such as gradients, polymorphisms, and rare color variants. Although natural selection explains much of the phenotypic variation found in the wild, genetic drift and heterozygote deficiency, as prominent in small and fragmented populations, may also affect phenotypic variability through the fixation of recessive alleles. The aim of this study was to test whether rare color variants in the wild could relate to a deficiency of heterozygotes, resulting from habitat fragmentation and small population size. We present an overview of all rare color variants in the order Carnivora, and compiled demographic and genetic data of the populations where they did and did not occur, to test for significant correlations. We also tested how phylogeny and body weight influenced the presence of color variants with phylogenetic generalized linear mixed models (PGLMMs). We found 40 color-variable species and 59 rare color variants. In 17 variable phenotypic populations for which genetic diversity was available, the average AR was 4.18, HO = 0.59, and HE= 0.66, and FIS= 0.086. We found that variable populations displayed a significant reduction in heterozygosity and allelic richness compared to non-variable populations across species. We also found a significant negative correlation between population size and inbreeding coefficients. Therefore, it is possible that small effective size had phenotypic consequences on the extant populations. The high frequency of the rare color variants (averaging 20%) also implies that genetic drift is locally overruling natural selection in small effective populations. As such, rare color variants could be added to the list of phenotypic consequences of inbreeding in the wild.
The diversity within amphibian communities in cultivated areas in Rwanda and within two selected, taxonomically challenging groups, the genera Ptychadena and Hyperolius, were investigated in this thesis. The amphibian community of an agricultural wetland near Butare in southern Rwanda comprised 15 anuran species. Rarefaction and jackknife analyses corroborated that the complete current species richness of the assemblage had been recorded, and the results of acoustic niche analysis suggested species saturation of the community. Surveys at many other Rwandan localities showed that the species recorded in Butare are widespread in cultivated and pristine wetlands. The species were readily distinguishable using morphological, bioacoustic, and molecular (DNA barcoding) features, but only eight of the 15 species could be assigned unambiguously to nominal species. The remaining represented undescribed or currently unrecognized taxa, including three species of Hyperolius, two Phrynobatrachus species, one Ptychadena species, and one species of Amietia. The diversity of the Ridged Frogs in Rwanda was investigated in two studies (Chapters III and IV). Three species of Ptychadena were recorded in wetlands in the catchment of the Nile. They can be distinguished by morphological characters (morphometrics and qualitative features) as well as by their advertisement calls and genetics. The Rwandan species of the P. mascareniensis group was shown to differ from the topotypic population as well as from other genetic lineages in sub-Saharan Africa and an old available name, P. nilotica, was resurrected from synonymy for this lineage. Two further Ptychadena species were identified among voucher specimens from Rwanda deposited in the collection of the RMCA, P. chrysogaster and P. uzungwensis. Morphologically they can be unambiguously distinguished from each other and the three other Rwandan species. A key based on qualitative morphological characters was developed, which allows unequivocal identification of specimens of all species that have been recorded from Rwanda. DNA was isolated from a Rwandan voucher specimen of P. chrysogaster, and the genetic analysis corroborated the species" distinct status.
A species of Hyperolius collected in the Nyungwe National Park was compared to all other Rwandan species of the genus and to morphologically or genetically similar species from neighbouring countries. Its distinct taxonomic status was justified by morphological, bioacoustic, and molecular evidence and it was described as a new species, H. jackie. A species of the H. nasutus group collected at agricultural sites in Rwanda was described as a new species in the course of a revision of the species of the Hyperolius nasutus group. The group was shown to consist of 15 distinct species which can be distinguished from each other genetically, bioacoustically, and morphologically.
The aerial performance, i.e. parachuting, of the Disc-fingered Reed Frog, Hyperolius discodactylus, was described. It represents a novel observation of a behaviour that has been known from a number of Southeast Asian and Neotropical frog species. Parachuting frogs, including H. discodactylus, exhibit certain morphological characteristics and, while airborne, assume a distinct posture which is best-suited for maneuvering in the air. Another study on the species addressed the validity of the taxon H. alticola which had been considered either a synonym of H. discodactylus or a distinct species. Type material of both taxa was re-examined and the status of H. alticola reassessed using morphological data from historic and new collections, call recordings, and molecular data from animals collected on recent expeditions. A northern and a southern genetic clade were identified, a divide that is weakly supported by diverging morphology of the vouchers from the respective localities. No distinction in advertisement call features could be recovered to support this split and both genetic and morphological differences between the two geographic clades are marginal and not always congruent and more likely reflect population-level variation. Therefore it was concluded that H. alticola is not a valid taxon and should be treated as a synonym of H. discodactylus.
This study was conducted in Nyungwe National Park (NNP); a biodiversity hotspot Mountain rainforest of high conservation importance in Central Africa, but with little knowledge of its insect communities including butterflies, good indicators of climate change, and forest ecosystem health. The study aimed at availing baseline data on butterfly species diversity and distribution in NNP, for future use in monitoring climate change-driven shifts and the effects of forest fragmentation on the biodiversity of Nyungwe. Butterflies were collected seasonally using fruit-baited traps and hand nets along elevational transects spanning from 1700 m up to 2950 m of altitude. Two hundred forty-two species including 28 endemics to the Albertine Rift and 18 potential local climate change indicators were documented. Species richness and abundance declined with increasing elevation and higher seasonal occurrence was observed during the dry season. This was the first study on the spatial and temporal distribution of butterflies in NNP and further studies could be conducted to add more species and allow a depth understanding of the ecology of Nyungwe butterflies.
Agricultural intensification is leading to a severe decline in farmland biodiversity worldwide. The resulting landscape simplification through the expansion of monocultures and removal of non-crop habitats has a major impact on arthropod communities in agricultural landscapes. While arable fields are often highly disturbed and ephemeral habitats that are unsuitable for many species, non-crop habitats in agroecosystems can provide important refugia. The creation of non-crop habitats through agri-environmental schemes (AES) in intensive agricultural landscapes, such as the ‘Maifeld’ region in western Germany, is intended to mitigate the negative effects of agricultural intensification, although the effectiveness of these measures for nature conservation is still controversial. Therefore, this work focuses on the taxonomic and functional diversity of beetles (Coleoptera) and spiders (Araneida), being important providers of ecosystem services, between wheat fields and different non-crop habitats, namely grassy field margins adjacent to wheat and oilseed rape fields, small- and large-scale set-aside areas sown with wildflowers, and permanent grassland fallows. Arthropods were collected between 2019 and 2020 using pitfall traps and suction sampling. Land-use type influenced beetle and spider diversity in the study area, with significantly higher values in grassland fallows than wheat fields. Surprisingly, species diversity differed little among all non-crop habitats, but all harboured distinct species assemblages. In particular, large long-term grassland fallows showed the largest within-group variation of beetle and spider assemblages and represented important habitats, especially for habitat specialists and threatened species, likely due to their variable soil moisture and complex habitat structure. In contrast, the homogeneous arthropod assemblages of wheat fields exhibited lower trait richness and were dominated by a few predatory species adapted to such disturbed, man-made habitats. Interestingly, all conservation measures complemented each other in that they contributed in different ways to supporting beetles and spiders in agricultural landscapes. Even small-scale non-crop habitats and existing habitat boundaries in an agricultural matrix appear to be valuable habitats for farmland arthropods by enhancing taxonomic diversity. Field margins and small wildflower-sown patches can link isolated non-crop habitats and contribute to a heterogeneous agricultural landscape. Consequently, a combination of various small- and large-scale greening measures leads to increased compositional and configurational landscape heterogeneity, resulting in improved beetle and spider diversity. Considering the ongoing loss of farmland biodiversity worldwide, agri-environmental schemes should be promoted in the future, as they are particularly important for arthropod conservation in intensive agricultural landscapes such as the Maifeld region.
The ongoing loss of species is a global threat to biodiversity, affecting ecosystems worldwide. This also concerns arthropods such as insects and spiders, which are especially endangered in agricultural ecosystems. Here, one of the main causing factors is management intensification. In areas with a high proportion of traditionally managed grassland, extensive hay meadows that are cut only once per year can still hold high levels of biodiversity, but are threatened by conversion into highly productive silage grassland. The Westerwald mountain range, western Germany, is such a region. In this thesis, I compare the local diversity of bees, beetles, hoverflies, leafhoppers, and spiders of five grassland management regimes along a gradient of land-use intensity. These comprise naturally occurring grassland fallows, three types of traditionally managed hay meadows, and intensively used silage grassland. By using three different sampling methods, I recorded ground-dwelling, flower-visiting, and vegetation-dwelling species. The results show that in most cases species richness and diversity are highest on fallows, whereas variation among different managed grassland types is very low. Also, for most sampled taxa, fallows harbour the most distinct species assemblages, while that of other management regimes are largely overlapping. Management has the largest effect on species composition, whereas environmental parameters are of minor importance. Long-term grassland fallows seem to be highly valuable for arthropod conservation, even in a landscape with a low overall land-use intensity, providing structural heterogeneity. In conclusion, such fallows should be subsidized agri-environmental schemes, to preserve insect and spider diversity.
Eine Ursache des Insektenrückgangs ist die Abnahme der für Arthropoden wichtigen Lebensräume. Der kleinstrukturierte Obstanbau als Dauerkultur mit vielfältigen Strukturen (Bäume, Grünland, offener Boden) kann als Refugium wirken. Gerade Dauerkulturen, welche über viele Jahre bestehen bleiben, können einen großen ökologischen Wert für Insekten und Spinnentiere darstellen, wenn die negativen Einflüsse der Bewirtschaftung durch gezielte Maßnahmen minimiert werden. Im Gegensatz zu den gut untersuchten Streuobstwiesen liegen bisher nur wenige oder ungenaue Daten über die Arthropodenfauna in Erwerbsobstanlagen vor. Ziele dieser Arbeit sind eine genauere Erfassung der Arthropodenfauna in Erwerbsobstanlagen, Benennung der Einflussfaktoren und Erarbeitung einer indikatorgestützten Bewertungsmethode mit Entwicklung von Maßnahmen zur Förderung der Biodiversität. Es wurde eine intensive Erfassung der Insekten und Spinnentiere auf Basis von Individuenzahlen, Verteilung der Tiere auf Großgruppen, Artenzahlen der Käfer (inkl. Rote Liste) und Wanzen, deren Diversität und der sie beeinflussenden Faktoren auf vier Erwerbsobstflächen und einer Streuobstwiese als Referenzfläche in der Gemeinde Zornheim (Rheinland-Pfalz) untersucht. Mittels des erarbeiteten Bewertungsbogens wurden die Auswirkungen der fünf Faktorenkomplexe: Sonderstrukturen, Anlagenstruktur, Beschattung, Mahdregime und Einsatz von Pflanzenschutzmitteln auf die Arthropodenfauna erhoben und die auf der Fläche zu erwartende Biodiversität ermittelt. Die visuelle Darstellung der Einflussfaktoren mit Netzdiagrammen zeigt biodiversitätsbeeinträchtigende Faktoren und ermöglicht so Empfehlungen zur Aufwertung der Biodiversität. Die Bewertungsmethode kann nach Verifizierung im Rahmen von erfolgsorientierten Agrarumwelt- und Klimamaßnahmen (AUKM), zur Anerkennung von Kompensationsmaßnahmen (z.B. PIK) und zur Ermittlung des ökologischen Wertes (Ökosystemdienstleistung) von Obstanlagen genutzt werden. In modifizierter Form könnte es ebenfalls im Bereich der Flächenbewertung in Landschafts- und Bauleitplanung eingesetzt werden.
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.
The protected areas of Rwanda are facing various challenges resulting from the anthropogenic activities of the surrounding communities especially in the adjacent area to Cyamudongo isolated rain forest, which results in climate change, soil degradation, and loss of biodiversity. Therefore, this study aims to broaden current knowledge on the impact of sustainable Agroforestry (AF) on the Carbon (C) stock and Biodiversity conservation on the surroundings of Cyamudongo isolated rain forest and Ruhande Arboretum.
To understand this, the permanent sample plots (PSPs) were established mainly in the designed four transects of four km long originating on the boundary of the Cyamudongo isolated rain forest following the slope gradient ranging from 1286 to 2015 m asl. A total number of 73 PSPs were established in the Cyamudongo study area while 3 PSPs were established in the Ruhande AF plot. The Arc Map GIS 10.4 was used to design and map the sampling areas while GPS was used for localization of collected items. Statistical significance was analyzed through the R-software especially for wood and soil variables while for biodiversity indicator species, MVSP Software 3.0 was used to determine the Shannon Diversity indices and similarities among species.
In this study, I have obtained comprehensive results demonstrating that in all study areas, the various AF tree species contribute differently to C stock and C sequestration and the amount of C stored and removed from the atmosphere depends on different factors such as tree species, plantation density, growth stage, or the age of establishment, applied management practices, wood specific density (WSD), wood C concentration, and climatic conditions. The estimated quantity of sequestrated C for 2 years and 34 years AF species were 13.11 t C ha -1 yr-1 (equivalent to 48 t CO2 ha -1 yr-1) and 6.85 t ha-1 yr-1 (equivalent to 25.1 t CO2 ha -1 yr-1) in Cyamudongo and Ruhande respectively. The estimated quantity of C stored by the Ruhande AF plot is 232.94 t ha-1. In Cyamudongo, the overall C stored by the AF systems was 823 t ha-1 by both young tree species established by the Cyamudongo Project (35.84 t ha-1) and C stored by existed AF species before the existence of the Project (787.12 t ha-1). In all study areas, the Grevillea robusta was found to contribute more to overall stored C compared to other species under this study.
The tests revealed differences in terms of nutrient contents (C, N, C: N ratio, K, Na, Ca, and Mg) for various AF tree species of Cyamudongo and Ruhande study areas. The differences in terms of correlation for various variables of AF tree species in different study areas varied with tree species, age, stage of growth, and tree shape. By comparing the correlation coefficients for various tree variables for young and mature AF tree species, the results showed a high correlation variability for young species than mature or old species recorded in different environmental conditions of Cyamudongo and Ruhande study areas.
The recorded soil pH mean value across in Cyamudongo study area is 4.2, which is very strongly acidic. The tests revealed that the soil pH, C, C: N ratio, OM, NH4+, NO3-+NO2-, PO43-, and CEC were significantly (P < 0.05) different in various soil depths whereas the N was not statistically significant. The pH, N, C: N ratio, CEC, NH4+, PO43-, and Al3+ showed a significant difference across land uses whereas the C and NO3-+NO2- did not show any statistical difference. All tested chemical elements showed a statistical difference as far as altitude ranges are concerned. The only NH4+, PO43-, and CEC showed significant differences with time whereas all other remaining chemical elements did not show any statistical significance. The bulk density of soil was statistically different across land uses and altitude ranges. The soil pH was very strongly correlated with CEC, Mg, and Ca in cropland (CL) whereas it was strongly correlated in both AF and natural forest (NF) except for Mg, which was moderately correlated in AF. Furthermore, its correlation with K was strong in CL, moderate in AF while it was weak in NF. Finally, the pH correlation with Na was weak in both AF and CL whereas it was negligible in NF. The overall estimated soil C stock of the study area was 16848 t ha -1.
The sustainable AF practices changed significantly the frequency of reptiles, amphibians, and flowering plants while there was no statistical change observed on ferns with time. In terms of species richness, 16 flowering plants, 14 ferns, 5 amphibians, and 3 reptiles were recorded and monitored. These findings add to a growing body of literature on the impact of AF on the C stock, soil improvement, and Biodiversity. It is recommended that further researches should be undertaken for the contribution of other AF tree species to the C stock found in the agricultural landscape around all protected areas of Rwanda and the impact on them on the soil and biodiversity.