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Traditional species identification based on morphological characters is laborious
and requires expert knowledge. It is further complicated in the case of
species assemblages or degraded and processed material. DNA-barcoding,
species identification based on genetic data, has become a suitable alternative,
yet species assemblages are still difficult to study. In the past decade
meta-barcoding has widely been adopted for the study of species communities,
due to technological advances in modern sequencing platforms and
because manual separation of individual specimen is not required. Here,
meta-barcoding is put into context and applied to the study of bee-collected
pollen as well as bacterial communities. These studies provide the basis
for a critical evaluation of the powers and limitations of meta-barcoding. Advantages
identified include species identification without the need for expert
knowledge as well as the high throughput of samples and sequences. In
microbiology, meta-barcoding can facilitate directed cultivation of taxa of interest
identified with meta-barcoding data. Disadvantages include insufficient
species resolution due to short read lengths and incomplete reference
databases, as well as limitations in abundance estimation of taxa and functional
profiling. Despite these, meta-barcoding is a powerful method for the
analysis of species communities and holds high potential especially for automated
biomonitoring.
I. Nowadays, tropical landscapes experience large-scale land use intensification and land conversion driven by increasing demand for resourses. Due to the continuously high demand for tropical timber and politically intended step increase in palm oil production, multiple rounds of logging and subsequent conversion to oil palm plantations became a regionally wide-spread land conversion pattern in Southeast Asia. Although many tree species and some animals are highly threatened by logging, a great number of species groups, such as birds or mammals, have been shown to persist in logged forests. Accordingly, many ecosystem services, such as dung removal, seed dispersal or the activity of scavengers, are functionally maintained in logged forests. In contrast, oil palm plantations have been shown to not only dramatically alter the species composition and reduce biodiversity, but also curtail many crucial biotic and abiotic ecosystem functions. The focus of this dissertation was to investigate the response of anuran species richness and community composition to logging and conversion to oil palm plantation in northern Borneo (chapter II). I analysed the diet of various frog species and their change with habitat degradation. Furthermore, I assessed the shift in the trophic position of the anuran community as well as the response of anuran phylogenetic, dietary, and functional diversity to logging and conversion to oil palm plantations (chapter III). Finally, the resilience of the predator-prey interaction between an ant-specialist toad and its ant prey was analysed using shifts in species-level interactions (chapter IV).
II. This part of the study compares the species richness, relative abundance and community composition of stream anuran assemblages among primary forests, repeatedly logged forests and oil palm plantations. I used a highly standardised sampling setup applying transect-based sampling. Surprisingly, most of the anuran species native to primary forests were able to survive in logged forest streams. In contrast, on average only one third of the forest species richness was found in oil palm plantation streams. However, a high percentage of canopy cover above the plantation streams was able to mitigate this loss substantially. This study demonstrates the high conservation value of logged forests for Southeast Asian anurans. In contrast, the conversion to oil palm plantations leads to a dramatic decline of forest species. However, they have a mainly unused potential to contribute to the protection of parts of the regional anuran biodiversity if conservation-oriented management options are implemented.
III. In this part, I analysed the shifts in trophic position and multiple diversity layers of Southeast Asian stream-dependent anuran species across a gradient of disturbance from primary forest through intensively logged forest to oil palm plantation. For this purpose, I identified the diet composition of 59 anuran species by means of stomach flushing. Furthermore, I use diet composition of frog species as well as species traits to calculate dietary and functional diversity, respectively. I found that the trophic position of the entire anuran community is elevated in heavily disturbed habitats. Furthermore, species diversity, phylogenetic species variation, dietary diversity, and functional diversity were reduced. However, beyond the effect of the decreased species richness, only phylogenetic species variability and functional diversity were significantly impacted by land conversion, indicating a non-random loss of phylogenetic groups and functionally unique species. Overall, the observed changes to species interactions and functional composition suggest a greatly modified role of anurans in altered habitats and major foodweb reorganisation. Such far-reaching changes to the way species groups interact are likely to threaten local biodiversity and ecosystem functioning in natural and particularly modified habitats. However, I could also show, that small-scale habitat quality, provided by riparian reserves, is able to mitigate the negative consequences of land conversion considerably.
IV. Here I assess how logging of rain forest and conversion to oil palm plantations affect the populations of the ant-specialist giant river toad (Phrynoidis juxtaspera), and availability and composition of its ant prey. I measured canopy cover as an estimate for the degree of disturbance. I found that toad abundance decreased with increasing disturbance. At the same time, ant community composition was altered, and local ground-foraging ant species richness increased with disturbance. However, for a given amount of canopy cover, primary forest supported more ant species than altered habitats. Despite these changes, composition of ants consumed by toads was only weakly affected by habitat change, with the exception of the invasive yellow crazy ant (Anoplolepis gracilipes), which was positively selected in oil palm plantations. This suggests that predator-prey interactions can be mostly maintained with habitat disturbance despite shifts in community composition, and even that some predators are capable of exploiting new prey sources in novel ecosystems.
V. I could show that anuran diversity and their trophic interaction is negatively impacted by logging and in particular by conversion to oil palm plantations. From species richness and community composition, my study expanded to phylogenetic, dietary and functional diversity. Furthermore, I investigated the interaction of a particular toad species with its preferred prey (ants), on species level. This increasing degree of detail in my study provided comprehensive results, beyond the detail of many related studies. Overall, conservation of the remaining forest in Southeast Asia is urgently required to protect anuran biodiversity and their trophic interactions.
1. Since the early nineteenth century describing (and understanding) patterns of distribution of biodiversity across the Earth has represented one of the most significant intellectual challenges to ecologists and biogeographers. Among the most striking patterns of species richness are: the latitudinal and elevational gradients, with peaks in number of species at low latitudes and somewhere at mid altitudes, although other patterns, e.g. declines with increasing elevation, are often observed. Even in highly diverse tropical regions, species richness is not evenly distributed but there are “hotspots” of biodiversity where an exceptional number of species, especially endemics, are concentrated. Unfortunately, such areas are also experiencing dramatic loss of habitat. Among vertebrate taxa, amphibians are facing the most alarming number of extinctions. Habitat destruction, pollution and emergence of infectious diseases such as chytridiomycosis, are causing worldwide population declines. Responses to these drivers can be multidirectional and subtle, i.e. they may not be captured at the species but at the genetic level. Moreover, present patterns of diversity can result from the influence of past geological, climatic and environmental changes.
In this study, I used a multidisciplinary and multilevel approach to understand how and to which extent the landscape influences amphibian diversity. Mount Kilimanjaro is an exceptional tropical region where the landscape is rapidly evolving due to land use changes; additionally, there is a broad lack of knowledge of its amphibian fauna. During two rainy seasons in 2011, I recorded anurans from the foothills to 3500 m altitude; in addition, I focused on two river frog species and collected tissue samples for genetic analysis and swabs for detection of chytridiomycosis, the deadly disease caused by Batrachochytrium dendrobatidis (Bd).
2. I analyzed how species richness and composition change with increasing elevation and anthropogenic disturbance. In order to disentangle the observed patterns of species diversity and distribution, I incorporated inferences from historical biogeography and compared the assemblage of Mt. Kilimanjaro and Mt. Meru (both recent volcanoes) with those of the older Eastern Arc Mountains. Species richness decreased with elevation and locally increased in presence of water bodies, but I did not detect effects of either anthropogenic disturbance or vegetation structure on species richness and composition. Moreover, I found a surprisingly low number of forest species. Historical events seem to underlie the current pattern of species distribution; the young age of Mt. Kilimanjaro and the complex biogeographic processes which occurred in East Africa during the last 20 million years prevented montane forest frogs from colonizing the volcano.
3. I focused on the genetic level of biodiversity and investigated how the landscape, i.e. elevation, topographic relief and land cover, influence genetic variation, population structure and gene flow of two ecologically similar and closely related river frog species, namely Amietia angolensis and Amietia wittei. I detected greater genetic differentiation among populations in the highland species (A. wittei) and higher genetic variation in the lowland species (A. angolensis), although genetic diversity was not significantly correlated with elevation. Importantly, human settlements seemed to restrict gene flow in A. angolensis, whereas steep slopes were positively correlated with gene flow in A. wittei. This results show that even ecologically similar species can respond differently to landscape processes and that the spatial configuration of topographic features combined with species-specific biological attributes can affect dispersal and gene flow in disparate ways.
4. River frogs of the genus Amietia seem to be particularly susceptible to chytridiomycosis, showing the highest pathogen load in Kenya and other African countries. In the last study, I collected swab samples from larvae of A. angolensis and A. wittei for Bd detection. Both species resulted Bd-positive. The presence of Bd on Mt. Kilimanjaro has serious implication. For instance, Bd can be transported by footwear of hikers from contaminated water and soil. Tourists visiting Mt. Kilimanjaro may translocate Bd zoospores to other areas such as the nearby Eastern Arc Mts. where endemic and vulnerable species may still be naïve to the fungus and thus suffer of population declines.
5. My study significantly contributed to the knowledge of the amphibian fauna of Mt. Kilimanjaro and of East Africa in general, and it represents a valuable tool for future conservation actions and measures. Finally, it highlights the importance of using a multidisciplinary (i.e. community ecology, historical biogeography, landscape genetics, disease ecology) and multilevel (i.e. community, species, population, gene) approach to disentangle patterns of biodiversity.