Animals living in marine sediments (the second largest habitat on earth) play a major role in global biogeochemical cycling. By feeding on organic matter from settled phytoplankton blooms they produce food for higher trophic levels and nutrients that can fuel primary production. In the Baltic Sea, anthropogenic stresses, such as eutrophication and introductions of invasive species, have altered phytoplankton dynamics and benthic communities. This thesis discusses the effects of different types of phytoplankton on the deposit-feeding community and the importance of benthic biodiversity for fate of the phytoplankton bloom-derived organic matter. Deposit-feeders survived and fed on settled cyanobacterial bloom material and in doing so accumulated the cyanobacterial toxin nodularin. Their growth after feeding on cyanobacteria was much slower than on a diet of spring bloom diatoms. The results show that settling blooms of cyanobacteria are used as food without obvious toxic effects, although they do not sustain rapid growth of the fauna. Since all tested species accumulated the cyanotoxin, negative effects higher up in the food web can not be ruled out. Both species composition and richness of deposit-feeding macrofauna influenced how much of the phytoplankton bloom material that was incorporated in fauna or retained in the sediment. The mechanism behind the positive effect of species richness was mainly niche differentiation among functionally different species, resulting in a more efficient utilization of resources at greater biodiversity. This was observed even after addition of an invasive polychaete species. Hence, species loss can be expected to affect benthic productivity negatively. In conclusion, efficiency in organic matter processing depends both on pelagic phytoplankton quality and benthic community composition and species richness. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: In press. Paper 5: Manuscript.</p>

Invasive species are generally problematic where they occur, especially in terms of ecology, economy and disease. Members of the genus Rattus Fischer, 1803 particularly, are known as one of the most destructive invasive species to date since they cause widespread damage on terrestrial and island ecosystems. Two Rattus species have historically been reported as invasive species in South Africa, Rattus rattus Linnaeus, 1758, which has a widespread distribution throughout the country and Rattus norvegicus Berkenhout, 1769 which is primarily distributed along the coast of South Africa. A third species, Rattus tanezumi Temminck, 1844 (which forms part of the R. rattus species complex), a south-east Asian endemic, was first reported in 2005 to also occur in South Africa (and Africa). As this species is morphologically similar to R. rattus, its identification is reliant on molecular typing approaches. In the current study, molecular, morphological and disease aspects of South African Rattus were assessed. The nature and extent of variation between the three species was investigated using cytochrome b sequences and extensive mitochondrial d-loop database for comparative purposes. D-loop data identified one, four and two haplotypes for R. tanezumi, R. rattus and R. norvegicus, respectively whereas cytochrome b data identified additional haplotypes for R. rattus and R. tanezumi. Pairwise sequence divergence was highest between R. norvegicus and R. tanezumi (12.5% for D-loop and 12.0% for cyt b). Rattus norvegicus was recovered in the central parts of South Africa for the first time and occurred sympatrically with R. tanezumi at one locality, whereas Rattus rattus and R. tanezumi occurred sympatrically at three localities. The external and qualitative cranial morphology of all three species was compared in an attempt to find differences that could be used to morphologically differentiate between these Rattus species. Whereas R. norvegicus can easily be distinguished from R. rattus and R. tanezumi, there are no discernible morphological differences to distinguish R. rattus and R. tanezumi. A taxonomic synthesis and an identification key of the three species of Rattus based on qualitative morphology, molecular and cytogenetic data using genetically-identified individuals is provided. Members of South African Rattus were also found to be carriers of the bacteria Bartonella Strong et al., 1915 and Helicobacter Goodwin et al., 1989 emend. Vandamme et al., 1991. Bartonella elizabethae (Daly et al., 1993) Brenner et al., 1993, occurring in Rattus around the world was for the first time recovered from South African Rattus. This bacterium has been associated with infective endocarditis in humans and may pose a threat to immuno-compromised individuals in rural South African communities where Rattus occurs commensally. Two Helicobacter species, H. rodentium Shen et al., 1997 and H. muridarum Lee et al., 1992, were identified neither of which have known zoonotic potential. Apart from contributing to general small mammal studies in Africa, the present study may have implications in epidemiological, agricultural, biological conservation, and invasion biology research associated with problem rodents in the southern African subregion and beyond. / Dissertation (MSc)--University of Pretoria, 2010. / Zoology and Entomology / unrestricted

abstract: Invasive plants harm the ecological properties of natural systems, human health, and local economies. However, the negative impacts of invasive species are not always immediately visible and may be disregarded by local communities if social benefits of control efforts are not clear. In this dissertation, I use a mixed-methods approach to investigate the drivers of invasive plant distribution, potential financially feasible management techniques to control invasion, and community forest user perceptions of those techniques. In this work, I aim to incorporate the diverse perspectives of local people and increase the long-term success of invasive species control activities in socio economically vulnerable populations. Integrating a spatially and temporally diverse data set, I explore the social and ecological drivers of invasive plant abundance across 21 buffer zone community forests in the Western Chitwan Valley of Nepal. I evaluate to what extent forest user and collective manager activities, the legacies of historic activities, and ecological properties influence present-day invasive plant abundance. I built upon this study to identify areas with critically high levels of invasion then initiated a three-year, community-based management intervention to evaluate traditional and adaptive land management approaches to control invasive plants. I found that both approaches reduced invasive plant abundance relative to the surrounding, untreated forest. I then interviewed focus groups to investigate their perceived efficacy of the various treatment types and found that almost all forest users and managers preferred the adaptive approach over the traditional management approach. Notably, forest users cited the importance of the availability of forest resources and lack of harmful plants in the plots that had undergone this method. Understanding how forest users relate to and experience invasive plants has been relatively understudied but can influence forest user engagement in different management approaches. For this reason, I performed in-depth ethnoecological interviews to explore how forest users perceive, how they utilize, and to what extent they value invasive plants. This mixed-methods approach contributes to a more holistic understanding of the role that local people play in invasive plant management and restoration activities. / Dissertation/Thesis / Doctoral Dissertation Environmental and Resource Management 2020

No description available.

This work is about diploids and tetraploids of Vicia cracca species, the two commonly occurring cytotypes. The first part is devoted to the distribution of cytotypes of this species in the secondary range in North America. It was hypothesised that polyploid species become invasive more frequently than diploid species. Their greater success may be given by greater variability of genes obtained by polyploidisation and gene subfunkcionalizing. All invasive populations of Vicia cracca species involved in this study were tetraploid. Based on this we can say that only tetraploids are invasive in this secondary colonized area. Polyploid species can be better competitors thanks to their expected better growth characteristics and stress resistance. Therefore the second part of this work is testing the hypothesis that polyploids are more variable in size of different parts of the plant body and therefore more able to grow even in conditions that are not suitable for diploids. As predicted by the EICA hypothesis (evolution of increased competitive ability), secondary colonized area also provide more space for further evolution and we can expect that growth characteristics of plants from the invasive range will differ from plants of the same ploidy from the original distribution range. This part of the work...

The aim of this thesis was to identify factors that contribute to invasiveness of species in the genus Impatiens. This genus is horticulturally attractive and includes several species that are known to have naturalized outside their native ranges, while others did not escape, in spite of being frequently cultivated. When looking for traits associated with invasiveness, it is useful to focus on congeneric species. Their traits and dispersal modes are less influenced by phylogeny, than when comparing unrelated species or even complete floras. This helps to account for traits that favour invasive species over native ones and thus identify potential invaders more precisely. A superior invader performance is attributed to a competitive advantage over native species that can lead in extreme case to competitive exclusion of the latter. Invasive and native species com- pete only if their niches overlap and the strength of competition depends on niche similarity. Importantly, invasive species are considered to be able to maintain their high competitiveness over a wide range of environmental conditions, while native ones often have narrower environ- mental optima. Lastly, competitive outcome can vary over life stages and depends on the degree of species dominance, which is rarely taken into account. Spread and...

Introduced species can become invasive and cause catastrophic alterations to the system they invade. Both zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) have caused significant ecosystem alterations wherever they have invaded. These Dreissena species have caused changes in water quality and biodiversity and have disrupted energy pathways which can have cascading effects on other trophic levels. Recently quagga mussels invaded Lake Powell, a reservoir located in the southwestern USA, creating the possibility of a trophic cascade that could alter energy flow in the reservoir and change the trophic niche structure of the fishes in the lake. However, due to Lake Powell’s large size, dynamic nature, and complex hydrological structure, the effects of quagga mussels on fish species is uncertain. To determine impacts of quagga mussels on Lake Powell fishes, we quantified trophic niches of five species of sport fish over three years (2017-2019) using stable isotopes of nitrogen, δ15N, and carbon, δ13C. We test the following hypothesis: quagga mussels will cause a shift in trophic niche in more pelagic fishes such that pelagic fishes decrease in trophic position and shift toward use of more littoral energy. In addition, we compare the trophic niche of these species with a previous study on the trophic niche of fish in Lake Powell prior to full colonization of the lake by quagga mussels (2014-2015). In general, fish in the southern region of the lake exhibited a trend of decreasing δ15N suggesting decreasing trophic position and an enrichment of δ13C indicating a littoral energy shift in some species. Fish in the northern region of the lake exhibited a slight increase in trophic position and a shift towards pelagic energy across the same time period. These shifts support the hypothesis with pelagic fish experiencing a trophic niche shift, in the direction predicted, but only in the southern region of Lake Powell. Additionally, this shift is not exclusive to pelagic fish, but happened in all five species. Sediment laden input from the Colorado River may offset the impact of quagga mussels in the northern region of the lake resulting in observed regional differences.

Increased biodiversity generally enhances terrestrial ecosystem productivity. While niche-use efficiency is thought to drive the biodiversity-productivity relationship, the mechanisms within niche-use efficiency are not well understood. A potential mechanism for niche-use efficiency is nutrient-use efficiency. To measure nutrient-use efficiency, we calculated nitrogen-resorption efficiencies (NRE) because nitrogen is an important growth limiting nutrient for forest productivity. We used a plantation implemented as a full factorial design that included two levels of competition, implemented as different planting densities (one- and two-meter planting densities), and three diversity levels (monocultures, two-, and three-species plantings) that included three hardwood tree species (northern red oak (<i>Quercus rubra</i>), black cherry (<i>Prunus serotin</i><i>a</i>), and American chestnut (<i>Castanea dentata</i>). For our nitrogen-resorption efficiency data, we found that NRE increased as diversity and planting density decreased, but the magnitude of the response varied among species. This outcome suggests that while increased diversity likely provides a release from intra-specific competition, different combinations of species will play a critical role in shaping biodiversity-productivity relationships. Forest nutrient cycling can also be influenced by herbivory. To address the effects of forest diversity on herbivory rates, we monitored rates of foliar damage along with foliar nitrogen content. To measure foliar nitrogen content, we collected spectral data from early, midseason, and late season foliar samples. To assess foliar damage, we collected and imaged leaves from two canopy positions in order to measure late season foliar area and estimate pre damaged foliar area. We found that diversity and foliar nitrogen content have a positive relationship, and diversity does influence canopy damage but the effects vary among species and density. Upon further analysis, we found that foliar nitrogen content and canopy damage are correlated. Meaning individual trees showed a release from intraspecific competition, which lead to an increase in available nutrients and higher canopy quality, showing that stands with higher canopy quality experienced higher levels of damage.<br>

No description available.

The Allideghi Wildlife Reserve in the Amibara District of Afar Regional State, Ethiopia, has international significance for harboring endangered Grevy's Zebra and other wildlife dependent on grasslands. The reserve is increasingly used by pastoral people and their herds. Impacts of livestock on native vegetation include direct effects of grazing and indirect effects from livestock-facilitated dispersal of an invasive plant, Prosopis juliflora. The main research objective was to determine effects of pastoralism and vegetation change on prospects for sustaining the Allideghi Wildlife Reserve as grassland habitat for Grevy's Zebra. Methods included use of driving surveys to quantify resource use by herbivores, vegetation analysis, and engagement with local people. Resource-use patterns of livestock across the Allideghi grassland were often positively affected by proximity of water, while that for wild ungulates was often negatively affected by proximity of people. Livestock concentration at a major borehole has created a large piosphere with concomitant reductions in herbaceous standing-crop, productivity, and species richness; plant species have shifted from grasses to forbs in severely grazed sites. Vegetation further from the borehole was resilient in response to moderate grazing pressure in terms of species composition and productivity. Since being introduced at a nearby commercial plantation in the 1970s, P. juliflora has been dispersed to the Allideghi Wildlife Reserve via livestock; cattle, sheep, and goats eat the pods and deposit seeds in manure at settlements and favored foraging areas. Prosopis juliflora greatly reduced species richness and basal cover of native herbaceous vegetation in the Allideghi grassland. Analysis of remotely sensed images from the past 30 years indicated major land-use change in the district due to agricultural expansion as well as land-cover change due to Prosopis encroachment and heavy grazing. Recent efforts have been undertaken by various agencies to control P. juliflora, via harvest in the district, but this has yielded variable and often negative results. Without a concerted effort to limit livestock grazing and control spread of P. juliflora, the future for the grassland and wildlife at the Allideghi Wildlife Reserve is grim. Agencies and policy makers need to promote science- and community-based approaches to help rectify the situation. (311 pages)