So Ka Yi Erica. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 243-255). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract --- p.iii / Contents --- p.ix / List of Tables --- p.xii / List of Figures --- p.xix / Chapter Chapter 1 --- General Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- General Objectives --- p.11 / Chapter 1.3 --- Study Site --- p.12 / Chapter 1.4 --- Organization of the Thesis --- p.13 / Chapter Chapter 2 --- "General Surveys on the Abundance of Algae and Herbivores in A Ma Wan, A Ye Wan and Lung Lok Shui, Tung Ping Chau, Hong Kong" / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Materials and Methods --- p.20 / Chapter 2.2.1 --- Study site --- p.20 / Chapter 2.2.2 --- Measurement of water temperature --- p.21 / Chapter 2.2.3 --- Measurement of algal percentage cover --- p.22 / Chapter 2.2.4 --- Measurement of herbivore density --- p.22 / Chapter 2.2.5 --- Investigation on the species richness and diversity of algae and herbivores --- p.23 / Chapter 2.2.6 --- Statistical analysis --- p.24 / Chapter 2.3 --- Results --- p.27 / Chapter 2.3.1 --- Measurement of algal abundance and diversity --- p.27 / Chapter 2.3.1.1 --- Percentage cover and morphology --- p.28 / Chapter 2.3.1.2 --- Species richness --- p.29 / Chapter 2.3.1.3 --- Species diversity --- p.29 / Chapter 2.3.1.4 --- Dominance and composition --- p.30 / Chapter 2.3.2 --- Measurement of herbivore abundance and diversity --- p.32 / Chapter 2.3.2.1 --- Density of herbivores --- p.32 / Chapter 2.3.2.2 --- Species richness --- p.33 / Chapter 2.3.2.3 --- Species diversity --- p.34 / Chapter 2.3.2.4 --- Dominance and composition --- p.34 / Chapter 2.3.3 --- Relationships between algae and herbivores --- p.37 / Chapter 2.3.3.1 --- Pairwise Pearson Correlation between algae and herbivores in different sites --- p.37 / Chapter 2.3.3.2 --- Canonical correlations between algal and herbivorous species --- p.38 / Chapter 2.3.4 --- "Water temperature and its relationships with the abundance, richness and diversity of algae and herbivores" --- p.39 / Chapter 2.4 --- Discussion --- p.40 / Chapter 2.4.1 --- Spatial distribution of algae and herbivores --- p.40 / Chapter 2.4.2 --- Seasonal distributions of algae and herbivores --- p.46 / Chapter 2.4.3 --- Interactions between algae and herbivores --- p.50 / Chapter Chapter 3 --- Growth of Algae in Herbivore-exclusion Manipulative Experiment / Chapter 3.1 --- Introduction --- p.106 / Chapter 3.2 --- Materials and Methods --- p.111 / Chapter 3.2.1 --- Study site --- p.111 / Chapter 3.2.2 --- Manipulative experiment --- p.111 / Chapter 3.2.3 --- Investigation on the manipulative experiment --- p.112 / Chapter 3.2.3.1 --- Species composition of algae and herbivores --- p.113 / Chapter 3.2.3.2 --- Percentage cover of algae and density of herbivores --- p.113 / Chapter 3.2.3.3 --- Sizes of herbivores --- p.113 / Chapter 3.2.4 --- Detecting the cage effect --- p.114 / Chapter 3.2.5 --- Statistical analyses --- p.114 / Chapter 3.3 --- Results --- p.117 / Chapter 3.3.1 --- Algae --- p.117 / Chapter 3.3.1.1 --- Percentage cover --- p.117 / Chapter 3.3.1.2 --- Species richness --- p.120 / Chapter 3.3.1.3 --- Composition between treatments --- p.121 / Chapter 3.3.1.4 --- Compositions between set-ups --- p.121 / Chapter 3.3.1.5 --- Effects from caging and clearing --- p.122 / Chapter 3.3.2 --- Herbivores --- p.123 / Chapter 3.3.2.1 --- Density --- p.123 / Chapter 3.3.2.2 --- Species richness --- p.124 / Chapter 3.3.2.3 --- Compositions between treatments --- p.124 / Chapter 3.3.2.4 --- Compositions between set-ups --- p.125 / Chapter 3.3.3 --- Relationships between algae and herbivores --- p.125 / Chapter 3.3.3.1 --- Abundance --- p.125 / Chapter 3.3.3.2 --- Composition --- p.126 / Chapter 3.3.4 --- Sizes of herbivores --- p.128 / Chapter 3.3.5 --- Irradiance between treatments --- p.128 / Chapter 3.4 --- Discussion --- p.129 / Chapter 3.4.1 --- Effects of clearing on algal and herbivore dynamics --- p.130 / Chapter 3.4.2 --- Effects of caging on algal and herbivore dynamics --- p.135 / Chapter 3.4.3 --- Effects of seasonality of clearing on algal and herbivore dynamics --- p.139 / Chapter 3.4.4 --- Interactions of algae and herbivores --- p.142 / Chapter Chapter 4 --- Feeding Behavior of Common Herbivores in the Artificial Food Experiment / Chapter 4.1 --- Introduction --- p.216 / Chapter 4.2 --- Materials and Methods --- p.218 / Chapter 4.2.1 --- Sample collections --- p.218 / Chapter 4.2.2 --- Production of artificial foods --- p.219 / Chapter 4.2.3 --- Feeding experiments --- p.219 / Chapter 4.2.4 --- Statistical analysis --- p.220 / Chapter 4.3 --- Results --- p.221 / Chapter 4.4 --- Discussion --- p.222 / Chapter Chapter 5 --- Summary and Conclusion --- p.233 / References --- p.243

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science Johannesburg, September 2015 / Plant functional traits provide a means to investigate the diverse ecological strategies employed by plants and a tangible link to assess how the variability in these traits might influence ecosystem processes and functioning. The aim of this dissertation has been to determine how plant and soil nutrient dynamics in a savanna environment are affected by two primary drivers, one a top-down driver, being herbivory by large mammalian herbivores and the other a bottom-up driver, the variable N2-fixation capacity of tree species. To the best of my knowledge this is the most comprehensive study to date to investigate the bioavailability of soil nutrients and the link between these availabilities and plant functional traits. Furthermore this study provides important insight into the use of a novel technology, ion exchange resin capsules in a South African savanna context. By studying a selection of plant functional traits (nutrient concentrations, ratios as well as specific leaf area, relative chlorophyll content and leaf dry matter content) and soil nutrients (suite of macro- and micronutrients) associated with two species of savanna tree of contrasting N2-fixation capacities, I went about investigating how herbivory differentially influences the nutrient dynamics of this system. Selecting individuals of the N2-fixing Acacia tortilis and the non-N2-fixing Combretum hereroense both inside an exclosure and on the adjacent land allowed me to determine the potential impacts by herbivores. These include both direct impacts from foraging and indirect impacts through the regulation of nutrient input pathways via deposition of dung and urine. The work compiled for this dissertation is based on the experimental work conducted in a mesic savanna system in the Marakele Park (PTY) Ltd. During the course of this dissertation, I investigated herbaceous and woody biomass in relation to protection from and exposure to herbivory, determining any differences in the functional leaf traits between individuals inside and outside the exclosure, if these differences were exhibited in the associated herbaceous biomass as well as a comprehensive assessment of the bioavailability of 15 important micro- and macronutrients using ion exchange resin capsules. These capsules were incubated in the soil over the entire summer rainfall period, providing a cumulative view of nutrient bioavailability during the growing season. In this work I also demonstrated whether particular nutrients are associated with specific drivers (i.e. herbivory, canopy position or N2-fixation). Furthermore, these results were then looked at together to suggest the mechanism by which herbivory and N2-fixation drive nutrient dynamics and make recommendations on the use of these results in managing savanna systems in the future. Between the two sites, aboveground herbaceous biomass was significantly greater when protected from herbivores than on the adjacent land. Both exposure to herbivory and N2-fixation capacity were found to alter plant functional traits. Herbivore presence was associated with an increase in herbivore-resistant or structural traits such as C/N, C/P, foliar C and SLA as well as a reduction in N and P content. These less palatable leaves were accompanied by a significantly lower availability of a number of important soil elements, namely NO3-N, inorganic N, P, K, Na, Cu, B, Mg, and S. This suggests a feedback loop between these two components of the ecosystem. N2-fixation capacity is associated with greater concentrations of elements such as N and P and a reduction in traits that are illustrative of a greater structural investment into leaves. Soil nutrient bioavailability however, shows a reduction in certain nutrients when associated with Acacia. A number of nutrients which show a reduction in availability are those which are essential to N2-fixation machinery, namely B and Fe but also lower bioavailabilities of Al and Mg. Finally, Ca, NO3-N, B, Fe, Al and inorganic N were found in greater quantities below the tree canopy than beyond it. In conclusion both herbivory by large mammalian herbivores and N2-fixation have significant effects on tree health, through their regulation of limiting nutrients and alteration of leaf traits. Given the changes which these drivers are capable of exerting on plant and soil nutrient dynamics, this has important consequences for ecosystem processes and functioning and highlights potential considerations in the long-term sustainable management of savannas.

The impact of grazers on the primary production of marine ecosystems has largely been explored in tropical environments. A number of studies support theories on the functional importance of grazers in the community structure of coral reefs. However, large-bodied grazers, like juvenile green turtles, co-occur with herbivorous fishes in subtropical and tropical regions throughout the world and we know little about their combined impact on macroalgal communities and whether they compete for macroalgal resources. My dissertation research was composed of four studies that were conducted simultaneously to further our understanding of plant/herbivore interactions in marine ecosystems. Studies were conducted at the Trident Basin, a non-public military facility within the Port Canaveral Inlet at Cape Canaveral, Florida, USA. The macroalgal study (Chapter 1), determined the spatial and temporal distribution of the macroalgal community. The foraging habits of juvenile green turtles were compared with the macroalgal abundance within the Basin and over time (Chapter 2). Selection ‘for’ specific macroalgal species (based on their availability in the macroalgae study) was used to determine the level of overlap and/or partitioning of resources among herbivorous fishes and juvenile green turtles (Chapter 3). The final empirical study (Chapter 4) measured the impact on thallus height, diameter and/or branching of macroalgae as well as the macroalgal community composition from caging experiments that excluded herbivorous fishes and juvenile green turtles. The algal community was predominantly composed of nine red and green macroalgal species that were persistent year-round. Grazer-resistant macroalgae were rarely observed. Green turtles foraged on many of these same macroalgae but also opportunistically foraged on flotsam, including anthropogenic debris (e.g., plastic). The gut content of the major herbivorous fishes in the community (Abudefduf saxatilis, Archosargus probatocephalus, Diplodus holbrooki, and Lagodon rhomboides) foraged as omnivores depending on where they were captured within the Basin area or their size. All herbivores showed selection for less abundant green algae (i.e., Ulva spp.). Results of the exclusion of juvenile green turtles and large herbivorous fishes in caging experiments suggest that grazing by these large-bodied herbivores had no impact on the composition of the macroalgal community and little impact on the morphological structure of the macroalgal species that were examined. Collectively these four studies contribute to a better understanding of how multiple grazers have evolved to forage in macroalgal communities without detrimental effects on their food resources. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Stable isotope analyses are powerful tools for reconstructing ancient ecologies and ecosystems, as they are independent of morphology and directly reflect dietary ecology. The application of stable isotope analyses, however, is not without limitations, as determination of food web dynamics using these methods often relies on poorly tested assumptions. The guiding thread of this thesis is the testing of foundational cornerstones on which these methods rely, in order to validate the suitability of applying these techniques to different mammalian clades, and to more reliably and confidently interpret the isotopic signals preserved in extinct organisms. The first chapter of this thesis tests the validity of an important assumption behind the interpretation of stable carbon isotope analyses for understanding diet in terrestrial mammalian herbivores: if, as assumed for almost two decades, mammalian bioapatite δ¹³C is enriched by 14‰ relative to dietary δ¹³C. By analyzing new isotopic data from a never before assessed herbivorous group spanning a broad range of body masses—sloths (Xenarthra, Mammalia)— and other mammals with experimentally controlled or observationally known diets, I discovered considerable variation in diet–bioapatite δ¹³C enrichment among mammals. Statistical tests (ordinary least squares, quantile, robust regressions, Akaike information criterion model tests) documented independence from phylogeny, and a previously unrecognized strong and significant correlation of δ¹³C enrichment with body mass for all mammalian herbivores. A single-factor body mass model outperformed all other single-factor or more complex combinatorial models evaluated, including for physiological variables (metabolic rate and body temperature proxies), and indicated that body mass alone predicts δ¹³C enrichment. These analyses, spanning more than 5 orders of magnitude of body sizes, yield a size-dependent prediction of isotopic enrichment across Mammalia and for distinct digestive physiologies, permitting reconstruction of foregut versus hindgut fermentation physiologies for fossils and refined mean annual paleoprecipitation estimates based on δ¹³C of mammalian bioapatite. Second, I sought to evaluate the existing paradigm governing identification of closed canopy rainforests in the fossil record using mammalian δ¹³C data: the presence of mammals with dietary δ¹³C <-31‰, which has only been observed in closed canopy rainforests in Equatorial Africa, the only other tropical ecosystem sampled extensively. This chapter provides a characterization of δ¹³Cbioapatite, δ¹³Chair and δ¹⁵Nhair of a modern mammalian community in western Amazonia, in Peru, to test if the isotopic structure of mammals in this Neotropical ecosystem is similar to those in African tropical rainforests. The results indicate that despite their marked geographical and taxonomic differences, median δ¹³Cdiet values from closed canopy rainforests in Amazonia (-27.4‰) and equatorial Africa (-26.9‰) are not significantly different. Amazonian mammals, however, seem to exploit a narrower spectrum of dietary resources than equatorial African mammals, as depicted by the absence of highly negative δ¹³Cdiet values previously proposed as indicative of rainforests (<-31‰). I hypothesize that differential effects of late Pleistocene extinction may be responsible for the ecological disparities among the two rainforests, by significantly reducing evolutionary time and dietary breadth reflected in the modern Amazonian mammalian community. Finally, the third chapter of this dissertation evaluates assumptions behind δ¹⁵N amino acid compound specific analyses in order to test the controversial hypothesis of carnivory and consumption of proteins of animal origin in fossil sloths. This analytical technique relies on three main assumptions. First, that the offset between the δ¹⁵N of glutamic acid (δ¹⁵NGlx) and phenylalanine (d15NPhe) in the organism under study will increase with increasing trophic level. Second, that the offset between δ¹⁵NGlx and δ¹⁵NPhe at the base of the food chain is relatively constant and has a value of -8.4‰ for C3 ecosystems. Third, that the trophic discrimination factor in all ecosystems (the difference in δ¹⁵NGlx relative to δ¹⁵NPhe with increasing trophic level) is 7.6‰. The results of my experiments conducted on extant xenarthrans (sloths and anteaters) with controlled diets document that only the first assumption holds true. Rather than relying on an equation with constants introducing uncertainties and that are not applicable to organisms feeding on a combination of items of different origin (e.g., C3 + C4 plants), δ¹⁵NGlx and δ¹⁵NPhe values by themselves can accurately reconstruct the trophic position of organisms. Indeed, the results on δ¹⁵NGlx and δ¹⁵NPhe herein obtained for five xenarthran species in controlled feeding experiments, combined with mammalian data available from the literature, show strong and significant correlations between these two AAs and with trophic positions. Both the TP equation and the regression analyses of δ¹⁵NGlx and δ¹⁵NPhe suggest that the Pleistocene fossil ground sloths 𝘔𝘺𝘭𝘰𝘥𝘰𝘯 𝘥𝘢𝘳𝘸𝘪𝘯𝘪𝘪 and 𝘕𝘰𝘵𝘩𝘳𝘰𝘵𝘩𝘦𝘳𝘪𝘰𝘱𝘴 𝘴𝘩𝘢𝘴𝘵𝘦𝘯𝘴𝘪𝘴 were not pure herbivores as commonly presumed, but rather that they were both mixed feeders/omnivores, incorporating items of animal origin in their diets.

In this study, I investigated the interaction between two megaherbivores, the African elephant and white rhinoceros, that has the potential to impact grazing lawns of which white rhino are the creators and maintainers and elephants are potentially the modifiers. I hypothesized that as elephants browse, they discard a variety of coarse woody debris onto the ground; should this woody debris (of varying amounts and sizes) fall onto grazing lawns, white rhino either move them, consume grass around the woody debris or abandon the lawn entirely. If high levels of woody debris are deposited here, grazing by white rhino is likely to be prevented, at which time I predicted that mesoherbivores would have a competitive advantage in accessing forage that white rhino cannot. I examined the mechanistic links between different levels of elephant-deposited woody debris and grass response at a point scale and feeding patch spatial scale of grazing lawns in an African savanna. In addition, I assessed the response of mesoherbivores in terms of vigilance behaviour with increasing levels of predation risk posed by increasing levels of woody debris. I present the first evidence of an indirect effect of elephant on white rhino foraging behaviour. I demonstrate how increasing levels of woody debris lead to a decreasing probability of foraging by white rhino. I also demonstrate how the probability of foraging by mesoherbivores increases as the amount of forage increases. However, since this study took place during a severe drought where resources are extremely limited, I was unable to properly separate the effects of elephant-deposited woody debris from the severe lack of rainfall on grass response and subsequently herbivore foraging behaviour. Due possibly to the drought, mesoherbivores responded less or not at all to risk factors such as woody debris therefore woody debris was not a predictor of vigilance behaviour in my study. This study contributes to our understanding of how the impacts of elephants, as ecosystem engineers, have cascading effects on savanna ecosystems. My study showed that elephant impact mediates the foraging behaviour of white rhino during a drought. However, under average rainfall periods, my original hypothesized effect of the indirect impacts of elephants on white rhino foraging and grazing lawn dynamics could still hold. This key hypothesis that I was unable to test under ‘normal’ conditions due to the drought is still valid and functionally important for understanding the ecosystem processes driving grazing lawn formation, persistence and composition in African savannas where elephants and white rhinos coexist.

The arctic tundra has been warming disproportionately faster than the global mean. Although the tundra has historically been a carbon sink, the current state of its carbon balance is highly uncertain. Large warming induced changes to tundra ecosystems complicate our ability to model tundra carbon cycling. In this dissertation I explore the impact of herbivores on dry heath vegetation and carbon flux, herbivore impact on dry heath tundra canopy, and lastly, the impact higher vegetation has on the conditions under which the tundra transitions from a carbon sink to a carbon source. Chapter 1 presents a study on the impact long term herbivore absence has on dry heath tundra. I measured vegetation cover, abundances of plant growth forms and carbon flux. I demonstrate the herbivore exclusion in this tundra ecosystem results in higher vegetation abundance and greater carbon uptake. Moreover, under average environmental conditions during the measurement period, I show that excluding herbivores resulted in net carbon uptake under average temperature and light conditions during the measurement period. In chapter 2 I build upon my result from chapter 1. I quantify differences in canopy structure due to herbivore exclusion and integrate this into carbon flux estimates. I show that that different herbivore assemblages have significantly different effect on carbon fluxes. Specifically, exclusion of large herbivores results in higher carbon uptake compared to exclusion of large and small herbivores. I also demonstrate that incorporating canopy structure results in significantly lower carbon uptake during morning and evening hours than carbon flux estimates based on my results from chapter 1 would suggest. In chapter 3 I quantify the conditions under which tussock tundra transitions from a carbon sink to source and how that is impacted by increasing vegetation abundance. I show that under low light, tundra with higher vegetation abundance must surpass higher temperatures to become carbon sources compared to tundra with lower vegetation abundance. However, under high light, the conditions are reversed, and tundra with higher vegetation abundance become carbon sources at lower temperatures than tundra with lower vegetation.

Spiders were sampled at Mpala Research Centre, Laikipia, Kenya by pitfall-trapping and sweep-netting from May 2001 to July 2002, at a Kenyan Long-term Exclosure Experiment. The aim was to establish species composition, checklist and examine spider responses to disturbances caused by cattle, megaherbivores (giraffe and elephants) and mesoherbivores (other ungulates) by looking at three levels of resolution, namely the overall community, guilds and individual species. This is the first controlled replicated experimental study on the effects on invertebrates (spiders) by different land uses (access by large herbivores). A total of 10,487 individuals from 132 species belonging to 30 families were recorded. The family Salticidae had the highest number of species (24), followed by Gnaphosidae (20), Araneidae and Lycosidae (15 each), Theridiidae and Thomisidae (8 each) and Zodariidae (4). Most of the other families had fewer than 4 species. Throughout the study period, species not previously sampled emerged after rainfall peaks. Exclosure treatments affected plant cover, spider diversity and total species mainly through the effects of cattle, whose presence significantly reduced relative vegetation cover. An increase in vegetation cover significantly increased the diversity, total species and species evenness of the overall spider community (total samples data set). Megaherbivores and mesoherbivores had no effects on overall spider diversity. Relative vegetation cover explained approximately 20-30% of variation in community diversity, species richness and species evenness. At the guild level of resolution, the exclosure treatments had no significant effects on diversity, species richness and species evenness of web builders, plant wanderers and ground wanderers. Plant wanderers were significantly and positively correlated with relative vegetation cover, which explained 17% of variation in their diversity. Six individual species responded strongly and in contrasting ways to the same environmental variables, indicating that this level was more sensitive to environmental changes than guilds or the overall spider community. Spider diversity, relative vegetation cover and rainfall varied at a temporal scale of months and not at a spatial scale of hundreds of metres. Only species diversity and species richness from sweep-netting samples and total species from pitfall-trapping varied significantly at a spatial scale of hundreds of metres. Ordination analysis revealed that sweep-netting samples were a better indicator of grazing impacts than pitfalltrapping or combined samples and grouped to reflect cattle grazing, non-cattle grazing and to a small extent the control treatments. Other ordination analyses showed that only samples from sweep-netting and not from pitfall-trapping, were spatially partitioned at a scale of hundreds of metres. This study concludes that the spider fauna of black cotton soil habitats is rich and useful for environmental monitoring and that monitoring of several individual species as indicator of grazing impacts in savanna could be useful and relatively easy.