published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

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The ecological role of large herbivores is increasingly recognized due to their ability to influence ecosystem functioning and their impacts on faunal and floral assemblages. Knowledge on the determinants of spatial utilization is crucial towards the successful management of these species according to objectives set for the conservation of biodiversity. While numerous studies have investigated the factors influencing the movements and habitat preferences of large northern hemisphere herbivores, few have focused on members of the African megaherbivore guild. In the context of fenced reserves, elephants have been implicated in the degradation of habitat resulting in negative impacts on biodiversity. Using a kernel analysis approach, I calculated home range size and utilization distributions for five separate herds from an elephant population in Hluhluwe-iMfolozi Park and examined possible determinants. I explored differences in utilization intensity between herds and seasons by comparing the rugosity of utilization distributions. I used a utilization distribution-weighted composition analysis to determine seasonal habitat preferences within the home range and examined the factors influencing daily movement characteristics within different habitats in different seasons. Substantial variation in home range size and location, utilization intensity, habitat preferences and movement responses was evident between herds. Spatial and temporal variation in resource distribution and intra-specific competition explained differences in home range size and utilization intensity. Larger herds underwent more fission-fusion events than small herds, possibly due to resource scarcity and greater competitive interactions. Elephants preferred greener habitats during the dry season and appeared to conform to optimal foraging principles. They utilized forest habitats more than others, selected larger patches with high densities of favoured food items and included greater proportions of common woody species in their diet. Large groups foraged close to rivers in the wet season and appeared to broaden foraging choices in the dry season by moving further away. Restricted displacements in the early morning and evening suggested crepuscular foraging activity while greater displacements at midday could not be explained by the need for water. This study highlights the importance of considering variation in animal movements and habitat utilization in overall conservation planning and when evaluating threats to sensitive habitats, particularly in fenced protected areas. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

Herbivores are important drivers and have a longstanding history in shaping our terrestrial environments. However, during the past decades, changes in woody vegetation in savanna and forest systems have been observed in southern Africa. Subsequently, concerns have been raised about the loss of (tall) trees in areas with elephant. The relative effects of browsing herbivores on vegetation and the potential browsing interaction with other herbivore species remain unclear and were examined using vegetation transects and exclosure experiments in savanna woodland and Sand Forest. Rainfall, fire and elephant were important savanna determinants. Especially rainfall positively affected woody densities, which were negatively affected by a longer exposure time to elephant, but not to elephant densities itself. In general, within South Africa’s savannas, tree height classes were absent from the population demography. Different height classes were likely to be impacted by different drivers. For example, seedling and sapling densities were greater with longer fire return periods and increased rainfall. The Sand Forest exclosure experiments showed that forest regeneration was impacted by nyala and both elephant and nyala, as the absence of both species increased tree densities. Both species combined, and individually, also affected tree species assemblages. In contrast, short term elephant access to a savanna area did not affect tree densities or species assemblages. In both savanna and Sand Forest elephant displaced mesoherbivores, and in Sand Forest both elephant and mesoherbivores displaced their smaller counterparts. The presence of competitive displacement also affected recruitment (i.e. seedlings and/or saplings) of woody vegetation both in Sand Forest and savanna. Thus, elephant and mesoherbivores exert direct and indirect (i.e. competitive displacement providing a window for recruitment) impact on vegetation. Active management of the herbivore species assemblage affects both vegetation and other herbivores, which effects potentially cascade into lower trophic levels, jeopardising biodiversity and ecosystem processes. Therefore, the full herbivore assemblage present and their combined and individual browsing effects need to be considered when setting management goals to conserve habitats and biodiversity across all trophic levels. In addition some contrasting results between Sand Forest and savanna emphasise the need for caution when extrapolating results from different areas and ecosystems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

Thesis (M.Sc.) - Carleton University, 2005. / Includes bibliographical references (p.58-63). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Chicago, Department of Organismal Biology and Anatomy, June 2000. / Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--Rhodes University, 2004. / Title from PDF t.p. (viewed on Apr. 23, 2006). Includes bibliographical references (leaves 122-136).

Macroinvertebrates associated with the aquatic plant, water stargrass (Heteranthera dubia), were sampled from 12 waterbodies in four regions of the United States from June to August 2005. Taxa richness, evenness, and diversity were lowest in the Lower Midwest (LMW) region, and higher in Northern sites, especially the Upper Midwest (UMW), and Northeast (NE). While relative abundance varied from site to site and region to region, utilization of the plant by functional groups remained fairly constant. Collector-gatherers consistently comprised the largest portion of invertebrates sampled. The shredder/ herbivore functional group comprised an average of 17 % of total groups. Through an exhaustive literature review, it was found that shredder/ herbivores of water stargrass have not been reported in the literature. Because of this, the herbivore group was analyzed separately and consisted of 2,383 specimens representing 23 species. The most common groups were Rhopalosiphum sp., Nectopsyche spp. and chironomids. No differences were found in herbivore diversity or evenness between sampling regions, but species richness was significantly different.

Herbivorous coral reef fishes play an important role in helping to structure their environment directly by consuming algae and indirectly by promoting coral health and growth. These fishes are generally separated into three broad groups: browsers, grazers, and excavators/scrapers, with these groupings often thought to have a fixed general function and all fishes within a group thought to have similar ecological roles. This categorization assumes a high level of functional redundancy within herbivorous fishes. However, recent evidence questions the use of this broad classification scheme, and posits that there may actually be more resource partitioning within these functional groupings. Here, I use a compound-specific stable isotope approach (CSIA) to show there appears to be a greater diversity of functional roles than previously assumed within broad functional groups. The δ13C signatures from essential amino acids of reef end-members (coral, macroalgae, detritus, and phytoplankton) and fish muscle were analyzed to investigate differences in resource use between fishes. Most end-members displayed clear isotopic differences, and most fishes within functional groups were dissimilar in their isotopic signature, implying differences in the resources they target. No grazers closely resembled each other isotopically, implying a much lower level of functional redundancy within this group; scraping parrotfish were also distinct from excavating parrotfish and to a lesser degree distinct between scrapers. This study highlights the potential of CSIA to help distinguish fine-scale ecological differences within other groups of reef organisms as well. These results question the utility of lumping nominally herbivorous fishes into broad groups with assumed similar roles. Given the apparent functional differences between nominally herbivorous reef fishes, it is important for managers to incorporate the diversity of functional roles these fish play.

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.