Browsing by Author "Lee-Thorp, Julia A"
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- ItemOpen AccessAnnals of ivory : perspectives on African elephant Loxodonta africana (Blumenbach 1797) feeding ecology from a multi-decadal record.(2008) Codron, Jacqueline; Lee-Thorp, Julia A; Sealy, JudithThis thesis explores the dietary responses of African elephants (Loxodonta africana) to environmental change by testing the hypothesis that diet switching (from predominantly browse-based to more grass-rich diets) is driven by cyclical patterns of climate and habitat change in a southern African savanna. Elephants are thought to have substantial impacts on their environments, primarily because they consume large amounts of vegetation over sustained periods. However, the woody plant composition of their diet varies considerably across space and through time, so that in some instances they have been found to be almost pure grazers. Tracking these changes by traditional approaches (e.g. field observations) is difficult because of the geographical and temporal constraints inherent to these methods. Stable light isotope tracking of diet allows diet switching to be studied over multiple space/time scales. Here, I use stable isotope data from elephant faeces, tail hair, and ivory to record short- (monthly), medium- (seasonal to annual), and long-term (decadal) ecological variability, respectively, of elephant diets in the Kruger National Park, South Africa. Results from faeces collected at monthly resolution for one year confirm findings of a previous study (based on biannually-collected samples over two years) that elephants generally consume more grass in the more wooded habitats of the northern Kruger Park, but that there is a greater degree of seasonal diet switching in southern Kruger Park habitats. Moreover, diet changes also relate to changes in underlying bedrock across Kruger Park. Isotopic time-series produced by serial profiling of tail hairs confirm patterns observed in faeces. Long-term diet histories of individuals are derived from serial isotope sampling of ivory, yielding records that represent several decades of an animal’s life, at sub-annual (seasonal) resolution. Overlaying individual ivory series in time produces the first, to my knowledge, multidecadal record of African elephant diet, dating from 1903 to 1993. Contrary to expectations, stable carbon, nitrogen, and oxygen isotope records from ivory do not correlate well with cyclical climate trends for the study region. Rather, pronounced diet shifts are observed during extreme climatic events (floods and droughts), and the greatest levels of intra- and inter-annual variability coincide with significant changes in park management policy during the 20th century, i.e. the introduction of water provision programs after the mid 1930s, and the onset of elephant population control in 1967. It is proposed that such direct intervention has played the biggest role in disturbance of elephant-plant equilibria during the 20th century, and further studies to improve our understanding of this phenomenon will be instrumental to development of appropriate management strategies for the 21st century.
- ItemOpen AccessCharacterising the Namaqualand Mudbelt: Chronology, Palynology and Palaeoenvironments(2009) Gray, Catherine Elizabeth Darnell; Meadows, Michael E; Lee-Thorp, Julia AThis multiproxy study explores the palaeoenvironmental record of two cores, H2 and H7, from the Namaqualand Mudbelt representing an arid and highly variable landscape. As bulk organic radiocarbon ages previously proved problematic, with anomalous reversals, the primary objective was to improve chronology and palaeoenvironmental reconstructions through high resolution 813C, 81SN and pollen analysis, with the aid of principal component analysis. Bulk organic radiocarbon dating of the surface sediment had previously yielded older than expected ages. New 210Pb analysis has established that these surface sediments are modem and radiocarbon ages are now recalibrated to yield an adjusted age of ±3 470 cal yr BP at the base of the more distal core, H7. Pollen spectra correlate well with stable isotopes and include recent disturbance indicators in the Succulent Karoo, Grassland, Karoo expansion, stock farming, impoundment, saltmarsh degradation and increase in domestic cereal cultivation. The proximal and distal mudbelt sites are, however, isotopically distinct, with 813C, inverse nitrogen and C/N ratios characterising H2 as more terrestrial. The excursion towards C3-rich values at around 6m depth in the proximal mudbelt suggests an increase in marine sources and C3 vegetation, while associated pollen aridity indicators implicate reduced inland flooding. This is contrasted against more humid conditions at 420 cm. Stronger upwelling occurred in near-surface distal mudbelt sediment and an influx of the Buffels River sediment flooded the region at ±3470 yr BP, indicating cooler, less arid conditions. 813C studies reveal the Lower Xobies palaeoflood deposit to be less C4-rich than expected, possibly due to sediment source, and is strikingly isotopically similar to the distal mudbelt. The palaeoenvironmental interpretation of the pollen assemblage, isotopes and chronology presents an improved understanding of the region represented in the mudbelt sediments. This corresponds well with established records of the last ±3 500 years and human induced land use change within the Orange River Catchment. Results also highlight the dynamics of the Orange River, which, combined with a highly variable climate, suggest that caution should be exercised to avoid over-interpreting the level at which environmental changes can meaningfully be reconstructed in arid landscapes, particularly those which are subject to sporadic and catastrophic flooding events.
- ItemOpen AccessDietary ecology and niche separation among three closely related species (Parapapio jonesi, Pp. whitei and Pp. broomi) of South African Plio-Pleistocene Cercopithecoidea from Makapansgat Limeworks site(2006) Fourie, Nicolaas Hofmeyer; Lee-Thorp, Julia A; Ackermann, Rebecca RogersThree sympatric, contemporaneous fossil cercopithecoid genera (Cercopithecoides, Parapapio and Theropithecus) are represented in assemblages from the Makapansgat Limeworks hominin locality in South Africa. The presence of such a variety of primate taxa in a single ecosystem at the same time suggests a certain degree of ecological and/or dietary differentiation between taxa. This research explores the possibility of dietary niche separation within this sample. Stable isotope (13C/12C, 180/160 ) and trace-element (Sr, Ba, Ca) techniques for palaeodietary analysis are employed to investigate papionin dietary ecology, and especially to search for evidence of subtle niche separation between the more closely related, morphologically similar taxa of the genus Parapapio. Previous studies of fossil cercopithecoid dietary ecology report disjunctions between dietary and taxonomic groupings, possibly as a result of the use of fragmentary specimens or isolated teeth and ensuing taxonomic uncertainty, or perhaps because of problems in the taxonomy itself. Because such taxonomic uncertainties impede the interpretation of dietary data, craniometric analyses were also performed to ground the dietary interpretations in a morphological context. Only complete or partially complete cranial specimens from which morphological craniometric measurements could also be taken were sampled. Dietary analyses indicated two widely differing dietary ecologies within the Cercopithecoides williamsi sample, consistent with published results for this taxon from Swartkrans and Sterkfontein. Results for Theropithecus darti indicated a predominantly C4 diet. Two overlapping dietary ecologies, loosely correlated to taxonomic groupings, were found within the genus Parapapio; specimens attributed to Pp. broomi tended to have C3-dominated diets with a larger rootstock component than Pp. whitei and Pp. jonesi, which included more C4 grasses in their diet. The morphological analyses found no clear taxonomic signal in the craniometric data for Parapapio, suggesting that the current taxonomic assignments of Parapapio specimens are problematic. Additionally, for all of the analysed anatomical regions, the Parapapio sample was no more variable than the single geographically circumscribed extant chacma baboon sample. To sum, while biogeochemical dietary indicators indicate distinct dietary ecologies within and between genera, disjunctions exist between the dietary categories and the taxonomic assignment of specimens. Given these results, and in light of the taxonomic concerns highlighted by the craniometric investigation, reinvestigation of papionin taxonomy at Makapansgat may be warranted.
- ItemOpen AccessDietary ecology of Chacma baboons (Papio Ursinus (Kerr, 1972) and Pleistocene Cercopithecoidea in Savanna environments of South Africa(2003) Codron, Daryl Mark; Lee-Thorp, Julia AThis dissertation deals with the dietary ecology of savanna-dwelling chacma baboons (Papio ursinus), and a number of fossil cercopithecoids, from modern and Pleistocene environments of South Africa, respectively, using principles of stable light isotope ecology. Previous studies of baboon ecology, based largely on direct observations, have not quantified spatial and temporal dietary variability. The dietary ecology of fossil cercopithecoids is even less clear.
- ItemOpen AccessThe ecological and evolutionary significance of browsing and grazing in savanna ungulates(2006) Codron, Daryl; Lee-Thorp, Julia A; Sealy, Judith; Sponheimer, MattIncludes bibliographical references (leaves 175-208).
- ItemMetadata onlyAn isotope comparison of elephant (Loxodonta africana) diets in the Kruger National Park and Welgevonden Game Reserve(2004) Codron, Jacqueline; Lee-Thorp, Julia A; Bond, William JThe diet of African elephants (Loxodonta africana (Blumenbach, 1797)) living in savanna environments is unresolved. Elephants are known to include varying proportions of grass and browse into their diet, but there is uncertainty as to whether they are primarily grazers or browsers. This has implications for conservation in Africa, as elephants are considered a keystone species in wildlife areas, and are associated with a number of management issues. This dissertation focuses primarily on spatial and temporal variability in grass consumption by savanna elephants.
- ItemOpen AccessA late quaternary history of Agulhas-Benguela interactions from two sediment cores on the western continental slope of South Africa(2002) Rau, Amanda Jane; Lee-Thorp, Julia A; Rogers, JohnChanges in circulation and productivity in the southeastern South Atlantic Ocean over the last 850 kyr are investigated through the multiproxy study of two giant piston cores, MD962080 and MD962084, retrieved from the Agulhas Bank and Olifants River continental slopes of South Africa. The stable oxygen isotope record of the benthic foraminifer, Cibicidoides wuellerstorfi, and the planktonic taxon, Globorotalia inflata, provide the stratigraphic framework from which the age models were created. The results indicate that biotic responses to surface hydrological changes in the study area are complex and involve both high- and low-frequency variations.
- ItemOpen AccessRevisiting the palaeoenvironments of the South African hominid-bearing Plio Pleistocene sites : new isotopic evidence from Sterkfontein(2001) Luyt, Julie; Lee-Thorp, Julia AThis thesis offers a revised palaeoenvironmental reconstruction of South African PlioPleistocene sites based on δ¹³C and δ¹⁸O isotopes extracted from enamel of fossil fauna. New isotopic results from Sterkfontein Members 4 and 5 are reported to supplement existing data from Makapansgat and Swartkrans in order to examine the changing environment from approximately 3 to 1.4 million years ago (Ma).
- ItemOpen AccessStable carbon isotope reconstruction of ungulate diet changes through the seasonal cycle(Southern African Wildlife Management Association, 2007) Codron, Daryl; Lee-Thorp, Julia A; Sponheimer, Matt; Codron, JacquiWe analysed stable carbon isotope ratios (ð13C) in faeces of 11 African ungulate species from three South African savanna environments to determine whether this approach is sufficiently sensitive to record short-term seasonal diet changes in browsers (BR), mixed-feeders (IM), and grazers (GR). At monthly intervals, faecal ð13C revealed variations in proportions of C3 (browse) to C4 (grass) biomass consumed that were not detected by broader dry versus wet season comparisons, including subtle diet shifts amongst BR and GR. However, trends in faeces were influenced by changes in C3 and C4 plant isotope composition of up to 3‰. Nonetheless, faeces and plants showed strongly similar patterns of variation through the seasonal cycle, so that small diet shifts can be reliably inferred, provided that the variations in plants are controlled for. Faecal ð13C of BR may be further influenced by consumption of isotopically different plant parts such as foliage versus fruit and flowers, and GR faeces may reflect differential utilization of grass following different photosynthetic sub-pathways. Future studies will need to incorporate data that capture isotopic variations in herbivore food sources, and if this is achieved, the approach may well become adopted as a routine addition to traditional methods for assessing diet, habitat use, and habitat condition.
- ItemOpen AccessUsing carbon isotope data of fossil bovid communities for palaeoenvironmental reconstruction(2003) Sponheimer, Matt; Lee-Thorp, Julia AReconstructing palaeoenvironments is a major focus of palaeoanthropological research. While many techniques are now available for exploring past environments, fossil bovids remain amongst the most widely utilized sources of environmental information. Most studies of fossil bovids, however, assume implicitly that bovid ecology is the same now as it was in the distant past. Because such uniformitarianist assumptions are not always valid, we have developed a method to provide palaeoenvironmental information from fossil bovids that requires no ecological assumptions. Here, we show that the percentages of C3 and C4 vegetation-consuming bovids in modern environments generally vary according to the amount of woody vegetation present. Application of this C3 / C4 index to the fossil bovid assemblage at Makapansgat shows that, based on carbon isotope data, the percentage of C3-consuming bovids is high, suggesting a great deal of woody vegetation in this vicinity about 3 million years ago.
- ItemOpen AccessUtilization of savanna-based resources by Plio-Pleistocene baboons(2005) Codron, Daryl; Luyt, Julie; Lee-Thorp, Julia A; Sponheimer, Matt; DeRuiter, Darryl; Codron, JacquiWe have determined the tooth enamel carbonate 13C values of five cercopithecoid taxa from the Plio-Pleistocene deposits of Swartkrans Members 1 and 2 and Sterkfontein Member 4. These data were used to determine the relative proportions of C3 and C4 biomass consumed by extinct baboons and contemporary non-human primates. We compared these results with data on modern Papio hamadryas ursinus from different savanna areas in South Africa, as well as with published isotopic data and dietary interpretations based on molar morphology of these taxa. The data reveal little evidence for use of grasses or grass-based foods by modern South African baboons. The fossil papionins Papio hamadryas robinsoni, Papio (Dinopithecus) ingens, and Parapapio spp., however, utilized more savanna-based C4 resources than previously predicted (particularly in the case of P. (D.) ingens). Theropithecus oswaldi had 13C values depicting, as expected, a largely grass-based diet, and we confirm earlier conclusions that this species incorporated a wider range of food items into its diet than do modern T. gelada, as reported in the literature. The colobine monkey, Cercopithecoides williamsi, made extensive use of savanna-.based C4 foods, confirming some degree of terrestrial foraging by the species.