published_or_final_version / Ecology and Biodiversity / Master / Master of Philosophy

One of the major costs of group living is increased competition due to social information. Social information allows foragers to gain information about the location and the quality of food patches from observing other group members. Ultimately, this allows social foragers to use resources more efficiently. However, the distribution and quality of food varies both spatially and temporally and social information may result in aggregations of foragers around favourable food patches when they are available. This results in individuals of various dominance ranks aggregating around food resources and competing for food. In order to understand how dominance and patch quality interact to determine foraging behaviour, various foraging models have been created. In particular, producer-scrounger social foraging models are used to understand foraging behaviour and patch choice under competitive conditions. In producer scrounger games, individuals can either find their own food patches (produce) or join other individuals at food patches (scrounge). This study focused on how the combination of patch holder dominance status and patch quality interacts to influence patch joining decisions by scroungers. According to producer-scrounger models scroungers only join patches held by subordinate individuals. However, I found that a scrounger will join any patch as long as the patch holder is not within the top five most ranked individuals in the herd. However, as patch quality increased, fewer of the top ranked patch holders were avoided at each patch quality. This suggests that foraging is a trade-off between the costs of an aggressive interaction and the benefits gained from each patch. Behavioural titrations found that the initial density of food at a patch needs to be 2.3 times greater for a scrounger to feed from the next dominant patch holder. At high patch qualities there was a threshold point where patch quality became the driving force behind patch joining decisions and no patch holders were avoided, no matter their dominance status. Scroungers that fed from the top ranked patch holders had the same intake rate when compared with feeding with subordinate patch holders. This could be due to an increased level of vigilance by the scrounger in order to avoid an aggressive interaction with the dominant patch holder. However, scrounger’s intake rate increased when they fed from dominant patch holders that were not the top ranked herd members. This suggests that only the top ranked herd members are aggressive enough to prevent scrounging attempts. A novel discovery of this study was that although the goats formed a linear dominance hierarchy, they did not forage in accordance with it, with lower ranking individuals avoiding dominant patch holders. This suggest that in social herbivores dominance hierarchies are not maintained to determine who has priority access to food. This study shows that even large differences in dominance are not sufficient enough to prevent scrounging decisions and only the top ranked patch holders have the ability to prevent joining attempts. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

With the purpose of improving the conservation management of Ithala Game Reserve and other similar reserves, the aims of this study were to determine the reserve's large mammalian herbivores' habitat occupancy, numbers and demographics, to investigate the feasibility of road strip counts as a census method for the same herbivores and to establish what environmental factors influence their habitat occupancy, numbers and demographics. Four years of demographic data were collected by vehicle transects on giraffe, kudu, wildebeest and impala. During the final two years additional positional data, using GPS, were collected on these and the reserve's other large herbivores. Sightings were recorded on the basis of habitat type occupied, a GIS was then used to define area sampled and hence derive habitat occupancy densities. GIS was further used to determine both absolute population sizes and, by over-laying other available GIS data, the relevance of distance to surface water, soil type and degree of slope to species' habitat preferences. Species showed non-random, significant habitat selections broadly in line with established preferences. Deterioration in habitat quality in winter generally lead to changes in habitat selection and the extent and nature of these changes related to the severity of resource pressure for individual species. This in turn was influenced by the species digestive strategy i.e. ruminant versus non-ruminant, grazer versus browser. Generally species showed a dry season move down the slope, moving, in some cases, onto heavier soils. Hartebeest, warthog, wildebeest and impala were strongly attracted to winter grass flushes. Lack of predation may be influencing the habitat selection decisions of impala and giraffe and kudu females, as well as allowing giraffe, wildebeest and impala to attain comparatively high densities. Giraffe density (effectively 1.8 km - 2) was abnormally high and their habitat quality poor, leading to a decline in numbers and low fecundity-related demographics. Wildebeest density (6 km -2) was also abnormally high and this may be instrumental in the poor performance of the rare tsessebe population, which is in decline and shows low fecundity-related demo graphics, increased dry season pressure on other grazers in general and impala 111 unexpectedly preferring browse habitats, rather than grasslands, in the wet season. Wildebeest fecundity declined in response to lower rainfall over the early period of lactation. Herbivores with an open social structure generally showed a dry season decrease in group size, although wildebeest and hartebeest showed, atypically, an Increase. Giraffe, zebra and impala adult sex ratios were comparatively less female biased, probably due to minimal predation. Territorial behaviour, virtually year round by wildebeest bulls and over the rut by impala bulls, imposed spatial sexual segregation between breeding and bachelor herds in these species. Outside of these periods, and generally in species not exhibiting territoriality, social sexual segregation was maintained and appeared to relate to differing activity budgets. Areas of concern for management are highlighted. Numbers results were generally acceptable and the method is proposed as a cost effective alternative in reserves with diverse topography. Underlying environmental determinants of habitat occupancy, numbers and demographics, together with associated annual or seasonal changes, were habitat quality, competition and predation. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2005.

The changes in plant quality and availability in space and time present a substantial problem to mammalian herbivores. As a result, these herbivores need to alter their foraging behaviour to maximize their energy gain at both small (plant level) and large (landscape level) scales. A megaherbivore, the African elephant (Loxodonta africana), has been shown to be selective in its foraging choices at both of these scales. Furthermore, the ratio of palatability:defences (e.g. fibre and total polyphenols) has been highlighted as an important determinant of habitat selection in elephants. The elephants in Ithala Game Reserve (IGR) frequently leave IGR during the wet season and forage outside the reserve. However, they predominantly feed on the low-nutrient granite soils of the reserve and return to a high-nutrient area with dolerite soils during the dry season. In an attempt to understand these seasonal movements, I focused on how the small-scale foraging decisions of the elephants lead to large-scale seasonal movements in IGR, KwaZulu-Natal. Plant availability was determined seasonally for seven target species across four areas in the reserve. Crude protein, fibre, energy and total polyphenols as well as the ratios of palatability:digestion-reducing substances were analysed in the wet and dry seasons. All factors and their interactions were significant in a MANOVA. Consequently, I employed a dimension-reducing Principal Components Analysis (PCA) to better understand the factors of greatest importance. The PCA highlighted four of the six most important factors to be the ratios of palatability:digestion-reducing substances. The other two important variables were total polyphenols (negative effect) and crude protein (positive effect). At small spatial scales, I found that the elephants were selective in their decisions, especially during the dry season. For example, the increased inclusion of the principal tree species Acacia nilotica from 2.9% in the wet season to 39.3% during the dry season appears to be a result of a decline in total polyphenols and fibre during the dry season. At large spatial scales, the elephants moved back into IGR from the low-nutrient granite soils in the east in response to an increase in forage quality in the west as the quality declined in the east at the same time. However, it is unclear as to why the elephants are leaving the reserve during the wet season. Some possible explanations for this are discussed.Key-words: acid detergent fibre, crude protein, Loxodonta africana, neutral detergent fibre, total polyphenols, plant part quality. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv., 2003. / Härtill 5 uppsatser.

Thesis (doctoral)--Humboldt-Universität zu Berlin, 1999. / Includes bibliographical references (p. 243-257).

Thesis (Ph. D. (Zoology and Entomology))--Rhodes University, 2005.

Les savanes sont des écosystèmes complexes pilotées par plusieurs mécanismes ascendant (ex: les nutriments du sol ou pluviométrie) ou descendant (ex: feu ou herbivorie), mais l'importance relative de ces mécanismes reste largement débattue. En particulier, le rôle des herbivores brouteurs (browsers) reste mal compris en tant que source de perturbation, et donc de force de pression descendante influant sur la dynamique des savanes. Dans cette étude, deux approches ont été développées pour aborder le rôle des perturbations dans la dynamique des savanes. Dans un première partie, j'ai utilisé une approche comparative inter-site pour explorer les réponses des communautés de plantes, et des principaux traits de ces plantes associés aux feuilles, branches, architecture et défense, aux variations de quatre facteurs : les nutriments dans le sol, la pluviométrie, la pression d'herbivorie et l'intensité du feu. Seize sites de savane, en Afrique du Sud et au Zimbabwe, ont été sélectionnés sur des gradients de chacun de ces facteurs. Les espèces ligneuses dominantes (>80 % de la biomasse) sur chaque site ont été identifiées et échantillonnées, afin de mesurer les traits des feuilles et des branches associés à l'appétence, architecture, ainsi qu'aux défenses physiques et chimiques de ces plantes. Des mesures ont également été faites pour estimer les effets des meso-brouteurs et mega-brouteurs. Des transects ont permis d'estimer la fréquence et l'intensité du feu sur chaque site, et l'effet sur les plantes. En préambule à l'analyse, et devant le manque de protocole standard pour estimer la fertilité des sols dans la littérature écologique, je propose une méthode et un échantillonnage afin de définir de manière robuste la fertilité des sols sur chaque site. Dans cette partie inter-site, huit traits principaux ont été comparés sur le gradient de qualité de sol et de pluviométrie, et bien que quelques relations statistiques existent entre les traits des feuilles, le sol et la pluviométrie, ces relations sont très faibles comparées à celle trouvées dans les méta analyses inter-biomes publiées dans la littérature. Cependant, ces approches interbiome sont dominées par des sites tempérés qui ont des niveaux de perturbations bien inférieurs à ceux des savanes africaines. L'évaluation des effets des meso-brouteurs et mega-brouteurs le long des gradients de sol et de pluviométrie sur vingt traits associés aux défenses structurelles et chimiques des plantes montre que les défenses structurelles sont plus corrélées aux caractéristiques du sol que les défenses chimiques, mais que seules les défenses structurelles sont fortement corrélées à l'impact par les brouteurs. Le niveau d'utilisation des plantes par les mesobrouteurs apparaît plus prévisible en fonction des traits des plantes que celui par les mégabrouteurs. Dans une deuxième partie présentent des résultats de deux études basées sur des expériences d'exclos. Dans le parc national de Kruger, la composition de la communauté, l'abondance et la démographie des ligneux dominants ont été estimées à l'intérieur et à l'extérieur de trois exclos de 40 ans, et les brouteurs apparaissent comme ayant un impact significatif sur la distribution, la densité et la structure des populations des espèces arbustives et arborées ayant des traits préférés : forte concentration en azote foliaire et faible teneur en défenses chimiques. L'interaction entre les effets des brouteurs et du feu semble aussi affecter le recrutement des juvéniles ligneux dans les grandes classes de taille. Dans le parc de Hluhluwe-iMfolozi, cinq exclos ont été utilisé pour tester l'effet des brouteurs sur l'architecture, la croissance, les défenses chimiques et structurelles des jeunes individus de sept espèces d'acacia. Des différences nettes apparaissent entre les espèces d'acacia de savane semi-aride et plus humide dans les traits associés à l'appétence, l'architecture et les défenses … [etc] / Savannas are complex ecosystems affected by several bottom-up (e.g. soil nutrient availability and rainfall) and top-down (e.g. fire and herbivory) drivers. However, the relative importance of bottom-up vs. top-down drivers in influencing savanna dynamics is still widely debated. Within the top-down (disturbance) category of drivers, the role of mammal browsers in particular in driving savanna functioning is still not well understood. Two approaches were adopted to determine the role of disturbance in savannas. Firstly, by using a comparative approach, I attempted to address the so-called ‘savanna problem’ by investigating how savanna woody plant community compositions and key plant traits relating to the leaves, stems, architecture, and defence are influenced by soil nutrient status, rainfall, fire and browsing. Sixteen sites were selected along gradients of these four drivers from savanna parks throughout South Africa and Zimbabwe. The dominant woody species (species that accounted for >80% of standing biomass) at each site were identified and sampled for the key leaf and stem traits relating to plant functioning, palatability, architecture, physical and chemical defences. Measurements were undertaken for each species in order to determine both meso-browser and mega browser impact. Transects were undertaken in order to determine the relative abundance and the effects of fire on each species at each site. Due to the current lack of standardized soil sampling protocols in the ecological literature, and uncertainty around the definition of what denotes a fertile or infertile soil, I propose a number of standardized protocols and sampled according to these established protocols in order to accurately determine the soil nutrient status at each site. Following this, the relationships between climatic variables and soil nutrients with both species means and community weighted means for eight key leaf traits were explored. Although some significant relationships were found between savanna leaf traits of woody plants, climate, soil nutrients and their interactions, these tended to be weaker than those found in meta-analyses. These broad-scale studies usually include sites from many biome types, many of which are from temperate regions where inherent levels of disturbance are typically much lower than in African savannas. The high levels of disturbance typically found in African savannas are thought to partially account for the high within site variability found in leaf traits and the weak relationships found between leaf traits, soil nutrients and rainfall. To assess the importance of resources vs. disturbance in savannas functioning, the effects of soil nutrients, rainfall, fire and both meso-browser and mega-browser impact on twenty savanna woody plant traits relating to plant palatability, chemical and structural defences were explored. Structural defences were found to be more strongly correlated with soil characteristics than chemical defences, while browser impact was found to be strongly correlated with structural defences but not with chemical defences. Actual browser utilisation tended to be more predictable for meso-browsers than mega-browsers. Secondly using an experimental approach, two sets of herbivore exclosures were utilized to directly test how mammal browsers influenced woody species distributions, abundance, population structure and plant traits relating to palatability and defence. The effects of three longterm herbivore exclosures in the Kruger National Park on savanna woody plant community compositions, population demographics and densities were determined. Browsers were found to have significant impacts on species distributions, densities and population structures by actively selecting for species with favourable traits, particularly higher leaf N. An interaction between browsers and fire which limited the recruitment of seedlings and saplings into larger size classes was also demonstrated… [etc]

A herbivoria por grandes mamíferos é um fator decisivo no direcionamento de comunidades vegetais, influenciando o crescimento, sobrevivência e reprodução das plantas. Os ungulados, quando exóticos, podem impactar os ecossistemas diferentemente de herbívoros nativos, gerando maiores efeitos nas comunidades de plantas. Os objetivos deste estudo foram avaliar se a presença de búfalos (densidade de 1 animal/ha) impacta as assembléias de plântulas e de arbustos numa floresta estacional semidecídua no sul do Brasil, além de inferir consequências para a manutenção da comunidade vegetal. Para isso realizamos duas abordagens no município de Sentinela do Sul: na primeira, estabelecemos um experimento de exclusão de bubalinos (duração de 14 meses) e na segunda, comparamos três áreas com presença e protegidas desses herbívoros por três e dez anos. Em ambas as abordagens, registramos as seguintes variáveis ecológicas: riqueza, altura média de plantas, cobertura vegetal, diversidade (Shannon), e biomassa. No experimento de exclusão, nenhuma das variáveis apresentou diferenças significativas perante presença e ausência de búfalos (após 14 meses). Na comparação das três áreas as comunidades vegetais mostraram diferenças qualitativas (composição de espécies) no contraste presença versus dez anos de exclusão de búfalos, e as variáveis riqueza e altura média sofreram, respectivamente, significativos incremento e decréscimo. A diferença observada para o incremento de diversidade de zero a dez anos de exclusão foi marginalmente significativa e a compactação do solo apresentou decréscimo em função do tempo de exclusão do gado. Portanto , os resultados do presente trrabalho indicam que as manchas florestais não respondem à remoção de búfalos em baixas densidades no curto prazo e, na ausência de grandes herbívoros, a floresta tende a incrementar sua complexidade via aumento de riqueza e diversidade. / Herbivory by large mammals is a key factor in plant communities, and has effects on growth, survival and reproduction of plants. Ungulates, when exotic, impact ecosystems in a different way compared to the native ones, and may have a more pronounced effect on plant communities. In this study we evaluated buffalo (1 animal/ha density) impact on the seedling and shrub assemblages in a semideciduous seasonal forest in southern Brazil and checked if such impact would affect plant community maintainability. To address these aims we conducted two studies in Sentinela do Sul County: 1. we established a buffalo exclusion experiment (during 14 months) and 2. compared three areas with presence and protected against these herbivores for three and ten years. In both studies, we measured the following ecological variables: plant cover, richness, diversity (Shannon), biomass and average height. In the exclusion experiment, any ecological variable showed significant differences between buffalo presence and absence plots. When the three areas were compared, the communities showed qualitative differences (species composition) in the contrast presence versus ten years of buffalo exclusion, and richness and average height showed, respectively, increase and decrease. The difference observed for an increase of diversity between zero and ten years exclusion was marginally significant, and soil compactation showed retraction in relation to livestock exclusion time. We conclude that forest spots don’t answer in short-term to low densities buffalo removal and, in the absence of large herbivores, the forest tends to develop its complexity by richness and diversity increase, in a long-term basis.