Sun Weng Hong. / Thesis submitted in: October 2002. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 116-121). / Abstracts in English and Chinese. / Chapter 1. --- Introduction --- p.7 / Chapter 2. --- Ant Colony Optimization (ACO) --- p.9 / Chapter 2.1 --- ACO vs. Traditional Routing --- p.10 / Chapter 2.1.1 --- Routing information --- p.10 / Chapter 2.1.2 --- Routing overhead --- p.12 / Chapter 2.1.3 --- Adaptivity and Stagnation --- p.14 / Chapter 2.2 --- Approaches to Mitigate Stagnation --- p.15 / Chapter 2.2.1 --- Pheromone control --- p.15 / Chapter 2.2.1.1 --- Evaporation: --- p.15 / Chapter 2.2.1.2 --- Aging: --- p.16 / Chapter 2.2.1.3 --- Limiting and smoothing pheromone: --- p.17 / Chapter 2.2.2 --- Pheromone-Heuristic Control --- p.18 / Chapter 2.2.3 --- Privileged Pheromone Laying --- p.19 / Chapter 2.2.4 --- Critique and Comparison --- p.21 / Chapter 2.2.4.1 --- Aging --- p.22 / Chapter 2.2.4.2 --- Limiting pheromone --- p.22 / Chapter 2.2.4.3 --- Pheromone smoothing --- p.23 / Chapter 2.2.4.4 --- Evaporation --- p.25 / Chapter 2.2.4.5 --- Privileged Pheromone Laying --- p.25 / Chapter 2.2.4.6 --- Pheromone-heuristic control --- p.26 / Chapter 2.3 --- ACO in Routing and Load Balancing --- p.27 / Chapter 2.3.1 --- Ant-based Control and Its Ramifications --- p.27 / Chapter 2.3.2 --- AntNet and Its Extensions --- p.35 / Chapter 2.3.3 --- ASGA and SynthECA --- p.40 / Chapter 3. --- Multiple Ant Colony Optimization (MACO) --- p.45 / Chapter 4. --- MACO vs. ACO --- p.51 / Chapter 4.1 --- Analysis of MACO vs. ACO --- p.53 / Chapter 5. --- Applying MACO in Load Balancing --- p.89 / Chapter 5.1 --- Applying MACO in Load-balancing --- p.89 / Chapter 5.2 --- Problem Formulation --- p.91 / Chapter 5.3 --- Types of ant in MACO --- p.93 / Chapter 5.3.1 --- Allocator. --- p.94 / Chapter 5.3.2 --- Destagnator. --- p.95 / Chapter 5.3.3 --- Deallocator. --- p.100 / Chapter 5.4 --- Global Algorithm --- p.100 / Chapter 5.5 --- Discussion of the number of ant colonies --- p.103 / Chapter 6. --- Experimental Results --- p.105 / Chapter 7. --- Conclusion --- p.114 / Chapter 8. --- References --- p.116 / Appendix A. Ants in MACO --- p.122 / Appendix B. Ants in SACO. --- p.123

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-05-19T18:08:20Z No. of bitstreams: 1 2016 - Corina Anah? Barrera.pdf: 2798404 bytes, checksum: 56ddd89ceb87a772a2bc0299c858947e (MD5) / Made available in DSpace on 2017-05-19T18:08:20Z (GMT). No. of bitstreams: 1 2016 - Corina Anah? Barrera.pdf: 2798404 bytes, checksum: 56ddd89ceb87a772a2bc0299c858947e (MD5) Previous issue date: 2016-02-24 / CNPq / Habitat loss is one of the main threats to global biodiversity. In fragmented habitats, species have more limited capacity for dispersal and as a result are at higher risk of extinction. However, different species respond differently to this kind of disturbance. Therefore, community structure, interspecific interactions, and ecological functions become altered, and the magnitude and direction of the changes are unpredictable. Host-parasitoid interactions are an example of interactions that can be highly impacted, and in the tropics, interactions between parasitoids and ants are among the most relevant. In the Neotropics, leaf-cutting ants are considered dominant herbivores and play a key role in ecosystem functioning. These ants can also become agricultural pests, and therefore their biological control is of high economic importance. An important group of natural enemies of leaf-cutting ants are the dipteran parasitoids of the family Phoridae. Interactions between phorid parasitoids and leaf-cutting ants in a fragmented region of the Atlantic Forest of Southeastern Brazil comprise a promising model system to study the impacts of habitat fragmentation, since phorids are the most important parasitoids of these ants and show a high degree of specialization for host ant species. The overall goal of this work was to study the effects of reduction in forest cover, one of the most important negative impacts of fragmentation, upon phorid parasitoids of the leaf-cutting ant Acromyrmex niger, a common species in the Southeastern Atlantic Forest. This work was conducted at the Guapia?u Ecological Reserve (REGUA) and surrounding areas in the State of Rio de Janeiro. Ten forest fragments of different sizes (five large >80 ha and five small <20 ha) were sampled, as well as three regions of continuous forest (>1000 ha). One to five colonies of A. niger were marked in the interior of each fragment and continuous forest location. At each nest, all of the phorids in interaction with the worker ants were collected for a period of 15 minutes and later identified in the laboratory. Additionally, approximately 200 worker ants were collected from each colony and maintained in the laboratory for the rearing of parasitoids. For the data analysis were made analysis of variance and simple regression. Were identified three genus of phorids: Myrmosicarius, Apocephalus and Neodohrniphora both observed in the field in interactions with the workers as reared in the laboratory from workers collected in the field. The total phorid abundance, total parasitism percentage, and genus richness of immature phorids were significantly greater in continuous forest sites than forest fragments, while there were no significant differences between large and small fragments. The abundance of Apocephalus and the parasitism percentage of Myrmosicarius were also greater in the continuous forest sites, but the difference was only significant in comparison to small forest fragments. These results have provided the first evidence about the effects of habitat size on the phorid-Acromyrmex system in tropical rain forest, through an evaluation of the abundance and richness of parasitoids as adults in the field and the reared of immature phorids in the laboratory. / A perda de habitats ? uma das principais amea?as para a biodiversidade global. Em ambientes fragmentados as esp?cies ficam com menor capacidade de dispers?o e suas intera??es s?o mais propensas ? extin??o. Todavia, as esp?cies s?o afetadas de maneira diferente por este tipo de perturba??o. Desta forma, a estrutura da comunidade, as intera??es interespec?ficas e as fun??es ecol?gicas s?o alteradas e a magnitude e dire??o das mudan?as s?o imprevis?veis. As intera??es parasit?ide-hospedeiro s?o um exemplo das que podem ser muito afetadas. Dentre elas, as intera??es entre parasit?ides e formigas est?o entre as mais relevantes. Certos grupos de formigas, como as cortadeiras, podem se tornar pragas agr?colas, portanto seu controle biol?gico ? de suma import?ncia. Essas formigas possuem um papel chave nos ecossistemas, pois s?o consideradas os herb?voros dominantes da regi?o Neotropical. Um grupo importante de inimigos naturais de formigas cortadeiras s?o os d?pteros parasit?ides da fam?lia Phoridae. Intera??es entre for?deos parasit?ides e formigas cortadeiras em uma regi?o fragmentada da Mata Atl?ntica comp?em um modelo bastante promissor para sua investiga??o como indicador dos impactos causados pela fragmenta??o de habitats, pois os for?deos s?o os parasit?ides mais importantes dessas formigas e possuem uma forte especializa??o nas mesmas. O objetivo geral deste trabalho foi estudar os efeitos da perda da superf?cie florestal sobre os for?deos parasit?ides da formiga cortadeira Acromyrmex niger, uma esp?cie comum na Mata Atl?ntica. Este trabalho foi realizado na Reserva Ecol?gica de Guapia?u (REGUA) e arredores no Estado do Rio de Janeiro. Foram amostrados dez fragmentos florestais de diferentes tamanhos (cinco grandes >80 ha e cinco pequenos <20 ha) e tr?s regi?es de floresta cont?nua (>1000 ha). Uma a cinco col?nias de A. niger foram marcadas no interior de cada fragmento e local de mata cont?nua. Sobre cada ninho, durante 15 minutos, todos os for?deos em intera??o com as oper?rias foram coletados e depois identificados. Tamb?m, em cada col?nia amostrada, foram coletadas aproximadamente 200 oper?rias e mantidas para cria??o dos parasit?ides. Para a an?lise de dados foram feitas an?lises de vari?ncia e regress?es simples. Foram identificados tr?s g?neros de for?deos: Myrmosicarius, Apocephalus e Neodohrniphora, tanto observados no campo em intera??es com as oper?rias quanto criados em laborat?rio a partir de oper?rias coletadas no campo. A abund?ncia total, a porcentagem de parasitoidismo total, a riqueza de g?neros de for?deos adultos observados no campo e a riqueza de g?neros de for?deos imaturos, foram significativamente maiores nos locais de floresta cont?nua sem diferen?as significativas entre fragmentos grandes e pequenos. A abund?ncia de Apocephalus e a porcentagem de parasitoidismo de Myrmosicarius tamb?m foram maiores em locais de mata cont?nua, mas com diferencias significativas s? em rela??o aos fragmentos pequenos. Os resultados ofereceram a primeira evidencia dos efeitos do tamanho do habitat sobre o sistema for?deo-Acromyrmex em floresta tropical ?mida, avaliando em conjunto a presen?a de for?deos adultos no campo e a porcentagem de parasitoidismo determinada atrav?s de m?todos experimentais no campo e no laborat?rio.

Plus de 150 espèces de grillons (Ensifères, Orthoptères) sont présentes en Nouvelle-Calédonie avec un taux d’endémisme de 90%. Cette microfaune, abondante dans les milieux forestiers et sensible aux conditions biotiques et abiotiques, peuvent être des bio-indicateurs de premier choix dans le suivi de la biodiversité. L’échantillonnage et l’enregistrement de l’activité acoustique (méta-acoustique) des communautés sous différentes conditions écologiques (invasions biologiques et dynamique forestière) est la base de ce travail de thèse.En bioacoustique : quelle est l’activité acoustique des communautés grillon en Nouvelle-Calédonie ? Cette activité varie-t-elle en fonction de la structure de la végétation (maquis, para-forestier et forêt dense) ? Finalement, est-ce que cette activité acoustique peut se décrire sous forme de « niches acoustiques », avec les paramètres du chant (temporels et spectraux), le nycthémère (l’heure de la journée) et les indices comportementaux (les postes de chants, le bruit ambiant) ?Fourmis invasives : est-ce que les fourmis envahissantes (Wasmannia auropunctata, Anoplolepis gracilipes et Pheidole megacephala) impactent les densités relatives et la diversité spécifique des populations d’Orthoptères ? Si oui, est-ce un phénomène de compétition par prédation directe (sur les œufs, juvéniles ou adultes) ou par compétition indirecte (site de chant et site de repos indisponible, accès à la reproduction réduit) ?Nous avons 3 principaux objectifs : (1) Taxonomie : accumuler des connaissances sur cette microfaune peu connue qui présente un taux d’endémisme supérieur à 90%. Créer et enrichir une collection de base et de référence sur les Orthoptères de Nouvelle-Calédonie ; (2) Ecologie fonctionnelle : déterminer l’impact des changements globaux (fourmis invasives et structure forestière) sur la dynamique et la structure des populations d’Orthoptères ; (3) Gestion du patrimoine : créer un outil de mesure non-invasif de la biodiversité des forêts néo-calédoniennes et de l’état des écosystèmes grâce à la bioacoustique de cette microfaune. / In the context of global biodiversity crisis at world scale, research of efficient environmental proxies are urgently required, especially in tropical island ecosystems, to better assess environment quality and select conservation priorities. In New Caledonia ecosystems, crickets have a dominant contribution to natural communities, according to their richness, diversity and range of colonized habitats. They are highly abundant in ecosystems and also have a high contribution to the soundscape with their ability to produce species-specific airborne signals. In this context of search of efficient environmental proxies, we measured the response of cricket communities in a ecological succession on utlramafic soils and facing the spread of 2 invasive ants (Wasmannia auropunctata and Anoplolepis gracilipes). Through both classical community census and bioacoustic approach through passive acoustic monitoring, we have been able to characterize specific cricket assemblage of species in each succession stage, with a striking sensitivity for biological invasions. Also, a global acoustic analysis of soundscape, greatly dominated by crickets, provides similar results without taxonomic or acoustic identification or knowledge. These preliminary results provide critical insights for the management of ecosystems, Our findings open up promising field of research in order to generalized innovative bio-indication concepts using cricket community in other cricket rich tropical regions

Maintenance of power plants is aimed at extending the life and reducing the risk of sudden breakdown of power generating units. Traditionally, power generating units have been scheduled for maintenance in periods to ensure that the demand of the system is fully met and the reliability of the system is maximized. However, in a deregulated power industry, the pressure of maintaining generating units is also driven by the potential revenue received by participating in the electricity market. Ideally, hydropower generating units are required to operate during periods when electricity prices are high and to be able to be taken offline for maintenance when the price is low. Therefore, determination of the optimum time periods for maintenance of generating units in a power system has become an important task from both a system reliability and an economic point of view. Due to the extremely large number of potential maintenance schedules, a systematic approach is required to ensure that optimal or near-optimal maintenance schedules are obtained within an acceptable timeframe. Metaheustics are high-level algorithmic frameworks that aim to solve combinatorial optimisation problems with a large search space in a reasonable computational run time. Inspired by the foraging behavior of ant colonies, Ant Colony Optimisation (ACO) is a relatively new metaheuristic for combinatorial optimisation. The application of ACO to a number of different applications has provided encouraging results when applied to scheduling, including the job-shop, flow-shop, machine tardiness and resource-constrained project scheduling problems. In this thesis, a formulation is developed that enables ACO to be applied to the generalized power plant maintenance scheduling optimisation (PPMSO) problem. The formulation caters for all constraints generally encountered as part of real-world PPMSO problems, including system demands and reliability levels, precedence rules between maintenance tasks, public holidays and minimum outage durations in the case of shortening of maintenance tasks. As part of the formulation, a new heuristic and a new local search strategy have been developed. The new ACO-PPMSO formulation has been tested extensively on two benchmark PPMSO problems from the literature, including a 21-unit and a 22-unit problem. It was found that the ACOPPMSO formulation resulted in significant improvements in performance for both case studies compared with the results obtained in previous studies. In addition, the new heuristic formulation was found to be useful in finding maintenance schedules that result in more evenly spread reserve capacity and resource allocations. When tested using a modified version of the 21-unit and the 22-unit problems, the new local search strategy specifically designed for duration shortening was found to be effective in searching locally for maintenance schedules that require minimal shortening of outage duration. The ACO-PPMSO formulation was also successfully able to cater for all constraints as specified in both original and the modified versions of the two benchmark case studies. In order to further test the ACO-PPMSO formulation developed, it was first applied to a scaled-down version of the Hydro Tasmania hydropower system (five power stations) and then to the full system (55 generating units). As part of the studies, the ACO-PPMSO formulation was linked with the simulation model used by Hydro Tasmania to assess the impact of various maintenance schedules on the total energy in storage of the system at the end of the planning horizon, the total thermal generation, the total number of days where the reliability level is not met, as well as the total unserved energy throughout the planning horizon. A number of constraints were considered, including the anticipated system demands, a 30% capacity reliability level, the minimum and maximum durations between related maintenance tasks, the precedence constraints and the minimum outage duration of each task in the case of shortening of maintenance tasks. The maintenance schedule was optimised for the maximum end-of-horizon total energy in storage, the minimum thermal generation and the minimum total outage durations shortened and deferred, under 77 different inflow conditions. The optimal maintenance schedule obtained compared favourably with that obtained by Hydro Tasmania over many years based on experience. Specifically, the ACO-PPMSO schedule results in higher end-of-horizon total energy in storage and satisfies both hard and soft constraints, which overall equates to over $0.5 million dollars of savings when compared to the schedule obtained using the practitioners’ experience and engineering judgment. The ACO-PPMSO algorithm was also shown to be a useful decision-making tool for scheduling maintenance under different circumstances when tested with four scenarios commonly encountered in practical maintenance scheduling problems. In conclusion, the ACO-PPMSO formulation developed, tested and applied as part of this thesis research provides a powerful and flexible means of obtaining optimal or near-optimal maintenance schedules for power plants. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1294672 / Thesis (Ph.D.) -- University of Adelaide, School of Civil and Environmental Engineering, 2007

Fire ants link their legs and jaws together to form functional structures called self- assemblages. Examples include floating rafts, towers, bridges, and bivouacs. We investigate these self-assemblages of fire ants. Our studies are motivated in part by the vision of providing guidance for programmable robot swarms. The goal for such systems is to develop a simple programmable element from which complex patterns or behaviors emerge on the collective level. Intelligence is decentralized, as is the case with social insects such as fire ants. In this combined experimental and theoretical study, we investigate the construction of two fire ant self-assemblages that are critical to the colony’s survival: the raft and the tower. Using time-lapse photography, we record the construction processes of rafts and towers in the laboratory. We identify and characterize individual ant behaviors that we consistently observe during assembly, and incorporate these behaviors into mathematical models of the assembly process. Our models accurately predict both the assemblages’ shapes and growth patterns, thus providing evidence that we have identified and analyzed the key mechanisms for these fire ant self-assemblages. We also develop novel techniques using scanning electron microscopy and micro-computed tomography scans to visualize and quantify the internal structure and packing properties of live linked fire ants. We compare our findings to packings of dead ants and similarly shaped granular material packings to understand how active arranging affects ant spacing and orientation. We find that ants use their legs to increase neighbor spacing and hence reduce their packing density by one-third compared to packings of dead ants. Also, we find that live ants do not align themselves in parallel with nearest neighbors as much as dead ants passively do. Our main contribution is the development of parsimonious mathematical models of how the behaviors of individuals result in the collective construction of fire ant assemblages. The models posit only simple observed behaviors based on local information, yet their mathe- matical analysis yields accurate predictions of assemblage shapes and construction rates for a wide range of ant colony sizes.

Downed woody material (fallen logs) offers spiders (Araneae) and ants (Hymenoptera: Formicidae) ideal nesting and foraging sites. In a maple forest of Forillon National Park, I compared spider and ant assemblages on, adjacent to, and away from fallen logs, and on these I tested the effects of log type and decay stage. In a second study, spider and ant assemblages were compared on, adjacent to, and away from fallen logs in different forest types. / In the first experiment spiders were highly affected by trap placement, and diversity was highest on the wood surface compared to the forest floor. In contrast, wood type and decomposition stage of logs had few significant effects on spiders. Log type did not affect the estimated number of spider species nor the spider catch rates. Decomposition stage did not affect spider collections, but less decayed logs were more diverse in spider than heavily decayed logs. / The second experiment showed that use of dead wood by spiders depends on forest type. Ant diversity and abundance was generally low, making it difficult to offer concrete conclusions related to log use by ant assemblages. This work brings additional support for the important role of dead wood to forest arthropod biodiversity.

In South Africa, the unsustainable use of natural resources by domestic livestock has led to resource depletion and serious land degradation. Rangeland degradation, especially bush encroachment and soil erosion, is particularly acute in the North-West Province, where all districts show signs of desertification and a loss of biodiversity resulting in a deterioration of human and animal health. This has a major impact on livestock productivity and the economic viability of livestock farming with serious consequences for the livelihoods of pastoral communities. It is important to recognise ecological change before irreversible changes occur. The aim of this study, which falls within the Global Environmental Facility Desert Margins Programme (GEF-DMP), was to investigate to what extent vegetation in combination with ant communities can be used as indicators of ecosystem change due to anthropogenic human induced land-use patterns and how can this information be used in land degradation management and biodiversity conservation in the semi-arid western rangelands of Southern Africa. Sites, representing a degradation gradient (relative poor and relative good rangeland condition extremes) within each of three Tribal-, three Commercial- and three Reserve areas, were surveyed. The impacts of these land uses on the herbaceous species composition, woody-, soil- and ant components were evaluated. Both the woody and herbaceous species components reflected the existence of a rangeland condition/degradation gradient across the larger study area. The herbaceous species composition reflected similar degradation tendencies within the Commercial and Reserve land uses, with sites being associated with low rangeland as well as high rangeland condition scores. The tendencies differed between these two land uses based on the woody degradation gradient. The entire Tribal herbaceous- and woody species components showed a transitional shift towards another state, which differed significantly from the Commercial and Reserve land uses. Both the Tribal herbaceous and woody components were associated with low to intermediate rangeland condition ranges, with no significant rangeland condition gradient existing within the Tribal land use. Understanding and quantification of the soil-vegetation dynamics hold important implications for rangeland degradation management. This study provided criteria for selecting the most appropriate measures when incorporating the soil parameters as additive data in the multivariate analyses with the vegetation, ant and nominal environmental data. Different land use practices resulted in different soil patterns, with significant gradients pertaining to the soil stratum and openness/woodiness groups. There was a significant though neglectable difference pertaining to the rangeland condition/degradation gradient based on the soil component. Ants have been extensively used as bio-indicators, also with regard to the monitoring of the environmental effects of rangeland pastoralism. Ant species compositional patterns and functional groups displayed congruent clustering and diversity patterns as those of the vegetation and soil components. In contrast to the vegetation components, ant assemblages did not reflect a degradation gradient, but rather reflected environmental changes (modifications) to the habitat structure and - heterogeneity as a result of different land use disturbances. Both vegetation and ant diversity measures were mainly associated with the Tribal land use. These diversity indices were indicators of habitat complexity, heterogeneity and moderate disturbance, rather than indicators of a rangeland condition/degradation gradient. The diversity patterns are best described by a dichotomy between the humped-shaped productivity/diversity and the habitat complexity/heterogeneity models. Vegetation and ant diversity measures for this study should be considered as environmental indicators of habitat disturbance rather than as biodiversity indicators. It is suggested that vegetation, soil and ant patterns are best described by the state-and-transition model, which encompasses both equilibrium and non-equilibrium systems. The resilient nature of these rangelands, typical of non-equilibrium systems, was reflected by the low to intermediate differences between land uses with regard to the herbaceous, woody, soil and ant components. However, densitydependent coupling of herbivores to key resources resulted in transitional shifts and modification of the vegetation composition and structure within and between land uses, displaying the equilibrium dynamics pertaining to these rangelands. Small disturbances in these rangelands may result in detrimental “snowball” interactive biotic-biotic /abiotic cascades. Spatial heterogeneous patterns within and between land uses as displayed by the vegetation, soil and ant parameters, necessitate that monitoring and management at patch, paddock and landscape scale should be conducted, cautioning against the extrapolation and over simplification of management strategies across all land uses. Because these arid rangelands are linked socio-ecological systems, it is not possible to address biophysical issues associated with land degradation without including the human dimensions. A “Key assessment matrix” is provided for monitoring and management purposes pertaining to land degradation and diversity aspects within and between the different land uses, and can be used by the land user, extension officer and scientist. / Thesis (Ph.D. (Botany))--North-West University, Potchefstroom Campus, 2007.

In South Africa, the unsustainable use of natural resources by domestic livestock has led to resource depletion and serious land degradation. Rangeland degradation, especially bush encroachment and soil erosion, is particularly acute in the North-West Province, where all districts show signs of desertification and a loss of biodiversity resulting in a deterioration of human and animal health. This has a major impact on livestock productivity and the economic viability of livestock farming with serious consequences for the livelihoods of pastoral communities. It is important to recognise ecological change before irreversible changes occur. The aim of this study, which falls within the Global Environmental Facility Desert Margins Programme (GEF-DMP), was to investigate to what extent vegetation in combination with ant communities can be used as indicators of ecosystem change due to anthropogenic human induced land-use patterns and how can this information be used in land degradation management and biodiversity conservation in the semi-arid western rangelands of Southern Africa. Sites, representing a degradation gradient (relative poor and relative good rangeland condition extremes) within each of three Tribal-, three Commercial- and three Reserve areas, were surveyed. The impacts of these land uses on the herbaceous species composition, woody-, soil- and ant components were evaluated. Both the woody and herbaceous species components reflected the existence of a rangeland condition/degradation gradient across the larger study area. The herbaceous species composition reflected similar degradation tendencies within the Commercial and Reserve land uses, with sites being associated with low rangeland as well as high rangeland condition scores. The tendencies differed between these two land uses based on the woody degradation gradient. The entire Tribal herbaceous- and woody species components showed a transitional shift towards another state, which differed significantly from the Commercial and Reserve land uses. Both the Tribal herbaceous and woody components were associated with low to intermediate rangeland condition ranges, with no significant rangeland condition gradient existing within the Tribal land use. Understanding and quantification of the soil-vegetation dynamics hold important implications for rangeland degradation management. This study provided criteria for selecting the most appropriate measures when incorporating the soil parameters as additive data in the multivariate analyses with the vegetation, ant and nominal environmental data. Different land use practices resulted in different soil patterns, with significant gradients pertaining to the soil stratum and openness/woodiness groups. There was a significant though neglectable difference pertaining to the rangeland condition/degradation gradient based on the soil component. Ants have been extensively used as bio-indicators, also with regard to the monitoring of the environmental effects of rangeland pastoralism. Ant species compositional patterns and functional groups displayed congruent clustering and diversity patterns as those of the vegetation and soil components. In contrast to the vegetation components, ant assemblages did not reflect a degradation gradient, but rather reflected environmental changes (modifications) to the habitat structure and - heterogeneity as a result of different land use disturbances. Both vegetation and ant diversity measures were mainly associated with the Tribal land use. These diversity indices were indicators of habitat complexity, heterogeneity and moderate disturbance, rather than indicators of a rangeland condition/degradation gradient. The diversity patterns are best described by a dichotomy between the humped-shaped productivity/diversity and the habitat complexity/heterogeneity models. Vegetation and ant diversity measures for this study should be considered as environmental indicators of habitat disturbance rather than as biodiversity indicators. It is suggested that vegetation, soil and ant patterns are best described by the state-and-transition model, which encompasses both equilibrium and non-equilibrium systems. The resilient nature of these rangelands, typical of non-equilibrium systems, was reflected by the low to intermediate differences between land uses with regard to the herbaceous, woody, soil and ant components. However, densitydependent coupling of herbivores to key resources resulted in transitional shifts and modification of the vegetation composition and structure within and between land uses, displaying the equilibrium dynamics pertaining to these rangelands. Small disturbances in these rangelands may result in detrimental “snowball” interactive biotic-biotic /abiotic cascades. Spatial heterogeneous patterns within and between land uses as displayed by the vegetation, soil and ant parameters, necessitate that monitoring and management at patch, paddock and landscape scale should be conducted, cautioning against the extrapolation and over simplification of management strategies across all land uses. Because these arid rangelands are linked socio-ecological systems, it is not possible to address biophysical issues associated with land degradation without including the human dimensions. A “Key assessment matrix” is provided for monitoring and management purposes pertaining to land degradation and diversity aspects within and between the different land uses, and can be used by the land user, extension officer and scientist. / Thesis (Ph.D. (Botany))--North-West University, Potchefstroom Campus, 2007.

The aim of this research proj ect was to produce compositionally modulated zincnickel and zinc-nickel-manganese coatings usi ng a single bath process by variation of the applied electroplating current density. These could then be considered as possible replacements for electroplated cadmium. Zinc-nickel electrodeposits from both a simple bath and one containing the complexant tris(hydroxymethyl)methylamine (TRIS) were produced using either bath or by selective electroplating onto mild steel, 2014-T6 aluminium and 2000 series aluminium alloy connector shells. Zinc-nickelmanganese coatings were electroplated onto mild steel, using both DC and pulse electroplating from sulphate based baths containing either the complexant TRIS or sodium citrate. The coatings and the various electrodeposition processes were evaluated by thickness measurements, cun'ent efficiency calculations, composition detennination using energy dispersive X-ray anal ys is and SEM to examine the morphology. Corrosion characteristics were investigated by neutral salt fog exposure, alternate immersion, atmospheric trials, and electrochemical immersion tests including potential monitoring, galvanic and polarisation measurements. Other properties such as microhardness and surface electrical conductivity were also investigated. Compositionally modulated zinc-nickel and ziJlc-nickel-manganese were successfully deposited from single baths with nickel contents ranging from 5-20% Ni and manganese contents varying from 0-12% Mn. Current efficiency measurements showed the efficiency to be low especially for the zinc-nickel-manganese coatings, which exhibited a distinct morphology when electroplated from the citrate bath. Corrosion testing indicated that both coatings had a lower corrosion resistance than cadmium especially in accelerated tests, with a reduction in corrosion resistance being seen as the nickel content was increased; due to a decrease in density of the electroplate. This, and increasing through-thickness porosity promoted ennoblement of zinc-nickel and zinc-nickel-manganese leading to the coatings becoming nonsacri ficial to the substrate in accelerated tests. Zinc-nickel-manganese showed less white rust than zinc-nickel and exhibited lligher micro-hardness than zinc, cadmium and zinc-nickel. Electrical measurements indicated that both coatings were sufficiently conductive to meet the surface conductivity requirements for use on electrical connector shells.

Thesis (Ph. D.)--Miami University, Dept. of Botany, 2005. / Title from second page of PDF document. Includes bibliographical references.