No description available.

Cognate words have a shared orthographic and semantic representation across languages: kniv (‘knife’) in Danish means the same as kniv in Swedish. Their shared form and meaning give cognates a special status in the bilingual mental lexicon and there is robust evidence that because of this special status they are processed faster than non-cognate words. This effect is called the Cognate Facilitation Effect and represents strong evidence that bilinguals do not have two separate mental lexicons, but rather one integrated lexicon for both of their languages with nonselective access. The present study is a replication of Vanlangendonck et al. (2020) with a different language constellation. For the aims of this project, early and late Danish-Swedish bilinguals were recruited to examine the effect of stimulus list composition on the Cognate Facilitation Effect by means of two experiments: one language-specific visual lexical decision task that contained control words from the participants’ L2 (Swedish), a set of cognates, interlingual homographs and pseudowords, and a second task in which half of the pseudowords were replaced by Danish (L2) words that had to evoke a “no” response. This change from a pure to a mixed list was expected to increase response competition and turn cognate facilitation into inhibition. However, the results showed a null Cognate Facilitation Effect both for early and for late bilinguals. These findings are discussed in terms of the assumptions of the BIA+ model of bilingual lexical processing and it is suggested that the presence of language-specific diacritics in the stimulus list has hindered the emergence of the Cognate Facilitation Effect.

Duration tuning in the mammalian inferior colliculus (IC) is created by the interaction of excitatory and inhibitory synaptic inputs. We used extracellular recording and paired-tone stimulation to measure the strength and time-course of the contralateral inhibition and offset-evoked excitation underlying duration-tuned neurons (DTNs) in the IC of the awake bat. The onset time of a short, best duration (BD), excitatory probe tone was varied relative to the onset of a longer-duration, non-excitatory (NE) suppressor tone. Spikes evoked by the roving BD tone were suppressed or facilitated when the stationary NE tone was varied in frequency or amplitude. When the NE tone frequency was presented away from the cell’s best excitatory frequency (BEF) or at lower SPLs, the onset of inhibition was relatively constant whereas the offset and duration of inhibition decreased. Excitatory and inhibitory frequency response areas were measured and best inhibitory frequencies matched best excitatory frequencies; however, inhibitory bandwidths were broader than excitatory bandwidths. Excitatory rate-level and inhibitory suppression-level functions were also measured and the dynamic ranges and inflection points were similar, which is hypothesized to play a role in the level tolerance of responses measured from DTNs. We compared the latency of offset-locked facilitation to the onset or offset of inhibition as a function of frequency and amplitude; we found that the facilitation was more related to the onset of inhibition. Moreover, facilitation typically preceded the offset of inhibition – suggesting that it is a separate excitatory input to DTNs and not a rebound from inhibition. We conclude that DTNs receive inputs that generate and preserve temporal selectivity. / Dissertation / Doctor of Philosophy (PhD)

The level of learner engagement, performance, self-efficacy, and enjoyment on a knot-tying task by college students who received positive verbal and non-verbal learning-oriented feedback by trained facilitators was examined. Secondary learner outcomes were learner perception of engagement and learner perception of facilitator support. Facilitator variables were attitude and competency. Changes in facilitators" attitudes toward (1) flow theory (Csikszentmihalyi, 1997), (2) systematic feedback (Ilgen, Fisher, & Taylor, 1979; Liden & Mitchell, 1985; Locke & Latham, 1985), and (3) hands-on learning (Joplin, 1995; Kolb, 1984; Pfieffer & Jones, 1985; Williamson, 1995) were examined. Facilitators" competence in (1) delivering learning-oriented feedback, (2) using verbal learning-oriented feedback to increase learner engagement, and (3) using nonverbal learning-oriented feedback to increase learner engagement was measured. One hundred twenty-six college students from an introductory human development class were randomly selected and randomly assigned to one of three treatment groups as facilitators, learners, or timekeepers for a knot-tying task. Twelve psychology majors, members of an independent study group in the same class, were trained as observers and randomly assigned to one of the three treatment groups. The treatment was the administration of learning-oriented feedback by trained facilitators during a knot-tying task. The primary findings were that learning-oriented feedback provided by trained facilitators increased learner engagement, learner self-efficacy, learner task enjoyment, learner perception of facilitator support, and learner perception of personal engagement in the task. Learner performance was not affected by the administration of learning oriented feedback. Facilitators showed significant change in their attitude toward flow theory, systematic feedback, and hands-on learning. It can be concluded that facilitators who received training in learning-oriented feedback had a greater effect on the affective side of learning (engagement, self-efficacy, enjoyment) than those who did not receive training. However, the training of facilitators in the use of learning-oriented feedback had no effect on learner performance. Further, teaching a task using facilitated verbal and nonverbal cues positively affects how facilitators feel about flow theory, hands-on learning, and feedback. Further research to verify effects of learning-oriented feedback on learner engagement using other tasks is suggested. Additional research to examine the attitudes of facilitators is suggested. / Ph. D.

Die Informationsverarbeitung im Nervensystem basiert auf der Signalübertragung an chemischen Synapsen. Um diese bei hochfrequenter Aktivität aufrecht erhalten zu können, ist das Nachfüllen von Neurotransmitter-gefüllten Vesikeln an die präsynaptische Membran von zentraler Bedeutung. Die glutamatergen Parallelfaser-Purkinjezelle-Synapsen (PF-PC-Synapsen) des Zerebellums weisen eine ausgeprägte und anhaltende Kurzzeitbahnung für bis zu 30 Aktionspotentiale (APs) bei hochfrequenter Aktivität auf, obwohl anfänglich nur eine vergleichsweise geringe Anzahl synaptischer Vesikel (~ 3) an der aktiven Zone gedockt ist. Dies wird durch ultra-schnelles Nachfüllen (Recruitment) im Millisekundenbereich ermöglicht, welches sogar zu einer Vergrößerung des Pools gedockter und freisetzungsbereiter Vesikel (Readily releasable pool, RRP) führt (Overfilling, Überfüllen). Es gibt Evidenz dafür, dass dieser Prozess mindestens teilweise Kalzium(Ca2+)-abhängig ist. Durch welche Kanäle das hierfür bereitgestellte Ca2+ in die Präsynapse gelangt, war bislang unklar. An PF-PC-Synapsen sind drei Subtypen spannungsabhängiger Ca2+-Kanäle (Cavs) vorhanden: Cav2.1 (P/Q Typ), Cav2.2 (N Typ) und Cav2.3 (R Typ). Diese stellen in jungen Mäusen (P8-10) gemeinsam das Ca2+ für die Freisetzung der Transmitter-Vesikel zur Verfügung. Während der Entwicklung verringert sich die Kopplungsdistanz zwischen Cav2.1-Kanälen und Ca2+-Sensor, sodass bei reiferen Tieren (P21–24) allein der Ca2+-Einstrom durch eng gekoppelte Cav2.1 zur Vesikelfreisetzung führt. Cav2.2 und Cav2.3 sind jedoch weiterhin an der Präsynapse vorhanden und tragen zum Aktionspotential(AP)-vermittelten Ca2+-Einstrom bei. Die Funktion dieser Kanäle in reiferen Tieren blieb bisher weitgehend ungeklärt. Vorliegend wurden folgende Hypothesen überprüft: 1. Ca2+-Einstrom durch Cav2.2 oder Cav2.3 ist für spontane, nicht AP-vermittelte Vesikelfreisetzung verantwortlich. 2. Ca2+-Einstrom durch Cav2.2 oder Cav2.3 stellt Ca2+ für ultra-schnelles Nachfüllen mit Überfüllen bereit. Um diese Hypothesen zu prüfen, wurden Whole-Cell Patch-Clamp Messungen an Purkinjezellen in akuten Hirnschnitten reifer (P21–24) C57BL/6 Mäuse durchgeführt und die Parallelfasern (PFs) extrazellulär in der Molekularschicht stimuliert. Zunächst wurde die Hypothese geprüft, ob Cav2.2 und Cav2.3 an der Ca2+-Bereitstellung für spontane Vesikelfreisetzung beteiligt sind. Dazu wurden sogenannte miniature excitatory postsynaptic currents (Miniatur-EPSCs, mEPSCs) der Purkinjezellen aufgezeichnet. Bei Erhöhung der extrazellulären Ca2+-Konzentration von 2 mM auf 5 mM zeigte sich eine deutliche Steigerung der mEPSC-Frequenz, was die Annahme stützt, dass die spontane Vesikelfreisetzung eine Ca2+-abhängige Komponente hat. Um Rückschlüsse auf die Beteiligung der Cav-Subtypen ziehen zu können, wurden Cav2 Subtyp-spezifische Toxinblocker eingesetzt. Ω-Agatoxin-IVA wurde zur Blockierung von Cav2.1 eingesetzt. Cav2.2 wurde mit Ω-Conotoxin GVIA und Cav2.3 mit SNX-482 blockiert. Unter dem Einfluss dieser Toxine konnte weder einzeln noch in Kombination ein Effekt auf die Frequenz der mEPSCs beobachtet werden. Dieses Ergebnis deutet darauf hin, dass die Funktion dieser Cav2s nicht die Ca2+-Bereitstellung für spontane Vesikelfreisetzung ist. Anschließend wurde der Einfluss der Blockade der Cav2 Subtypen auf das Vesikel-Nachfüllen untersucht. Dazu wurden Parallelfasern zunächst fünf Mal bei einer Frequenz von 20 Hz extrazellulär stimuliert und die hervorgerufenen EPSCs aufgezeichnet. Hieraus wurde das Verhältnis aus den Amplituden des zweiten bis fünften EPSCs zur Amplitude des ersten EPSCs berechnet (Ai/A1). Diese Paarpulsverhältnisse sollten sich bei einem durch Cav2-Blocker beeinträchtigtem Vesikel-Nachfüllen verkleinern. Ein solcher Effekt war jedoch bei dieser kurzen Aktivierung mit 5 Stimuli nicht zu beobachten. Da die in-vivo-Aktivität an der PF-PC-Synapse aus längeren, hochfrequenten Trains besteht und sie in der Lage ist, auch bei länger anhaltender Stimulation zu bahnen, wurde ein weiteres Experiment mit Trains aus 50 Stimuli durchgeführt. Hierbei sollte während oder zumindest gegen Ende des Trains ein Gleichgewicht aus Freisetzung und Nachfüllen (Steady State) erreicht werden. Dazu war es erforderlich, die extrazelluläre Ca2+-Konzentration auf 6 mM zu erhöhen. Die aufgezeichneten EPSC-Amplituden wurden in einem kumulativen Plot aufgetragen und mit einer Methode nach Schneggenburger et al. ausgewertet. Dabei wird der Gleichgewichtsbereich mit einer linearen Funktion gefittet, deren Anstieg ein Maß für die Nachladerate und deren y-Achsenabschnitt ein Maß für das Dekrement des RRP ist. Durch spezifische Blockade einzelner Cav-Subtypen kann man Aussagen über deren Einfluss auf Vesikel-Nachfüllen und RRP treffen. Unter Hinzugabe von Ω Agatoxin IVA konnte, wie erwartet, eine starke Reduktion bereits bei der ersten EPSC-Amplitude beobachtet werden, da der Ca2+-Einstrom durch Cav2.1 entscheidend für die Freisetzungswahrscheinlichkeit der Vesikel (pv) ist. Hierdurch erklärt sich die beobachtete Abnahme des RRP-Dekrements. Der Anstieg der Geraden im Gleichgewichtszustand zeigte sich durch Ω-Agatoxin-IVA nicht signifikant verändert. Allerdings könnte ein möglicher Effekt durch die starke Reduktion der pv maskiert sein. Daher wurde in einem weiteren Versuch eine reduzierte Dosis (100 nM statt 250 nM) Ω Agatoxin-IVA eingesetzt. Hier zeigte sich neben dem Effekt auf das RRP-Dekrement außerdem ein vermindertes Nachfüllen der Vesikel. Dieser Effekt wurde bei voller Dosis vermutlich maskiert und weist darauf hin, dass Ca2+-Einstrom durch Cav2.1 zur Aufrechterhaltung des Vesikel-Nachfüllens beiträgt. Bei Blockade von Cav2.3 mit SNX-482 konnte kein signifikanter Einfluss auf Vesikel-Nachfüllen oder RRP festgestellt werden. Unter dem Einfluss des Cav2.2-Blockers Ω-Conotoxin GVIA zeigte sich ein interessanter Effekt: Die Nachladerate wurde durch die Toxinapplikation selektiv reduziert. Hieraus lässt sich schlussfolgern, dass die Bereitstellung von Ca2+ für das Vesikel-Nachfüllen eine Funktion des Cav2.2 an dieser Synapse darstellt. Das RRP-Dekrement blieb davon unbeeinflusst, was zu dem beschriebenen Befund passt, nach dem Cav2.2s in diesem Alter nicht an der Vesikelfreisetzung beteiligt sind. Unter Cav2.1-Block dagegen, blieben die EPSC-Amplituden am Ende verhältnismäßig unbeeinflusst, während die ersten stark reduziert waren. Dieser Befund passt zu der Annahme, dass Ω-Agatoxin-IVA pv stark verringert, während das Nachfüllen über den erhaltenen Ca2+-Einstrom durch Cav2.2 weiterläuft. Anhand unserer Daten ist allerdings nicht auszuschließen, dass ein Unterschied zwischen früh und spät im Train rekrutierten Vesikeln hinsichtlich deren Kopplung an Cav2.1 oder Cav2.2 besteht. Im Anschluss an die Trains mit 50 Stimuli wurde eine Erholungsphase aufgezeichnet. Hierbei wurde mit konsekutiv steigenden Interstimulus-Intervallen die Regeneration der EPSC-Amplituden bis etwa auf das Ausgangsniveau aufgezeichnet. Der Zeitverlauf der Erholung wurde mittels biexponentieller Funktionen gefittet. Bei der Applikation von Ω Agatoxin-IVA zeigte sich der Gleichgewichtszustand ohne Depression, während er unter Ω Conotoxin GVIA und SNX-482 eine deutliche Depression aufwies. Ω-Agatoxin-IVA führte zu einer signifikant beschleunigten Erholung. Dieser Effekt resultiert aber am ehesten aus der starken Reduktion von pv und der fehlenden Depression. Sowohl der Zeitverlauf der Erholung als auch die EPSC-Amplituden während der kurzen Aktivierung mit 5 Stimuli waren unbeeinflusst von Cav2.2- und Cav2.3-Block. Gemeinsam spricht dies für das Vorhandensein eines basalen Nachfüllens, welches zusätzlich zum Ca2+-abhängigen Nachfüllen mit Einstrom durch Cav2.1 und Cav2.2 stattfindet. Das Ziel der Studie bestand darin, die Funktion der Cav2.2- und Cav2.3-Kanäle im präsynaptischen Bouton der reifen Parallelfaser zu erforschen. Obwohl spontane Vesikelfreisetzung zumindest teilweise Ca2+-abhängig zu sein scheint, war keiner der untersuchten Cav2-Kanäle bedeutsam beteiligt. Bei Cav2.3 konnte des Weiteren keine Relevanz für das Nachfüllen festgestellt werden. Für Cav2.2-Kanäle konnte jedoch die Funktion als Ca2+-Bereitsteller für das Nachfüllen bei anhaltender synaptischer Transmission identifiziert werden. Zusammenfassend bestätigen unsere Daten den maßgeblichen Einfluss von Cav2.1 auf pv und zeigen eine wichtige Funktion von Cav2.2: die Erhaltung der synaptischen Effektivität unter anhaltender, hochfrequenter Aktivität an der Parallelfaser. Es bleibt die Frage offen, inwiefern diese Befunde auch für andere kleine glutamaterge Synapsen, beispielsweise im Neocortex, zutreffen. Auch dort konnte der entwicklungsbedingte Wechsel von gemeinsamer Steuerung der Vesikelfreisetzung durch Cav2.1 und Cav2.2 zu alleiniger Steuerung durch Cav2.1 beobachtet werden. Gleichzeitig bleibt auch hier die Ca2+-Signalgebung durch Cav2.2 erhalten.:Einleitung 1 Aufbau und Funktion chemischer Synapsen 1 Kurzzeitbahnung und Vesikel-Nachfüllen 2 Parallelfaser-Purkinjezelle-Synapse als Modellsystem 4 Experimenteller Aufbau und Auswertungsmethoden 7 Publikation 9 Zusammenfassung 24 Literaturverzeichnis 28 Darstellung des eigenen Beitrags 31 Erklärung über die eigenständige Abfassung der Arbeit 32 Lebenslauf 33 Danksagung 34

Invasive plants can displace native species, deteriorate native forest, and change plant communities and ecosystem functions. Native plant populations are fundamentally impacted by invasive species because of the interactions between invasive species and native plants. This study focuses on understanding the extent, mechanisms and consequences of interaction between a non-indigenous invader Ailanthus altissima and its functionally similar native species Robinia pseudoacacia in the Mid-Appalachian region, from an individual scale to a regional scale. These two subject species are common and coexist in early-successional eastern deciduous forest. The interactions between these two common species are important to community structure and canopy tree regeneration. To address the type and extent of interactions of these two species, a greenhouse experiment utilizing various species proportions, nutrient levels and seed sources was performed. In addition, a common-garden experiment with various species densities and proportions over three consecutive growing seasons was performed in a more natural condition than that of the greenhouse experiment. We found at the seedling stage, the dominant interaction was competition, and R. pseudoacacia was the winner both above- and belowground. The allelopathic compounds of A. altissima may have inhibited nodulation of R. pseudoacacia. Ailanthus altissima seedlings from its native region had slightly stronger competitive abilities compared with the seedlings from its invaded range. In the common garden experiment, R. pseudoacacia plants grew quicker than A. altissima, but A. altissima inhibited the growth of R. pseudoacacia by interspecific competition. The negative impact of A. altissima on R. pseudoacacia became larger as time progressed. To assess the community-level consequences of the two species, we conducted a forest mapping and a complete target-tree-based forest survey, and analyzed regional-scale data from the Forest Inventory Analysis Data Base. The two target species were significantly associated with themselves and with each other. Community species composition and diversity were significantly different across sites. A negative impact of both species on the understory community diversity and tree regeneration at the neighborhood scale was detected; while at a regional level, tree diversity in the FIA plots with either A. altissima or R. pseudoacacia was higher than the reference plots. / Ph. D.

Positive biotic interactions such as mutualism, commensalism and facilitation are ubiquitous in nature, but historically have received considerably less research attention than negative interactions such as competition, predation and parasitism. The paucity of research on positive interactions is particularly evident in stream ecosystems and in vertebrate communities. Stream fishes clearly provide an ideal system for advancing research on positive interactions. Many minnows (Cyprinidae) of eastern North America engage in a potentially mutualistic reproductive interaction known as nest association, in which individuals of one species (nest associates) spawn in nests constructed by host species. In nest association, hosts provide unsilted gravel substrate for spawning nest associates, and increased parental care to associate broods. High associate: host egg ratios can create a dilution effect, reducing the probability that host eggs will be preyed upon by egg predators. Nest associative interactions are common, but are relatively understudied compared to other interactions among stream fishes. The goals of this study were to apply general ecological models to this novel system to (a) gain new insight into the mechanisms structuring nest associative stream fish communities, and (b) to use inference from stream fish communities to potentially expand and improve the general ecological models. These goals required completion of three objectives, including (1) examining the influence of abiotic and biotic contexts on reproductive behavior and fitness outcomes between a cyprinid host and associate, using the biological markets model to generate predictions; (2) examining the utility of the nest web framework (previously only used for cavity nesting vertebrate communities) and the stress gradient hypothesis (previously applied almost exclusively to plant communities) for predicting which associate species spawn on nests built by various nest building species, and the consequences of these choices, respectively; and (3) using two-species occupancy modeling to determine the relative influence of biotic interactions and habitat covariates on the co-occurrence of a host and two nest associates. To accomplish these goals, I conducted a large-scale experiment to manipulate presence of mutualists (Nocomis leptocephalus, host; Chrosomus oreas, associate), egg predators (biotic context) and habitat quality (abiotic context). I conducted behavioral nest observations and conducted repeated stream fish stream fish community surveys to collect demographic data. I constructed a nest web from observational data, and implemented structural equation modeling through an information-theoretic framework to identify nest web plausibility across a large spatial extent. I tested some predictions of the stress gradient hypothesis by regressing juveniles-per-nest and a metric of cyprinid community structure on a composite measure of physical stress (scaled gradients of catchment-scale agricultural land use and catchment area). I used two-species occupancy modeling to model co-occurrence of N. leptocephalus hosts and two associates, C. oreas and Clinostomus funduloides, and used an information-theoretic framework to compare hypotheses representing the importance of biotic interactions, habitat covariates or both at determining species co-occurrence. Results corroborated some (but not all) model predictions, and identified room for improvement in each of the general models. Nest associative spawning by C. oreas was not context dependent; C. oreas did not spawn in the absence of a reproductively active male N. leptocephalus at any treatment level. However, the net fitness outcome of host and associate species was mutualistic, and the interaction outcome switched from commensalistic to mutualistic with abiotic context. N. leptocephalus reproductive success was improved by C. oreas presence in less-silted habitats, but not in heavily-silted habitats. This is most likely because broods were subject to predation in both habitat types, but were also negatively affected by siltation in silted habitats. Accordingly, egg dilution by associates was not sufficient to support a mutualistic relationship in less favorable habitats. Results suggest that the biological markets model may be a useful tool for predicting fitness outcomes of nest associative mutualism, but may not be as useful for predicting the behavioral outcomes of obligate mutualisms. Future applications of the biological markets model should carefully consider species traits, specifically the degree to which trading behavior is obligate for participants. Future work with this model will yield more insight by considering highly facultative associates. Nest webs constructed from nest observational data suggested an interaction topology in which strong (nearly-obligate) associates relied most frequently on N. leptocephalus nests, and less frequently on nests constructed by Campostoma anomalum. Weak (facultative) associates were seldom associated with nests constructed by either species, and probably spawned before hosts began nesting activity. Structural equation models corroborated this topology throughout the New River basin, although some less-supported model evidence specified some nest association by weak associates. Juveniles-per-nest of strong associates responded positively to physical stress, while this metric for other cyprinid reproductive groups showed no relationship. Proportional representation of Nocomis and strong associates also increased predictably with physical stress. This study suggests that the nest web framework can be informative to systems outside the ones for which it was developed; future studies may be able to use this framework to better understand the role of habitat-modifying species in communities other than cavity nesting terrestrial vertebrates and nest associative stream fishes. This work extended the nest web framework by (a) modeling the outcomes of interactions instead of the interactions themselves, and (b) by using structural equation modeling to test nest web predictions with an information-theoretic framework. This study also suggests that the stress gradient hypothesis can be useful for understanding interaction dynamics in vertebrate communities; this represents the first direct evidence that this model can be used in vertebrate communities. Further, I demonstrate that the stress gradient hypothesis may be extended to predict community structure. However, more research in a diversity of systems will be needed to determine the extent to which this can be applied. This study provides some of the first evidence of large-scale positive co-occurrence patterns in vertebrates. However, the precise roles of habitat covariates and biotic interactions were species-specific. Occupancy results suggest that co-occurrence between N. leptocephalus and nest associate C. funduloides is driven only by reproductive behavioral interactions. Alternatively, evidence suggests that co-occurrence between N. leptocephalus and C. oreas is driven by both nest association and habitat covariates. That two-species occupancy modeling can be a useful tool for comparing difficult-to-test hypotheses involving biotic interactions at large spatial scales. This study represents the first quantitative, multi-scale treatment of positive interactions in stream ecosystems. This study demonstrates that applying general ecological models to stream fish communities can yield new insights about both the study system and the models themselves. While models of negative interactions, food webs and dispersal have been applied to stream fishes, we stand to gain much ground by also considering positive biotic interactions. In doing so, stream fish ecologists will also be able to contribute to the advancement of general ecology, and thus raise awareness for these understudied ecosystems and taxa. / Ph. D.

Anecdotal evidence in the media and from personal conversations suggests that inflammatory rhetoric in the collaborative governance setting is increasing, especially during public meetings about sustainable development projects. Planners, mediators, facilitators, and government officials are facing a shutting down of public deliberation by "new activists" who are engaging in public forums in very emotional and uncompromising ways. This dissertation is a direct examination of actions by new activists. It includes two case studies in Roanoke, Virginia, as well as a broader look at the inflammatory rhetoric and disruptions in local public meetings now occurring across the country. / Ph. D.

This study explores the training of Psychology tutors at the University of South Africa's (UNISA) learning centres with a view to providing a paradigm shift in tutor training and contributing towards new ways of thinking about education and training in South Africa. It furthermore opens up alternative ways of thinking about the process of facilitation in general. Although the study focuses on tutor training within the discipline of Psychology, the outcomes of the study are applicable to tutor training and tutoring in general, and make a valuable contribution in identifying the basic principles underlying tutor training in other disciplines as well. An ecosystemic approach encourages the trainer-trainee system to become aware of how they affect each other's thinking and behaviour. The basic principles underlying the process of facilitation that emerge in the study, therefore apply equally to the training of tutors and the tutoring of learners by others. These principles provide guidelines in terms of the processes involved in tutor development, as well as inform the issues and themes around which the sharing of ideas can be choreographed in the field of tutor training and tutoring. In conclusion, the information generated in the study focuses specifically on student support in the form of face-to-face tutorials in the distance education setting, the form of tertiary education which is most accessible to many historically disadvantaged learners in South Africa today. More generally, it will make a valuable contribution in the current educational context in South Africa, where student support is of the utmost importance in striving for equality in education, and where the focus is on outcomes-based education. / Curriculum and Instructional Studies / D.Litt. et Phil. (Psychology)

Les écosystèmes herbacés méditerranéens, caractérisés par une importante biodiversité, ont subi de considérables changements d‟usage. Désormais, leur conservation est devenue insuffisante au regard de l‟augmentation des dommages causés par les activités humaines. La restauration écologique apparaît donc comme un outil approprié pour participer à leur préservation. Des recherches préalables sur les différents compartiments de l‟écosystème ainsi que sur les facteurs responsables de l‟assemblage de leurs communautés avant et après dégradations sont donc nécessaires afin de mettre en place des méthodes de restauration adaptées à ces écosystèmes. Ainsi, en utilisant comme modèle biologique les Coussouls de Crau et leurs friches post-culturales (Bouches-du-Rhône, France), représentatif de nombreux écosystèmes steppiques méditerranéens, nous avons choisi de déterminer et d‟étudier les principaux filtres potentiellement responsables de l‟organisation de cette communauté végétale. Le pâturage ovin, les changements trophiques du sol, les phénomènes de compétition et la capacité de reproduction et/ou de dispersion des espèces, identifiés lors d‟une première étude sur la régénération de la steppe, ont ainsi été étudiés dans trois expérimentations différentes. Deux protocoles de restauration écologique in situ (transfert de foins et semis d‟espèces structurantes) et un protocole d‟expérimentation ex-situ testant les interactions d‟une sélection d‟espèces de la steppe ont permis de réaliser ces recherches. Nos principaux résultats montrent que les filtres de reproduction/dispersion, le niveau trophique du sol, la compétition et le régime de perturbations récurrentes lié au pâturage ovin ont un rôle déterminant dans les changements de la composition et de la structure de la communauté et ils expliquent ainsi en partie le ralentissement de sa dynamique successionnelle vers la steppe de référence. Nous avons également pu démontrer que ces filtres interagissaient entre eux. Au niveau de la recherche appliquée, les protocoles testés favorisent le retour de la végétation steppique, néanmoins la composition des parcelles restaurées reste toujours très différente de l‟écosystème de référence à très court terme (deux à trois années après la restauration). Cela démontre que même si nous comprenons mieux aujourd‟hui les facteurs expliquant l‟organisation de cette communauté, il est cependant toujours difficile de la restaurer dans son intégralité car il n‟est pas aisé de manipuler et de trouver un équilibre entre l‟action de ces différents facteurs. Il est donc désormais plus que nécessaire de poursuivre ces recherches fondamentales et appliquées notamment au niveau des processus de maturation et de structuration des vieilles communautés végétales herbacées. / Mediterranean herbaceous ecosystems which are characterized by a high biodiversity have been submitted to a lot of changes in use. Their conservation is not sufficient enough and ecological restoration seems to be an adapted solution to improve conservation efforts as it can mitigate damages induced by human activities. To develop restoration methods adapted to these ecosystems, preliminary researches on the different communities composing an ecosystem and the filters which are responsible for community assemblage before and after disturbance are necessary. Representative of numerous Mediterranean steppe ecosystems, the “Coussouls de Crau” and their ex-arable-fields (Bouches-du-Rhône, France) are the biological models used to identify and study the principal filters potentially responsible for organizing the plant communities. Sheep grazing, trophic changes, competition and reproduction and /or species dispersal, were identified in a first study on steppe regeneration; these filters were then the core of the following three research experiments. We carried out two in-situ restoration protocols (hay transfer and sowing foundation species) and one ex-situ experiment testing interactions between a selection of steppe species. The main results show that reproduction, seed dispersal, soil trophic level, competition, extensive sheep grazing are filters which have a determinant role in structuring the communities, in determining plant composition and partly in explaining the slow dynamics towards the reference steppe. Also, we show that filters interact between them. For applied restoration, the tested methods promote steppe vegetation come back, but in the short term (two or three years after restoration), the composition of restored areas remains different to the reference ecosystem. Even if we understand better the different factors which explain community organization, these results demonstrate that it is difficult to restore it integrally because it is not easy to manipulate and find an equilibrium between the different filters actions. Now it is necessary to continue these fundamental and applied researches, in particular on the maturation and structure of the old herbaceous plant communities.