Bibliography: leaves 108-128. / ix, 128, [10] leaves, [32] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Maternal protein secretions from the parthenogenetic endoparasitoid wasp Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae) were analysed regarding their ability to protect the parasitoid egg against the host immune system. These secretions include nucleic acid-free glycoproteins, called virus-like particles (VLPs) that are produced in the ovarian calyx gland. Results found that VLP-free calyx fluid has the ability to actively suppress host defence reactions, rather than VLPs on the egg surface being solely responsible for the protection of the egg. It was shown the VLP-free calyx fluid contains serine protease-inhibitor activity capable of transiently inhibiting melanogenisis and hemocyte spreading in the host. This indicates that immediately after oviposition the egg surface is not fully protected against host defence reactions. However, at later stages the egg seems to have acquired an immunologically inert surface, and is therefore protected after the suppressive activity of the calyx fluid has disappeared. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1999

Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1999. / Bibliography: leaves 108-128.

Bibliography: leaves 108-128. Maternal protein secretions from the parthenogenetic endoparasitoid wasp Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae) were analysed regarding their ability to protect the parasitoid egg against the host immune system. These secretions include nucleic acid-free glycoproteins, called virus-like particles (VLPs) that are produced in the ovarian calyx gland. Results found that VLP-free calyx fluid has the ability to actively suppress host defence reactions, rather than VLPs on the egg surface being solely responsible for the protection of the egg. It was shown the VLP-free calyx fluid contains serine protease-inhibitor activity capable of transiently inhibiting melanogenisis and hemocyte spreading in the host. This indicates that immediately after oviposition the egg surface is not fully protected against host defence reactions. However, at later stages the egg seems to have acquired an immunologically inert surface, and is therefore protected after the suppressive activity of the calyx fluid has disappeared.

An examination of the Desmodium canescens complex (D. canescens; D. tweedyi; D. illinoense) has resulted in the delimitation of a previously unreported alliance between D. canescens and D. tweedyi. The following points support this view: (a) morphological data taken from herbarium and garden specimens indicate that for many characters, the mean values of D. canescens and D. tweedy are not significantly different (b) breeding experiments have shown that artificial interspecific hybridization is possible between D. canescens and D. tweedyi (c) cytological studies have shown that D. canescens and D. tweedyi have a base number of x = 11, while D. illinoense has a base number of x = 10. A new combination is suggested: Desmodium canescens var. tweedyi (Britt.) Williams.

Inland sand dunes supporting Grey Hair-grass Corynephorus canescens are a declining European habitat designated for conservation under the EU’s Habitats Directive. In Britain they are confined to a handful of sites in East Anglia and the West Midlands. This study investigated the relationships of the British populations to each other and to populations on five sites in Poland, where C. canescens is still widespread. It also conducted exploratory investigations into factors relevant to the conservation of this ecosystem, particularly in the West Midlands. Data were collected chiefly from 1m2 quadrat samples and direct sampling, which recorded the plants and animals present together with parameters such as vigour and fecundity in C. canescens, amounts of bare sand and litter, and measures of erosion and grazing. These data were variously analysed including by CANOCO multivariate analysis and, for the vegetation, TWINSPAN analysis. 153 taxa of plants and 251 of invertebrates were identified. Though strongly distributed on a regional basis, both flora and invertebrate fauna showed relationships particularly between Polish and West Midlands sites. Analysis of the vegetation suggested that West Midlands vegetation had some associations with C. canescens habitats in Europe and that East Anglian vegetation had links with British coastal C. canescens habitats. The invertebrate fauna showed some complex community relationships in Poland and the West Midlands but less so in East Anglia, while assemblages of invertebrates were associated with various vegetational and abiotic factors. Rabbits and hares were the only vertebrates regularly exploiting C. canescens habitats, which they grazed and, in the former case, produced sand disturbances for colonisation by C. canescens. Ants and to a lesser degree some other invertebrates also produced sand disturbances. Observations made in a preliminary cultivation study in the West Midlands suggested that C. canescens may have a biennial phenology, high fecundity, low germination rates and limited dispersal powers in that region. A trampling investigation suggested that C. canescens may be very sensitive to heavy uncontrolled trampling and to vegetational succession under protection. Stages in succession of the C. canescens community were identified, and suggestions for further study and the conservation of C. canescens were drawn up.

During the last decades, the global change of the environment has caused a dramatic loss of habitats and species. In Central Europe, open habitats are particularly affected. The main objective of this thesis was to experimentally test the suitability of wild megaherbivore grazing as a conservation tool to manage open habitats. We studied the effect of wild ungulates in a 160 ha game preserve in NE Germany in three successional stages (i) Corynephorus canescens-dominated grassland, (ii) ruderal tall forb vegetation dominated by Tanacetum vulgare and (iii) Pinus sylvestris-pioneer forest over three years. Our results demonstrate that wild megaherbivores considerably affected species composition and delayed successional pathways in open habitats. Grazing effects differed considerably between successional stages: species richness was higher in grazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Species composition changed significantly in the Corynephorus and ruderal sites. Grazed ruderal sites had turned into sites with very short vegetation dominated by Agrostis spp. and the moss Brachythecium albicans, most species did not flower. Woody plant cover was significantly affected only in the pioneer forest sites. Young pine trees were severely damaged and tree height was considerably reduced, leading to a “Pinus-macchie”-appearance. Ecological patterns and processes are known to vary with spatial scale. Since grazing by megaherbivores has a strong spatial component, the scale of monitoring success of grazing may largely differ among and within different systems. Thus, the second aim of this thesis was to test whether grazing effects are consistent over different spatial scales, and to give recommendations for appropriate monitoring scales. For this purpose, we studied grazing effects on plant community structure using multi-scale plots that included three nested spatial scales (0.25 m2, 4 m2, and 40 m2). Over all vegetation types, the scale of observation directly affected grazing effects on woody plant cover and on floristic similarity, but not on the proportion of open soil and species richness. Grazing effects manifested at small scales regarding floristic similarity in pioneer forest and ruderal sites and regarding species richness in ruderal sites. The direction of scale-effects on similarity differed between vegetation types: Grazing effects on floristic similarity in the Corynephorus sites were significantly higher at the medium and large scale, while in the pioneer forest sites they were significantly higher at the smallest scale. Disturbances initiate vegetation changes by creating gaps and affecting colonization and extinction rates. The third intention of the thesis was to investigate the effect of small-scale disturbances on the species-level. In a sowing experiment, we studied early establishment probabilities of Corynephorus canescens, a key species of open sandy habitats. Applying two different regimes of mechanical ground disturbance (disturbed and undisturbed) in the three successional stages mentioned above, we focused on the interactive effects of small-scale disturbances, successional stage and year-to-year variation. Disturbance led to higher emergence in a humid and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens establishment was competition, while in the dry year water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. We conclude that wild ungulate grazing is a useful tool to slow down succession and to preserve a species-rich, open landscape, because it does not only create disturbances, thereby supporting early successional stages, but at the same time efficiently controls woody plant cover. However, wild ungulate grazing considerably changed the overall appearance of the landscape. Additional measures like shifting exclosures might be necessary to allow vulnerable species to flower and reproduce. We further conclude that studying grazing impacts on a range of scales is crucial, since different parameters are affected at different spatial scales. Larger scales are suitable for assessing grazing impact on structural parameters like the proportion of open soil or woody plant cover, whereas species richness and floristic similarity are affected at smaller scales. Our results further indicate that the optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. Further, at the landscape scale, facilitation by late successional species may be an important mechanism for the persistence of protected pioneer species. / Der globale Wandel führte in den letzten Jahrzehnten zu einem drastischen Habitat- und Artenschwund, von dem in Mitteleuropa offene Lebensräume besonders betroffen sind. Hauptziel dieser Arbeit war es, experimentell zu untersuchen, ob Wildtierbeweidung eine geeignete Methode für das Offenlandmanagement ist. Der Wildtiereffekt wurde über drei Jahre in einem 160 ha großen Wildtiergehege im NO Deutschlands in drei Sukzessionsstadien untersucht: (i) Corynephorus canescens-dominierte Kurzgrasrasen, (ii) durch Tanacetum vulgare dominierte ruderale Staudenfluren und (iii) Pinus sylvestris-Vorwälder. Wildtierbeweidung beeinflusste die Artenzusammensetzung entscheidend und verzögerte die Sukzession, wobei sich die Beweidungseffekte zwischen den Sukzessionsstadien unterschieden. Die Artenzahl war in den beweideten Ruderal- und Vorwaldflächen deutlich höher als in den unbeweideten, nicht jedoch in den Corynephorus-Flächen. Die Artenzusammensetzung wurde in den Corynephorus- und den Ruderal-Flächen verändert. Ruderal-Flächen entwickelten sich durch die Beweidung zu einem durch Agrostis spp. dominierten Vegetationstyp mit niedriger Vegetationshöhe, in dem die meisten Arten nicht zur Blüte kamen. Die Gehölzdeckung wurde in den beweideten Vorwaldflächen signifikant reduziert. Junge Kiefern wurden stark geschädigt und in ihrer Wuchshöher reduziert. Analyse und Interpretation einer Untersuchung sind abhängig vom Beobachtungsmaßstab. Das zweite Ziel dieser Arbeit war es, zu testen, ob Beweidungseffekte über verschiedene räumliche Skalen konsistent sind, sowie Empfehlungen für geeignete Monitoring-Maßstäbe zu geben. Der Effekt von Wildtierbeweidung auf die Vegetation dreier Sukzessionsstadien wurde mittels genesteter Dauerflächen untersucht (0.25 m2, 4 m2, 40 m2). Über alle Vegetationstypen zusammen beeinflusste der Beobachtungsmaßstab den Beweidungseffekt auf die Gehölzdeckung sowie auf die floristische Ähnlichkeit, aber nicht auf den Anteil offenen Bodens und die Artenzahl. Betrachtet man die Vegetationstypen getrennt, so zeigte sich der Beweidungseffekt auf kleinen Skalen in den Vorwaldflächen und den ruderalen Flächen hinsichtlich der Ähnlichkeit und in den ruderalen Flächen hinsichtlich der Artenzahl. Die Richtung der Skaleneffekte auf die floristische Ähnlichkeit unterschied sich zwischen den Vegetationstypen: Während sich beweidete und unbeweidete Corynephorus-Flächen auf der mittleren und der großen Skala signifikant voneinander unterschieden, war dies im Kiefernvorwald auf der kleinsten Skala der Fall. Störungen führen zu Vegetationsveränderungen, die die Einwanderungs- und Aussterberaten von Arten beeinflussen. Das dritte Ziel dieser Arbeit war es, den Effekt kleinräumiger Störungen auf der Art-Ebene zu untersuchen sowie deren Interaktion mit dem Sukzessionsstadium und der jährlichen Variabilität. In einem Aussaatexperiment wurde das Etablierungsverhalten von Corynephorus canescens, einer Schlüsselart sandiger Offenhabitate, in drei Sukzessionsstadien und unter zwei Störungsregimes (gestört vs. ungestört) untersucht. In einem feuchten Jahr führten Störungen zu höheren, in einem trockenen Jahr dagegen zu niedrigeren Keimraten. Solange die Bodenfeuchtigkeit hoch genug war, war Konkurrenz der wichtigste limitierende Faktor für die Etablierung von C. canescens, während im trockenen Jahr Wasser zum entscheidenden Faktor wurde. Auf die Überlebensraten hatten Störungen keinen Einfluss. In feuchten Jahren waren die Keimraten in offenen Sukzessionsstadien höher, während sie im trockenen Jahr im späten Sukzessionsstadium höher waren. Spätere Sukzessionsstadien können also für die Persistenz von C. canescens eine wichtige Rolle spielen. Da Wildtierbeweidung sowohl Störungen verursacht und dadurch frühe Sukzessionsstadien fördert, als auch die Gehölzdeckung reduziert, ist sie eine besonders geeignete Maßnahme, um artenreiche, offene Landschaften zu erhalten. Sie kann jedoch zu teilweise drastischen Veränderungen der Landschaft führen, so dass zusätzliche Maßnahmen wie wechselnde Auskoppelungen notwendig sein können, um ein reiches Mosaik verschiedener Sukzessionsstadien mit einer hohen Gesamtartenzahl zu erhalten. Weiterhin ist die Untersuchung von Beweidungseffekten auf verschiedenen Maßstabsebenen von großer Bedeutung, da verschiedene Parameter auf unterschiedlichen Skalen beeinflusst werden. Größere Skalen sind geeignet, um den Beweidungseinfluss auf Strukturparameter wie den Anteil offenen Bodens oder der Gehölzdeckung zu erfassen, während für die Erfassung der Veränderung des Artenreichtums und der floristischen Ähnlichkeit kleinere Skalen besser geeignet sind. Unsere Ergebnisse zeigen außerdem, dass kleinräumige Störungen die Keimung von C. canescens fördern, wobei Störungen direkt vor der Samenausbreitung und nicht in trockenen Jahren durchgeführt werden sollten. Auf Landschaftsebene kann die Förderung durch Arten späterer Sukzessionsstadien ein wichtiger Mechanismus für die Persistenz geschützter Pionierarten sein.

An experimental study of laboratory populations of the stored-products moth, Cadra cautella (Lepidoptera: Phycitidae) and its larval parasitoid, Venturia canescens (Hymenoptera: Ichneumonidae) identified and quantified density- and age-dependent demographic characteristics of the host-parasitoid system. Host imago longevity and fecundity depended on larval weight at pupation. Observed effects of C. cautella larval competition for food on larval mortality, stage duration, and weight at pupation were successfully captured in a mathematical model. Host larval age significantly influenced inter-stage cannibalism and susceptibility to mortality resulting from parasitoid oviposition wounds. Both larval parasitoid developmental rates and adult parasitoid attack rates depended on host larval age. Long-term population experiments of host and host-parasitoid populations revealed that host populations fluctuated with a period slightly in excess of host generation time and that parasitoid populations were in synchrony with host populations.

Universiẗat, Diss., 2004--Kiel.

The Stress-gradient hypothesis predicates a change of interspecies relations from negative to positive according to the stress gradient. The basic assumption is that the presence of one species (the facilitator) makes the growth of other species easier. In this study was determined based on the 5years experiment, whether the interspecies interactions (i.e. the importance of facilitation and competition) changes according to the hydrological conditions. Three wetland species (Calamagrostis canescens, Carex elongata and Deschampsia cespitosa) were planted in experimental pots with the presence and absence of the dominant species (Carex elata). The hydrological gradient (= the stress gradient) was simulated by three types of hydrological conditions: dry, fluctuating and wet. The success of the species within the specific conditions was correlated with the fitness-related characteristics of the plants including the biomass, the number of ramets and the height of the plants. Following hypotheses were tested: i) at a low intensity of stress (with the wet treatment), the C. elata represents a competitor for other species. On the other hand, at a high intensity of stress (with the dry treatment), the C. elata represents a facilitator, making it easier to the other coexisting species to grow. This presumption was confirmed only with the D. cespitosa, which was more successful under dry treatment with the presence of a dominant species, which facilitated it. With the other two species the change of interspecific relations was not observed and the relationships remained negative. Furthermore the results showed, that in the dry treatment with the presence of a dominant species, there was a lower intensity of competition among the coexisting species. The experiment showed, that the interactions of particular species with dominant species can vary according to the stress gradient. The hydrological gradient also influences the character and intensity of interactions among the species.

In dié studie is sekere aspekte van voedingswaarde van droogtebestandegewasse, tussen twee seisoene en op drie verskillende lokaliteite nl Hatfield, Mier en Lovedale, geondersoek. Die spesies wat met mekaar vergelyk is, was: C. sturtii, A. nummularia, A. halimus A. canescens(Santa Rita), A. canescens (Veldreservaat 1), en A. canescens(Rincon). Die twee seisoene was herfs en winter. Uit dié resultate kan die volgende afleiding gemaak word:betekenisvolle(P < 0.05) laer blaar-totstamverhouding gedurende die winter as die herfs kon by die onderskeie proefpersele van, C. sturtii en A. canescens (Veld 1)(Hatfield); A. canescens(Veld 1) en A. canescens(Rincon)(Mier); A. canescens(Veld 1) en A. canescens(Santa Rita)(Lovedale), waargeneem word. In teenstelling met die bogenoemde bevindinge het A. nummularia(Lovedale) betekenisvol (P < 0.05) hoër blaar-totstamverhouding in die winter as die herfs gehad. Vir A. canescens (Santa Rita) het die Mier proefperseel betekenisvolle (P < 0.05) hoër blaar-tot-stamverhouding as die ander twee lokaliteite getoon. By al drie proefpersele, vir alle spesies, is die blaar RP % sowel as die IVDMV % van die blare betekenisvol (P < 0.05) hoër as dié van stamme. Vir al die spesies geoes by Mier, was die NBV % in die winter betekenisvol (P < 0.05) hoër as in die herfs. C. sturtii (Lovedale) het geen betekenisvolle (P > 0.05) verskille in die chemiese samestelling tussen seisoene getoon nie, terwyl die ander spesies wel betekenisvolle (P < 0.05) verskille getoon het. Slegs in die geval van A. nummularia kon betekenisvolle (P < 0.05) verskille in IVDMV % tussen lokaliteite waargeneem word. Indien die tempo van degradasie (c) gedurende die herfs by Hatfield geoes, tussen spesies vergelyk word, het A. canescens (Veld 1)betekenisvolle (P < 0.05) hoër c-waarde as dié vanaf A. nummularia en A.canescens (Santa Rita) gehad. Slegs monsters op Hatfield gedurende die herfs geoes kon betekenisvolle (P < 0.05) verskille in PD tussen A. canescens (Veld1) en A. nummularia waargeneem word. Slegs by Mier, in die herfs, het A. nummularia betekenisvol(P < 0.05) hoër ED as A. canescens (Veld 1) gehad. Vir wintermonsters kon geen betekenisvolle (P > 0.05) verskille in die c-waarde tussen spesies en lokaliteite waargeneem word nie. Wintermonsters, geneem te Mier, het A. canescens (Veld 1) betekenisvol (P < 0.05) laer PD as die ander spesies gehad, terwyl by Lovedale het A. canescens(Santa Rita) betekenisvol (P < 0.05) laer PD as die ander spesies gehad. A. nummularia het betekenisvol (P < 0.05) hoër ED as die ander spesies, by Mier en Lovedale, vir monsters wat gedurende winter geoes is, gehad. Wanneer gasproduksiewaardes tussen spesies vergelyk word, het A. canescens (Veld 1) betekenisvol (P < 0.05) minder gas as die ander spesies, vir inkubasie tye 20,30 en 44 ure, geproduseer. Betekenisvolle (P < 0.05) verskille in die a-waarde kon tussen die hoë C. sturtii en die lae A. canescens. (Santa Rita), maar nie tussen die ander spesies, waargeneem word. Betekenisvollen (P < 0.05) verskille in die b-waarde kon tussen: C. sturtii (145.1 ml/g DM), A. canescens (Veld 1)(127.9 ml/g DM)en A. canescens (Rincon)(164.9 ml/g DM) waargeneem word. Betekenisvolle verskille (P < 0.05) in die tempo van gasproduksie kon net tussen die hoë C. sturtii (0.086/h) en die lae A. canescens (Santa Rita)(0.065/h) waargeneem word. Betekenisvolle (P < 0.05) verskille in die potensiële gasproduksie (a + b) kon tussen: C. sturtii, A. canescens. (Veld 1) en A. canescens (Rincon) waargeneem word. Droogtebestande gewasse kan as medium tot lae kwaliteit voerbronne beskou word,wat op strategiese tye(droogte tye) benut kan word. ENGLISH : The nutritive value of four drought tolerant crops were investigated at three localities during two seasons. The species which have been compared, were C. sturtii, A. nummularia, A. halimus, A. canescens (Santa Rita), A. canescens (Field reserve 1), and (Rincon). The two seasons were autumn and winter. A significantly (P < 0.05) lower leaf-to-stem ratio was recorded for the species <i<C. sturtii and A. canescens (Field 1) at Hatfield, while at Mier A. canescens (Field 1) and A. canescens (Rincon) were found to have significant (P < 0.05)lower values in the winter than in the autumn. At Lovedale, the winter leaf-to-stem ratios were significantly (P < 0.05) lower than in the autumn for A. canescens (Field 1) and A. canescens (Santa Rita). In contrast to the above, A. nummularia had a significantly (P < 0.05) higher leaf-to-stem ratio in winter than in autumn at Lovedale. Overall, A. canescens (Santa Rita) harvested at Mier had a significantly (P < 0.05) higher leaf-to-stem ratio than material from the other two sites. At all the sampling sites and for all accessions the CP % and the IVDMD % of the leaves were significantly (P < 0.05) higher than those of the stems. The NDF % in most of the species harvested during winter, was significantly (P < 0.05) higher than those harvested during autumn. C. sturtii was the only species for which no significant (P > 0.05) differences in the chemical composition could be found between the two seasons. Only in the case of A. nummularia could significant (P < 0.05) differences in the IVDMD % be found between localities. A. canescens (Field 1) harvested during autumn at Hatfield, had a significantly higher rate of passage(c) than A. nummularia and A. canescens (Santa Rita). Samples harvested at Hatfield in autumn also produced significant (P < 0.05) differences in PD between A. canescens (Field 1) and A .nummularia. Mier was the only sampling site where significantly (P < 0.05) higher (A. nummualaria) and lower (A. canescens(Field1)) ED were observed for samples taken during autumn. No significant (P > 0.05) differences in the rate of passage (c) were observed between species or sampling sites for samples taken during the winter. Winter samples taken from A. canescens (Field 1) at Mier and A. canescens (Santa Rita) taken from Lovedale, showed significantly (P < 0.05) lower PD than the other species. A. nummularia had significantly (P < 0.05) higher ED than the other species harvested at Mier and Lovedale, during winter. When gas production values between species were compared it was clear that A. canescens (Field1) produced significantly (P < 0.05) less gas compared to the other species at incubation times of 20, 30 and 44 hours. Significant (P < 0.05) differences in the a-values were also observed between the high C. sturtii and the low A. canescens (Santa Rita) values. Significant (P < 0.05) differences in the b-value were observed between C. sturtii (145.1ml/g DM), A. canescens (Field 1)(127.9 ml/g DM) and A. canescens (Rincon)(164ml/g DM). C. sturtii (0.086/h) and A. canescens (Santa Rita)(0.065/h) were the only species that differed significantly (P < 0.05) in terms of the rate of passage(c). Significant (P < 0.05) differences in the potential gas production (a + b) were observed between C.sturtii, A. canescens (Field 1) and A. canescens (Rincon). Drought resistant crops can be considered as a medium to low quality source of fodder which can be used at strategic times, especially during periods of drought. Copyright / Dissertation (MScAgric)--University of Pretoria, 2010. / Animal and Wildlife Sciences / unrestricted