Chemically mediated interactions have important ecological and evolutionary effects on populations and communities. Despite recognition that herbivory can significantly affect the biomass and composition of freshwater macrophyte communities, there are few investigations of chemical defenses among freshwater vascular plants and mosses and none of freshwater red algae. This study compares the palatability of five species of freshwater red algae (Batrachospermum helminthosum, Boldia erythrosiphon, Kumanoa sp., Paralemanea annulata, and Tuomeya americana) that occur in the southeastern United States relative to two co-occurring macrophytes (the chemically defended aquatic moss Fontinalis novae-angliae and the broadly palatable green alga Cladophora glomerata). We assessed the potential role of structural, nutritional, and chemical traits in reducing macrophyte susceptibility to generalist crayfish grazers. Both native and non-native crayfish significantly preferred the green alga C. glomerata over four of the five species of red algae. B. erythrosiphon was palatable, while the cartilaginous structure of P. annulata reduced its susceptibility to grazing, and chemical defenses of B. helminthosum, Kumanoa sp., and T. americana rendered these species as unpalatable as the moss F. novae-angliae. Extracts from these latter species reduced feeding by ~30-60% relative to solvent controls if tissues were crushed (simulating herbivore damage) prior to extraction in organic solvents. However, if algae were first soaked in organic solvents that inhibit enzymatic activity and then crushed, crude extracts stimulated or had no effect on herbivory. B. helminthosum, Kumanoa sp., and T. americana all exhibited "activated" chemical defenses in which anti-herbivore compounds are produced rapidly upon herbivore attack via enzymatic processes. In an additional accept/reject behavioral assay, B. helminthosum extracts reduced the number of crayfish willing to feed by >90%. Given that three of the five red algal taxa examined in this study yielded deterrent crude extracts, selection for defensive chemistry in freshwater rhodophytes appears to be substantial. Activated chemical defenses are thought to be an adaptation to reduce the resource allocation and ecological costs of defense. As such, activated chemical defenses may be favored in freshwater red algae, whose short-lived gametophytes must grow and reproduce rapidly. Roughly 20% of the known chemical defenses produced by marine algae are activated; further examination is needed to determine whether the frequency of activated chemistry is higher in freshwater red algae compared to their marine counterparts. Continued investigation of chemical defenses in freshwater red algae will contribute to among-system comparisons, providing new insights in the generality of plant-herbivore interactions and their evolution.

Document formatted into pages; contains 46 pages. / Title from PDF of title page. / Thesis (M.S.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Herbivore abundances are determined by a set of interacting factors that vary among different habitat types. Specifically, herbivore abundances in monocultures and polycultures may be governed by the same set of factors but with varying influences in the different habitats. In addition, monophagous and polyphagous herbivores may respond differently to the same set of influencing factors. I examined several abiotic and biotic factors in manipulated monocultures and polycultures of Borrichia frutescens in a west central Florida salt marsh. The experimental plots differed in both plant diversity and aboveground habitat structure to see how each component of diversity contributed to variability in the abiotic and biotic factors and how those factors were related to differences in herbivore abundances. The monoculture treatment involved clipping all above ground non-host plant material to achieve a host plant monoculture. The polyculture treatments involved pinning all non-host plant material to achieve a polyculture with reduced above ground habitat structure. The second polyculture treatment was a control in which the naturally diverse plots were unmanipulated. Two monophagous and one polyphagous herbivores were chosen for this study because of their abundance and availability in the field. The two monophagous herbivores on the host plant Borrichia frutescens were Pissonotus quadripustulatus (Homoptera:Delphacidae) and Asphondylia borrichiae (Diptera: Cecidomyiidae) both of which have been well studied in the field where the current experiment took place. The polyphagous herbivore was Cyarda acutissima (Homoptera: Flatidae), a poorly known invasive from Cuba. Soil salinity and host plant leaf nitrogen content were the abiotic factors measured. Herbivore abundances, percent egg and gall parasitism by parasitoids, spider abundances on host plant stems and ground spider abundances were the biotic factors measured. Both salinity and host plant leaf nitrogen were significantly different among the different treatments with clipped plots having the highest salinity and leaf nitrogen content. Population densities of both of the monophagous herbivores were not significantly different between treatments. The polyphagous herbivore had significantly higher abundances in the pinned and control plots than in the clipped plots. Stem spider abundances were not significantly different among treatments. Ground spiders, however, were significantly more abundant in control and pinned plots than clipped plots. Parasitism of both monophagous herbivores was not significantly different between treatments but was generally higher in the control plots. The results suggest that for monophagous herbivores bottom-up and top-down factors act antagonistically in monocultures but for the polyphagous herbivore, the presence of multiple host plants is more influential in diverse plots even given the higher abundances of generalist predators. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

The effects of artificially supplied perennial water on soil properties, vegetation dynamics and the distribution of large herbivores was investigated in southeastern Zimbabwe. Data collection took place between March 1997 and July 1998. Water points were situated primarily on three different soil types (clay-loam, sandy-clay-loam and sand), and in four different vegetation types (Hill communities, Colophospermum mopane veld, Acacia nigrescens woodland and Albizia petersiana woodland). One water point in C. mopane veld (Bandama) had been closed two years prior to data collection, while another, in the Hill community (Manyoka), had been introduced, two years prior to data collection. Changes in physical (infiltration) and chemical (organic carbon and nutrients) properties of soils around water points were largely restricted to within 100 m of water. Chemical enrichment of the soil occurred only at water points that had been in place for more than two years. Soil surface conditions were altered to distances beyond 100 m from water. Manyoka (the new water point) was an exception, with extreme changes limited to within 100 m of water. Herbaceous and woody species composition changed in response to distance from water with changes best described by asymptotic equations. Changes in species composition of the woody component appeared to be longer lasting than changes to the herbaceous component. Most perennial grass species declined close to water, but Urochloa mosambicensis increased close to water in areas outside of the Hills. Herbaceous species diversity was adversely affected by distance from water on sandy soils (Hill communities and A. petersiana woodland), but was largely unaffected on clay-loam (A. nigrescens woodland) and sandy-clay-loam soils (C. mopane veld). Woody species composition and density was altered out to 500 m from perennial water in Acacia nigrescens woodland on clay-loam soils. Results suggest that this vegetation type may be susceptible to bush encroachment close to water. Trends in woody canopy utilisation were generally similar to trends in woody species composition, and it is proposed that the former may be used to indicate future changes in the latter. Conversion of trees to shrubs was highest at Manyoka (the new water point) indicating that woody destruction by elephants is extreme during the initial years following water introduction. Large herbivore biomass was greatest close to water (< 1 km) during the dry season but not during the wet season. Herbivore species distributions appeared to be influenced by the position of perennial water, but since all range was within easy access of water, it is unlikely that animal distributions were constrained directly by the position of surface water. It is more likely that herbivores were spatially separated on the basis of habitat type. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.

The influence of herbivory, grass competition and grazing system on emergence, growth and survival of Acacia seedlings in burnt and unburnt areas was investigated in their first growing season, from September 1997 to May 1998. The study was aimed at determining possible reasons for the increase in woody plant density in semi-arid savannas, specifically the effect of excluding small-mouthed herbivores from domestic and livestock systems, and switching from continuous grazing to rotational grazing systems. The effect of fire intensity and maximum fire temperature on seed viability, germination and mortality, specifically with regard to back versus head fires and seed size , were investigated. Variability among species in the number of seedlings emerging generally resembled differences in viability. Emergence of Acacia karroo and Acacia tortilis was poorer than that of Acacia nilotica under grass competition. Emergence was lower in burnt and open areas, the latter depending on Acacia species. Herbivory did not affect seedling emergence, in both domestic and wildlife systems. Seedling survival and growth was adversely affected by small-mouthed herbivores in both domestic and livestock systems, whilst large-mouthed herbivores exerted no direct effects on woody seedlings, except to a small degree by trampling. Seedlings showed better growth and survival under low grass competition, which also resulted in greater leaf-to-height ratios , indicating that grass interference with irradiance affects woody seedlings. This effect appeared to be greater for cattle and rotational grazing, and for burning, in domestic and wildlife systems respectively. Woody seedling establishment was also better in burnt areas. Whilst seedling growth was better under rotational than continuous grazing, survival was not significantly different. Grass competition influenced seedling establishment to a greater extent than herbivory, whilst burning made a greater impact than grass competition. Seed mortality in response to maximum fire temperature was inversely related to seed size, and trends in seed germination and mortality, although very variable, appeared to be influenced by threshold fire intensities and maximum temperatures. Back fires had hotter maximum temperatures and fire intensities at ground level than head fires, which result in greater seed mortality following fire. Based on the current study it is likely that the removal of grass competition, burning, and a change from continuous to rotational grazing systems, and small-mouthed to large-mouthed herbivores, will result in an increase in woody seedling establishment. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

No description available.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 1999. / Härtill 5 uppsatser.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2002. / Härtill 6 uppsatser.

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

Thesis (Ph. D.)--University of Pretoria, 2008. / Title from PDF title page (viewed on Nov. 11, 2008). Includes bibliographical references.

Made available in DSpace on 2016-06-02T19:30:01Z (GMT). No. of bitstreams: 1 6046.pdf: 2350666 bytes, checksum: aed9a60807abef9e46cdb0ad2d5f6de5 (MD5) Previous issue date: 2014-04-28 / Financiadora de Estudos e Projetos / This is the first and most complete study of parasitoid wasps fauna associated with endophagous herbivores reared from flower-heads of Asteracea. A total of 36 remnants of Cerrado were sampled around São Paulo states, Brazil. 15,372 specimens of 192 species of parasitoid wasps were reared from 74 species of family Asteraceae. The subfamilies Eulophidae (Chalcidoidea) and Braconidae (Ichneumonoidea) represented most than a half of parasitoid wasps species. In addition to presenting a rich fauna of parasitoids, this study also addresses ecological issues regarding the main determinants of the parasitoid species richness from Brazilian savannah. The availability of food resources has crucial role in determining the species richness of parasitoids. In the first chapter of this thesis, we verified the role of geographical distribution of plants on the accumulation of natural enemies of their endophagous herbivores. In the second chapter, we verified through a path analysis which was the effect of local richness and phylogenetic diversity of plant species and their herbivores endophagous of flower-heads on local parasitoid species richness. In the third chapter we tested through an analysis of randomization if the patterns of the proportions of species of three trophic levels were consistent or stochastic. We conclude that both plants and their associated herbivores play a key role in determining the species richness of parasitoids in the Cerrado biome and the principals determinants of parasitoid wasps species richness were geographical distribution of plants, plant and herbivore richness, and the phytophysiognomy where species live. Due copyrights, all chapters of this thesis can be found published online in Neotropical Entomology, Insect Conservation and Diversity and Biota Neotropica magazines. / O presente estudo representa o primeiro e mais completo levantamento da fauna de vespas parasitoides associados a herbívoros endófagos de capítulos de Asteraceae. As coletas de dados foram realizadas em 36 remanescentes de Cerrado do Estado de São Paulo, Brasil. Um total de 15.372 espécimes de 192 morfoespécies de Hymenoptera foram criados a partir dos capítulos de 74 espécies da família Asteraceae. As famílias Eulophidae (Chalcidoidea) e Braconidae (Ichneumonoidea) representaram mais da metade das espécies encontradas. Além de apresentar uma rica fauna de parasitoides, este estudo também aborda questões ecológicas a respeito dos principais determinantes da riqueza de parasitoides na savana brasileira. A oferta dos recursos tem papel fundamental na determinação da riqueza das espécies de parasitoides. No primeiro capítulo desta tese verificamos o papel da distribuição geográfica das plantas sobre o acúmulo de espécies de inimigos naturais de seus herbívoros endófagos. No segundo capítulo verificamos através de uma análise de rota qual foi o efeito da riqueza e diversidade filogenética locais das espécies de plantas e de seus herbívoros endófagos de capítulos sobre a riqueza local de parasitoides. No terceiro capítulo testamos através de uma análise de aleatorização, se os padrões das proporções das espécies dos três níveis tróficos entre as fisionomias foram consistentes ou se estocásticos. Concluímos que tanto plantas como seus herbívoros associados exercem um papel fundamental na determinação da riqueza de espécies de parasitoides no domínio do Cerrado. Os temas contidos nesta tese foram organizados em capítulos independentes e estão elaborados em formato de artigos para as revistas Neotropical Entomology, Insect Conservation and Diversity e Biota Neotropica.