Since the 'discovery' of the high abundance of viruses in aquatic environments, it has been generally assumed that viruses in lakes are similar to those in oceans. I directly compared these two systems using a large, robust data set. Viral abundance was significantly different among the surveyed environments. The relationship between viral and bacterial abundance indicated a fundamental difference between lakes and oceans, and suggested that viruses infecting phytoplankton may be more important in lakes. Molecular techniques (PCR & DGGE) were used to document spatial and temporal variations in the richness of viruses that infect eukaryotic phytoplankton (Phycodnaviridae) in lakes at the Experimental Lakes Area (ELA). Phycodnavirus richness was highest in the eutrophic lake, and during the spring/early summer in all the lakes. Viral richness was closely associated with phytoplankton abundance and composition. As a result, richness was influenced by trophic status, while patterns of richness were affected by regional climatic conditions. Phylogenetic analysis of environmental Phycodnavirus DNA polymerase (pol) sequences indicated that freshwater Phycodnaviruses are genetically different from cultured isolates and marine environmental sequences. A genetic distance analysis indicated that pol sequences > 7 % different infected different host species. Therefore, the 20 different freshwater sequences likely infected nine different hosts. Multivariate statistics identified seven possible phytoplankton hosts, including chlorophytes, chrysophytes, diatoms and dinoflagellates. Finally, the modified dilution experiment was evaluated as an approach for estimating viral-mediated phytoplankton mortality in two lakes at the ELA. Experiments resulted in non-significant apparent growth rate regressions. While a model analysis, indicated that the method was sensitive to poorly constrained parameters such as burst size and length of the lytic cycle, making it unsuitable for estimating mortality rates in these lakes. These studies indicate that Phycodnaviridae are a genetically rich and dynamic component of lakes. Their richness is influenced by both the chemical and physical components of their environment. Although the presence of these viruses indicates that they are a source of phytoplankton mortality, the magnitude of their impact on structuring phytoplankton communities awaits methodological advances. Nonetheless, these findings support the view that viruses infecting phytoplankton are ecologically important components of lake ecosystems.

Similar ecosystems may be expected where climates and landforms on different continents match. The most detailed tests of such convergence have examined mediterranean areas of Europe, North and South America. This thesis compares mediterranean Australia and southern Africa, two relatively nutrientpoor areas largely neglected in previous studies. Inparticular, two study areas very similar in climate, landform and soils were compared, one at the Barrens on the south coast of Western Australia and the other at the Caledon coast in the southwestern Cape of South Africa. The less frequent, but heavier, rain in Australia probably led t o the anomalous presence of trees there. The height and density of vegetation appeared only weakly related to soil nutrients but strongly correlated with moisture. Conversely, nutrient status rather than climate appeared to govern many of those features of plants that interacted with animals, such as flowers and fruits . This applied particularly to ants, which took seeds bearing elaiosomes, and birds, which took fleshy fruits . Soil fertility thus determined the occurrence of agents which both consumed plants and aided their propagation. Climate, soil and fire, together with the consequent regimes of fiutrient cycling and predation, determined the relativeroles played by endotherms, such as mammals, and by ectotherms, such as reptiles, amphibians and their invertebrate prey. Despite close matching, small differences in physical factors remained between the two study areas, with commensurate differences in their biological communities. It is suggested that co-adaptation is not a major cause of differences between ecosystems on different continents but rather a consequence of inevitable differences in physical conditions.

Tall tuart (Eucalyptus gomphocephala) trees are a defining element of the landscape of Perth and the coastal plain to the north and south. However, with the health of some tuart stands deteriorating, most notably at Yalgorup south of Perth, concerns are heightening that the already fragmented tuart ecosystem will continue to contract, leaving a cultural and ecological scar in the landscape. Like many other eucalypt ecosystems, tuart woodlands have had a long association with fire and are believed to have been frequently burnt by the Aborigines prior to European settlement. Today, fragmentation and European land management practices have led to a lower frequency of fire across most remaining woodlands, but also episodes of intense fire at shorter intervals in some areas. Individual fire events as well as fire regimes have the potential to shape the structure, composition and extent of ecosystems, and eucalypt ecosystems are no different. Thus, the impact of fire and fire regimes on tuart health and regeneration was investigated in this study. A survey of the woodlands at Yalgorup revealed tuart decline was present across a range of sites with contrasting fire histories. Tuart health was poorest at the longest unburnt site (35 years) and the site burnt by frequent wildfire (three fires in 13 years), suggesting these extreme fire regimes had played a role in the decline. Nevertheless, low ratings of tree health at sites burnt approximately once per decade, point to factors other than fire playing a role in the decline of tuart at Yalgorup. The tuart populations at Yalgorup were dominated by individuals in larger size-classes and there was a significant negative relationship between tree size and the probability of tree mortality. In one stand in Yalgorup National Park, 38 % of the tuart saplings/trees had died. It follows that the regeneration and development of tuart seedlings into adults will need to occur within the next one to two decades if these woodlands are to persist. Seedling counts confirmed that tuart regeneration was virtually absent in unburnt areas, as is common with eucalypt species. Interpretations of size-class distributions suggested controlled burning contributed little to recruitment, whereas in areas subject to wildfire outside Yalgorup, tuart had regenerated in abundance such that size-class distributions were skewed towards the smaller size-classes. A repeat survey of plots established in 1976 supported anecdotal reports that the mid-storey tree peppermint (Agonis flexuosa) was increasing in density and height in Yalgorup. The skew towards the smallest size-class within peppermint populations at Yalgorup and the presence of seedlings ( > 200 seedlings ha-1) within areas not recently burnt (at least four years since fire) brought into focus the differing mode of regeneration for this species in comparison to tuart. In further contrast to tuart, mature peppermints were in good health with no dead trees reported in the population surveys. A possible role for competition in tuart decline was highlighted by significant negative correlation between peppermint density and tuart health. Together, these results suggest that a general drift from tuart woodland to peppermint forest appears entrenched. Comparative studies of the bark thickness, fire response and resprouting behaviour of tuart and peppermint illustrated the capacity of individuals of both species to persist with recurrent fire. As adults or juveniles, tuart and peppermint resprouted following complete canopy scorch, and often from crown branches: an ability not uncommon for co-occurring tree species and shrubs in this environment. Survival was between 75 and 100 % for fully-scorched tuarts in size-classes ranging from small saplings to trees across six sites. From the small sample of peppermints available for comparison, seedlings and small saplings appeared to be more vulnerable to mortality by fire; only 45 % of individuals with a diameter at breast height ¡Ü 1 cm survived following complete canopy scorch from a controlled burn. With thicker bark, a reliance on stem epicormic buds rather than a lignotuber for resprouting and a greater capacity for height growth, the fire resistance and post-fire recovery of tuart would be expected to differ from that for peppermint. Opportunities for managers to exploit these differences in their burning prescriptions so as to address the drift from tuart to peppermint dominance were outlined. In addition, results indicating a positive response in canopy condition for tuarts with < 10 % canopy scorch following a controlled burn imply that tuart vigour may benefit more immediately from fire. But, observations also revealed that spikes in intensity within controlled burns can damage large unhealthy trees and thereby accelerate the decline process. Thus, the application of fire to declining tuart stands needs to be conducted skillfully. Patterns of growth and survival for tuart and peppermint seedlings were linked to the contrasting ability of the species to establish at burnt and unburnt sites. The purported importance of ashbeds in tuart establishment was demonstrated; at the end of summer (February) at a recently burnt site (Golden Bay), the mean height of tuart seedlings on ashbeds was three times that for those off ashbeds, and the survival rate on and off the ashbeds was 35 % and 15 %, respectively. Therefore, while important, tuart seedlings were not dependent on ashbeds in this instance. The hardy nature of peppermint seedlings when compared to tuart was illustrated when the species were planted in an unburnt area of tuart-peppermint woodland at Yalgorup; nine months after planting, 38 % of the peppermint seedlings survived while only 9 % of the tuart survived. Most of the mortality was linked with the summer-drought period and it was suspected that peppermint seedlings were more drought tolerant. A complementary glasshouse experiment showed that tuart had a greater shoot:root ratio than peppermint, which may be one factor in the greater sensitivity of this species to drought. Further, this experiment revealed that with an increase in nutrient supply, the proportional increment in rooting depth for tuart (1.6 times) was significantly greater than for peppermint (0.3 times). An increased availability of nutrients in ashbeds following fire, particularly for phosphorous, was measured within tuart woodland. Therefore, it was inferred that the availability of nutrients was a critical factor increasing the growth, rooting depth and consequently the greater survival of tuarts on ashbeds. Overall, tuart was concluded to share the Competitor strategy (after Grime) in common with many other eucalypts: rapid growth and the attainment of a large size. On the other hand, peppermint exhibits some of the traits of the Stress Tolerator strategy (after Grime): low minimum resource requirements for growth and survival. The consequence of the increasing cover of peppermint on tuart establishment was explored in field experiments with planted tuart seedlings. No significant impact on seedling growth or survival was observed. There was a declining trend in the seedling growth rates under the high compared to the low peppermint density treatments as the second summer of the experiment was approached, although a statistical difference could not be shown. Peppermint density also had no significant influence on damage to the seedlings from insect attack or the foliar pathogen Mycosphaerella cryptica. Overall, insects and M. cryptica had only an incidental impact on the seedlings: the mean level of canopy damage per affected seedling was < 10 % for either of these two damage agents. Soil type, specifically whether growth occurred on an ashbed was demonstrated to be the most important factor in tuart growth and survival in the 18 months following planting. Although survival was superior on ashbeds (88 %), mean survival was > 50 % in unburnt soil 18 months after planting indicating the potential for restorative plantings to occur in some woodlands between fires. Tuart decline, and the role of altered fire regimes in the decline is complex and further avenues of research were emphasized. Nevertheless, the findings of this and other studies are sufficient to enable purposeful actions to conserve and restore tuart woodlands; recommendations regarding the application of fire with a view to these goals are presented in the final discussion.

Diss. (sammanfattning) Uppsala : Univ., 2004. / Härtill 6 uppsatser.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 5 uppsatser. Med sammanfattning på svenska och tyska.

Thesis (M. Sc.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 146-156).

Thesis (M.S.)--University of Toledo, 2005. / Typescript. "A thesis [submitted] as partial fulfillment of the requirements of the Master of Science degree in Biology." Bibliography: leaves 45-50.

Made available in DSpace on 2014-06-11T19:35:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-19Bitstream added on 2014-06-13T18:47:07Z : No. of bitstreams: 1 alves_rcp_dr_botib.pdf: 4373370 bytes, checksum: 868dbf433604bb75f86e445787dedfc8 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os organismos planctônicos são a base das cadeias alimentares no ecossistema aquático e os herbívoros zooplanctônicos, em particular, são importantes para o fluxo de energia nos ecossistemas aquáticos, sendo um elo entre os produtores primários e níveis tróficos mais elevados. Este estudo se propôs a ampliar o conhecimento da herbivoria do zooplâncton sobre o fitoplâncton em uma lagoa marginal ao rio Paranapanema. Foi realizado um experimento in situ, com instalação de enclosures com paredes de polietileno fechados no fundo que permitiram a realização de quatro tratamentos: 0% da densidade natural de zooplâncton (apenas fitoplâncton), 50 % (metade da densidade natural), 100% (densidade natural) e 150% (densidade acima da natural). A variação da densidade do zooplâncton foi conseguida por meio de filtração da água por rede de abertura de malha de 50μm. Água da lagoa também foi coletada. Todos os tratamentos foram realizados em tréplica. O experimento durou 18 dias. As coletas foram realizadas a cada seis dias (quatro coletas). A temperatura foi obtida em campo e água foi coletada para análise de oxigênio dissolvido, saturação, pH, condutividade elétrica, concentrações de fósforo total, nitrogênio total, material em suspensão total, material em suspensão orgânico, material em suspensão inorgânico, clorofila-a e feofitina-a. Foram coletadas também amostras de zooplâncton e fitoplâncton que foram contadas e identificadas, normalmente, até ao nível de espécie. Rotifera teve sua abundância relativa alterada em todos os tratamentos, com o favorecimento de Keratella cochlearis e Polyarthra vulgaris provavelmente porque o enclosure as protegeu de predadores. Cladocera foi dominado em todos os tratamentos por Bosmina freyi e B. hagmanni, bioindicadores de eutrofização... / The planktonic organisms are the basis of food chains in the aquatic ecosystems, and the grazer zooplankton, specifically, are very important to energy flow in the aquatic ecosystems, being a link between primary producers and higher trophic levels. The aim of this study is enhance the knowledge of zooplankton grazing over phytoplankton in a lateral lake by Paranapanema River, Brazil. The experiment was conducted in situ, with installation of enclosures of polyetilene walls, closed at the bottom, which allowed the manipulation of four treatments: 0% of the natural density of zooplankton (phytoplankton only); 50% (half of natural density); 100% (natural density) and 150% (a higher density than the natural). The zooplankton density range was obtained by water filtration in zooplankton web with 50μm mesh. The water of the lake was collected either. All the treatments were made using three replications each one. The experiment was carried out for 18 days. The samplings were made each six days (four samplings). The water temperature was measured at field, and a water sample was collected for dissolved oxygen, saturation, pH, conductivity, and concentrations of total phosphorus, total nitrogen, total suspended matter, organic suspended matter, inorganic suspended matter, chlorophyll-a and pheophytin-a analyses. Samples of zooplankton and phytoplankton were also taken. They were counted and identified until specie level, mostly. Rotifera had its relative abundance changed in all treatments, showing the increasing of Keratella cochlearis and Polyarthra vulgaris, probably because the enclosures protected them from predators. Cladocera dominated all treatments by Bosmina freyi and B hagmanni, which are bioindicators of water euthophication. The absolute abundance of this group was the one that best responded... (Complete abstract click electronic access below)

Made available in DSpace on 2014-10-09T12:54:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:21Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

Orientador: Raoul Henry / Banca: Claudia Fileto / Banca: Danielli Cristina Granado Romero / Banca: Maria Stela Maioli Castilho Noll / Banca: Silvia Maria Caglierani / Resumo: Os organismos planctônicos são a base das cadeias alimentares no ecossistema aquático e os herbívoros zooplanctônicos, em particular, são importantes para o fluxo de energia nos ecossistemas aquáticos, sendo um elo entre os produtores primários e níveis tróficos mais elevados. Este estudo se propôs a ampliar o conhecimento da herbivoria do zooplâncton sobre o fitoplâncton em uma lagoa marginal ao rio Paranapanema. Foi realizado um experimento in situ, com instalação de enclosures com paredes de polietileno fechados no fundo que permitiram a realização de quatro tratamentos: 0% da densidade natural de zooplâncton (apenas fitoplâncton), 50 % (metade da densidade natural), 100% (densidade natural) e 150% (densidade acima da natural). A variação da densidade do zooplâncton foi conseguida por meio de filtração da água por rede de abertura de malha de 50μm. Água da lagoa também foi coletada. Todos os tratamentos foram realizados em tréplica. O experimento durou 18 dias. As coletas foram realizadas a cada seis dias (quatro coletas). A temperatura foi obtida em campo e água foi coletada para análise de oxigênio dissolvido, saturação, pH, condutividade elétrica, concentrações de fósforo total, nitrogênio total, material em suspensão total, material em suspensão orgânico, material em suspensão inorgânico, clorofila-a e feofitina-a. Foram coletadas também amostras de zooplâncton e fitoplâncton que foram contadas e identificadas, normalmente, até ao nível de espécie. Rotifera teve sua abundância relativa alterada em todos os tratamentos, com o favorecimento de Keratella cochlearis e Polyarthra vulgaris provavelmente porque o enclosure as protegeu de predadores. Cladocera foi dominado em todos os tratamentos por Bosmina freyi e B. hagmanni, bioindicadores de eutrofização... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The planktonic organisms are the basis of food chains in the aquatic ecosystems, and the grazer zooplankton, specifically, are very important to energy flow in the aquatic ecosystems, being a link between primary producers and higher trophic levels. The aim of this study is enhance the knowledge of zooplankton grazing over phytoplankton in a lateral lake by Paranapanema River, Brazil. The experiment was conducted in situ, with installation of enclosures of polyetilene walls, closed at the bottom, which allowed the manipulation of four treatments: 0% of the natural density of zooplankton (phytoplankton only); 50% (half of natural density); 100% (natural density) and 150% (a higher density than the natural). The zooplankton density range was obtained by water filtration in zooplankton web with 50μm mesh. The water of the lake was collected either. All the treatments were made using three replications each one. The experiment was carried out for 18 days. The samplings were made each six days (four samplings). The water temperature was measured at field, and a water sample was collected for dissolved oxygen, saturation, pH, conductivity, and concentrations of total phosphorus, total nitrogen, total suspended matter, organic suspended matter, inorganic suspended matter, chlorophyll-a and pheophytin-a analyses. Samples of zooplankton and phytoplankton were also taken. They were counted and identified until specie level, mostly. Rotifera had its relative abundance changed in all treatments, showing the increasing of Keratella cochlearis and Polyarthra vulgaris, probably because the enclosures protected them from predators. Cladocera dominated all treatments by Bosmina freyi and B hagmanni, which are bioindicators of water euthophication. The absolute abundance of this group was the one that best responded... (Complete abstract click electronic access below) / Doutor