Habitat dynamics in the bed sediments of an intermittent upland stream

The effects of the hydrological regime on temporal changes to physical characteristics of substratum habitat, sediment texture of surface sediments (<10 cm), were investigated in a sub-tropical headwater stream over four years. Surface discharge was measured together with vertical hydraulic gradient and groundwater depth in order to explore features of sediment habitat that extend beyond the streambed surface. Whilst the typical discharge pattern was one of intermittent base flows and infrequent flow events associated with monsoonal rain patterns, the study period also encompassed a drought and a one-in-a-hundred-year flood. Rainfall and discharge did not necessarily reflect the actual conditions in the stream. Although surface waters were persistent long after discharge ceased, the streambed was completely dry on several occasions. Shallow groundwater was present at variable depths throughout the study period, being absent only at the height of the drought. The streambed sediments were mainly gravels, sand and clay. Finer sediment fractions showed a marked change in grain size over time, although bedload movement was limited to a single high discharge event. In response to a low discharge regimen (drought), sediments characteristically showed non-normal distributions and were dominated by finer materials. A high-energy discharge event produced a coarsening of sands and a diminished clay fraction in the streambed. Particulate organic matter from sediments showed trends of build-up and decline with the high and low discharge regimes, respectively. Within the surface sediment intersticies three potential categories of invertebrate habitat were recognised, each with dynamic spatial and temporal boundaries.

Tree-ring based hydroclimate reconstruction over northern Vietnam from Fokienia hodginsii: eighteenth century mega-drought and tropical Pacific influence

We present here the first statistically calibrated and verified tree-ring reconstruction of climate from continental Southeast Asia.The reconstructed variable is March-May (MAM) Palmer Drought Severity Index (PDSI) based on ring widths from 22 trees (42 radial cores) of rare and long-lived conifer, Fokienia hodginsii (Po Mu as locally called) from northern Vietnam. This is the first published tree ring chronology from Vietnam as well as the first for this species. Spanning 535 years, this is the longest cross-dated tree-ring series yet produced from continental Southeast Asia. Response analysis revealed that the annual growth of Fokienia at this site was mostly governed by soil moisture in the pre-monsoon season. The reconstruction passed the calibration-verification tests commonly used in dendroclimatology, and revealed two prominent periods of drought in the mid-eighteenth and late-nineteenth enturies. The former lasted nearly 30 years and was concurrent with a similar drought over northwestern Thailand inferred from teak rings, suggesting a ``mega-drought'' extending across Indochina in the eighteenth century. Both of our reconstructed droughts are consistent with the periods of warm sea surface temperature (SST)anomalies in the tropical Pacific. Spatial correlation analyses with global SST indicated that ENSO-like anomalies might play a role in modulating droughts over the region, with El Nio (warm) phases resulting in reduced rainfall. However, significant correlation was also seen with SST over the Indian Ocean and the north Pacific,suggesting that ENSO is not the only factor affecting the climate of the area. Spectral analyses revealed significant peaks in the range of 53.9-78.8 years as well as in the ENSO-variability range of 2.0 to 3.2 years.

Dynamics of contour, object and face processing in the human visual cortex

The neural basis of visual perception can be understood only when the sequence of cortical activity underlying successful recognition is known. The early steps in this processing chain, from retina to the primary visual cortex, are highly local, and the perception of more complex shapes requires integration of the local information. In Study I of this thesis, the progression from local to global visual analysis was assessed by recording cortical magnetoencephalographic (MEG) responses to arrays of elements that either did or did not form global contours. The results demonstrated two spatially and temporally distinct stages of processing: The first, emerging 70 ms after stimulus onset around the calcarine sulcus, was sensitive to local features only, whereas the second, starting at 130 ms across the occipital and posterior parietal cortices, reflected the global configuration. To explore the links between cortical activity and visual recognition, Studies II III presented subjects with recognition tasks of varying levels of difficulty. The occipito-temporal responses from 150 ms onwards were closely linked to recognition performance, in contrast to the 100-ms mid-occipital responses. The averaged responses increased gradually as a function of recognition performance, and further analysis (Study III) showed the single response strengths to be graded as well. Study IV addressed the attention dependence of the different processing stages: Occipito-temporal responses peaking around 150 ms depended on the content of the visual field (faces vs. houses), whereas the later and more sustained activity was strongly modulated by the observers attention. Hemodynamic responses paralleled the pattern of the more sustained electrophysiological responses. Study V assessed the temporal processing capacity of the human object recognition system. Above sufficient luminance, contrast and size of the object, the processing speed was not limited by such low-level factors. Taken together, these studies demonstrate several distinct stages in the cortical activation sequence underlying the object recognition chain, reflecting the level of feature integration, difficulty of recognition, and direction of attention.

Molecular Dynamics in [(CH8)aN]z Cd14 A Proton Magnetic Relaxation Study

second moment measurements are carried out on [(CH,),N], CdI, in the temperature range 77 to 400 K. The results are interpreted based on a molecular dynamical model of randomly reorienting methyl groups and isotropically tumbling tetramethyl ammonium group. The relaxation data show contributions from spin-rotation interaction at high temperatures and presence of inequivalent methyl groups. The correlation times and associated activation energies, connected with this model, are calculated from the data. The structure in the absorption line and in the free-induction decay signal at 77 K indicates the possibility of tunnelling motion of the methyl groups. Im Temperaturbereich 77 bis 400 K werden an [(CH,),N],CdI, Protonen-Spin-Gitter-Relaxationsexperimente (bei Larmorfrequenzen von 10,20 und 30 MHz) und Messungen des zweiten Moments durchgefiihrt. Die Ergebnisse werden an Hand eines molekularen dynamischen Modells sich statistisch umorientierender Methylgruppen und isotrop taumelnder Tetramethyl-Ammoniumgruppen interpretiert. Die Relaxationswerte zeigen Beitriige von Spin-Rotations-Wechselwirkung bei hohen Temperaturen und die Anwesenheit von inaquivalenten Methylgruppen. Die Korrelationszeiten und verknupften Aktivierungsenergien, die mit diesem Model1 verbunden sind, werden am den Werten berechnet. Die Struktur in der Absorptionslinie und im Abklingsignal der freien Induktion bei 77 K zeigt die Moglichkeit einer Tunnelbewegung der Methylgruppen.

Grazing management influences the dynamics of populations of Stylosanthes hippocampoides (Oxley fine stem stylo)

This paper describes a study to identify those factors which control the persistence of the Subtropical legume Stylosanthes hippocampoides, formerly S. guianensis cv. Oxley (fine stem stylo). The dynamics of S. hippocampoides populations was recorded in permanent quadrats at 2 stocking rates in a grazing study conducted between 1987 and 1992 in south-eastern Queensland. Density of mature plants fluctuated between 10 and 60 plants/m(2) during the 5 years with the major contributing factors being variations in seedling recruitment and survival, which, in turn, reflected the size of the soil seed bank and seasonal rainfall. Plant density was consistently higher at the lower stocking rate of 1 beast/1.5 ha compared with 1 beast/1 ha; however, the effect of stocking rate was minor compared with fluctuation due to seasonal variation in rainfall. The maximum life span of the original plants exceeded 5 years, while the survival of seedling cohorts was strongly impacted by seasonal rainfall. Total exclosure from grazing during summer increased the size of the soil seed bank although a precise time period during summer was not identified, while grazing at the lower stocking pressure produced the same outcome. It was concluded that the large seasonal variation that occurs in S. hippocampoides density is driven by large seasonal variation in seedling recruitment, which, in turn, is influenced by the size of the soil seed bank.

Esr study of (SO4)2- dynamics in relation to the ferroelectric phase transition in ammonium sulfate

Ferroelectric phase transition in ammonium sulfate has been studied by ESR of CrO43- radical substituting for SO42- ion in (NH4)2SO4. In addition to discontinuous changes at Tc, certain continuous changes are observed in ESR parameters of this probe below Tc, which reflect the role of the sulfate ion in the phase transition. A microscopic mechanism of the phase transition is proposed and discussed in terms of the change of orientation of the sulfate tetrahedron through a finite angle. The degree of the change of orientation below Tc is thought to be the possible order parameter of the phase transition.

Inter-seasonal population dynamics and pest status of Bemisia tabaci (Gennadius) biotype B in an Australian cropping system

Bemisia tabaci, biotype B, commonly known as the silverleaf whitefly (SLW) is an alien species that invaded Australia in the mid-90s. This paper reports on the invasion ecology of SLW and the factors that are likely to have contributed to the first outbreak of this major pest in an Australian cotton cropping system, population dynamics of SLW within whitefly-susceptible crop (cotton and cucurbit) and non-crop vegetation (sowthistle, Sonchus spp.) components of the cropping system were investigated over four consecutive growing seasons (September-June) 2001/02-2004/05 in the Emerald Irrigation Area (EIA) of Queensland, Australia. Based on fixed geo-referenced sampling sites, variation in spatial and temporal abundance of SLW within each system component was quantified to provide baseline data for the development of ecologically sustainable pest management strategies. Parasitism of large (3rd and 4th instars) SLW nymphs by native aphelinid wasps was quantified to determine the potential for natural control of SLW populations. Following the initial outbreak in 2001/02, SLW abundance declined and stabilised over the next three seasons. The population dynamics of SLW is characterised by inter-seasonal population cycling between the non-crop (weed) and cotton components of the EIA cropping system. Cotton was the largest sink for and source of SLW during the study period. Over-wintering populations dispersed from weed host plant sources to cotton in spring followed by a reverse dispersal in late summer and autumn to broad-leaved crops and weeds. A basic spatial source-sink analysis showed that SLW adult and nymph densities were higher in cotton fields that were closer to over-wintering weed sources throughout spring than in fields that were further away. Cucurbit fields were not significant sources of SLW and did not appear to contribute significantly to the regional population dynamics of the pest. Substantial parasitism of nymphal stages throughout the study period indicates that native parasitoid species and other natural enemies are important sources of SLW mortality in Australian cotton production systems. Weather conditions and use of broad-spectrum insecticides for pest control are implicated in the initial outbreak and on-going pest status of SLW in the region.

Ecological impacts of feral pig diggings in north Queensland rainforests

This two-year study examined the impacts of feral pig diggings on five ecological indicators: seedling survival, surface litter, subsurface plant biomass, earthworm biomass and soil moisture content. Twelve recovery exclosures were established in two habitats (characterised by wet and dry soil moisture) by fencing off areas of previous pig diggings. A total of 0.59 ha was excluded from further pig diggings and compared with 1.18 ha of unfenced control areas. Overall, seedling numbers increased 7% within the protected exclosures and decreased 37% within the unprotected controls over the two-year study period. A significant temporal interaction was found in the dry habitat, with seedling survival increasing with increasing time of protection from diggings. Feral pig diggings had no significant effect on surface litter biomass, subsurface plant biomass, earthworm biomass or soil moisture content.

Predicting risk and benefit a priori in biological control of invasive plant species: a systems modelling approach

While the method using specialist herbivores in managing invasive plants (classical biological control) is regarded as relatively safe and cost-effective in comparison to other methods of management, the rarity of strict monophagy among insect herbivores illustrates that, like any management option, biological control is not risk-free. The challenge for classical biological control is therefore to predict risks and benefits a priori. In this study we develop a simulation model that may aid in this process. We use this model to predict the risks and benefits of introducing the chrysomelid beetle Charidotis auroguttata to manage the invasive liana Macfadyena unguis-cati in Australia. Preliminary host-specificity testing of this herbivore indicated that there was limited feeding on a non-target plant, although the non-target was only able to sustain some transitions of the life cycle of the herbivore. The model includes herbivore, target and non-target life history and incorporates spillover dynamics of populations of this herbivore from the target to the non-target under a variety of scenarios. Data from studies of this herbivore in the native range and under quarantine were used to parameterize the model and predict the relative risks and benefits of this herbivore when the target and non-target plants co-occur. Key model outputs include population dynamics on target (apparent benefit) and non-target (apparent risk) and fitness consequences to the target (actual benefit) and non-target plant (actual risk) of herbivore damage. The model predicted that risk to the non-target became unacceptable (i.e. significant negative effects on fitness) when the ratio of target to non-target in a given patch ranged from 1:1 to 3:2. By comparing the current known distribution of the non-target and the predicted distribution of the target we were able to identify regions in Australia where the agent may be pose an unacceptable risk. By considering risk and benefit simultaneously, we highlight how such a simulation modelling approach can assist scientists and regulators in making more objective decisions a priori, on the value of releasing specialist herbivores as biological control agents.

Management of plant invasions mediated by frugivore interactions

1. Some of the most damaging invasive plants are dispersed by frugivores and this is an area of emerging importance in weed management. It highlights the need for practical information on how frugivores affect weed population dynamics and spread, how frugivore populations are affected by weeds and what management recommendations are available. 2. Fruit traits influence frugivore choice. Fruit size, the presence of an inedible peel, defensive chemistry, crop size and phenology may all be useful traits for consideration in screening and eradication programmes. By considering the effect of these traits on the probability, quality and quantity of seed dispersal, it may be possible to rank invasive species by their desirability to frugivores. Fruit traits can also be manipulated with biocontrol agents. 3. Functional groups of frugivores can be assembled according to broad species groupings, and further refined according to size, gape size, pre- and post-ingestion processing techniques and movement patterns, to predict dispersal and establishment patterns for plant introductions. 4. Landscape fragmentation can increase frugivore dispersal of invasives, as many invasive plants and dispersers readily use disturbed matrix environments and fragment edges. Dispersal to particular landscape features, such as perches and edges, can be manipulated to function as seed sinks if control measures are concentrated in these areas. 5. Where invasive plants comprise part of the diet of native frugivores, there may be a conservation conflict between control of the invasive and maintaining populations of the native frugivore, especially where other threats such as habitat destruction have reduced populations of native fruit species. 6. Synthesis and applications. Development of functional groups of frugivore-dispersed invasive plants and dispersers will enable us to develop predictions for novel dispersal interactions at both population and community scales. Increasingly sophisticated mechanistic seed dispersal models combined with spatially explicit simulations show much promise for providing weed managers with the information they need to develop strategies for surveying, eradicating and managing plant invasions. Possible conservation conflicts mean that understanding the nature of the invasive plant-frugivore interaction is essential for determining appropriate management.

Lantana (Lantana camara) Seed Bank Dynamics: Seedling Emergence and Seed Survival.

Seed persistence is poorly quantified for invasive plants of subtropical and tropical environments and Lantana camara, one of the world's worst weeds, is no exception. We investigated germination, seedling emergence, and seed survival of two lantana biotypes (Pink and pink-edged red [PER]) in southeastern Queensland, Australia. Controlled experiments were undertaken in 2002 and repeated in 2004, with treatments comprising two differing environmental regimes (irrigated and natural rainfall) and sowing depths (0 and 2 cm). Seed survival and seedling emergence were significantly affected by all factors (time, biotype, environment, sowing depth, and cohort) (P < 0.001). Seed dormancy varied with treatment (environment, sowing depth, biotype, and cohort) (P < 0.001), but declined rapidly after 6 mo. Significant differential responses by the two biotypes to sowing depth and environment were detected for both seed survival and seedling emergence (P < 0.001). Seed mass was consistently lower in the PER biotype at the population level (P < 0.001), but this variation did not adequately explain the differential responses. Moreover, under natural rainfall the magnitude of the biotype effect was unlikely to result in ecologically significant differences. Seed survival after 36 mo under natural rainfall ranged from 6.8 to 21.3%. Best fit regression analysis of the decline in seed survival over time yielded a five-parameter exponential decay model with a lower asymptote approaching −0.38 (% seed survival = [( 55 − (−0.38)) • e (k • t)] + −0.38; R2 = 88.5%; 9 df). Environmental conditions and burial affected the slope parameter or k value significantly (P < 0.01). Seed survival projections from the model were greatest for buried seeds under natural rainfall (11 yr) and least under irrigation (3 yr). Experimental data and model projections suggest that lantana has a persistent seed bank and this should be considered in management programs, particularly those aimed at eradication.

The dynamics of individual teacher autonomy: A case study of teachers' work in a Queensland secondary school

The emphasis on collegiality and collaboration in the literature on teachers' work and school reform has tended to underplay the significance of teacher autonomy. This thesis explores the dynamics of teachers' understandings and experiences of individual teacher autonomy (as contrasted with collective autonomy) in an independent school in Queensland which promoted itself as a 'teachers' school' with a strong commitment to individual teacher autonomy. The research was a case study which drew on methodological signposts from critical, feminist and traditional ethnography. Intensive fieldwork in the school over five months incorporated the ethnographic techniques of observation, interviews and document analysis. Teachers at Thornton College understood their experience of individual autonomy at three interrelated levels--in terms of their work in the classroom, their working life in the school, and their voice in the decision-making processes of the school. They felt that they experienced a great deal of individual autonomy at each of these three levels. These understandings and experiences of autonomy were encumbered or enabled by a range of internal and external stakeholder groups. There were also a number of structural influences (community perceptions, market forces, school size, time and bureaucracy) emerging from the economic, social and political structures in Australian society which influenced the experience of autonomy by teachers. The experience of individual teacher autonomy was constantly shifting, but there were some emergent patterns. Consensus on educational goals and vision, and strong expressions of trust and respect between teachers and stakeholders in the school, characterised the contexts in which teachers felt they experienced high levels of autonomy in their work. The demand for accountability and desire for relatedness motivated stakeholders and structural forces to influence teacher autonomy. Some significant gaps emerged between the rhetoric of a commitment to individual teacher autonomy and decision-making practices in the school, that gave ultimate power to the co-principals. Despite the rhetoric and promotion of non-hierarchical structures and collaborative decision-making processes, many teachers perceived that their experience of individual autonomy remained subject to the exercise of 'partial democracy' by school leaders.