435 research outputs found
A synthesis of growth rates in marine epipelagic invertebrate zooplankton
No full textWe present the most extensive study to date of globally compiled and analysed weight-specific growth rates in marine epi-pelagic invertebrate metazoan zooplankton. Using specified selection criteria, we analyse growth rates from a variety of zooplanktonic taxa, including both holo- and mero-planktonic forms, from over 110 published studies. Nine principal taxonomic groups are considered, the copepods (number of individual data points (n) - 2,528); crustaceans other than copepods (n - 253); cnidarians (n = 77); ctenophores (n = 27); chaetognaths (n = 87); pteropods (n = 8);polychaetes (n = 12); thaliaceans (n = 88); and larvaceans (n = 91). The copepods are further examined by subdividing them into broadcasters or sac-spawning species, and as nauplii (N1–N6), copepodities (C1–C5) and adults (C6).
For each taxonomic group relationships between growth, temperature and body weight are examined using a variety of methods. Weight-specific growth tends to increase with increasing temperature and with decreasing body weight in the crustacean group. Growth does nor relate to body weight in the case of chaetognaths and larvaceans, but does increase with temperature. In the cnidarian and ctenophore groups growth does not relate to temperature, but is negatively related to body size. For the thaliaceans growth increases with both increasing body weight and temperature. In the entire broadcasting copepod data set, weight-specific growth increases with increasing temperature and decreasing body weight. In sac-spawners, growth increase with increasing temperature, and increases with decreasing body weight at temperatures below 20°C, but decrease with body weight at temperatures above this.
Comparison between the different taxa shows important differences and similarities. Our extensive synthesis of data generally confirms that larvaceans, pteropods, cnidarians and ctenophores have rates of weigth-specific growth that are typically greater than the copepods, chaetognaths and other crustaceans of similar carbon weight. For the cnidarians, ctenophores adn larvaceans groth rates are almost always greater than the general relationship describing copepod growth, and are also at the upper limits or beyond the maximum rates for copepods of a similar weight. For the pteropods, growth rates are generally greater than those of copepods, although the data set was limited to a single carnivorous species in a single study (i.e. Clione limacina). The thaliaceans have the highest growth rates for animals with body weights greater than around 1mg C ind−1, with rates of up to 2.1 d−1 for Pegea bicaudata. Whilst the larvaceans can achieve rates
of 2 d−1 in warm tropical waters (28°C), and as high as > 3 d−1 for < 0.2 mg C individual−1 animals of Oikopleura diocia. These are possibly the highest rates every recorded in epi-pelagic metazoans. Reasons for the differences between taxonomic groups are discussed in relation to intrinsic and extrinsic factors and limitations.
The importance of this investigation not only lies in it being the most comprehensive overview of patterns of growth to date, but because the data set highlight the gaps in measurements and current knowledge. We examine the inadequacies in the current data sets, and in the methods being used to measure growth and production. Most of the data are for animals collected from coastal and estuarine waters, and it is clear that for a fuller understanding there is an urgent need for work in the open ocean, and for investigations outside temperature regions. There is also a need to explore the role of food availability, and how food concentrations in incubations, and under food saturation, relate to those experienced in the natural environment
Nitrogen limitation and life history adaptation in the grasshopper "Omocestus viridulus"
No full textThe role of plant-mediated constraints to herbivore populations in terrestrial ecosystems remains relatively poorly understood. One aim of this study was therefore to explore the effects of low host plant nitrogen (N) content on herbivore performance and feeding behaviour, and thereby to evaluate the utility of the N limitation and nutrient balance concepts. The grass-feeding grasshopper Omocestus viridulus (Orthoptera: Acrididae) provided a well-suited model system as the species exhibits high tissue N demands (11.3 % N dw) compared to other herbivores, and uses a relatively poor food source in the wild (median N content: 2.2 % dw). Using N-poor soil and fertilizer, natural host grasses of contrasting N contents (high vs. low N) were grown in pots in the greenhouse. Juvenile performance experiments were then carried out with first generation (F1) offspring of grasshoppers caught in the field at three sites in Switzerland. The experiments were conducted both in a climate chamber and in outdoor cages under natural climatic conditions. I consistently found lower growth rates in grasshoppers reared on low N grasses, leading to somewhat prolonged development (13 % in the laboratory, 7 % outdoors) and slightly (4 – 5 %) smaller adult size. Juvenile mortality was low (always < 20 %) and similar among the food N treatments. As N contents differed strongly between the experimental grass treatments (e.g. 1.6 % vs. 4.3 % N dw in the climate chamber trial), my results suggest that natural food quality imposes no relevant nutritional constraint on grasshopper performance. Separate laboratory experiments on feeding behaviour served to investigate how grasshoppers cope with low quality food. First, female last-instar nymphs were allowed to feed singly on either high or low N grass (non-choice setting) over a 16 h period. The food’s initial fresh weight was known and converted to dry weight using constants. Individual food consumption was subsequently calculated by subtracting the dry weight of the food leftovers from the initial dry mass (gravimetrical method). This experiment showed that grasshoppers facing N-poor grass displayed substantially elevated food consumption (82 % higher on average) compared to conspecifics fed N-rich food. The animals thus compensated for lower nutritional quality by eating more. In a choice experiment, single grasshopper nymphs were offered high and low N grass simultaneously during a 28 h period. Individual consumption of both foods was calculated gravimetrically and revealed a striking preference for fertilized grass. On average, N-poor grass only accounted for some 20 % of the total ingested plant dry mass. It is argued that the proportion of consumed high N (protein-rich) and low N (energy-rich) grass likely represents the outcome of nutrient balancing. Proximately, the observed food selection can be explained by the modulation of taste receptor responsiveness via metabolic feedback, and/or associative learning of the spatial location of the different food sources. Overall, my results disagree with simple bottom-up predictions of herbivore population control, such as N limitation. Rather, this investigation provides
evidence for a high ability of arthropod herbivores to balance their nutrient intake, and thus corroborates a body of work performed with synthetic diets.
Another set of experiments using the same study organism was aimed at exploring the hypothesis that life history differentiation along a climatic gradient may have allowed a species to extend its geographic range. To this end, a total of eleven O. viridulus populations from eastern Switzerland were selected to span the species’ entire altitudinal range (410 – 2440 m). Temperature measurements and phenological surveys repeated in regular intervals at four field sites allowed quantifying the decline of available heat sums with increasing elevation, and its immediate effect on development rates. During the relatively cool season of 2002, embryonic development at 2215 m altitude started nearly three month later than at 410 m, and nymphal hatching and adult emergence were delayed by roughly two month. This implied a strong truncation of the reproductive period in high altitude animals, a situation predicted by life history theory to promote the evolution of shortened time to maturity (faster juvenile development). During the following, climatically favourable year, the phenological delay in the field of high altitude relative to lowland populations was less pronounced. This suggested that the variance in available season length increases with altitude, and that the strength of natural selection owing to time constraints at high elevation fluctuates considerably. In order to investigate adaptive (genetic) divergence in grasshopper life history, several traits determining development time (or time to maturity) were compared across the eleven study populations under common garden conditions, using offspring of field-caught animals. Embryonic development rates were found to increase according to the population’s altitude of provenance, with embryos from highest altitudes completing development some ten percent faster than lowland animals. This was found both at 27 °C and 19 °C incubation temperature, genotype by temperature interactions thus proved unimportant. Similarly, nymphal development accelerated with elevation of origin, the maximal difference between high and low altitude populations again amounting to roughly ten percent. In contrast, the stage of embryonic overwintering diapause, a pivotal determinant of developmental timing in annual organisms, was constant across six inspected populations from different altitudes. Embryonic development was always arrested just before the onset of embryonic rotation. This result agrees with data from other members of the same subfamily (Gomphocerinae), but disagrees with life history responses to seasonal time constraints reported for other Orthoptera. The documented lack of flexibility (genetic variation) in the diapause stage is therefore best understood as a phylogenetic constraint. This investigation offers strong support for the hypothesis of life history adaptation to local climates, although the degree of differentiation in intrinsic development rate among the populations is relatively modest and essentially limited by the conserved diapause stage. As a result, the immediate influence in the wild of decreasing temperatures along the altitudinal gradient overwhelms the genetic response observed in the laboratory, thus providing an example of cryptic evolution.
Life history theory generally predicts a trade-off between short juvenile development and large adult size, assuming invariant growth rates within species. This basic assumption has been explicitly tested in few organisms. The relationship between growth rate, juvenile development time and body size was examined in O. viridulus grasshoppers from 13 populations from different altitudes (including the populations mentioned above). All experiments were performed with first generation offspring at 32 °C in the climate chamber. I hypothesized that time constraints imposed by the altitudinal decline in season length, and arising from the advantage of earlier emergence of males relative to females (protandry), should have favoured increased intrinsic growth rates in high altitude animals and in the male sex. However, growth rates were similar across the populations. Instead, accelerated development with increasing elevation resulted in an altitudinal body size cline, with animals from the highest sites exhibiting roughly 12 % smaller adult size on average compared to lowland conspecifics. This size pattern was also observed in field animals. As I found a positive correlation between female body size and the number of eggs per clutch (but not offspring size), adaptation of O. viridulus to alpine climates involves a life history trade-off between time to maturity (development time) and fecundity, mediated by body size. An additional (fifth) nymphal stage, inserted before the penultimate nymphal stage and leading to an extended (by 20 %) developmental period and 12 % larger adult size, occurred in some females from low altitude. Individuals with five as opposed to four nymphal stages displayed significantly (5 %) smaller hatchling size, indicating that the insertion of the additional stage is contingent on maternal investment in the egg. It is argued that the absence of the five-stage developmental pathway from high elevation populations likely represents a side effect of the evolution of lower critical size thresholds in high altitude grasshoppers to accelerate development. Contrary to expectations, males were found to grow at substantially lower rates than females. This finding suggests that O. viridulus males not only experience protandry selection, but simultaneous selection for small size associated with reduced energetic requirements during mate search. Relatively slow growth in males probably allows the independent optimization of development time and body size among the sexes. My data further revealed that within populations, large individuals consistently developed faster than small individuals, resulting in a negative correlation between development time and size. This pattern could neither be ascribed to sib competition, as it was expressed in individuals both reared in groups and individually, nor to small hatchling size, a maternal effect. Hence, genetic variation in growth rate among individuals within populations seems probable. This study illustrates that the evolutionary response of intrinsic growth rate to different types of time constraints can greatly differ. I found stasis in growth rate among grasshopper populations in relation to seasonality, but highly divergent growth between the sexes owing to protandry selection. Further, ontogenetic evolution at the among-population level cannot necessarily be predicted based on within-population trait associations. The sign of the time-
size correlation was positive among populations, but negative among individuals within populations. Finally, I illustrate that detailed ontogenetic comparisons can shed light on the developmental cause (here a shift in critical size thresholds) underlying phenotypic evolution
Carer impact on self-management by people with advanced cancer living with changing eating habits
No full textBackground: Internationally there is interest in supporting selfmanagement, as a way of enhancing the quality of life of people living with illness and reducing the economic cost of care. This is the first study to examine the impact of carers on self-management behaviour by cancerpatients. Methods: The research was an in-depth mixed methods study ofweight loss and eating difficulties in people with advanced cancer. The study participants included 32 patient-carer pairs receiving palliative home care inthe South of England in either 2003 or 2005. Semi-structured interviews were analysed using both content and thematic approaches, which revealed self-management of changing eating habits1. This paper reports aninterpretation of the way carers were found to impact on patient selfmanagement.Results: All carers wanted to help patients and many weretroubled by uncertainty about the adequacy of their caregiving. However, patients gave examples both of carer behaviours that promoted selfmanagement and conversely of those that were experienced as disabling. This paper critiques the patient focus of most intervention that aims to support self-management. Drawing on the example of people with advanced cancer managing eating difficulties, it argues that self-management might best be facilitated using a family focused approach to supportive cancer care.Conclusions: Further work is needed to establish the ways in which carers can be helped to support patient self-management. Acknowledgement: The author would like to thank Macmillan Cancer Support UK for funding this study
Selecting candidate marine reserves: a test of the efficacy of current approaches
No full textIn an attempt to understand the relationship between the 'species-based' and 'spaces-based' approaches to marine conservation, this thesis examined: first, their relative efficiencies at selecting a set of marine reserves and second, the influence spatial aggregation had on the shape of the reserve system. Results demonstrated that: (a) a reserve system designed with a moderate degree of spatial aggregation most minimised the area, number of reserves and perimeter of the system most effectively; (b) neither focal species nor habitats alone were capable of capturing the desired level of representation; but (c) habitats acted as a better surrogate for capturing conservation features than do species; (d) 'species-based' and 'spaces-based' approaches can be combined to create an efficient reserve system designed to capture the full range of biodiversity; and, (e) when that approach was taken, reserve designs built using benthic habitat data, were more efficient at meeting the representation targets than species or other habitats alone
The reflective process among undergraduate dental students: the impact of age, gender, learning styles, learning approaches and the dental environment
No full textPhDAim:
To investigate the effect of age, gender, socioeconomic status, academic achievement, learning styles, learning approaches, and the learning environment on the reflective process.
Methods:
All dental undergraduate students studying at King AbdulAziz University Faculty of Dentistry (KAUFD) agreed to participate on three occasions of approximately six month intervals between February 2008 and June 2009 (QMREC2007/67). Four previously validated structured questionnaires including demographic details were used to determine students’ learning style (Felder and Soloman, http://www.ncsu.edu/felder-public/ILSpage.html [ILS]), approach to learning and studying (Entwistle, http://www.ed.ac.uk/etl [ALSI]), reflection (Sobral, 2005 [RLS]) and perception of their educational environment as determined by the Dundee Ready Educational Environment Method (Roff et al. 2005, [DREEM]). Multiple linear regression was used to investigate the independent effects on the questionnaires.
Results:
A total of 624 students (F=347, M=277) were included in the analysis. ILS assessed the undergraduate learning styles: 20.7% active learners, 47.9% sensing, 68.2% visual and 18.1% sequential learners. Sudents adopted different approaches simultaneously. The mean overall DREEM score was (112.76, SD19.54) indicating a more positive view of their environment. Fifty eight percent were ample in their ability to reflect. Females, older students, and from higher socioeconomic background reflect more. In the final student learning model, reflection was positively associated with a deep approach, organised/effort approach, academic self perception and perception of learning, whilst a surface approach was negatively associated with reflection. Students with higher academic achievement were able to
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reflect and adopt an organised/effort approach, whilst students with lower grades had low reflective scores and adopt a surface approach.
Conclusion:
KAUFD dental students demonstrate sensing and visual learning styles. An effective learning environment that facilitates reflection results in the development of self directed learners. Self directed students take control over their own learning and are able to employ strategies such as a deep and organised approach to studying that can influence and optimise their learning and academic performance
Deans gathered for the New Student Convocation
No full textDeans are gathered for the New Student Convocation, from left to right Bernard J. Sloan, Roland P. Ficken, Sara E. Barger, John C. Snider, Lucinda Lee Roff, J. Barry Mason, Kenneth C. Randall, Robert A. Griffin, James D. Yarborough, Philip M. Turner, L. Edward Mullins, Ronald W. Rogers, Judith L. Bonner, Rodney W. Roth, E. Roger Sayers, and James G. Taaffe. Caption on back: Photograph taken August 24, 1995 in the President's Lounge at Coleman Coliseum where the deans, et. al. had gathered for the New Student Convocation
Does egg production represent adult female copepod growth? A call to account for body weight changes
No full textAn almost universal assumption in determining growth in copepods is that, over short periods, an individual adult female's net growth is equal to the amount of material expelled as eggs. This assumption relies upon adult body mass being in steady-state between the start and end of the same period. We explore different situations where this assumption is violated. Initially, concepts of how adult body weight and egg output are coupled over time are addressed. Using a refined concept of growth, we show that using typical 24 h incubation methods to measure egg output in sac spawners or broadcasters that produce clutches of eggs with a periodicity of >1 d may give correct mean population growth rates, but erroneous individual rates (including maximum and minimum individual growth, and measurements of individual variability such as coefficient of variation). Measurements derived from laboratory and field studies are then used to explore errors associated with the steady-state assumption. Decoupling of egg production from assimilation, and non-steady-state body weight in large lipid-storing higher-latitude species are relatively well documented, yet growth estimates allowing for such changes have almost never been made. Errors are not limited only to such species, however, and changing adult body weights can occur in small temperate and tropical species too. Body weight can increase or decrease whether or not eggs are exuded over the same period. The errors that can arise if we assume that the output of eggs by females equals their net growth rate are large and variable; in our compilation they range from -208% (i.e. egg output being 9.7% of body carbon weight per day, but adult carbon weight simultaneously declining by 13.7% d-1) to +71% (i.e. egg output being 1.5% of body carbon weight per day, and adult carbon weight simultaneously increasing by 4.3% d-1). Using measurement of the natural variability in adult body weights, we determined that in order to be able to discriminate significant changes in body weight of 1 and 10% respectively, >1000 and <100 replicates are necessary, if applying typical sacrificial weighing methods. If we are to make accurate estimates of growth in adult copepods, then changes in body weight are of fundamental importance. We make initial recommendations for tackling these problems and reducing errors in the future.</p
Principal coordinates analysis (PCO) of subtropical coral community composition along eastern Australia (A).
No full text<p>Bubble plots overlaid onto PCO displaying B) mean coral taxa richness, C) mean percent coral cover, and D) proportion of Acroporidae and E) Dendrophylliidae cover of the total coral cover.</p
A Multidimensional Analysis of Climate Projections on the Great Barrier Reef
No full textTropical coral reefs are increasingly threatened due to global warming. Corals live within a narrow thermal threshold making them one of the most sensitive species to changes in temperature. Recent warming events on the Great Barrier Reef (GBR) (2016, 2017, 2020) have caused mass coral mortality on approximately 30% of the reef (Bozec et al., 2020; Hughes, Kerry et al., 2018). This research focuses on the development and implementation of a 1-D semi-dynamic downscaling method to improve climate projections on the GBR. Coral stress metrics are used to provide detailed projections on the magnitude and frequency of warming for four socio-economic pathways (SSP) under the 6th phase of the Climate Model Intercomparison Project. Following a chapter on methods and model validation, the results in chapter 3 reveal the importance of adhering to the lowest possible emissions trajectory which limits warming to 1.5°C by the end of the century. This scenario keeps projected warming to slightly above current conditions. Under the higher emissions trajectories (~4°C and ~5°C of global average warming) coral stress metrics quadruple present-day warming conditions which would result in annual mass coral mortality events by 2080. In chapter 4, climate refugia have been identified from present-day conditions based on downscaled surface temperature outputs in agreement with observations. The lower emissions trajectories maintain these locations as refugia while the higher emissions trajectories reveal the loss of these increasingly valuable locations. Areas of climate refugia can be attributed to tidal and wind energy fluctuations providing relief from warming. However, this advantage does not persist after global warming exceeds ~3°C. Refugia are more likely to persist in the northern GBR under increased warming even though recent evidence suggests there are fewer refugia in this region. Atmospheric spatial patterns on the GBR under warming above ~3° C reveal a change in wind and shortwave radiation patterns driving a loss in the identified climate refugia locations. Lastly, stratification was tested in chapter 5 to determine if increases in stratification could provide thermal relief to bottom temperature waters from 0-50 m under increased warming into the future using downscaled bottom temperature projections. Chapter 5 results demonstrate that warming influences bottom temperatures of stratified locations, showing little support for deeper reefs to act as a climate refuge. The temporal, spatial, and bottom temperature analysis of downscaled climate projections provides insight into the consequences of a warming planet for the GBR and can be used to inform management and policy decisions to protect coral reefs
Fabrication and characterization of microscale HfO2-based Memristors
No full textMemristors are metal/insulator/metal devices whose resistance can be switched between two different states (i.e. the low resistive state LRS, and the high resistive state, HRS) by applying a proper voltage value over the two metal contacts [1], [2]. Their simple structure makes memristors prone to extreme down scaling and 3-D stacking potentiality, and excellent compatibility with the complementary metal-oxide-semiconductor (CMOS) technology. Moreover, because of their low power consumption and high speed, memristors are rightly considered the elemental bricks for a next generation of high-density nonvolatile memories. HfO2 has attracted much attention as an oxide material for memristor application, due to its natural compatibility to CMOS technology [2]. Pulsed laser deposition (PLD) is a low cost thin films growth technology, which has been widely utilised for depositing high quality HfO2 thin films [3]. It suits perfectly memristors’ fabrication needs, because it gives the possibility to finely modify oxides properties by changing growth parameters. In this work we report on the fabrication and electrical characterization of microscale Pt/HfO2/Cu memristors (see Fig. 1). To this aim, HfO2 thin films were grown by PLD on Si/SiO2/Ti/Pt substrates. Afterwards, 200 nm-thick Cu pads of 50 × 50 μm2 were defined by direct laser-writing microlithography and subsequent lift-off. All devices were electrically characterised at room temperature by performing two-probe I–V measurements by means of a Versastat 3 (Princeton Applied Research) connected to a Karl Suss probe station. The bias voltage was swept from – 0.5 to 0.5 V while simultaneously measuring the current. Fig. 2 shows the typical bistable I–V curve shown by the fabricated devices. Resistances at the LRS and HRS were measured at 0.42 V and resulted RON = 19 W and ROFF = 3921 W, respectively. Consequently, the ROFF/RON ratio was 195, which is suitable for memory applications. The endurance of these devices has not proved satisfactory yet, probably due to the absence of any current compliance protection in our measurement setup which led, after a small number of cycles, to devices failure due to oxide breakdown. We noticed also a larger variability of ROFF with the number of measured devices than the variability of RON. In conclusion, microscale HfO2-based memristors grown by PLD showed a remarkable ROFF/RON ratio but a poor endurance. This suggests that further work must address the lifetime of our devices, especially by investigating the HfO2 thin film quality and applying a proper current compliance
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