Species richness and evenness in Australian birds

Species richness and evenness are the two major components of biodiversity, but the way in which they are interrelated is a subject of contention. We found a negative relationship between the two variables for bird communities at 92 woodland sites across Australia and sought an explanation. Actual evapotranspiration (AET) was by far the best predictor of species richness. When AET was controlled for, the relationship between richness and evenness became nonsignificant. Richness is greater at sites with higher AET because such sites support a greater number of individuals. However, such sites have a greater number of rare species, resulting in lower evenness. A complicating factor is that evenness is best predicted by degree of vegetation cover, with sparsely vegetated sites having significantly lower evenness. We conclude that there are two competing ecological processes, related to energy and water availability, that determine richness and evenness. The first drives total abundance (leading to high richness, low evenness), while the second drives productivity and niche availability (leading to high richness, high evenness). The relative strength of these two processes and the observed relationship between richness and evenness are likely to depend on the scale of the analysis and the species and range of habitats studied.

On the impact of second phase particles on twinning in magnesium alloys

Deformation twinning is an important deformation mode in magnesium alloys. Despite this, little is known on the extent to which the stress for twinning can be altered by a dispersion of second phase particles. The current paper presents a series of findings on the role of differently shaped particles on both the stress required for twinning and the characteristics of the twins that form. It is shown that plate shaped particles are, as one might expect, an effective strengthener to {10-12} twinning. When precipitate plates form on the basal planes, the relative hardening of basal slip is minor in comparison to that seen for twinning. This provides opportunity for the alloy designer to control the apparent critical resolved shear stresses (CRSS) for the different deformation modes. Possible sources for the hardening of twins are discussed.

Effect of the degree of crystallinity on the electrochemical behavior of Mg65Cu25Y10 and Mg70Zn25Ca5 bulk metallic glasses

The effect of varying the percent crystallinity on the electrochemical behavior of Mg65Cu25Y10 and Mg70Zn25Ca5 bulk metallic glasses was studied. The alloys were heat-treated to achieve desired microstructures ranging from fully amorphous to fully crystalline, providing a systematic basis for subsequent testing. Potentiodynamic experiments in 0.01 M sodium chloride (NaCl) were used, whereby both the amorphous and partially crystallized samples were observed to have more noble corrosion potentials and lower anodic kinetics. However, this was accompanied by more rapid cathodic kinetics relative to their fully crystalline counterparts, meaning that corrosion rates were not significantly lower in the amorphous state. To describe the electrochemical response as a function of the degree of crystallinity, differential scanning calorimetry (DSC), scanning electron microscopy, x-ray diffraction (XRD), and electrical conductivity measurements were undertaken, where it was found that crystallinity alone is not necessarily the controlling factor and microchemistry that evolves upon devitrification, plays a key role in the electrochemical response of these materials.

Using second life to teach about marketing in second life

There are compelling reasons for educators to consider incorporating virtual worlds (VWs) in their marketing curriculum. That said, the ways in which VWs can be implemented into the teaching curriculum are many and varied. This article reports on two studies in which notionally similar graduate classes are taught about marketing in Second Life (SL). The degree of student and instructor immersion is intentionally varied: One class is taught entirely in SL, by a technically expert instructor, while novice/intermediate instructors teach the second class in an interactive tutorial setting. Taken together, these studies offer marketing educators insights into developing “full” and “lite” approaches to teaching in SL, thereby lowering the barrier to uptake of the technology by catering to a broader spectrum of both instructor and student competencies, interests, and abilities.

Graduate attributes as a focus for institution-wide curriculum renewal: innovations and challenges

Curtin University's Curriculum 2010 (C2010) initiative aimed at ensuring degree programs were excellent and sustainable. Before C2010, graduate attributes were not universally emphasised and indicators showed room for improvement in generic skills. C2010 focused on embedding graduate attributes through three strategies. The first was embedding graduate attributes in degree programs and mapping for constructive alignment of outcomes and assessments. The second strategy was related: programs were reviewed drawing on evidence including perspectives of graduates, employers and program teams on the relative importance of graduate attributes and the extent to which they were generally demonstrated or developed. The third strategy was a university-wide eportfolio system enabling students' self- and peer-assessment of graduate attributes. Since completion of C2010, proxy indicators show improvement. However, this paper highlights the challenges associated with graduate attributes and renewal. These include: academic staff engagement, the time needed for innovations to come to fruition and evidencing achievement of graduate attributes.

Optimal second best taxation of addictive goods in dynamic general equilibrium: a revenue raising perspective

In this paper we derive conditions under which optimal tax rates for addictive goods exceed tax rates for non-addictive consumption goods within a rational addiction framework where exogenous government spending cannot be financed with lump sum taxes. We reexamine classic results on optimal commodity taxation and find a rich set of new findings. Two dynamic effects exist. First, households anticipating higher future addictive tax rates reduce current addictive consumption, so they will be less addicted when the tax rate increases. Therefore, addictive tax revenue falls prior to the tax increase. Surprisingly, the optimal tax rate on addictive goods is generally decreasing in the strength of tolerance, since strong tolerance strengthens this tax anticipation effect. Second, high current tax rates on addictive goods make households less addicted in the future, affecting all future tax revenues in a way which depends on how elasticities are changing over time. Classic results on uniform commodity taxation emerge as special cases when elasticities are constant and the addiction function is homogeneous of degree one. Finally, we also study features of addictive goods such as complementarity to leisure that, while not directly related to the definition of addiction, are nonetheless properties many addictive goods display.

Benefits of education at the intensive margin: childhood academic performance and adult outcomes among American immigrants

Using the Children of the Immigrants Longitudinal Study (CILS), we examine the associationbetween education at the intensive margin and twenty pecuniary and non-pecuniary adultoutcomes among first- and second-generation American immigrant youth. Education at theintensive margin is measured by two widely used standardized math and reading test scores,national percentile rankings on these tests and cumulative grade point average (GPA) in bothmiddle and high school. Our findings provide evidence that the academic achievement ofimmigrant children in early adolescence is an accurate predictor of later life outcomes. Wealso examine a novel hypothesis that relative academic performance of immigrant children inhigh school compared to middle school, which could be an indicator of change in adolescentaspirations and motivation as well as the degree of adaptation and assimilation to the hostcountry, has an effect on their adult outcomes even after controlling for the levels ofacademic performance in middle and high school. The results suggest that an improvementin GPA from middle school to high school is associated with favorable adult outcomes.Several sensitivity tests confirm the robustness of main findings.

Difference-form persuasion contests

We explore the equilibrium properties of two types of "difference-form" persuasion contest functions derived in Skaperdas and Vaidya in which contestants spend resources to persuade an audience. We find that both types of functions generate interior pure strategy Nash equilibria unlike Baik and Che and Gale with characteristics different to existing literature. For one type of function, we find that the reaction function of each player is "flat" and nonresponsive to the level of resources devoted by the rival so that the "preemption effect" as defined by Che and Gale is absent. Further, the equilibrium is invariant to the sequencing of moves. For the second type of function, which applies when there is asymmetry among contestants with regard to the quality of evidence, we find that the reaction functions of the stronger and weaker players have gradients with opposite signs relative to Dixit and therefore their incentive to precommit expenditures in a sequential move game is also different. For both types of functions, the extent of rent dissipation is partial. From the equilibrium analysis, we are also able to establish the potential effects of some specific factors affecting persuasion such as evidence potency, the degree of truth, and bias on aggregate resource expenditures and welfare.