Consequences of variation in predator attack for the evolution of the selfish herd

There is a strong body of evidence that patterns of collective behaviour in grouping animals are governed by interactions between small numbers of individuals within the group. These findings contrast with study of the ‘selfish herd’, where increasingly complex individual-level movement rules have been proposed to explain the rapid increase in aggregation observed when prey groups are startled by or detect a predator. While individuals using simple rules take into account the position of only a few neighbours, those using complex rules incorporate multiple neighbours, and their relative distance, to determine their movement direction. Here, we simulate the evolution of selfish herd behaviour to assess the conditions under which simple and complex movement rules might evolve, explicitly testing predictions arising from previous work. We find that complex rules outperform simple ones under a range of predator attack strategies, but that simple rules can fix in populations particularly when they are already in the majority, suggesting strong positive frequency dependence in rule success. In addition, we explore whether a movement rule derived from studies of collective behaviour (where individuals use the position of seven neighbours to determine movement direction) performs as successfully as more complex rules, finding again positive frequency dependence in rule success, and a particular role for predator attack strategy (from within or outside the group)

Student perceptions of their autonomy at University

© 2017, The Author(s). Learner autonomy is a primary learning outcome of Higher Education in many countries. However, empirical evaluation of how student autonomy progresses during undergraduate degrees is limited. We surveyed a total of 636 students’ self-perceived autonomy during a period of two academic years using the Autonomous Learning Scale. Our analysis suggests that students do not perceive themselves as being any more autonomous as they progress through University. Given the relativity of self-perception metrics, we suggest that our results evince a “red queen” effect. In essence, as course expectations increase with each year, each student’s self-perceived autonomy relative to their ideal remains constant; we term this the “moving goalpost” hypothesis. This article corroborates pedagogical literature suggesting that providing students with opportunities to act autonomously and develop confidence is key to developing graduates who have the independence that they need in order to be successful in the workplace

In vitro Staining of Denture Liners and Potential for Color Correction Using Commonly Available Denture Cleansers

Background: Denture liners are routinely used as part of immediate denture therapy, following surgery involving edentulous tissues, and to improve the function and stability of existing removable prostheses. Appropriate application of denture liners can facilitate patient comfort during prolonged therapy and prior to placement of definitive restorations. However, concern has been raised regarding the susceptibility of common denture liners to agent-induced color change which, in turn, adversely impacts the esthetic appeal of the associated removable prosthesis. Objective: The purpose of the study was to evaluate the color stability of denture liners exposed to commonly encountered food stains and commonly used denture cleaning solutions. Method: Disk samples, 20mm in diameter, were fabricated consisting of two layers: a 2mm thick denture base resin layer (Lucitone 199®, Dentsply, York, PA) and a 2mm thick denture liner layer. Three groups of 45 samples were prepared, each group representing a different denture liner, including: a silicone liner group (Silk Line™, J. Morita USA, Irvine, CA); a methyl methacrylate-free resin liner group (GC Reline™, GC America, Inc., Alsip, IL); and a polyethyl methacrylate resin liner group (Kooliner™, GC America, Inc., Alsip, IL). An equal number of samples from each liner group were assigned to one of three staining agents, including: cola (Coca-Cola Company, Atlanta, GA); grape juice, and coffee. Following a 12hr. staining cycle, samples from each staining agent were equally distributed to one of three soaking fluids for 12hrs., including: two different effervescing cleaning agents (Efferdent, New Brunswick, NJ, and Polydent, Philadelphia, PA) and distilled water. This stain-soak cycle was continuously repeated, changing the soaking solution every day. Denture liner color measurements were made (Labscan XE Spectrocolorimeter, Hunter Associates Laboratory, Reston, VA) on the 1st, 15th, 30th, 45th, and 60th day and color differences (ΔE) were calculated. Results: Statistical analysis revealed that all liners experienced substantial color change from baseline to 2-weeks. From 2-weeks to 8-weeks, no statistically significance color change was recorded for any of the staining agent-soaking solution combinations. When comparing results for the different liner types, the silicone liner demonstrated significantly increased overall staining as compared to the resin liners. Conclusions: This study suggests: (1) exposing denture liners investigated to the staining agents used resulted in clinically discernible color changes; (2) use of denture cleansers had little beneficial effect on liner discoloration as compared to immersion in water; (3) following initial liner color change at two weeks, little to no further color change was noted regardless of staining agent or soaking fluid; (4) the silicone liner demonstrated the greatest color change when compared to the resin liners; and (5) conventional denture cleansers were statistically similar (p \u3e 0.05) to water with respect to the improvement of discolorations evaluated in this study