The Effects of Intraspecific Variation of Crayfish Behavior on Nutrient Cycling in Aquatic Environments

Human activities are rapidly altering species traits at a global scale. Yet, there remains a critical need to determine whether trait variation within species affects ecosystem responses to global change. In particular, intraspecific variation in feeding behavior can have strong effects on ecosystem processes, such as nutrient cycling in streams. Crayfish are dominant consumers in streams and play key roles in controlling important stream dynamics such as nutrient cycling. We hypothesized that within-population, individual variation in crayfish foraging behavior is associated with differences in nutrient excretion. The objectives of this study were to (i) to quantify individual differences in foraging behavior and boldness of crayfish using a giving up density (GUD) approach. (ii) to quantify individual differences in nutrient excretion of crayfish. (iii) to test whether foraging rate, boldness, and excretion rate are repeatable traits in the laboratory setting and (iv) to examine whether there is a relationship between individual variation in foraging rate, boldness, and excretion. These objectives were explored with both behavioral and excretion assays, and general linear and nonlinear mixed models as well as ANOVA tests. We found that behavior and excretion were repeatable and that behavior is associated with ammonium excretion. The finding that crayfish foraging behavior is associated with differences in nutrient excretion has important implications for invasion ecology and nutrient cycling. It is known that behavioral changes occur along with invasion. These behavioral changes can significantly impact the nutrient excretion, and therefore nutrient dynamics within invaded environments.No embargoAcademic Major: Environmental Scienc

AN ECONOMIC APPROACH TO MUNICIPAL WASTE MANAGEMENT POLICY IN IRELAND, 2010

Ireland is at an important junction in refining and implementing its municipal waste management policies. While significant progress has been made in recent years in encouraging the use of recycling as an alternative to landfill, the State has to meet legally binding targets that will become increasingly challenging from 2010 onwards

Explaining semantic short-term memory deficits:evidence for the critical role of semantic control

Patients with apparently selective short-term memory (STM) deficits for semantic information have played an important role in developing multi-store theories of STM and challenge the idea that verbal STM is supported by maintaining activation in the language system. We propose that semantic STM deficits are not as selective as previously thought and can occur as a result of mild disruption to semantic control processes, i.e., mechanisms that bias semantic processing towards task-relevant aspects of knowledge and away from irrelevant information. We tested three semantic STM patients with tasks that tapped four aspects of semantic control: (i) resolving ambiguity between word meanings, (ii) sensitivity to cues, (iii) ignoring irrelevant information and (iv) detecting weak semantic associations. All were impaired in conditions requiring more semantic control, irrespective of the STM demands of the task, suggesting a mild, but task-general, deficit in regulating semantic knowledge. This mild deficit has a disproportionate effect on STM tasks because they have high intrinsic control demands: in STM tasks, control is required to keep information active when it is no longer available in the environment and to manage competition between items held in memory simultaneously. By re-interpreting the core deficit in semantic STM patients in this way, we are able to explain their apparently selective impairment without the need for a specialised STM store. Instead, we argue that semantic STM patients occupy the mildest end of spectrum of semantic control disorders

3D Fabrication and Characterisation of Electrically Receptive PCL-Graphene Scaffolds for Bioengineered In Vitro Tissue Models

Polycaprolactone (PCL) is a well-established biomaterial, offering extensive mechanical attributes along with low cost, biocompatibility, and biodegradability; however, it lacks hydrophilicity, bioactivity, and electrical conductivity. Advances in 3D fabrication technologies allow for these sought-after attributes to be incorporated into the scaffolds during fabrication. In this study, solvent-free Fused Deposition Modelling was employed to fabricate 3D scaffolds from PCL with increasing amounts of graphene (G), in the concentrations of 0.75, 1.5, 3, and 6% (w/w). The PCL+G scaffolds created were characterised physico-chemically, electrically, and biologically. Raman spectroscopy demonstrated that the scaffold outer surface contained both PCL and G, with the G component relatively uniformly distributed. Water contact angle measurement demonstrated that as the amount of G in the scaffold increases (0.75–6% w/w), hydrophobicity decreases; mean contact angle for pure PCL was recorded as 107.22 ± 9.39°, and that with 6% G (PCL+6G) as 77.56 ± 6.75°. Electrochemical Impedance Spectroscopy demonstrated a marked increase in electroactivity potential with increasing G concentration. Cell viability results indicated that even the smallest addition of G (0.75%) resulted in a significant improvement in electroactivity potential and bioactivity compared with that for pure PCL, with 1.5 and 3% exhibiting the highest statistically significant increases in cell proliferation

Early Stages of Homopolymer Collapse

Interest in the protein folding problem has motivated a wide range of theoretical and experimental studies of the kinetics of the collapse of flexible homopolymers. In this Paper a phenomenological model is proposed for the kinetics of the early stages of homopolymer collapse following a quench from temperatures above to below the theta temperature. In the first stage, nascent droplets of the dense phase are formed, with little effect on the configurations of the bridges that join them. The droplets then grow by accreting monomers from the bridges, thus causing the bridges to stretch. During these two stages the overall dimensions of the chain decrease only weakly. Further growth of the droplets is accomplished by the shortening of the bridges, which causes the shrinking of the overall dimensions of the chain. The characteristic times of the three stages respectively scale as the zeroth, 1/5 and 6/5 power of the the degree of polymerization of the chain.Comment: 11 pages, 3 figure