Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts

Seagrass beds provide important habitat for a wide range of marine species but are threatened by multiple human impacts in coastal waters. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. Motivated by extensive field surveys and literature information, we analyzed the structural features of food webs associated with Zostera marina across 16 study sites in 3 provinces in Atlantic Canada. Our goals were to (i) quantify differences in food-web structure across local and regional scales and human impacts, (ii) assess the robustness of seagrass webs to simulated species loss, and (iii) compare food-web structure in temperate Atlantic seagrass beds with those of other aquatic ecosystems. We constructed individual food webs for each study site and cumulative webs for each province and the entire region based on presence/absence of species, and calculated 16 structural properties for each web. Our results indicate that food-web structure was similar among low impact sites across regions. With increasing human impacts associated with eutrophication, however, food-web structure show evidence of degradation as indicated by fewer trophic groups, lower maximum trophic level of the highest top predator, fewer trophic links connecting top to basal species, higher fractions of herbivores and intermediate consumers, and higher number of prey per species. These structural changes translate into functional changes with impacted sites being less robust to simulated species loss. Temperate Atlantic seagrass webs are similar to a tropical seagrass web, yet differed from other aquatic webs, suggesting consistent food-web characteristics across seagrass ecosystems in different regions. Our study illustrates that food-web structure and functioning of seagrass habitats change with human impacts and that the spatial scale of food-web analysis is critical for determining results

Transcription-driven twin supercoiling of a DNA loop: A Brownian dynamics study

The torque generated by RNA polymerase as it tracks along double-stranded DNA can potentially induce long-range structural deformations integral to mechanisms of biological significance in both prokaryotes and eukaryotes. In this paper, we introduce a dynamic computer model for investigating this phenomenon. Duplex DNA is represented as a chain of hydrodynamic beads interacting through potentials of linearly elastic stretching, bending, and twisting, as well as excluded volume. The chain, linear when relaxed, is looped to form two open but topologically constrained subdomains. This permits the dynamic introduction of torsional stress via a centrally applied torque. We simulate by Brownian dynamics the 100 mus response of a 477-base pair B-DNA template to the localized torque generated by the prokaryotic transcription ensemble. Following a sharp rise at early times, the distributed twist assumes a nearly constant value in both subdomains, and a succession of supercoiling deformations occurs as superhelical stress is increasingly partitioned to writhe. The magnitude of writhe surpasses that of twist before also leveling off when the structure reaches mechanical equilibrium with the torsional load. Superhelicity is simultaneously right handed in one subdomain and left handed in the other, as predicted by the "transcription-induced twin-supercoiled-domain" model [L. F. Liu and J. C. Wang, Proc. Natl. Acad. Sci. U.S.A. 84, 7024 (1987)]. The properties of the chain at the onset of writhing agree well with predictions from theory, and the generated stress is ample for driving secondary structural transitions in physiological DNA. (C) 2004 American Institute of Physics

Past and future adaptation pathways

Adaptation pathways are increasingly being used as a foresight tool to help guide the implementation of climate change adaptation and deliberate transformation. This paper applies a pathways lens as a hindsight tool to provide new understanding about past change and adaptation relevant for improving future adaptation pathways approaches. Four case studies of past adaptations to change are examined: Solomon Islands Communities, Canadian forest-dependent communities, a Transylvanian village, and responses to climate adaptation policies in Australia. The results highlight that responses to change in these diverse case studies involve complex transitions that gradually create new conditions and trajectories; manifest as multiple but inter-related pathways of change and response at different social or spatial scales (e.g. different paths for different households or communities); have legacies and continuities across time that affect future pathways of change; are affected by power in complex ways; and can create further change and need for adaptation. Analyses also highlight that when working with prospective adaptation approaches as a response to climate change there is a need to consider: (1) underlying assumptions, values and principles associated with the future; (2) the existence of inter-connected multiple pathways and their implications for reinforcing existing social inequalities; and (3) how understanding past change provides inspiration for new and transformative futures. Overall, the paper concludes that shifts towards analyses for change rather than simply about change, such as adaptation pathways, will require more careful consideration of underlying ontological assumptions about the relationships between past, present and future

An Uncanny Nature: Taking a Side Road to Aesthetic Appreciation of Environment

Ive always been drawn to all things uncanny, which is how I believe I ended up devoting so much time to the study of philosophy. Those little moments of dissonance within the structure of our everyday lives that give us a glimpse of what\u27s going on beneath the surface without bringing the surface world to a halt seemed to me deliciously charged with creative potential. In spite of the anxiety that such moments may instill, I find the simple fact that there is always more going on than meets the eye both humbling as well as intriguing; thus, I\u27ve gone about my life with the impression that the result of encounters with the uncanny heighten our curiosity about the world and our place in it, and teach us to be more aware of the presence of others who might not share our interests or point of view. I was taken aback to learn of the uncanny\u27s ill repute in Western aesthetic discourse, and I thought I ought to set about trying to figure out what the root of that was and make an effort to salvage the positive aspects of the uncanny from the dustbin of the Tradition. Within this body of work I present a substantial glimpse of the uncanny and outline how its potential comes to light in the work of Freud and Heidegger. I then present the experience of the uncanny through the lens of Japanese aesthetics and its role in Zen Buddhist practice in order to further illuminate its positive potential in ethical terms. This is followed by an overview and critique of the dominant strands in contemporary environmental aesthetic discourse that fail to acknowledge the potential of the uncanny. Lastly, I argue that the cultivation of an appreciation of the uncanny has a crucial role to play in reacquainting Western culture with nature on more respectful and sustainable terms. Generally, I hope to show how the experience of the uncanny and opportunities to cultivate an appreciation of it can play a major role in reshaping the relationship between culture and nature in the direction of dialogue instead of domination

Brownian Dynamics Simulation of Knot Diffusion along a Stretched DNA Molecule

Manipulation of individual DNA molecules by optical tweezers has made it possible to tie these molecules into knots. After stretching the DNA molecules the knots become highly localized. In their recent study, Quake and co-authors investigated diffusion of such knots along stretched DNA molecules. We used these data to test the accuracy of a Brownian dynamics simulation of DNA bending motion. We simulated stretched DNA molecules with knots 3(1), 4(1), and 7(1), and determined their diffusion coefficients. Comparison of the simulated and experimental results shows that Brownian dynamics simulation is capable of predicting the rates of large-scale DNA rearrangements within a factor of 2