Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
1,003
result(s) for
"Swan, C."
Sort by:
Dendritic network structure constrains metacommunity properties in riverine ecosystems
1. Increasingly, ecologists conceptualize local communities as connected to a regional species pool rather than as isolated entities. By this paradigm, community structure is determined through the relative strengths of dispersal-driven regional effects and local environmental factors. However, despite explicit incorporation of dispersal, metacommunity models and frameworks often fail to capture the realities of natural systems by not accounting for the configuration of space within which organisms disperse. This shortcoming may be of particular consequence in riverine networks which consist of linearly -arranged, hierarchical, branching habitat elements. Our goal was to understand how constraints of network connectivity in riverine systems change the relative importance of local vs. regional factors in structuring communities. 2. We hypothesized that communities in more isolated headwaters of riverine networks would be structured by local forces, while mainstem sections would be structured by both local and regional processes. We examined these hypotheses using a spatially explicit regional analysis of riverine macroinvertebrate communities, focusing on change in community similarity with distance between local communities [i.e., distance-decay relationships; (DDRs)], and the change in environmental similarity with distance. Strong DDRs frequently indicate dispersal-driven dynamics. 3. There was no evidence of a DDR in headwater communities, supporting our hypothesis that dispersal is a weak structuring force. Furthermore, a positive relationship between community similarity and environmental similarity supported dynamics driven by local environmental factors (i.e., species sorting). In mainstem habitats, significant DDRs and community x environment similarity relationships suggested both dispersal-driven and environmental constraints on local community structure (i.e., mass effects). 4. We used species traits to compare communities characterized by low vs. high dispersal taxa. In headwaters, neither strength nor mode (in-network vs. out of network) of dispersal changed our results. However, outcomes in mainstems changed substantially with both dispersal mode and strength, further supporting the hypothesis that regional forces drive community dynamics in mainstems. 5. Our findings demonstrate that the balance of local and regional effects changes depending on location within riverine network with local (environmental) factors dictating community structure in headwaters, and regional (dispersal driven) forces dominating in mainstems.
Journal Article
Laboratory investigation of crest height statistics in intermediate water depths
This paper concerns the statistical distribution of the crest heights associated with surface waves in intermediate water depths. The results of a new laboratory study are presented in which data generated in different experimental facilities are used to establish departures from commonly applied statistical distributions. Specifically, the effects of varying sea-state steepness, effective water depth and directional spread are investigated. Following an extensive validation of the experimental data, including direct comparisons to available field data, it is shown that the nonlinear amplification of crest heights above second-order theory observed in steep deep water sea states is equally appropriate to intermediate water depths. These nonlinear amplifications increase with the sea-state steepness and reduce with the directional spread. While the latter effect is undoubtedly important, the present data confirm that significant amplifications above second order (5–10%) are observed for realistic directional spreads. This is consistent with available field data. With further increases in the sea-state steepness, the dissipative effects of wave breaking act to reduce these nonlinear amplifications. While the competing mechanisms of nonlinear amplification and wave breaking are relevant to a full range of water depths, the relative importance of wave breaking increases as the effective water depth reduces.
Journal Article
The interaction between steep waves and a surface-piercing column
Experimental observations are presented of a single surface-piercing column subject to a wide range of surface gravity waves. With the column diameter, D, chosen such that the flow lies within the drag-inertia regime, two types of high-frequency wave scattering are identified. The first is driven by the run-up and wash-down on the surface of the column in the vicinity of the upstream and downstream stagnation points. The second concerns the circulation of fluid around the column, leading to the scattering of a pair of non-concentric wavefronts. The phasing of the wave cycle at which this second mode evolves is dependent upon the time taken for fluid to move around the column. This introduces an additional time-scale, explaining why existing diffraction solutions, based upon a harmonic analysis of the incident waves, cannot describe this scattered component. The interaction between the scattered waves and the next (steep) incident wave can produce a large amplification of the scattered waves, particularly the second type. Evidence is provided to show that these interactions can produce highly localized free-surface effects, including vertical jetting, with important implications for the setting of deck elevations, the occurrence of wave slamming and the development of large run-up velocities.
Journal Article
A laboratory study of wave crest statistics and the role of directional spreading
This paper concerns the crest height statistics arising in sea states that are broad banded in both frequency and direction. A new set of laboratory observations are presented and the results compared with the commonly applied statistical distributions. Taken as a whole, the data confirm that the crest-height distributions are critically dependent upon the directionality of the sea state. Although nonlinear effects arising at third order and above are most pronounced in uni-directional seas, the present data show that they are also important in directionally spread seas, provided the seas are sufficiently steep and not too short crested. The data also highlight the limiting effects of wave breaking. With individual breaking events dependent upon the local wave steepness, the directionality of the sea state again plays a significant role. Indeed, the present observations confirm that the two competing processes of nonlinear amplification and wave breaking can have a profound influence on the crest-height distributions leading to significant departures from established theory. In such cases, the key parameters are the sea state steepness and directional spread; the latter acting to counter the former in terms of nonlinear changes in the crest-height distributions.
Journal Article
DNA Methylation Patterns in Cord Blood DNA and Body Size in Childhood
Epigenetic markings acquired in early life may have phenotypic consequences later in development through their role in transcriptional regulation with relevance to the developmental origins of diseases including obesity. The goal of this study was to investigate whether DNA methylation levels at birth are associated with body size later in childhood.
A study design involving two birth cohorts was used to conduct transcription profiling followed by DNA methylation analysis in peripheral blood. Gene expression analysis was undertaken in 24 individuals whose biological samples and clinical data were collected at a mean ± standard deviation (SD) age of 12.35 (0.95) years, the upper and lower tertiles of body mass index (BMI) were compared with a mean (SD) BMI difference of 9.86 (2.37) kg/m(2). This generated a panel of differentially expressed genes for DNA methylation analysis which was then undertaken in cord blood DNA in 178 individuals with body composition data prospectively collected at a mean (SD) age of 9.83 (0.23) years. Twenty-nine differentially expressed genes (>1.2-fold and p<10(-4)) were analysed to determine DNA methylation levels at 1-3 sites per gene. Five genes were unmethylated and DNA methylation in the remaining 24 genes was analysed using linear regression with bootstrapping. Methylation in 9 of the 24 (37.5%) genes studied was associated with at least one index of body composition (BMI, fat mass, lean mass, height) at age 9 years, although only one of these associations remained after correction for multiple testing (ALPL with height, p(Corrected) = 0.017).
DNA methylation patterns in cord blood show some association with altered gene expression, body size and composition in childhood. The observed relationship is correlative and despite suggestion of a mechanistic epigenetic link between in utero life and later phenotype, further investigation is required to establish causality.
Journal Article