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Streamlining of plant patches in streams 总被引:1,自引:0,他引:1
1. Plants in shallow streams often grow in well‐defined monospecific patches experiencing a predictable unidirectional flow, though of temporally variable velocity. During maximum patch development in summer we studied: (i) the shape and streamlining of 59 patches of Callitriche cophocarpa, (ii) allometric relationships between canopy size and sediment area colonized by roots (root area) and (iii) fine‐scale flow gradients for a representative patch exposed to a range of velocities to evaluate relationships between patch shape and physical impact. 2. Canopy and root area viewed from above were elongated and streamlined in the flow direction, while uniform vegetative growth in all directions from a single colonizing shoot would have generated a circular form. Canopies were slightly wider in the upstream part than in the gradually tapering part downstream and the maximum height to length ratio averaged 0.25. The canopy and root area of the patches were more elongate and slender in sites with shallow water, where currents accelerate alongside patches and restrict lateral expansion, compared to deeper sites where currents can pass above the canopy. Similarly, the frontal area relative to planform area or root area was significantly lower in shallow water . Canopy shape and indices of streamlining did not change significantly with approach velocity (0.02–0.40 m s?1), either because canopy shape is not sensitive to approach velocity or summer velocities were too low to induce such changes. 3. Sediment elevation within patches (avg. 4.1 cm) increased significantly with patch length, but did not differ between unstable sand or more stable coarse sediment for the same patch length. Shape of canopy and root area did not change significantly with sediment type. 4. Pressure drag on the canopy as a whole is probably reduced by its rounded front, restricted height and overall slender form with a low frontal area, while the downstream overhanging canopy increases drag compared to an ideal streamlined object. Across a 100‐fold range of root areas from 0.01 to 1 m2, the frontal area of the canopy increased 29 times, planform area increased 38 times and volume increased 76 times, suggesting a trade‐off between physical impact of flow, light interception and anchoring strength. 5. The canopy was compressed at high approach velocities, with low current velocity within the canopy while steep velocity gradients developed across the exposed outer surfaces as the diverted flow accelerated. Because drag processes are additive, and exist at different spatial scales and Reynolds numbers on the surface and inside of plant canopies, direct measurements on entire canopies under controlled conditions are needed to test the functional importance of their shape, size and porosity to flow. 相似文献
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STEPHEN J. THACKERAY TIMOTHY H. SPARKS MORTEN FREDERIKSEN SARAH BURTHE PHILIP J. BACON JAMES R. BELL MARC S. BOTHAM TOM M. BRERETON PAUL W. BRIGHT LAURENCE CARVALHO TIM CLUTTON‐BROCK ALISTAIR DAWSON MARTIN EDWARDS J. MALCOLM ELLIOTT RICHARD HARRINGTON DAVID JOHNS IAN D. JONES JAMES T. JONES DAVID I. LEECH DAVID B. ROY W. ANDY SCOTT MATT SMITH RICHARD J. SMITHERS IAN J. WINFIELD SARAH WANLESS 《Global Change Biology》2010,16(12):3304-3313
Recent changes in the seasonal timing (phenology) of familiar biological events have been one of the most conspicuous signs of climate change. However, the lack of a standardized approach to analysing change has hampered assessment of consistency in such changes among different taxa and trophic levels and across freshwater, terrestrial and marine environments. We present a standardized assessment of 25 532 rates of phenological change for 726 UK terrestrial, freshwater and marine taxa. The majority of spring and summer events have advanced, and more rapidly than previously documented. Such consistency is indicative of shared large scale drivers. Furthermore, average rates of change have accelerated in a way that is consistent with observed warming trends. Less coherent patterns in some groups of organisms point to the agency of more local scale processes and multiple drivers. For the first time we show a broad scale signal of differential phenological change among trophic levels; across environments advances in timing were slowest for secondary consumers, thus heightening the potential risk of temporal mismatch in key trophic interactions. If current patterns and rates of phenological change are indicative of future trends, future climate warming may exacerbate trophic mismatching, further disrupting the functioning, persistence and resilience of many ecosystems and having a major impact on ecosystem services. 相似文献
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OLE SEBERG FLS SIGNE FREDERIKSEN 《Botanical journal of the Linnean Society. Linnean Society of London》2001,136(1):75-97
A cladistic analysis, primarily based on morphology, is presented from 40 diploid taxa representing the 24 monogenomic genera of the Triticeae. General problems related to the treatment of hybrids and supposedly allopolyploid heterogenomic taxa are highlighted. Special emphasis is given to taxa not traditionally included in Aegilops s.J. Most of the 33 characters used in the analysis are coded as binary. The only four multistate characters in the matrix are treated as unordered. Three diploid species of Bromus are used as outgroup. The number of equally parsimonious trees found is very large (approx. 170000; length = 107, ci = 0.36, ri = 0.75) and the strict consensus tree has an expectedly low level of resolution. However, most of the equally parsimonious trees owe their existence to an unresolved Aegilops clade. If this clade is replaced by its hypothetical ancestor, the number of equally parsimonious trees drops dramatically (48; length = 78, ci = 0.45, ri = 0.76). When trees for which more highly resolved compatible trees exist are excluded, only two trees remain. Bremer support is used as a measure of branch support. The trees based on morphology and on molecular data are largely incongruent. 相似文献
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Distribution and quantitative development of aquatic macrophytes in relation to sediment characteristics in oligotrophic Lake Kalgaard, Denmark 总被引:6,自引:0,他引:6
SUMMARY. The distribution and quantitative development of aquatic macrophytes have been studied in oligotrophic Lake Kalgaard, Denmark. The vegetation is dominated by isoetid species, which are widely distributed (about 40% of the lake bottom) compared to emergent and floating-leaved macrophytes (about 4%). Littorella uniflora dominates at depths of 0–2 m and Isoetes lacustris from 2.0 to 4.5m. Within the colonization area the mean midsummer biomass of Littorella is 112g organic dry weight m−2 and that of Isoetes, 66 gm−2 . The total biomass of these two species constitutes 99% of the biomass of submerged macrophytes.
The perennial Littorella shows only small seasonal biomass variations. The vegetational biomass, the above-ground fraction of the biomass, and the weight of individual plants all increased with the organic content of the sediment at water depths from 0 to 0.75 m. At the same time the interstitial concentrations of carbon dioxide, extractable inorganic nitrogen, and exchangeable inorganic phosphorus increased, thus supporting the hypothesis that an increasing organic content of the sediments at this low level creates a physiologically richer medium for the plants.
The isoetid growth form is discussed in relation to the chemical environment of oligotrophic, softwater lakes. 相似文献
The perennial Littorella shows only small seasonal biomass variations. The vegetational biomass, the above-ground fraction of the biomass, and the weight of individual plants all increased with the organic content of the sediment at water depths from 0 to 0.75 m. At the same time the interstitial concentrations of carbon dioxide, extractable inorganic nitrogen, and exchangeable inorganic phosphorus increased, thus supporting the hypothesis that an increasing organic content of the sediments at this low level creates a physiologically richer medium for the plants.
The isoetid growth form is discussed in relation to the chemical environment of oligotrophic, softwater lakes. 相似文献
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TOBY J. REYNOLDS MICHAEL P. HARRIS RUTH KING ROBERT L. SWANN DAVID C. JARDINE MORTEN FREDERIKSEN SARAH WANLESS 《Ibis》2011,153(4):818-831
Spatiotemporal variation in survival may be an important driver of multi‐population dynamics in many wild animal species, yet few scientific studies have addressed this issue, primarily due to a lack of sufficiently comprehensive and detailed datasets. Synchrony in survival rates among different, often distant, subpopulations appears to be common, caused by spatially correlated environmental conditions or by movement of animals from different sites such that their ranges overlap. Many seabird populations are effectively isolated during the breeding season because colonies are widely separated, but over the winter, birds disperse widely and there may be much mixing between different populations. The non‐breeding season is also the period of main mortality for seabirds. Using mark–recapture and ring‐recovery data, we tested for spatial, temporal and age‐related correlations in survival of Common Guillemots Uria aalge among three widely separated Scottish colonies that have varying overlap in their overwintering distributions. Survival was highly correlated over time for colonies/age‐classes sharing wintering areas and, except in 2004, was essentially uncorrelated for those with separate wintering areas. These results strongly suggest that one or more aspects of the winter environment are responsible for spatiotemporal variation in survival of British Guillemots, and provide insight into the factors driving large‐scale population dynamics of the species. 相似文献
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We studied juvenile survival of 20 cohorts of Common Guillemot Uria aalge chicks colour-ringed on the Isle of May, Scotland, using both live observations at the colony and dead recoveries, allowing estimation of fidelity to the colony as well as survival. In this seabird, chicks leave the colony when only partly grown and are cared for by the male parent for several weeks afterwards. First-year survival varied strongly between cohorts, with a mean of 56% (range 30–91%). We did not identify any covariates which could explain this variation, whether relating to climate, population size or prey density. Survival was low during two regime shift episodes in the North Sea (1987–90 and 2000 onwards). Early hatched chicks were substantially more likely to survive than those hatching later in most years, whereas body condition at ringing had no detectable effect. Ringing recoveries indicated that mortality was highest in mid-winter, i.e. well after the cessation of paternal care. These results do not support the hypothesis that variation in prey quantity or energy content before fledging is a primary driver of variation in juvenile survival. Rather, it seems that chicks of high-quality parents are more likely to survive, as high-quality females tend to lay earlier in the season, and high-quality males presumably are better able to prepare their chicks to survive their first winter at sea. Very few (4%) Guillemots emigrated permanently before age 3 years, but from age 5 onwards 25–30% of birds annually left the colony or otherwise became unobservable. 相似文献