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1.
P. W. Glynn S. B. Colley N. J. Gassman K. Black J. Cortés J. L. Maté 《Marine Biology》1996,125(3):579-601
The reproductive ecology of Pavona gigantea Verrill and Gardineroseris planulata (Dana) was investigated in the equatorial eastern Pacific region from 1985 to 1994. These zooxanthellate scleractinian corals were adversely affected in this region during the 1982–1983 El Niño warming event. Both species were hermaphroditic, with individual colonies showing sequential cosexual development, thus resulting in dominantly outbreeding reproduction. Sexuality was mixed, with high percentages of gonochoric and hermaphroditic colonies in both species. Approximately 1:1 male-to-female gonad ratios were found in gonochoric and hermaphroditic colonies combined. Broadcast spawning was observed in P. gigantea in the Galápagos Islands, and the sudden disappearance of mature gametes and the presence of spent gonads suggest that G. planulata is also a broadcast spawner. Colonies of both species with 200 cm2 (10 cm diam) live tissue were nonreproductive. Estimated ages of the youngest reproductive colonies were 11 yr for P. gigantea and 20 yr for G. planulata. The percentage of all colonies of P. gigantea with gonads at nonupwelling sites (Caño Istand, Costa Rica and Uva Island, Panamá) ranged from 37 to 47%, respectively; colonies with gonads from upwelling environments (Saboga and Taboga Islands, Panamá) ranged from 31 to 39%, respectively, and reproductively active colonies from the thermally variable Galápagos islands comprised 40% of the collections. Compared with P. gigantea, the numbers of sexually active G. planulata colonies were roughly onehalf at nonupwelling Caño Island (20%) and Uva Island (25%) sites, or less (10%) at the upwelling Saboga Island site. Peak reproductive activity in P. gigantea occurred during the rainy season at all study sites. In the nonupwelling Costa Rican (Caño Island) and Panamainan (Uva Island) sites, mean monthly sea-surface temperatures (SSTs) were high (28 to 29°C), but slightly lower than in the dry season (29°C). In the upwelling Gulf of Panamá (Saboga and Taboga Islands), reproduction occurred after mean monthly SSTs increased from 24 to 28–29°C. In the Galápagos Islands, reproductive activity peaked during sea warming, when mean monthly SSTs reached 25°C. Sexually active colonies of G. planulata, present only at the main collection sites of Caño and Uva Islands, were also observed during the wet season. The presence of mature or spawned gonalds in both species mostly around new and full lunar phases suggests that spawning is at least weakly synchronized with moon phase. Fecundity estimates disclosed the following nonsignificant differences between sites for P. gigantea, expressed as egg production cm-2 colony surface surface yr-1: Galápagos (10 300 to 30 800), Uva Island (4900 to 9800), Caño Island (1800 to 7400), Saboga Island (600 to 1300) Taboga Island (1200 to 2400). Fecundity estimates for G. planulata were considerably lower: Uva Island (700 to 1400), Caño Island (500 to 1000). The sexual recruitment of P. gigantea into El Niño-Southern Oscillation (ENSO) 1982–1983-disturbed, equatorial eastern Pacific coral communities has been low, with only moderate recovery evident since 1983. G. planulata has revealed no sexual recruitment where seed populations are absent or rare (Caño Island, Galápagos Islands), and only low recruitment (Panamá) in areas with colonies that survived the ENSO disturbance. 相似文献
2.
The reproductive ecology of two eastern Pacific zooxanthellate coral species was examined as part of a continuing series of studies relating bleaching/mortality events caused by the El Niño–Southern Oscillation disturbance, and is described for study sites in Costa Rica, Panamá, and the Galápagos Islands (Ecuador). This study deals with the sibling agariciid species Pavona varians and Pavona sp.a over a 13?yr period (1985 to 1997). Both Pavona species are broadcast-spawners with some gonochoric, but mostly sequential hermaphroditic colonies. Minimum colony sizes (and ages) at first reproduction were 5?cm (5?yr) and 3?cm (2 to 3?yr), respectively, in P. varians and Pavona sp.a. In the Panamá and Galápagos populations, gonochoric colonies spawn eggs or sperm at least monthly. Six fecundity attributes were not significantly different in the two species, but the eggs of P. varians are white to beige and positively buoyant, and those of Pavona sp.a are dark green and neutrally to negatively buoyant. Eggs of both species lack zooxanthellae. Both species are reproductively active year-round, with maximum activity in the dry season in the nonupwelling Gulf of Chiriquí, and in the wet season in the upwelling Gulf of Panamá. Spawning is predominantly during full moon, and possibly also at new moon at most study sites. Spawning in P. varians and Pavona sp.a is 12?h out of phase, with the former species spawning ~1?h before sunrise and the latter about 1?h after sunset. The fecundity of Pavona spp. at Caño and the Galápagos Islands was much greater (19?900 to 27?900 eggs cm?2?yr?1) than at all Panamá sites (14?800 to 19?800 eggs cm?2?yr?1). Intraspecific crosses in both species resulted in swimming planula larvae after 25 to 36?h. Recruitment of P. varians was highest in Panamá, moderate in Costa Rica, and nil in the Galápagos Islands, matching, respectively, the contributions of P. varians to the pre-1982/1983 El Niño coral-population abundances in these areas. Recruitment success of P. varians at Uva Island was significantly related to maximum monthly positive sea surface-temperature (SST) anomalies that occurred in the year preceding recruitment over the period 1982 to 1996; recruitment failed when SST anomalies exceeded 1.6 to 1.9?C° during the severe ENSO events of 1982/1983 and 1997/1998. 相似文献
3.
P. W. Glynn S. B. Colley J. L. Maté I. B. Baums J. S. Feingold J. Cortés H. M. Guzmán J. C. Afflerbach V. W. Brandtneris J. S. Ault 《Marine Biology》2012,159(9):1917-1932
Two zooxanthellate, scleractinian species present in the equatorial eastern Pacific, Psammocora stellata and Psammocora profundacella, were examined in terms of their reproductive biology and ecology at four study sites, non-upwelling (Ca?o Island, Costa Rica, and Uva Island, Panamá), upwelling (Gulf of Panamá, Panamá), and seasonally varying thermal environments (Galápagos Islands). Both species were gonochoric broadcast spawners lacking zooxanthellae in mature ova. Mature gametes and spawned gonads are present around full moon; however, no spawning was observed naturally or in outdoor aquaria. Mature gametes occurred in P. stellata at Ca?o Island for nearly 6?months, and year round at Uva Island, both non-upwelling sites. Reproductively active colonies occurred mostly in the warmer months in the Gulf of Panamá and Galápagos Islands. In the Galápagos Islands, where collecting effort was greatest for P. profundacella, mature gametes were also most prevalent during the warm season. Annual fecundity was high in both species, 1.3–1.8?×?104?ova?cm?2?year?1 in P. stellata and 1.2–2.0?×?104?ova?cm?2?year?1 in P. profundacella. Compared to other eastern Pacific corals, P. stellata was relatively resistant to ENSO-related bleaching and mortality, especially populations inhabiting deep (12–20?m) coral communities. Rapid recovery and persistence of Psammocora spp. can be attributed to several factors: (a) relative resistance to bleaching, (b) deep refuge populations, (c) broadcast spawning, (d) protracted seasonal reproduction, (e) high fecundity, and (f) asexual propagation. 相似文献
4.
Pre-spawning reproductive biology and population structure of the sea cucumber Isostichopus fuscus were analysed at the Caamaño Island, Galápagos Islands, Ecuador on a monthly basis between January 1995 and June 1996. An average of 25 individuals of all sizes were collected each month. Using microscopic characteristics of the gonads three gonadal stages were described: (1) immature; (2) mature, and (3) spent. Mature individuals showed statistically different morphometric characteristics. I. fuscus was continuously sexually mature throughout the year independent of changes in sea water temperature. Mean oocyte diameter indicated planktotrophic larval development. Mean fecundity for this species was 567,884 (±95,528 SE) eggs per gonad. Size at first maturity was between 161.0 and 170.9 g drained weight and the smallest individual found with mature gonads had a drained weight between 121.0 and 130.9 g. The population sampled ranged between 13 and 31 cm (81.0–400.0 g) with less than 10% of the population of individuals ≥25 cm (≥300.0 g). No juveniles were recorded. 相似文献
5.
Maren N. Vitousek 《Behavioral ecology and sociobiology》2009,64(1):105-113
Changes in mate selectivity can significantly alter the direction and strength of sexual selection. When the direct cost of mate search increases selectivity often declines; however, little is known about how the relative cost of mate search affects investment in mate choice. Here, I investigate whether male and female Galápagos marine iguanas (Amblyrhynchus cristatus) alter their investment in mate choice behaviors when resources are limited and the relative cost of mate search is increased. Moderate resource limitation had little effect on male reproductive behavior: in both years, a similar number of males were territorial, and the mean display rate and copulation success of territorial males did not differ. In contrast, female mate search appeared to be affected by the prevailing environmental conditions. During the reproductive season following a moderate El Niño event, when food availability declined, females were in poorer body condition, assessed fewer territorial males, and mated with a male with lower relative reproductive success. Circulating hormone levels also differed between years: when resource availability was limited, receptive females had higher levels of testosterone and stress-induced corticosterone. The frequency and magnitude of climatic fluctuations are expected to increase in the future across many regions of the globe. Determining how sexual selection is shaped by changes in resource availability is vital for predicting the impact of climate change. 相似文献
6.
"Covering" or "heaping" behaviour is common to a number of regular echinoids living in a variety of different habitats. Many theories have been proposed to explain this behaviour, among which are several that link covering to light, including ultraviolet (UV) light. However, previous investigations of this light theory have been largely qualitative. In the present study, we used a systematic laboratory protocol to examine quantitatively the covering behaviour of the shallow water echinoid, Paracentrotus lividus, under four different light regimes: white light (400-700 nm), UV-A+B (315-400 nm), UV-A (320-400 nm), and darkness. These experiments demonstrated that light, in particular UV light, influences the covering behaviour of P. lividus. Under the UV regimes, significantly more individuals were found to display covering behaviour, and individuals spent more time at the base of aquaria, farthest from the light source. Moreover, covering items were retained for the longest period of time under the UV-A+B regime. We propose that protection against the harmful effects of UV radiation may be one of the functions of covering behaviour in P. lividus. 相似文献
7.
Seed and fruit dispersal along watercourses favours the long-distance migration of invasive species, not only for aquatic or wetland species, but also for terrestrial wind-dispersed plants, like the Japanese knotweed. The present paper aims at investigating the role of watercourses in the dispersal of the knotweed due to its frequent occurrence on riverbanks and production of fertile achenes (type of fruit of the Japanese knotweed). This dispersal occurs along two steps after the fruits deposit on the water surface: floatation first and then sinking towards the bottom of the watercourse. Regarding the first step, the effects of agitation of the water, temperature, surface tension and luminosity on the achenes floatability are experimentally studied. While no influence of luminosity is observed, an increase of temperature greatly decreases the floating time. Floating time also decreases as the contact between water and the fruit is enhanced (through submersion of achenes, agitation of the water or lower surface tension). Regarding the second step, the fall velocity of the fruits in water at rest is measured and appears to be independent of the seed history (floating time). 3D helical motions are systematically observed with constant tangential velocity with respect to the falling velocity. The trajectory of the fruits in a shear flow is then measured and the evolution of their velocity components along the sinking process is discussed. Finally, the contribution of both steps to the long-distance migration of the seeds is estimated. 相似文献
8.
Stefanie Jacob Andreas Dötsch Sarah Knoll Heinz-R. Köhler Eike Rogall Dominic Stoll Selina Tisler Carolin Huhn Thomas Schwartz Christian Zwiener Rita Triebskorn 《Environmental Sciences Europe》2018,30(1):48
Background
Due to the rising number of type 2 diabetes patients, the antidiabetic drug, metformin is currently among those pharmaceuticals with the highest consumption rates worldwide. Via sewage-treatment plants, metformin enters surface waters where it is frequently detected in low concentrations (µg/L). Since possible adverse effects of this substance in aquatic organisms have been insufficiently explored to date, the aim of this study was to investigate the impact of metformin on health and development in brown trout (Salmo trutta f. fario) and its microbiome.Results
Brown trout embryos were exposed to 0, 1, 10, 100 and 1000 µg/L metformin over a period from 48 days post fertilisation (dpf) until 8 weeks post-yolk sac consumption at 7 °C (156 dpf) and 11 °C (143 dpf). Chemical analyses in tissues of exposed fish showed the concentration-dependent presence of metformin in the larvae. Mortality, embryonic development, body length, liver tissue integrity, stress protein levels and swimming behaviour were not influenced. However, compared to the controls, the amount of hepatic glycogen was higher in larvae exposed to metformin, especially in fish exposed to the lowest metformin concentration of 1 µg/L, which is environmentally relevant. At higher metformin concentrations, the glycogen content in the liver showed a high variability, especially for larvae exposed to 1000 µg/L metformin. Furthermore, the body weight of fish exposed to 10 and 100 µg/L metformin at 7 °C and to 1 µg/L metformin at 11 °C was decreased compared with the respective controls. The results of the microbiome analyses indicated a shift in the bacteria distribution in fish exposed to 1 and 10 µg/L metformin at 7 °C and to 100 µg/L metformin at 11 °C, leading to an increase of Proteobacteria and a reduction of Firmicutes and Actinobacteria.Conclusions
Overall, weight reduction and the increased glycogen content belong to the described pharmaceutical effects of the drug in humans, but this study showed that they also occur in brown trout larvae. The impact of a shift in the intestinal microbiome caused by metformin on the immune system and vitality of the host organism should be the subject of further research before assessing the environmental relevance of the pharmaceutical.9.
Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parents investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.Communicated by D. Gwynne 相似文献
10.
Colonial photosynthetic marine organisms often exhibit morphological phenotypic plasticity. Where such plasticity leads to
an improved balance between rates of photosynthesis and maintenance costs, it is likely to have adaptive significance. To
explore whether such phenotypic plasticity leads to more favourable within-colony irradiance for reef-building branching corals,
this relationship was investigated for two coral species Acropora humilis and Stylophora pistillata, along a depth gradient representing light habitats ranging from 500 to 25 μmol photons m−2 s−1, during 2006 at Heron Island, Great Barrier Reef (23.44°S, 151.91°E). In the present study changes in flow-modulated mass
transfer co-varied with light as a function of depth. In low-light (deep) habitats, branch spacing (colony openness) in A. humilis and S. pistillata was 40–50% greater than for conspecifics in high-light environments. Also, branches of A. humilis in deep water were 40–60% shorter than in shallow water. Phenotypic changes in these two variables lead to steeper within-colony
light attenuation resulting in 38% higher mean internal irradiance (at the tissue surface) in deep colonies compared to shallow
colonies. The pattern of branch spacing was similar for S. pistillata, but this species displayed an alternate strategy with respect to branch length: shade adapted deep and cave colonies developed
longer and thinner branches, allowing access to higher mass transfer and irradiance. Corals in cave habitats allowed 20% more
irradiance compared to colonies found in the deep, and had a 47% greater proportion of irradiance compared to colonies in
the shallow high-light environment. Such phenotypic regulation of internal light levels on branch surfaces partly explains
the broad light niches of many branching coral species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
11.
The mussel species Mytilus edulis L. and M. trossulus Gould coexist and hybridize throughout a large area that includes the north coast of Maine and Atlantic Canada. Previous studies provided genetic evidence for limited hybridization between the two species for mussels >15 mm. The present study used two genetic markers (ITS, Glu-5) to examine the genetic composition of early life-history stages by sampling veliger and pediveliger larvae, juveniles (<2.0 to 15.0 mm shell length) and adults (>15 mm shell length) in Trinity Bay, Newfoundland, during three consecutive years (1995–1997) to determine if differential mortality limits the relative abundance of hybrids. The relative frequency of the two species and the different hybrid genotypes was similar among the larvae, juveniles and small adult mussels. The double hybrid genotype (F1-like) was the rarest genotype observed. There was no evidence for differential mortality during the early life-history stages, and factors limiting production of hybrids appear to operate before the late larval stage. The observed frequency of hybrids is probably due to a combination of pre- and postzygotic reproductive isolating mechanisms operating early in the mussels life history. M. trossulus dominated the early life-history stages, possibly due to a higher population density and a greater reproductive output than M. edulis. Differential mortality may explain the observed decrease in frequency of M. trossulus and increase in frequency of M. edulis with increasing shell length. A similar frequency of hybrid mussels from larvae to the size class of 55 mm shell length may indicate a rate of mortality intermediate between the two parental species. The M. edulis–M. trossulus hybrid zone appears to be maintained by reproductive isolating mechanisms limiting the production of hybrids and life-history differences that allow the two species to coexist.Communicated by J.P. Grassle, New Brunswick 相似文献
12.
In the cooperatively breeding red-cockaded woodpecker (Picoides borealis), male helpers are subordinate to male breeders and do not mate with females, even when unrelated to the breeding female
within their group or through extra-group matings, yet exhibit reproductive hormone profiles similar to those of breeders.
We investigated whether reproduction might be suppressed in helper males via high levels of the stress hormone corticosterone.
We also examined effects of group size and season on corticosterone levels by comparing baseline and maximal plasma levels
of corticosterone between helper males and breeding males, and among helper males and breeders of both sexes living in groups
of different sizes throughout the reproductive cycle. We also measured plasma levels of estrogen, progesterone, and testosterone
to examine other potential hormonal differences between helpers and breeders. Male status did not explain variation in any
hormones; therefore, our data do not support the hypothesis that helper males are reproductively suppressed via corticosterone
or the other hormones investigated. However, the presence of two or more helper males in a group tended to reduce baseline
corticosterone in breeding and helper males, but not breeding females, suggesting that helper males reduce parental effort
of other male group members. Seasonally, maximal corticosterone peaked during the nestling provisioning phase for breeding
and helper males, but not breeder females, suggesting that males show an increased response to stressors posing a potential
threat to survival of offspring. 相似文献
13.
In south-western Australia, the isopod Limnoria agrostisa commonly burrows into leaf clusters and immature shoots of Amphibolis griffithii. The isopod also burrows into the sheath and rhizomes of Posidonia species. In A. griffithii, the isopod consumes new tissue within the sheath, damaging or destroying the meristem. This results in malformation of new
leaves or destruction of whole leaf clusters with the potential to reduce the photosynthetic area of a shoot. The isopod has
been found in all but one meadow of A. griffithii examined over 1,000 km of the Western Australian coastline. It was present throughout the year and showed little variation
in abundance. Young were produced year round, but were more abundant in the summer months. Females, 3.5 mm in length or larger,
produced 2–5 young that were brooded within the leaf cluster or base of an immature shoot. Within a meadow, 40–70% of shoots
and 10–20% of leaf clusters were damaged by isopods. Seasonal trends were not consistent, but damage appeared to be higher
in summer when isopod abundance was higher. Approximately 40% of clusters were destroyed by isopod damage. Isopods attack
shoots of all ages, but damage was often located on apical clusters. There was no evidence that isopod damage initiated branching
or leaf cluster formation. Estimations of clusters damaged or destroyed may be conservative, as only those clusters remaining
on a shoot could be counted, and cluster loss could not be quantified. Examination of defoliated stems on upright shoots and
horizontal rhizomes indicated that many were destroyed by isopods. The effect of L. agrostisa although substantial appears to be a feature of healthy seagrasses throughout southern Australia. 相似文献
14.
The cost of reproduction for the terminal spawning onychoteuthid squid, Moroteuthis ingens, was analysed using measures of condition and tissue biochemistry. Both males and females showed a dramatic drop in the weight of the gonad in stage 6 (spent) individuals. The mantle weight and nidamental gland weight of females also decreased during the maturation process. Males, however, had a marked increase in both the penis and spermatophoric complex weight in spent individuals, while female oviducal gland weight and nidamental gland length also increased in stage 6 individuals. Residual analysis indicated that testis growth was not developing at the expense of mantle growth, although there was a suggestion of cost to the fins. Females showed that the development of the ovary occurred at a cost to both the mantle and fins. Overall body condition also declined with maturity stage for both males and females, with stage 6 individuals of both sexes in poor condition. Very few females had eggs in the oviducts, suggesting that the oviducts are used as ducts instead of storage organs. Proximal analysis revealed a loss of constituents within the mantle during maturation, with an associated increase in water, indicating the remobilization of energy from the mantle to fuel reproduction. This study suggests that the digestive gland is not used as an energy store in this species.Communicated by M.S. Johnson, Crawley 相似文献
15.
The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters
of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population
density of O. similis ranged from 110 to 9,630 ind m−3 and averaged 1,020 ± 336 ind m−3. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included
a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in
late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch
size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature,
while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female−1 day−1 and 0.0011 ± 0.003 day−1, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m−3 day−1 (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive
parameters appeared to be controlled by hydrological factors and food conditions. 相似文献
16.
Lars W. Clement Stephan C. W. Köppen Willi A. Brand Martin Heil 《Behavioral ecology and sociobiology》2008,62(6):953-962
Mutualisms can be exploited by parasites—species that obtain resources from a partner but provide no services. Though the
stability of mutualisms in the presence of such parasites is under intensive investigation, we have little information on
life history traits that allow a species to be a successful mutualist or rather a parasite, particularly in cases where both
are closely related. We studied the exploitation of Acacia myrmecophytes by the ant, Pseudomyrmex gracilis, contrasting with the mutualistic ant Pseudomyrmex ferrugineus. P. gracilis showed no host-defending behavior and had a negative effect on plant growth. By preventing the mutualist from colonization,
P. gracilis imposes opportunity costs on the host plant. P. gracilis produced smaller colonies with a higher proportion of alates than did the mutualist and thus showed an “r-like” strategy. This appears to be possible because P. gracilis relies less on host-derived food resources than does the mutualist, as shown by behavioral and stable isotope studies. We
discuss how this system allows the identification of strategies that characterize parasites of mutualisms. 相似文献
17.
18.
The paper focuses on the numerical simulation of the exchange flow between open water and floating vegetation, which plays an important role in maintaining the ecological balance by transporting nutrient matter. The simulation was conducted using a new solver developed upon OpenFOAM. A modified RNG k-ε turbulence model, which is expected to model both the high- and low-Reynolds number flows correctly, was used to determine the eddy viscosity. Several particular terms were added into the momentum equations and turbulence model equations to model the effects of vegetation and buoyancy. Among these terms, the term for the effect of vegetation in the ε-equation was re-modelled. The model was validated by properly predicting the profiles of mean velocity and turbulent kinetic energy for flows through suspended canopies. The density flow between open and vegetated water was simulated with the same conditions as those of the experiment conducted by Zhang and Nepf. The predicted results agreed well with the experimental data and provided more detailed information of such exchange flow. The convection between the root layer and the layer beneath the roots, which was not observed in the experiment, was observed in the numerical simulation. 相似文献
19.
Gentoo penguins Pygoscelis papua show considerable plasticity in their diet, diving, and foraging behaviors among colonies; we expected that they might exhibit
similar variability over time, at a single site, since flexible foraging habits would provide a buffer against changes in
prey availability. We examined interannual changes in the foraging strategies and diet of gentoo penguins in the South Shetland
Islands, Antarctica, over 5 years with variable prey abundance. Antarctic krill Euphausia superba was the primary diet item, and fish the secondary, though the importance of these items varied among years. Diving behavior
also varied over time: different dive depth distributions were observed among years. Nonetheless, chick-rearing success remained
relatively constant, indicating that gentoo penguins were able to maintain chick provisioning by altering their foraging strategy
among years. Variable abundance of krill in the region did not have observable impacts on the diet, foraging behaviors or
chick-rearing success of gentoo penguins. We suggest that foraging plasticity may be one reason that gentoo penguin populations
have remained stable in the region, while their congeners (P. antarctica and P. adeliae) with less flexible foraging strategies have declined. 相似文献
20.
Northern shrimp Pandalus borealis (Krøyer) larvae hatch in the northern Gulf of St. Lawrence from early May to the end of June, and larval development occurs over a range of relatively cold water temperatures. Because of the long duration of the pelagic phase and the difficulty of sampling all successive larval stages at sea, we used laboratory experiments to assess the effects of water temperature on larval development and growth. In spring 2000, P. borealis larvae were reared from hatching to the first juvenile stages (i.e., stage VI and VII) at three temperatures (3, 5, and 8°C) representing conditions similar to those in spring in the northern Gulf of St. Lawrence. Larval development and growth were dependent on temperature, with longer duration and smaller size (cephalothorax length, CL, and dry mass, DM) at 3°C relative to the 5 and 8°C treatments. There were no significant differences in the morphological characters of the different stages among treatments, indicating that regular moults occurred at each temperature. The results suggest a negative impact of cold temperatures (lower intra-moult growth rates and smaller size) and, possibly, higher cumulative mortality due to longer development time that could affect the success of cohorts at sea. However, CL and DM for stage III and later larvae were smaller than those of larvae identified at the same developmental stage in field locations. It is possible that the diet offered to larvae in this experiment (Artemia nauplii, either newly hatched nauplii or live adults, depending on the developmental stage) was not optimal for growth, even though it is known to support successful P. borealis larval development. In the field, there is the possibility that phytoplankton contributes to the larval diet during the first stages and stimulates development of the digestive glands. Furthermore, the nutritional quality of the natural plankton diet (e.g., high protein content, fatty acid composition) might be superior and favourable to higher growth rates even at lower temperatures.Communicated by R.J. Thompson, St. Johns 相似文献