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1.
Abstract. Females of the specialist parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), were released in a wind tunnel into host-odour plumes dispersed by winds of three velocities and winds whose speed was changed while the wasps were engaged in upwind flight. In steady winds of 61, 122 and 183 cms--1, wasps maintained similar 'preferred' ground speeds by adjusting their airspeed, while turning to a lesser degree as wind velocity increased. In winds of changing velocity (either increasing or decreasing within a 60–100 cm s-1 range), wasps lowered their rate of upwind progress, leading to more tortuous tracks. During changing wind speeds longitudinal image flow decreased. Wasps flying in host-odour plumes 10 cm and 20 cm above the flight tunnel floor in a 122 cm s-1 wind had similar ground speeds; thus their rate of ventral visual image flow varied two-fold. M.croceipes may 'aim' upwind by comparing how changes in the course angle vary with the direction of visual image flow. During changing wind velocities the relationship between changes in visual and flight muscle generated torque is ambiguous. Under these conditions most wasps cast, a manoeuvre characterized by wide lateral excursions across the wind without upwind progress. Once wind speed stabilizes, flight straightens out and upwind flight resumes.  相似文献   

2.
In this paper, the normal and extreme wind conditions for power at 12 coastal locations along China’s coastline were investigated. For this purpose, the daily meteorological data measured at the standard 10-m height above ground for periods of 40–62 years are statistically analyzed. The East Asian Monsoon that affects almost China’s entire coastal region is considered as the leading factor determining wind energy resources. For most stations, the mean wind speed is higher in winter and lower in summer. Meanwhile, the wind direction analysis indicates that the prevalent winds in summer are southerly, while those in winter are northerly. The air densities at different coastal locations differ significantly, resulting in the difference in wind power density. The Weibull and lognormal distributions are applied to fit the yearly wind speeds. The lognormal distribution performs better than the Weibull distribution at 8 coastal stations according to two judgement criteria, the Kolmogorov–Smirnov test and absolute error (AE). Regarding the annual maximum extreme wind speed, the generalized extreme value (GEV) distribution performs better than the commonly-used Gumbel distribution. At these southeastern coastal locations, strong winds usually occur in typhoon season. These 4 coastal provinces, that is, Guangdong, Fujian, Hainan, and Zhejiang, which have abundant wind resources, are also prone to typhoon disasters.  相似文献   

3.
Wind as an ecological factor   总被引:1,自引:0,他引:1  
Wind has long been regarded as an important ecological factor in forests owing to the dramatic damage hurricanes can wreak. However, the long-term wind regime of a site also exerts a strong influence on the growth of trees. A relatively large amount is known about the acclimation of trees to wind but less about intra- or interspecific adaption to high winds. In fact, changes resulting from the effect of wind may have a greater effect on the ecology of forests than the more acute effects of destructive stroms. Improved understanding of the mechanical effects of wind is helping foresters manage their plantations and may help us to account better for local and geographical variations in forest ecology.  相似文献   

4.
Climatic conditions and landscape features often strongly affect species' local distribution patterns, dispersal, reproduction and survival and may therefore have considerable impacts on species' fine-scale spatial genetic structure (SGS). In this study, we demonstrate the efficacy of combining fine-scale SGS analyses with isotropic and anisotropic spatial autocorrelation techniques to infer the impact of wind patterns on plant dispersal processes. We genotyped 1304 Azorella selago (Apiaceae) specimens, a wind-pollinated and wind-dispersed plant, from four populations distributed across sub-Antarctic Marion Island. SGS was variable with Sp values ranging from 0.001 to 0.014, suggesting notable variability in dispersal distance and wind velocities between sites. Nonetheless, the data supported previous hypotheses of a strong NW-SE gradient in wind strength across the island. Anisotropic autocorrelation analyses further suggested that dispersal is strongly directional, but varying between sites depending on the local prevailing winds. Despite the high frequency of gale-force winds on Marion Island, gene dispersal distance estimates (σ) were surprisingly low (<10 m), most probably because of a low pollen dispersal efficiency. An SGS approach in association with isotropic and anisotropic analyses provides a powerful means to assess the relative influence of abiotic factors on dispersal and allow inferences that would not be possible without this combined approach.  相似文献   

5.
Using an integrated physical and biological approach, we examined across-shelf advection and exchange and the associated transport of bivalve larvae in the presence of a strong coastal current separated from the coast by a stratified inshore environment. We tested the hypothesis that the interface of the coastal current and inshore waters can act as an ecological barrier to across-shelf transport of larvae but can be overcome by wind- or tidally-induced transport. Our study region in the Gulf of Maine encompasses a coastal current that diverges from the coast as it moves downshelf. The region inshore of this current is home to several species that exhibit limited recruitment in spite of extensive upshelf larval sources. Analysis of surface water temperatures and wind velocities revealed episodic decreases in temperature along the coast correlated with alongshelf (but not upwelling) winds, indicating wind-forced onshore movement of the cold coastal current. Such wind-driven onshore migrations are more common along the northern portion of the study region where the coastal current is near the coast, tidal currents are strong, and wind directions are more conducive to onshore migration, but rarer further south where the interface between inshore waters and the coastal current is further offshore and suitable wind events are less common. The distribution of bivalve larvae was consistent with the physical measurements. There was little across-shelf variation in larval abundance where the current abuts the coast, indicating strong across-shelf exchange of larvae, but strong across-shelf variation in larval density where the stratified inshore waters separate the current from the coast, indicating weak across-shelf transport of larvae. Our results suggest that the interface between the coastal current and inshore waters may constitute a major ecological barrier to larval dispersal in the southern part of the region that may only be overcome by rare, strong wind-forced events.  相似文献   

6.
Trees have the ability to respond to local environmental cues by expressing particular phenotypes across their canopy through a mechanism known as intracanopy plasticity. In this study, intracanopy plasticity of Olea europaea subsp. europaea was analyzed by sampling leeward and windward canopy exposures of individuals occurring in an area with sustained strong wind conditions. A suite of morphofunctional and reproductive traits was measured at these contrasting canopy positions and, for comparison, also in wind-protected trees. Furthermore, the pattern of intracanopy plasticity of these plants was compared to that previously documented in a closely related species, Olea europaea subsp. guanchica. Plants exposed to strong winds displayed substantial differences between leeward and windward exposures in most of the study traits. Leeward exposures experienced a mean reduction of 73% in wind speed as compared to windward ones, and displayed a modular phenotype matching that observed in wind-protected plants. Wind-exposed plants, however, were comparatively smaller and had fewer and smaller inflorescences, since inflorescence size was positively associated with crown size. The two closely related species showed similar crown and leaf sizes between populations exposed to strong winds, and intracanopy responses were comparable for most traits. These observations suggest that intracanopy plasticity resulted in the expression of contrasting phenotypes within individuals, which allowed trees to persist under sustained wind stress, although at the cost of a reduced reproductive fitness. In addition, this study gives support to the idea that intracanopy responses are conserved among closely related taxa evolving in different habitats, but experiencing a comparable limiting factor.  相似文献   

7.
Due to their restricted foraging range, flightless seabirds are ideal models to study the short-term variability in foraging success in response to environmentally driven food availability. Wind can be a driver of upwelling and food abundance in marine ecosystems such as the Southern Ocean, where wind regime changes due to global warming may have important ecological consequences. Southern rockhopper penguins (Eudyptes chrysocome) have undergone a dramatic population decline in the past decades, potentially due to changing environmental conditions. We used a weighbridge system to record daily foraging mass gain (the difference in mean mass of adults leaving the colony in the morning and returning to the colony in the evening) of adult penguins during the chick rearing in two breeding seasons. We related the day-to-day variability in foraging mass gain to ocean wind conditions (wind direction and wind speed) and tested for a relationship between wind speed and sea surface temperature anomaly (SSTA). Foraging mass gain was highly variable among days, but did not differ between breeding seasons, chick rearing stages (guard and crèche) and sexes. It was strongly correlated between males and females, indicating synchronous changes among days. There was a significant interaction of wind direction and wind speed on daily foraging mass gain. Foraging mass gain was highest under moderate to strong winds from westerly directions and under weak winds from easterly directions, while decreasing under stronger easterly winds and storm conditions. Ocean wind speed showed a negative correlation with daily SSTA, suggesting that winds particularly from westerly directions might enhance upwelling and consequently the prey availability in the penguins'' foraging areas. Our data emphasize the importance of small-scale, wind-induced patterns in prey availability on foraging success, a widely neglected aspect in seabird foraging studies, which might become more important with increasing changes in climatic variability.  相似文献   

8.
Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and airspeed to show only a marginal increase in strong winds. The swifts were often moving "backwards", heading straight into the wind but being overpowered by wind speeds exceeding their airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing.  相似文献   

9.
Abstract: Birds flying within windfarms can be killed when they collide with wind turbines. Raptors, especially red-tailed hawks (Buteo jamaicensis), are more susceptible to collisions than other birds, which may be attributable to their specific foraging and flight behavior. To more fully understand the problem, and to reduce raptor mortality, it is necessary to acquire more information on habitat use and flight behavior by raptors inhabiting windfarms. Between June 1999 and June 2000, we watched raptors for 346 hours in the Altamont Pass Wind Resource Area, the largest windfarm in North America. We recorded flight behavior in relation to characteristics of the topography such as slope aspect, elevation, and inclination and in relation to various weather variables including wind speed and wind direction. We found that red-tailed hawk behavior and their use of slope aspect differed according to wind speed. Hawks perched more often in weak winds than in strong. Red-tailed hawks were more likely to soar during low wind conditions and kite during strong wind, particularly on hillsides that faced into the wind as opposed to hillsides shielded from the wind. This is likely a result of their use of deflection updrafts for lift during flight. During our study, when winds were strong and from the south-southwest, kiting behavior occurred on south-southwestern facing slopes with inclines of greater than 20% and peak elevations greater than adjacent slopes. Accordingly, mitigation measures to decrease red-tailed hawk fatalities should be directed specifically to these areas and others fitting this general model. Wind farm managers can power down turbines at the top of these hazardous slopes when they pose the greatest danger—when winds are strong and facing perpendicularly to the slope.  相似文献   

10.
In this paper we describe fall nocturnal migration at three localities in eastern New York, one adjacent to the Hudson River, the other two 30 km to the west in a topographically more uniform area. Migrants at both study areas moved southwest in winds not out of the west and were, therefore, seemingly unaffected by the river. In west winds, however, birds away from the river moved south-southeast whereas those in the vicinity of the river flew a track west of south paralleling the river. In addition, a relative increase in the number of migrants along the river compared to away was observed in west winds as birds presumably became concentrated near the river. We conclude that on most autumn nights migrants passing through this area have a preferred track direction toward the southwest and in strong winds from the west and northwest they are drifted. Upon reaching the vicinity of the Hudson River, some birds alter their headings yielding a track direction that closely parallels the river resulting in at least a partial compensation for wind drift. No alternative hypothesis is consistent with all the data.  相似文献   

11.
Flight dynamics theories are influenced by two major topics: how birds adapt their flight to cope with heterogeneous habitats, and whether birds plan to use the wind field or simply experience it. The aim of this study was to understand the flight dynamics of free-flying Cory’s shearwaters in relation to the wind characteristics on the coastal upwelling region of continental Portugal. We deployed recently miniaturised devices—global positioning system loggers to collect precise and detailed information on birds’ positions and motions. Prevalent winds were blowing from the north-east and adults used those winds by adjusting their flight directions mainly towards north-west and south-west, flying with cross and tail winds, respectively, and avoiding head winds. This is confirmation that Cory’s shearwaters use a shear soaring flying strategy while exploiting the environment for food: adults foraged mainly with cross winds and their ground speed was not constant during all foraging trips as it changed dynamically as a result of the ocean surface shear winds. During travelling phases, ground speed was strongly influenced by the position of the bird with regard to the wind direction, as ground speed increased significantly with increasing tail wind component (TWC) values. Adults appear to choose foraging directions to exploit ambient wind, in order to improve shear soaring efficiency (cross winding) and exploit diurnal changes in tail wind strength to maximise commuting efficiency. We report, for the first time, precise ground speed values (GPS-derived data) and computed actual flight speed values (using TWC analysis) for Cory’s shearwater.  相似文献   

12.
How animals respond to varying environmental conditions is fundamental to ecology and is a question that has gained impetus due to mounting evidence indicating negative effects of global change on biodiversity. Behavioural plasticity is one mechanism that enables individuals and species to deal with environmental changes, yet for many taxa information on behavioural parameters and their capacity to change are lacking or restricted to certain periods within the annual cycle. This is particularly true for seabirds where year-round behavioural information is intrinsically challenging to acquire due to their reliance on the marine environment where they are difficult to study. Using data from over 13,000 foraging trips throughout the annual cycle, acquired using new-generation automated VHF technology, we described sex-specific, year-round activity budgets in Cape gannets. Using these data we investigated the role of weather (wind and rain) on foraging activity and time allocated to nest attendance. Foraging activity was clearly influenced by wind speed, wind direction and rainfall during and outside the breeding season. Generally, strong wind conditions throughout the year resulted in relatively short foraging trips. Birds spent longer periods foraging when rainfall was moderate. Nest attendance, which was sex-specific outside of the breeding season, was also influenced by meteorological conditions. Large amounts of rainfall (> 2.5 mm per hour) and strong winds (> 13 m s-1) resulted in gannets spending shorter amounts of time at their nests. We discuss these findings in terms of life history strategies and implications for the use of seabirds as bio-indicators.  相似文献   

13.
For procellariiform seabirds, wind and morphology are crucial determinants of flight costs and flight speeds. During chick‐rearing, parental seabirds commute frequently to provision their chicks, and their body mass typically changes between outbound and return legs. In Antarctica, the characteristic diurnal katabatic winds, which blow stronger in the mornings, form a natural experimental setup to investigate flight behaviors of commuting seabirds in response to wind conditions. We GPS‐tracked three closely related species of sympatrically breeding Antarctic fulmarine petrels, which differ in wing loading and aspect ratio, and investigated their flight behavior in response to wind and changes in body mass. Such information is critical for understanding how species may respond to climate change. All three species reached higher ground speeds (i.e., the speed over ground) under stronger tailwinds, especially on return legs from foraging. Ground speeds decreased under stronger headwinds. Antarctic petrels (Thalassoica antarctica; intermediate body mass, highest wing loading, and aspect ratio) responded stronger to changes in wind speed and direction than cape petrels (Daption capense; lowest body mass, wing loading, and aspect ratio) or southern fulmars (Fulmarus glacialoides; highest body mass, intermediate wing loading, and aspect ratio). Birds did not adjust their flight direction in relation to wind direction nor the maximum distance from their nests when encountering headwinds on outbound commutes. However, birds appeared to adjust the timing of commutes to benefit from strong katabatic winds as tailwinds on outbound legs and avoid strong katabatic winds as headwinds on return legs. Despite these adaptations to the predictable diurnal wind conditions, birds frequently encountered unfavorably strong headwinds, possibly as a result of weather systems disrupting the katabatics. How the predicted decrease in Antarctic near‐coastal wind speeds over the remainder of the century will affect flight costs and breeding success and ultimately population trajectories remains to be seen.  相似文献   

14.
Aeolian dunes controlled by regional climate have been formed in many coastal areas of the Mediterranean Sea during the Quaternary. Generally, they are formed under a landward-blowing wind, and comprise numerous reworked penecontemporaneous shallow-marine carbonate grains. Along the eastern mid-Adriatic Sea, late Pleistocene aeolian and alluvial sands occur as isolated patches in karstic depressions on several islands and the Pelje?ac Peninsula. At most localities, the sands consist of a mixture of mostly carbonate rock fragments and siliciclastic material. A higher proportion of shallow-marine bioclasts was found only at one locality. The terrestrial material was transported to the coastal area by at least two rivers: paleo-Cetina and paleo-Neretva River, and was subsequently reworked and transported by wind, resulting in aeolian deposition. Sandy units of various thicknesses exhibiting sharp erosional bedding planes and cross-bedding are interpreted as representing aeolian dunes and sand sheets controlled by a complex wind regime. The mineralogical composition at almost all localities indicates near-river flood plains as the main sand source. Although the area was affected by strong winds blowing landward and parallel to the coast, they significantly deviated due to the local topography produced by the tectonically deformed and karstified carbonate basement. In this way, the late Pleistocene aeolian deposits on the mid-Adriatic islands differ from deposits from most Quaternary Mediterranean coastal aeolian belts, as they contain very small quantities of penecontemporaneous shallow-marine carbonate grains and were deposited by winds blowing in varying directions instead of prevailing landward-blowing winds.  相似文献   

15.
To minimize the risk of colliding with the ground or other obstacles, flying animals need to control both their ground speed and ground height. This task is particularly challenging in wind, where head winds require an animal to increase its airspeed to maintain a constant ground speed and tail winds may generate negative airspeeds, rendering flight more difficult to control. In this study, we investigate how head and tail winds affect flight control in the honeybee Apis mellifera, which is known to rely on the pattern of visual motion generated across the eye—known as optic flow—to maintain constant ground speeds and heights. We find that, when provided with both longitudinal and transverse optic flow cues (in or perpendicular to the direction of flight, respectively), honeybees maintain a constant ground speed but fly lower in head winds and higher in tail winds, a response that is also observed when longitudinal optic flow cues are minimized. When the transverse component of optic flow is minimized, or when all optic flow cues are minimized, the effect of wind on ground height is abolished. We propose that the regular sidewards oscillations that the bees make as they fly may be used to extract information about the distance to the ground, independently of the longitudinal optic flow that they use for ground speed control. This computationally simple strategy could have potential uses in the development of lightweight and robust systems for guiding autonomous flying vehicles in natural environments.  相似文献   

16.
The interaction between different meteorological conditions recorded in Badajoz (SW Spain) over a 13-year period has been studied. The results were used for analysis of the effect of these conditions on atmospheric concentrations of Plantago and Brassicaceae pollen grain. For both types of pollen there was a positive effect of NE winds and a negative effect of SW winds which could not be explained by the location of the sources, because these species are very abundant all around the sampling station. The two effects were interpreted on the basis of the action of these winds on temperatures and relative humidity, because these conditions physically and biologically directly determine the concentrations of these types of pollen. Wind from the west is associated with an increase of wind speed and a decline in calm periods; wind from the south is associated with increased rainfall and humidity; wind from the opposite directions is associated with a decrease in these meteorological conditions. These main associations can explain the variation in pollen concentration, although there are also variations in seasons and years. These types of pollen also behave differently, so wind speed reduces the concentration of pollen from Plantago but increases it from Brassicaceae. Beyond the immediate application of the analysis to this specific case, there is a clear interest in observing the interaction between meteorological factors to gain a broader perspective for interpretation of the results of aerobiological studies aimed at determining the effect of these factors on the release and transport of particles into the air.  相似文献   

17.
Svend Th. Andersen 《Grana》2013,52(2-3):57-63
Pollen deposition in a mixed deciduous forest in South Jutland, Denmark, was studied by means of pollen analyses (Andersen, 1970) and pollen collectors. In this connection it was important to know the wind conditions outside and inside the forest. Wind velocities and wind directions in the flowering seasons were measured at 2 stations in a 3-year period. High wind velocities prevail above the forest in spring and summer. At such wind velocities the difference in loss of large and small pollen grains by filtration in the tree tops is reduced. The winds inside the forest tend to turn into the direction of easiest flow. The velocities are about 20% of the outside wind before and 12–15% after the leafing. Single pollen grains released from the trees will be carried wide distances before deposition in the spring, and it is suggested that the tree pollen falls to the ground rather in aggregates or included in rain-drops.  相似文献   

18.
Mechanical stability of trees under dynamic loads   总被引:3,自引:0,他引:3  
Tree stability in windstorms and tree failure are important issues in urban areas where there can be risks of damage to people and property and in forests where wind damage causes economic loss. Current methods of managing trees, including pruning and assessment of mechanical strength, are mainly based on visual assessment or the experience of people such as trained arborists. Only limited data are available to assess tree strength and stability in winds, and most recent methods have used a static approach to estimate loads. Recent research on the measurement of dynamic wind loads and the effect on tree stability is giving a better understanding of how different trees cope with winds. Dynamic loads have been measured on trees with different canopy shapes and branch structures including a palm (Washingtonia robusta), a slender Italian cypress (Cupressus sempervirens) and trees with many branches and broad canopies including hoop pine (Araucaria cunninghamii) and two species of eucalypt (Eucalyptus grandis, E. teretecornus). Results indicate that sway is not a harmonic, but is very complex due to the dynamic interaction of branches. A new dynamic model of a tree is described, incorporating the dynamic structural properties of the trunk and branches. The branch mass contributes a dynamic damping, termed mass damping, which acts to reduce dangerous harmonic sway motion of the trunk and so minimizes loads and increases the mechanical stability of the tree. The results from 12 months of monitoring sway motion and wind loading forces are presented and discussed.  相似文献   

19.
 Afternoon observations in summer comparing shoreline with inland atmospheric conditions were made during onshore winds at Victoria, British Columbia, Canada. The onshore wind came from a cool water surface. Mean monthly water temperatures near to shore were between 11 and 11.5° C. The onshore wind brought lower air, ground surface radiant and sky radiant temperatures; lower humidity and greater wind speed. All of these combine to produce a cooler human environment at the shoreline than inland. The relative importance of climatic elements in producing the cooler environment was assessed using sensitivity analyses with eight different human thermal exchange models/indices. Air temperature and wind speed had the greatest effect, followed by ground surface radiant temperature, sky radiant temperature and humidity. Wind speed is the most practical element to consider when trying to maximize human comfort along the shoreline. Received: 9 July 1996 / Revised: 31 March 1997 / Accepted: 14 April 1997  相似文献   

20.
It has been hypothesized that global warming will strengthen upwelling‐favorable winds in the Northern Humboldt Current System (NHCS) as a consequence of the increase of the land–sea thermal gradient along the Peruvian coast. The effect of strengthened winds in this region is assessed with the use of a coupled physical–biogeochemical model forced with projected and climatological winds. Strengthened winds induce an increase in primary production of 2% per latitudinal degree from 9.5°S to 5°S. In some important coastal upwelling sites primary production is reduced. This is due to a complex balance between nutrient availability, nutrient use efficiency, as well as eddy‐ and wind‐driven factors. Mesoscale activity induces a net offshore transport of inorganic nutrients, thus reducing primary production in the coastal upwelling region. Wind mixing, in general disadvantageous for primary producers, leads to shorter residence times in the southern and central coastal zones. Overall, instead of a proportional enhancement in primary production due to increased winds, the NHCS becomes only 5% more productive (+5 mol C m?2 year?1), 10% less limited by nutrients and 15% less efficient due to eddy‐driven effects. It is found that regions with a initial strong nutrient limitation are more efficient in terms of nutrient assimilation which makes them more resilient in face of the acceleration of the upwelling circulation.  相似文献   

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