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1.
We studied interactions between animal disturbance (geese, carp, and muskrat) and elevation in a field experiment in tidal freshwater marshes of the Patuxent River, Maryland, United States. Vegetation changes were recorded in fenced and unfenced plots in high and low marsh community types for 2 yr using measurements of areal cover and within-plot frequency (which were averaged to create a dominance index), Leaf Area Index (LAI), and aboveground biomass. We related light environment to differences in vegetation using below-canopy measurements of Photosynthetically Active Radiation (PAR). In the low marsh, total cover of all species, cover of annual species, biomass, and LAI were significantly higher in plots fenced to exclude animals (exclosures) than in unfenced plots (fenced/unfenced total cover=76/40%, annual cover=45/10%, biomass=936/352 g m?2, LAI=3.3/1.4). PAR was significantly lower in fenced than unfenced plots (fenced/unfenced=115/442 μmol s-1 m?2). Despite the strong effect of fencing on biomass, species richness per plot (i.e., the number of species per plot, or species density) was not affected significantly by fencing in the low marsh. Most of the observed differences in cover, biomass, LAI, and PAR were due to variation in the abundance of the herbaceous annual speciesBidens laevis (dominance index fenced/unfenced=45/10%) andZizania aquatica (30/12%). In the high marsh community, fencing had only minor effects on plant community composition and did not significantly affect species richness, cover, biomass, PAR, or LAI. Our results show that animals can dramatically affect low marsh vegetation, primarily via physical disturbance or herbivory of shallowly rooted seedlings of annual species. 相似文献
2.
Quin J. Kinler Robert H. Chabreck Noel W. Kinler R. G. Linscombe 《Estuaries and Coasts》1990,13(3):337-340
The effect of tidal flooding on survival of juvenile muskrats (Ondatra zibethicus) was investigated in a brackish marsh in Louisiana by examining 50 muskrat lodges each month from July 1984 to June 1985 and tidal data over a 19-yr period. Tide levels increased at a rate of 1.58 cm yr?1 during the 19-yr period prior to the study, and during the study nest chambers in muskrat lodges were flooded on 43 d. Seventy-seven captured litters averaged 2.2±0.3 young per litter. older litters were less common than younger litters, but the number of young per litter did not differ among 5-d age classes, suggesting that mortality factors usually affected entire litters. The frequency of tidal flooding prior to opening of lodges each month was associated negatively with the number of litters and number of young per litter. If marsh subsidence and sea level rise continue, tidal flooding will become more prevalent and litter mortality will likely increase. 相似文献
3.
It is becoming more apparent that commonly used statistical methods (e.g. analysis of variance and regression) are not the
best methods for estimating limiting relationships or stressor effects. A major challenge of estimating the effects associated
with a measured subset of limiting factors is to account for the effects of unmeasured factors in an ecologically realistic
matter. We used quantile regression to elucidate multiple stressor effects on end-of-season biomass data from two salt marsh
sites in coastal Louisiana collected for 18 yr. Stressor effects evaluated based on available data were flooding, salinity
air temperature, cloud cover, precipitation deficit, grazing by muskrat, and surface water nitrogen and phosphorus. Precipitation
deficit combined with surface water nitrogen provided the best two-parameter model to explain variation in the peak biomass
with different slopes and intercepts for the two study sites. Precipitation deficit, cloud cover, and temperature were significantly
correlated with each other. Surface water nitrogen was significantly correlated with surface water phosphorus and muskrat
density. The site with the larger duration of flooding showed reduced peak biomass, when cloud cover and surface water nitrogen
were optimal. Variation in the relatively low salinity occurring in our study area did not explain any of the variation inSpartina alterniflora biomass. 相似文献
4.
The muskrat (Ondatra zibethicus) is presumed to have undergone a rapid phyletic size decrease near the end of the Pleistocene. Evolutionary changes in the size of middle to late Wisconsinan (ca. 32,000–12,300 14C yr B.P.) muskrats from the Aucilla River, Jefferson County, Florida, were reconstructed by examining length and width of the lower first molar (m1). Body mass, estimated from m1 length, was relatively stable from 32,000 to 16,000 14C yr B.P. and decreased only slightly by 12,300 14C yr B.P. If the size trend found in the Aucilla River material is characteristic of the southeastern United States, a body size decrease after 12,300 14C yr B.P. is needed to explain the smaller size of modern populations. It was previously thought that the length/width (l/w) ratio of the muskrat m1 was a paleoenvironmental indicator based on its presumed correlation with latitude in modern populations. We examined the length and width of modern muskrats from several geographic regions and found only a very weak trend in the size of the m1 between northern and southern populations; however, highly significant differences were found between regions of similar latitude. Our data indicate that chronoclines in the m1 of the Aucilla muskrat material and other such documented trends among fossil muskrats have paleoenvironmental significance, but it is not yet clear which environmental variables can best be predicted from them. 相似文献
5.
Indoor radon mapping and its relation to geology in Hungary 总被引：2，自引：0，他引：2
Mihály Minda György Tóth István Horváth Ivan Barnet Krisztián Hámori Eszter Tóth 《Environmental Geology》2009,57(3):601-609
Indoor radon mapping may show stronger dependence on geological formations if the measured homes are one-storied houses with
no basement. In Hungary, 17,244 homes were investigated on the yearly average of indoor radon concentrations; among these
homes, there were 6,154, one-storied, no-basement houses. In Hungary, 21 geological units were created relevant for indoor
radon index characterized by lithology, the position of the ground water table, and the gas permeability. Maps were drawn
of different topography (counties, grid, geological units) and different values (maximum, mean, indoor radon indexes). A kind
of standardization of houses was that only the one-storied, no-basement ones were chosen, but from geological point of view some more information was gained when the wall materials (bricks or adobe) were also taken
into account. (“Adobe” is made of clay and straw in Hungary, and not burned as brick, just dried on sunshine). Enhanced indoor
radon values can be observed on the bedrock of Cenozoic volcanic rocks and their eroded materials deposited on the local alluvial
valleys. Another group with relatively increased indoor radon values can be connected to granite bodies. The grid method is
useful for covering large state or even continental areas. For practical public use and detailed radon risk mapping geological
or administrative unit-systems could yield more reasonable and useful results. 相似文献
6.
A.A. Kureshy 《Cretaceous Research》1980,1(2):93-100
The Cretaceous larger Foraminifera of Pakistan are restricted to the Upper Cretaceous belonging to the species of Orbitoides Lepidorbitoides, Omphalocyclus, and Siderolites. The species of these genera are quite distinct in comparison to other assemblages of the Tethys region. None of these species are identical in the Mediterranean or Caribbean regions, with the exception of few concordant species of Orbitoides recorded in the deep-sea cores of Bahama Island. The paleo-ecological factor is the most important consideration in paleogeographic distribution of the Upper Cretaceous larger Foraminifera. 相似文献
7.
Barrier islands are exposed to the wind and wave action from storms, which often disturbs both the geomorphology and vegetation. Conservation and restoration efforts for these important habitats could be improved with knowledge of how native plants respond to storms. We analyzed 10 years of annual data of vegetation of St. George Island, Florida, in the Gulf of Mexico, to quantify how the plant community responds to major storms and to predict which dune species might be appropriate for restoration after storm damage across dune zones. This prediction was tested with six plant species that differed in their storm response—from highly negative (local extinction in response to storms) to highly positive (increased abundance in response to storms). We measured transplant survival and growth (plant height and number of shoots) over 2 years in a restoration experiment across three major dune zones. We found that different species can be useful for restoration purposes in different dune zones, depending on both short- and longer-term management strategies. Uniola paniculata is a particularly strong restoration candidate across all dune zones, whereas Muhlenbergia capillaris and Schizachyrium maritimum would be beneficial for restoration in the interdune area. Fimbristylis spp. and Sporobolus virginicus demonstrate the strongest potential for restoration in the interdune and backdune areas. Restoration of disturbed areas often involves the seeding or transplanting of species to stabilize the landscape and initiate the return of the original vegetation. We show that the performance of native species, in response to storms, especially in conjunction with information on plant life history, can be useful for identifying the best species to use for restoration. 相似文献
8.
Zhuolun Li Nai’ang Wang Yu Li Zhenyu Zhang Mengna Li Chunyu Dong Rong Huang 《Environmental Earth Sciences》2013,68(1):1-12
Drinking water quality was investigated in seven rural villages surrounding Mount Kasigau in southeastern Kenya, where water is piped from unprotected dammed streams and springs in the Kasigau cloud forest down to taps, kiosks, and tanks in the villages. Analyses were conducted for nutrients, trace metals, and pathogen indicators in water from community taps, water stored in homes, and collection points along the pipelines up to catchment dams on the mountain. Water was relatively free from nutrient and trace-metal contamination; however, all samples were contaminated with total coliforms and nearly all were contaminated with Escherichia coli. There was no discernable pattern in the extent of contamination from the catchment dams to the villages. In each of three villages chosen for further study, six residents were selected for a more in-depth investigation. Water quality was generally worse in water stored in those homes compared to water collected at the village taps. The quality of drinking water in homes where treatment was applied was no better than in homes with no water treatment. The Kasigau villages, as many other areas in the developing world, need inexpensive and effective water treatment, as well as an assessment of the effectiveness of sanitary and hygienic practices. 相似文献
9.
《Cretaceous Research》2012,33(6):833-840
Nautilus subplicatus Steinmann, 1895 is a latest Cretaceous species of nautiloid which is common in southern South America (Chile, Argentina) and the Antarctic Peninsula and which is best assigned to the genus Eutrephoceras Hyatt, 1894. Nautilus dorbignyanus Forbes in Darwin, 1846 and Nautilus valenciennii Hupé in Gay, 1854 are here considered to be senior synonyms which later authors have apparently overlooked. The type material of these two taxa is reillustrated. On the basis of this and additional material it is demonstrated that only a single nautiloid species occurs in the Quiriquina Formation of late Maastrichtian age. For this we propose to use N. dorbignyanus as the oldest available name. 相似文献
10.
A thin phosphate-granule conglomerate within the Upper Cretaceous (middle Campanian) Rattlesnake Mountain sandstone member of the Aguja Formation preserves a diverse chondrichthyan and osteichthyan fauna. This highly fossiliferous deposit (the ‘Ten Bits Microsite’) yielded about 5000 teeth, spines, and denticles in a small amount of matrix (c. 150 kg). About 30 identifiable species of sharks, rays, and bony fishes are recognized. Two of the three most abundant chondrichthyan species at Ten Bits (Scapanorhynchus texanus and Ischyrhiza mira) are also the most common species in other middle to late Campanian marine vertebrate faunas along the Gulf and Atlantic Coastal Plain. The myliobatiform rays Brachyrhizodus and Rhombodus that occur at Ten Bits also appear to be characteristic of the Gulf and Atlantic Coast, as are lamniform sharks such as Cretalamna and Serratolamna. These taxa are entirely absent or extremely rare in Western Interior Campanian faunas. In contrast, some small orectolobiform sharks (Cantioscyllium, Chiloscyllium, Columbusia) and small rays (Protoplatyrhina) found at Ten Bits are common in shallow water faunas of the Western Interior and Texas Coastal Plain, but rarely reported from the eastern Gulf or Atlantic Coast. The common Western Interior ray Myledaphus bipartitus does not occur at Ten Bits or in any Gulf or Atlantic Coast fauna. Ptychotrygon agujaensis is abundantly represented in the Ten Bits fauna, but unknown in correlative marine faunas. Although Ptychotrygon occurs in all Western Interior, Gulf and Atlantic Coastal Plain faunas, it is represented elsewhere by apparently endemic species at each collection site. The differences between Western Interior, Gulf, and Atlantic Coastal Plain faunas probably reflect latitudinal variation in water temperature or salinity, or different oceanic water circulation patterns between the Western Interior Seaway and the Gulf or Atlantic Coast that restricted the distributions of some marine fish species. The Ten Bits fauna shares typical species with both Western Interior and Gulf and Atlantic Coast faunas, reflecting its position at the border between these provinces; however, the dominant taxa found at Ten Bits are the same as those found on the Gulf and Atlantic Coast, and indicate that western Texas was more closely allied biogeographically with that province than with the Western Interior of North America. One species tentatively identified in the Ten Bits fauna on the basis of a single tooth, Igdabatis cf. I. indicus, is otherwise known only from southern Europe and Asia, although a similar large myliobatid ray also occurs rarely in Texas Coastal Plain faunas. These occurrences indicate that western Texas may have been near the northern limit of the range for some tropical Tethyan marine vertebrate species. 相似文献
11.
Lichen distribution and growth were examined at several sites in the Canadian Rockies between Mt. Robson and Banff townsite to determine the feasibility of lichenometry on calcareous deposits. The only lichen common enough to be of use is Xanthoria elegans, a bright orange lichen with round or elliptical thalli. It is not an ideal species for lichenometry because (a) it grows fairly quickly and has a range of only a few centuries, (b) growth is influenced by the presence of animal dung, (c) parts of some thalli weather away before maximum size is attained, (d) thalli may thicken as well as grow laterally with age, (e) the species is succeeded by other species relatively quickly in heavily forested environments, and (f) the species is not abundant on some deposits due to sometimes-unexplained environmental influences. However, when used with caution the species is still useful for dating purposes.A growth curve for Xanthoria elegans was developed using moraines dated dendro-chronologically and man-made structures. After an ecesis interval of one or two decades the lichen grows at a rate of 0.68 mm/yr for several decades, then slows down to a rate of 0.22 mm/yr. 相似文献
12.
The genus Debrunia is characterized by its myophoral organisation: the left valve posterior myophore is an erect plate, the anterior is a bulge or a crest, myophores of right valve are on shell wall, the ligament groove is inconspicuous and the cardinal apparatus tends to be shifted posteriorly. Shell habit varies from low conical to elongated cylindrical, and the shape of the left valve ranges from capuloid to flat. The taxonomic revision of Debrunia species of the Mediterranean regions reveals the presence of thirteen species, among which seven are described as new. Multiple Component Analysis and Cluster Analysis document the existence of five groups of species in correspondence with the height of the left valve and the commissural diameter. The longevity of Debrunia is high, 32 Myr, whereas its species have shorter durations which account for a significant biostratigraphic potential within the Valanginian–Albian time span. Debrunia has its FO (First occurrence) in the lower Valanginian and its LO (Last occurrence) in the Albian. Its developmental phase starts in the Hauterivian, marked by an increasing species diversity and a biogeographic expansion; and peaks in the late Barremian, followed by a collapse in diversity and a specific turnover, coeval with the “Agriopleura extinction event”. The mid-Aptian crisis is expressed by a drastic decline in species diversity, controlled by the overall restriction or demise of carbonate platforms in European regions. As elevators, Debrunia species tend to build dense monospecific aggregations and some of them possess a remarkable bioconstructional potential. The contribution of Debrunia to rudist communities is significant throughout the history of the genus. 相似文献
13.
Nesting colonial waterbirds along the Atlantic Coast of the United States face a number of landscape-level threats including human disturbance, mammalian predator expansion, and habitat alteration. There have been changes from 1977 to the mid-1990s in use of nesting habitats and populations of a number of seabird species of concern in the region, including black skimmersRynchops niger Linnaeaus, common ternsSterna hirundo Linnaeaus, gull-billed ternsSterna nilotica Linnaeaus, least ternsSterna antillarum Lesson, royal ternsSterna maxima Boddaert, and sandwich ternsSterna sandvicensis Cabot. These species form colonies primarily on the following habitat types: large, sandy barrier or shoal islands, natural estuarine or bay islands (mostly marsh) man-made islands of dredged deposition materials (from navigation channels), and the mainland. Significant changes in the use of the dredged material islands have occurred for these species in New Jersey and North Carolina, but not in Virginia. Population declines and changes in bird habitat use appear to be at least partially associated with the conditions and management of the existing dredged material islands, coastal policy changes associated with creating new dredged material islands, and competing demands for sand for beach augmentation by coastal communities. As these and other coastal habitats become less suitable for colonial waterbirds, other man-made sites, such as, bridges and buildings have become increasingly more important. In regions with intense recreational demands, coastal wildlife managers need to take a more aggressive role in managing natural and man-made habitats areas and as stakeholders in the decision-making process involving dredged materials and beach sand allocation. 相似文献
14.
H. L. Carson 《GeoJournal》1983,7(6):543-547
The Hawaiian Drosophila project has been in progress for 20 years. Recently, emphasis has been placed on studies of genetic variability in natural populations. The data generated are of extraordinary interest for understanding the genetic basis of evolution. The findings are relevant not only to islands forms but also to species in continental ecosystems. Chromosomal, electrophoretic and morphometric studies of specimens from local populations (demes) of island species have shown them generally to be as rich in genetic variability as demes of widespread continental species. The main difference between continntal and insular species is that the latter have smaller total population sizes insular species have fewer demes. On high volcanic islands, the most striking mode of speciation is through one or a few inter-island or inter-volcano founders. The case of Drosophila silvestris from the island of Hawaii is presented. Enforced isolation appears to foster genetic divergence. An unexpected results is that the founder effect does not drasticaly reduce genetic variablity. Rather, it appears to induce a shift in the polygenic heterozygous balances that underlie the genetics of quantitative characters, especially those dealing with mating behavior.In view of these findings, the well-known exuberance of novel adaptations and species observed on isolated oceanic islands is understandable. 相似文献
15.
During the 1992 spawning season of river herring, three sites in a tributary of the Rappahannock River, Virginia, were studied to characterize spawning and nursery habitats of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) and to identify differences in habitat use along an upstream to downtream gradient. The sites were sampled (using drift and dip nets and a plankton sampler) and habitat variables were measured on a 5-d, four-time interval rotation: at the end of 5 d, each site had been sampled once at dawn, noon, dusk, and midnight. Considerable non-overlap in spawning seasonality was apparent between species. For both species, densities of river herring adults, eggs, and yolk-sac larvae were highest at the upstream site, indicating 1) that the upstream site is more important for spawning than downstream areas, and 2) these species do not use different spawning areas in this stream. Densities of post-yolk-sac larvae did not differ significantly among sites, indicating post-spawning dispersal to downstream areas. The upstream site was smaller in area, more acidic, had faster water flow, clearer water, more vegetation, and siltier substrate than the downstream sites. At times, pH levels in the upstream site were within the lethal range reported for blueback herring larvae. Possible reasons for selection of the upstream habitat include: 1) adults may migrate as far upstream as possible to avoid predation or potential competition with other species of fish for spawning habitat; or 2) adults may historically enjoy greater spawning success in the upstream habitat due to physicochemical features of this area. More study is needed to determine the reasons for river herring use of upstream habitats in Virginia streams. 相似文献
16.
17.
The authors reassessed the taxonomic distinction of Iteravis huchzermeyeri and Gansus zheni, which are two species of Ornithuromorpha based on specimens from the same locality in western Liaoning and derive from the Jehol Biota. The detailed comparisons of the holotype and referred specimens of both species, reveal no anatomical features that distinguish these taxa as separate species. Some minor differences are considered to relate to ontogenetic or interspecific differences. The stratigraphic occurrence for both specimens is the Lower Cretaceous Jiufotang Formation. Accordingly, the authors conclude that Iteravis huchzermeyeri has priority, by 15 days, for this taxon and that Gansus zheni is a junior synonym. The diagnosis of Iteravis huchzermeyeri is revised based on further study on all specimens referred to this species. Its generic distinction from Gansus is maintained thereby removing a potential genus-level correlation linking Xiagou Formation in Gansu Province with the Jiufotang Formation in Liaoning Province. 相似文献
18.
Mohammed Gameil Franz T. Fürsich Mohammed H. Mandurah 《Arabian Journal of Geosciences》2013,6(11):4271-4278
Genus Polyphylloseris is a scleractinian colonial coral that has been established by d’Orbigny (1849) from the Neocomian of Yonne, France. The genus is characterized by having elevated domal calices that are mammillar or craterlike in shape and with porous confluent septa. Columella is absent or rudimentary, and the lower surface of the corallum is covered with a thick and wrinkled holotheca. Specimens having the above-mentioned characteristics have been collected from the Upper Jurassic Arousiah Member of the Masajid Formation (Callovian–Oxfordian) of Gebel Maghara, Northern Sinai, Egypt. They are characterized by having a cupolate colonial form and porous pennulate septa which reach 40–50 in number. Based on these characters and other characters such as density of septa, height, and width of mammillar calices, the studied material is attributed to a new species named Polyphylloseris magharensis. The new species is a first undoubted record of Polyphylloseris in the Jurassic. Previously recorded undoubted ages of the genus are Early and Late Cretaceous. The fewer number of septa and the smaller-sized and closer mammillar calices allow differentiation of the species from other species such as Polyphylloseris icaunensis d’Orbigny and Polyphylloseris convexa d’Orbigny. 相似文献
19.
Coastal wetlands worldwide have been negatively impacted by humans, causing decreases in the vegetation used as a refuge from predation by juveniles of many species. This study examined juvenile fiddler crab densities and species composition (Uca pugnax, Uca pugilator, and Uca minax), and their use of gastropod shells (Littorina littoraria), at three low and three high impact sites on barrier islands in southeast Georgia. On six dates in June–August 2010, samples were taken from 10 quadrats (1 m2) at each site to determine juvenile fiddler crab densities and species composition, as well as gastropod shell densities and percent shell use. Multiplex PCR was used to identify juvenile fiddler crabs to species. Juvenile fiddler crab densities were lower at high impact sites, while gastropod shell densities and shell use were similar at both low and high impact sites. Species compositions differed between low and high impact sites on the substrate and in shells, with more U. pugilator and U. minax at high impact sites. A change in fiddler crab densities and species composition could cause a substantial change in southeastern salt marshes. 相似文献
20.
Eric Dowty 《Physics and Chemistry of Minerals》1987,14(1):67-79
A fully automated method for computing frequencies and atomic displacements of normal modes, giving synthetic infrared and Raman spectra, has been developed for use on small computers. No expertise in group theory or the mathematics of normal-mode calculation are required to use the computer program. The method takes full account of symmetry and is applicable to any crystal or molecule. Force constants can be specified in terms of any two-atom “bonds” or three-atom angles. The essential steps in the computer program are: (1) Locate all atoms in the unit cell or molecule and compute displacement vectors for each internal coordinate; (2) Convert the basis of the force constants from bonds and angles to cartesian displacements; (3) Construct the full-matrix irreducible representations of the point or factor group in question, using appropriate symmetry matrices and polynomial basis functions; (4) Derive the symmetry coordinates in terms of cartesian displacements using the projection/transfer-operator technique; (5) construct secular equations for each species with Wilson's f–g method; (6) solve for frequencies and atomic motions; and (7) use simple models of infrared and Raman intensities to calculate spectra. 相似文献