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101.
Seasonal clutch size variation of multi-brooded bird species: comparisons between breeding season and latitudes 总被引:2,自引:0,他引:2
Single- and multi-brooded species of birds differ in their seasonal patterns of clutch size. Single-brooded species start with a maximum clutch size that declines continuously as the season progresses, whereas the clutch sizes of multi-brooded species usually increase to a mid-season maximum peak and then decrease progressively until the end of the breeding season. Previous studies have shown that multi-brooded migrant species present seasonal patterns that are similar to single-brooded species at high latitudes but similar to multi-brooded non-migratory species at lower latitudes. We studied the Greenfinch Carduelis chloris and Goldfinch C. carduelis populations in eastern Spain (Sagunto, Valencia) between 1975 and 2002 to compare seasonal variations in clutch sizes between years with early and late starts to the breeding season. The period over which clutch sizes increase was longer when the breeding season started earlier. The Goldfinch population showed no pattern of initial increase in clutch size when there was a late start to the breeding season: a late start shortens the season giving them less time to breed, and may also coincide with maximum food availability. Thus, the pattern of single-brooded species was observed. In the Greenfinch population, a trend toward the seasonal pattern of single-brooded species was also observed when the following indices were compared: clutch size increase, modal timing, initial slope and timing of maximum clutch size. We have also compared the seasonal patterns of clutch size of both species in eastern Spain with the patterns observed in Britain. Our results show that for both Goldfinches and Greenfinches, the non-migrant southern populations of Sagunto in eastern Spain do not tend towards a more multi-brooded seasonal pattern of clutch size than the migrant Goldfinches of Britain. 相似文献
102.
THOMAS SERVAIS OLIVER LEHNERT JUN LI GARY L. MULLINS AXEL MUNNECKE ALEXANDER NÜTZEL MARCO VECOLI 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2008,41(2):99-109
The Early Palaeozoic phytoplankton (acritarch) radiation paralleled a long-term increase in sea level between the Early Cambrian and the Late Ordovician. In the Late Cambrian, after the SPICE δ13 Ccarb excursion, acritarchs underwent a major change in morphological disparity and their taxonomical diversity increased to reach highest values during the Middle Ordovician (Darriwilian). This highest phytoplankton diversity of the Palaeozoic was possibly the result of palaeogeography (greatest continental dispersal) and major orogenic and volcanic activity, which provided maximum ecospace and large amounts of nutrients. With its warm climate and high atmospheric CO2 levels, the Ordovician was similar to the Cretaceous: a period when phytoplankton diversity was at its maximum during the Mesozoic. With increased phytoplankton availability in the Late Cambrian and Ordovician a radiation of zooplanktonic organisms took place at the same time as a major diversification of suspension feeders. In addition, planktotrophy originated in invertebrate larvae during the Late Cambrian–Early Ordovician. These important changes in the trophic chain can be considered as a major palaeoecological revolution (part of the rise of the Palaeozoic Evolutionary Fauna of Sepkoski). There is now sufficient evidence that this trophic chain revolution was related to the diversification of the phytoplankton, of which the organic-walled fraction is partly preserved. 相似文献
103.
Coralliophilid gastropods include a large number of described
species,grouped in at least seven to 10 'genera' according to their
shellmorphology. They are considered closely related to Muricidaeand
ranked as a family on its own or as a subfamily of muricids.Their
phylogenetic position and relationships are still notdefined. The
little anatomical work so far done on this groupseems to indicate a
relatively high level of homogeneity, atleast in the alimentary
system. There is a need for an independentphylogenetic framework to
understand their position and relationshipwithin the muricoideans,
and their internal systematics andphylogeny. We have addressed this
problem by means of parsimonyanalysis of 609 aligned positions of the
sequences coding forthe 12S rDNA. Four coralliophilid sequences
representing thesame number of commonly recognized lineages
(Babelomurex, Latiaxis,Coralliophila, Galeropsis = Quoyula) were
analysed, along withthree sequences of muricoid genera (Stramonita,
Phyllonotus,Nucella) representing as many subfamilies of Muricidae,
plusthe sequence of the buccinoidean Fasciolaria as outgroup. Maximum
parsimonyand neighbour-joining analysis of the dataset, with
increasingweighing of transversions versus transitions, yielded
similartopologies. Two major outcomes resulted from the analyses:
first,the coralliophilid sequences included herein are always
monophyletic,with very high bootstrap support in all analyses. This
is inagreement with the few anatomical data gathered so far that
suggestcoralliophilids are relatively homogeneous. Secondly, the
sister-groupof the coralliophilids among the analysed sequences is
representedby Stramonita, with high bootstrap support in all
analyses.This is in a good agreement with previous molecular analyses
andwith the morphological evidence that Rapaninae are the closest
sistergroup of coralliophilids. According to the present results,the
rank of the coralliophilids should be the same as Rapaninae,therefore
a subfamilial status (Coralliophilinae) seems reasonable. (Received 14 August 2000; accepted 30 October 2000) 相似文献
104.
105.
106.
Ozone induced emissions of biogenic VOC from tobacco: relationships between ozone uptake and emission of LOX products 总被引:5,自引:0,他引:5
JONATHAN BEAUCHAMP ARMIN WISTHALER ARMIN HANSEL EINHARD KLEIST MARCO MIEBACH ÜLO NIINEMETS ULI SCHURR & JÜRGEN WILDT 《Plant, cell & environment》2005,28(10):1334-1343
Volatile organic compound (VOC) emissions from tobacco ( Nicotiana tabacum L. var. Bel W3) plants exposed to ozone (O3 ) were investigated using proton-transfer-reaction mass-spectrometry (PTR-MS) and gas chromatography mass-spectrometry (GC-MS) to find a quantitative reference for plants' responses to O3 stress. O3 exposures to illuminated plants induced post-exposure VOC emission bursts. The lag time for the onset of volatile C6 emissions produced within the octadecanoid pathway was found to be inversely proportional to O3 uptake, or more precisely, to the O3 flux density into the plants. In cases of short O3 pulses of identical duration the total amount of these emitted C6 VOC was related to the O3 flux density into the plants, and not to ozone concentrations or dose–response relationships such as AOT 40 values. Approximately one C6 product was emitted per five O3 molecules taken up by the plant. A threshold flux density of O3 inducing emissions of C6 products was found to be (1.6 ± 0.7) × 10−8 mol m−2 s−1 . 相似文献
107.
MARCO ALBANI DAVID MEDVIGY GEORGE C. HURTT† PAUL R. MOORCROFT 《Global Change Biology》2006,12(12):2370-2390
Atmospheric measurements and land‐based inventories imply that terrestrial ecosystems in the northern hemisphere are taking up significant amounts of anthropogenic cabon dioxide (CO2) emissions; however, there is considerable disagreement about the causes of this uptake, and its expected future trajectory. In this paper, we use the ecosystem demography (ED) model to quantify the contributions of disturbance history, CO2 fertilization and climate variability to the past, current, and future terrestrial carbon fluxes in the Eastern United States. The simulations indicate that forest regrowth following agricultural abandonment accounts for uptake of 0.11 Pg C yr?1 in the 1980s and 0.15 Pg C yr?1 in the 1990s, and regrowth following forest harvesting accounts for an additional 0.1 Pg C yr?1 of uptake during both these decades. The addition of CO2 fertilization into the model simulations increases carbon uptake rates to 0.38 Pg C yr?1 in the 1980s and 0.47 Pg C yr?1 in the 1990s. Comparisons of predicted aboveground carbon uptake to regional‐scale forest inventory measurements indicate that the model's predictions in the absence of CO2 fertilization are 14% lower than observed, while in the presence of CO2 fertilization, predicted uptake rates are 28% larger than observed. Comparable results are obtained from comparisons of predicted total Net Ecosystem Productivity to the carbon fluxes observed at the Harvard Forest flux tower site and in model simulations free‐air CO2 enrichment (FACE) experiments. These results imply that disturbance history is the principal mechanism responsible for current carbon uptake in the Eastern United States, and that conventional biogeochemical formulations of plant growth overestimate the response of plants to rising CO2 levels. Model projections out to 2100 imply that the carbon uptake arising from forest regrowth will increasingly be dominated by forest regrowth following harvesting. Consequently, actual carbon storage declines to near zero by the end of the 21st century as the forest regrowth that has occurred since agricultural abandonment comes into equilibrium with the landscape's new disturbance regime. Incorporating interannual climate variability into the model simulations gives rise to large interannual variation in regional carbon fluxes, indicating that long‐term measurements are necessary to detect the signature of processes that give rise to long‐term uptake and storage. 相似文献
108.
MARCO AVANZINI LAURA PIÑUELA JOSÉ CARLOS GARCÍA‐RAMOS 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2012,45(2):238-252
Avanzini, M., Piñuela, L. & García‐Ramos, J.C. 2011: Late Jurassic footprints reveal walking kinematics of theropod dinosaurs. Lethaia, Vol. 45, pp. 238–252. This study describes a set of theropod footprints collected from the Late Jurassic Lastres Formation (Asturias, N Spain). The footprints are natural casts (tracks and undertracks) grouped into three morphotypes, which are characterized by different size frequency, L/W relationship and divarication angles: ‘Grallatorid’ morphotype, ‘Kayentapus–Magnoavipes’ morphotype, ‘Hispanosauropus’ morphotype. The tracks were produced in firm, stiff and soft sediments. The infills of deep tracks, which are typically formed in soft mud, lack fine anatomical details, but they can reveal the walk kinematics of the trackmaker through the morphology of internal track fills and sinking traces. In all footprints, a horizontal outwardly directed translation movement and rotation are recognizable. The amount and geometry of digit penetration in the ground also show a pronounced difference. It can be inferred from the described sample that different theropoda‐related ichnogenera share common kinematics. □Asturias, dinosaur footprint, late jurassic, theropods, walking kinematics. 相似文献
109.
Sugar demand of ripening grape berries leads to recycling of surplus phloem water via the xylem 下载免费PDF全文
MARKUS KELLER YUN ZHANG PRADEEP M. SHRESTHA MARCO BIONDI BHASKAR R. BONDADA 《Plant, cell & environment》2015,38(6):1048-1059
We tested the common assumption that fleshy fruits become dependent on phloem water supply because xylem inflow declines at the onset of ripening. Using two distinct grape genotypes exposed to drought stress, we found that a sink‐driven rise in phloem inflow at the beginning of ripening was sufficient to reverse drought‐induced berry shrinkage. Rewatering accelerated berry growth and sugar accumulation concurrently with leaf photosynthetic recovery. Interrupting phloem flow through the peduncle prevented the increase in berry growth after rewatering, but interrupting xylem flow did not. Nevertheless, xylem flow in ripening berries, but not berry size, remained responsive to root or shoot pressurization. A mass balance analysis on ripening berries sampled in the field suggested that phloem water inflow may exceed growth and transpiration water demands. Collecting apoplastic sap from ripening berries showed that osmotic pressure increased at distinct rates in berry vacuoles and apoplast. Our results indicate that the decrease in xylem inflow at the onset of ripening may be a consequence of the sink‐driven increase in phloem inflow. We propose a conceptual model in which surplus phloem water bypasses the fruit cells and partly evaporates from the berry surface and partly moves apoplastically to the xylem for outflow. 相似文献
110.
Characters associated with the mandibular canal are differently distributed amongst proboscidean lineages and provide useful information on the systematics and relationships of proboscideans. The aim of this paper is to describe the pattern of the mandibular canal and its associated foramina in proboscideans in order to fully appreciate the extent of interspecific variation of these structures within the group and to discuss its systematic and phylogenetic value. Outgroup comparison indicates that the condition presented by the basal proboscidean Phosphatherium is morphotypic for proboscideans. Primitive proboscidean characters are: the low position of the mandibular foramen, and its crescent‐shaped outline, the occurrence of a coronoid foramen (canal), the occurrence of two lateral mental foramina, the posterior one at the level of (or slightly behind) the posterior margin of the symphysis, the anterior one in a more distal position, the absence of a medial mental foramen (MMF), the mandibular canal set just below the tooth row. The occurrence of a single lateral mental foramen may represent a shared derived character of Daouitherium, Numidotherium, and Barytherium. A unique derived feature of the Elephantinae mandible is the occurrence of a medial mental foramen on the medial side of the incisive part of the mandible. MMFs have never been observed in other proboscideans excluding elephantines. The very high frequency of MMFs observed in Mammuthus meridionalis–Mammuthus trogontherii–Mammuthus primigenius (>93 per cent of the studied specimens) could be considered a synapomorphy of this group. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 391–413. 相似文献