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41.
42.
作者描述了产自塔里木盆地的HistiodellaHass的四个种,并探讨了它们与中国北方和北美中大陆暖水型牙形石及中国南方和北大西洋冷水型牙形石的对比关系。认为Histiodellasinuosa带对比北美中大陆牙形石动物群3的下部、中国南方Amorphognathusvariabilis带下部和中国北方Aurilobodusleptosomatus-Loxodusdissectus带下部。Histiodellaholodentata带下部相当于中国北方Aurilobodusleptosomatus-Loxodusdissectus带中部或中国南方的Amorphognathusvariabilis带至Eoplacognathussuecicus带的下部。Histiodellakristinae带对比北大西洋区的Eoplacognathussuecicus带中上部和中国北方的Tangshanodustangshanensis带。Histiodellabellburnensis带对比北大西洋区的Eoplacognathussuecicus带的上部到Eoplacognathusfoliaceus带下部。HistiodellaHass与北大西洋区和中国北方区典型牙形石的共同出现可以作为一个桥梁,建立起北美中大陆、北大西洋、塔里木盆地及华北地区牙形石的对比关系。 相似文献
43.
Peter J. Hancock 《Hydrobiologia》2006,568(1):255-262
Previous studies on recovery in hyporheic communities have found that communities rapidly return to pre-disturbance levels.
However, most of these studies have concentrated on small floods or ones with short return periods. I studied the impact of
a large 1 in 6 year flood on the hyporheic community at 2 sites in the Hunter River, a large coastal river in New South Wales
with a mean daily flow of 15 m3 s−1. The flood peaked at 1270 m3 s−1 and afterwards invertebrate densities at the 2 sites were 83 and 67% less than they were before. Recovery to pre-flood densities
was slow but was aided by increases in the oligochaete and cyclopoid populations. At Site 1, there was a boom in oligochaete
and cyclopoid numbers 61 d after the flood, but the communities resumed their pre-flood densities by Day 139. Recovery at
Site 2 took 139 d. Most groundwater taxa (stygobites) living in the hyporheic zone did not recover from the disturbance when
compared to non-stygobites. Apart from Microturbellaria and the harpacticoid Parastenocaris sp., numbers of all stygobite taxa continued to decline after the flood, becoming absent after 61 d. The poor recovery of
stygobites is probably due to their adaptations for survival in the relatively stable groundwater environment. This study
shows that hyporheic communities are sensitive to large bed-moving floods and supports the hypothesis that ecotonal species
with a strong affinity to one ecosystem can be poor at recovering from disturbances that occur in an adjacent ecosystem. 相似文献
44.
Hideyuki Doi Elena I. Zuykova Eisuke Kikuchi Shuichi Shikano Keiichi Kanou Natalia Yurlova Elena Yadrenkina 《Hydrobiologia》2006,571(1):395-400
We investigated spatial changes in the isotope ratios of the plankton food web in Lake Chany, Siberia, Russia, especially
at an estuarine transition zone of the lake. The δ13C values of particulate organic matter (POM) varied among the sampling sites, and increased with increasing pH of the lake
water. This may reflect a shift by phytoplankton from using CO2 to using bicarbonate for photosynthesis with increasing pH. The δ13C values of zooplankton community also changed at each site along with those of the POM. This was indicative of carbon isotope
changes of plankton food webs between the stations along an environmental gradient. 相似文献
45.
Tatiana A. Trifonova Ekaterina Y. Alkhutova 《International journal of phytoremediation》2016,18(12):1209-1220
This study considered the possibility of using plant community phytomass for the assessment of soil pollution with heavy metals (HM) from industrial wastes. The three-year-long field experiment was run under the regional natural meadow vegetation; the polymetallic galvanic slime was used as an industrial waste contaminant. It is shown that soil contamination primarily causes decrease of phytomass in the growing phytocenosis. The vegetation experiments determined nonlinear dependence of cultivated and wild plant biomass on the level of soil contamination; it is described by the equations of logistic and Gaussian regression. In the absence of permanent contaminants, the soil is self-cleaned over time. It reproduces phytomass mainly due to the productivity increase of the most pollution-tolerant species in the remaining phytocenosis. This phenomenon is defined as environmental hysteresis. Soil pollution by industrial waste leads to the loss of plant biodiversity. The research shows that the study of the HM impact on ecosystems is expedient given the consideration of the “soil–phytocenosis–pollutant” complex in the “dose–response” aspect. The reaction of phytocenosis on HM showing decline in phytomass leads to serious limitations in the choice of accumulating plants, because the adsorbed HM are rejected through phytomass. 相似文献
46.
SAD‐B kinase regulates pre‐synaptic vesicular dynamics at hippocampal Schaffer collateral synapses and affects contextual fear memory 下载免费PDF全文
47.
Diversity of plants in cocoa agroforests in the humid forest zone of Southern Cameroon 总被引:2,自引:1,他引:2
Denis J. Sonwa Bernard A. Nkongmeneck Stephan F. Weise Maturin Tchatat Akin A. Adesina Marc J. J. Janssens 《Biodiversity and Conservation》2007,16(8):2385-2400
In the humid forest zone of Southern Cameroon, farmers generally associate cocoa with native and exotic trees in complex agroforestry
systems. Despite the socio-economic and ecological importance of these systems, few studies have investigated their plant
composition. We investigated tree composition of cocoa agroforests along a gradient of market access, population density and
resource use intensity in the humid forest zone of southern Cameroon, comprising (i) the sub-region of Yaoundé, (ii) the sub-region
of Mbalmayo, and (iii) the sub-region of Ebolowa. Market access, population density and resource use intensity all decreased
from the first to the third sub-region. We quantified the diversity of tree species associated with cocoa within individual
agroforests, among agroforests in the same region, and among the three sub-regions, and classified the tree species according
to their main uses. A total of 9.1 ha belonging to 60 cocoa agroforests were inventoried in 12 villages. We encountered a
total of 206 tree species with an average of 21 tree species per agroforest. In the more urbanized area around Yaoundé, agroforests
were less diverse than in the other sub-regions. In all of the agroforests, food producing tree species tended to be more
frequent than other species. Two thirds of the food trees were native forest species and one third was introduced. From Ebolowa
to Yaoundé, the density of food producing trees doubled and the density of exotic food-producing species increased relative
to native species. Some local species producing high-value non-timber forest products were found in the agroforests, but their
density was far lower than that of exotic tree species. The agroforests also provide medicine, charcoal and other products
for household consumption and sale. We conclude that unless there are specific efforts to promote local forest tree species
in cocoa agroforests, these will progressively lose importance with increasing market access, population pressure and land
use intensity. 相似文献
48.
In northwestern Iberia, two largely allopatric Lacerta lepida mitochondrial lineages occur, L5 occurring to the south of Douro River and L3 to the north, with a zone of putative secondary contact in the region of the Douro River valley. Cytochrome b sequence chromatograms with polymorphisms at nucleotide sites diagnostic for the two lineages were detected in individuals in the region of the Douro River and further north within the range of L3. We show that these polymorphisms are caused by the presence of four different numts (I-IV) co-occurring with the L3 genome, together with low levels of heteroplasmy. Two of the numts (I and II) are similar to the mitochondrial genome of L5 but are quite divergent from the mitochondrial genome of L3 where they occur. We show that these numts are derived from the mitochondrial genome of L5 and were incorporated in L3 through hybridization at the time of secondary contact between the lineages. The additional incidence of these numts to the north of the putative contact zone is consistent with an earlier postglacial northward range expansion of L5, preceding that of L3. We show that genetic exchange between the lineages responsible for the origin of these numts in L3 after secondary contact occurred prior to, or coincident with, the northward expansion of L3. This study shows that, in the context of phylogeographic analysis, numts can provide evidence for past demographic events and can be useful tools for the reconstruction of complex evolutionary histories. 相似文献
49.
Mitochondrial DNA (mtDNA) is the traditional workhorse for reconstructing evolutionary events. The frequent use of mtDNA in such analyses derives from the apparent simplicity of its inheritance: maternal and lacking bi-parental recombination. However, in hybrid zones, the reproductive barriers are often not completely developed, resulting in the breakdown of male mitochondrial elimination mechanisms, leading to leakage of paternal mitochondria and transient heteroplasmy, resulting in an increased possibility of recombination. Despite the widespread occurrence of heteroplasmy and the presence of the molecular machinery necessary for recombination, we know of no documented example of recombination of mtDNA in any terrestrial wild vertebrate population. By sequencing the entire mitochondrial genome (16761bp), we present evidence for mitochondrial recombination in the hybrid zone of two mitochondrial haplotypes in the Australian frillneck lizard (Chlamydosaurus kingii). 相似文献
50.
Polly Campbell Lena Arvalo Heather Martin Charles Chen Shuzhen Sun Ashlee H. Rowe Michael S. Webster Jeremy B. Searle Bret Pasch 《Ecology and evolution》2019,9(22):12886-12896
Behavioral barriers to gene flow often evolve faster than intrinsic incompatibilities and can eliminate the opportunity for hybridization between interfertile species. While acoustic signal divergence is a common driver of premating isolation in birds and insects, its contribution to speciation in mammals is less studied. Here we characterize the incidence of, and potential barriers to, hybridization among three closely related species of grasshopper mice (genus Onychomys). All three species use long‐distance acoustic signals to attract and localize mates; Onychomys arenicola and Onychomys torridus are acoustically similar and morphologically cryptic whereas Onychomys leucogaster is larger and acoustically distinct. We used genotyping‐by‐sequencing (GBS) to test for evidence of introgression in 227 mice from allopatric and sympatric localities in the western United States and northern Mexico. We conducted laboratory mating trials for all species pairs to assess reproductive compatibility, and recorded vocalizations from O. arenicola and O. torridus in sympatry and allopatry to test for evidence of acoustic character displacement. Hybridization was rare in nature and, contrary to prior evidence for O. torridus/O. arenicola hybrids, only involved O. leucogaster and O. arenicola. In contrast, laboratory crosses between O. torridus and O. arenicola produced litters whereas O. leucogaster and O. arenicola crosses did not. Call fundamental frequency in O. torridus and O. arenicola was indistinguishable in allopatry but significantly differentiated in sympatry, a pattern consistent with reproductive character displacement. These results suggest that assortative mating based on a long‐distance signal is an important isolating mechanism between O. torridus and O. arenicola and highlight the importance of behavioral barriers in determining the permeability of species boundaries. 相似文献