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91.
Much of community-ecology theory describes (or even assumes) constraints on the coexistence of species. These constraints are often described using functional characters as an index to the niche of the species. The hypothesis/assumption is that those species which are too similar in functional characters, and hence in niche, cannot coexist. However, this body of theory is rarely tested. We attempted a test by making a prediction of texture convergence that follows logically from the theory, yet is simple enough to test – one based on similarity of ecological assembly between the patches of a community. We used replicate quadrats within twelve herbaceous communities. Eleven characters were measured, that were intended to reflect the functional above-ground niche of the species. We examined each character in turn, to test for ecological convergence to a similar mean within each community, with species either weighted equally (i.e. using species presence) or weighted by their biomass. Convergence with species weighted by their biomass was seen in chlorophyll content, indicating a significant tendency for each patch in a community to comprise a rather constant mixture of species types in terms of their different chlorophyll contents. In terms of species presence, texture divergence occurred in leafiness (LAR), specific leaf area (SLA) and leaf inclination, i.e. there was more variation between quadrats within a site than expected at random. However, significant results were sparse: the bulk of evidence is for no significant departure from a null model, i.e. no support for a widespread body of ecological theory. 相似文献
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93.
Here, we review progress and prospects to explicitly test for long distance dispersal biogeographic events. Long distance dispersal represents a “jump” across some kind of barrier, such as a topographic feature or a zone of unsuitable climate and may include repeated jumps, or stepping‐stone dispersals. Long distance dispersals were considered integral for explaining the organization of biodiversity at large and small scales by early biogeographers, such as Darwin and Wallace. Darwin, Wallace, and others envisioned that long distance dispersals were predictable events because the vectors for dispersal, such as animals, winds, and currents, behaved in non‐random ways. However, these early biogeographers found that dispersal was hard to observe, and, later, with the advent of the theory of Continental Drift, vicariance became regarded as a better scientific explanation for the arrangement of biodiversity, because it represented a falsifiable hypothesis. Thus, long distance dispersal was reduced to a nuisance parameter in biogeography; a random possibility that could never fully be ruled out in a scenario in which evidence supported vicariance. Today, there is strong interest to more fully integrate long distance dispersal into understanding the assembly and organization of biodiversity on earth. In this review, we discuss progress and prospects for explicitly testing long distance dispersal hypotheses including through uses of molecular, morphological, paleontological, and informatics methods. We focus on hypothesis testing of long distance dispersals involved in the assembly of the flora of North America, which is a robust preliminary study system on account of its extant and extinct biodiversity being well‐catalogued. 相似文献
94.
95.
Jun Wen AJ Harris Yash Kalburgi Ning Zhang Yuan Xu Wei Zheng Stefanie M. Ickert-Bond Gabriel Johnson Elizabeth A. Zimmer 《植物分类学报:英文版》2018,56(4):297-308
Vitis L. (the grape genus) is the economically most important fruit crop, as the source of grapes and wine. Phylogenetic relationships within the genus have been highly controversial. Herein, we employ sequence data from whole plastomes to attempt to enhance Vitis phylogenetic resolution. The results support the New World Vitis subgenus Vitis as monophyletic. Within the clade, V. californica is sister to the remaining New World Vitis subgenus Vitis. Furthermore, within subgenus Vitis, a Eurasian clade is robustly supported and is sister to the New World clade. The clade of Vitis vinifera ssp. vinifera and V. vinifera ssp. sylvestris is sister to the core Asian clade of Vitis. Several widespread species in North America are found to be non‐monophyletic in the plastome tree, for example, the broadly defined Vitis cinerea and V. aestivalis each needs to be split into several species. The non‐monophyly of some species may also be due to common occurrences of hybridizations in North American Vitis. The classification of North American Vitis by Munson into nine series is discussed based on the phylogenetic results. Analyses of divergence times and lineage diversification support a rapid radiation of Vitis in North America beginning in the Neogene. 相似文献
96.
97.
Series resistance compensation for whole-cell patch-clamp studies using a membrane state estimator 总被引:2,自引:0,他引:2 下载免费PDF全文
Whole-cell patch-clamp techniques are widely used to measure membrane currents from isolated cells. While suitable for a broad range of ionic currents, the series resistance (R(s)) of the recording pipette limits the bandwidth of the whole-cell configuration, making it difficult to measure rapid ionic currents. To increase bandwidth, it is necessary to compensate for R(s). Most methods of R(s) compensation become unstable at high bandwidth, making them hard to use. We describe a novel method of R(s) compensation that overcomes the stability limitations of standard designs. This method uses a state estimator, implemented with analog computation, to compute the membrane potential, V(m), which is then used in a feedback loop to implement a voltage clamp; we refer to this as state estimator R(s) compensation. To demonstrate the utility of this approach, we built an amplifier incorporating state estimator R(s) compensation. In benchtop tests, our amplifier showed significantly higher bandwidths and improved stability when compared with a commercially available amplifier. We demonstrated that state estimator R(s) compensation works well in practice by recording voltage-gated Na(+) currents under voltage-clamp conditions from dissociated neonatal rat sympathetic neurons. We conclude that state estimator R(s) compensation should make it easier to measure large rapid ionic currents with whole-cell patch-clamp techniques. 相似文献
98.
MG Mullender NA Blom M De Kleuver JM Fock WMGC Hitters AMC Horemans CJ Kalkman JEH Pruijs RR Timmer PJ Titarsolej NC Van Haasteren Tol-de MJ Van Jager AJ Van Vught BJ Van Royen 《Scoliosis》2008,3(1):1-14
Background
Children with neuromuscular disorders with a progressive muscle weakness such as Duchenne Muscular Dystrophy and Spinal Muscular Atrophy frequently develop a progressive scoliosis. A severe scoliosis compromises respiratory function and makes sitting more difficult. Spinal surgery is considered the primary treatment option for correcting severe scoliosis in neuromuscular disorders. Surgery in this population requires a multidisciplinary approach, careful planning, dedicated surgical procedures, and specialized after care.Methods
The guideline is based on scientific evidence and expert opinions. A multidisciplinary working group representing experts from all relevant specialties performed the research. A literature search was conducted to collect scientific evidence in answer to specific questions posed by the working group. Literature was classified according to the level of evidence.Results
For most aspects of the treatment scientific evidence is scarce and only low level cohort studies were found. Nevertheless, a high degree of consensus was reached about the management of patients with scoliosis in neuromuscular disorders. This was translated into a set of recommendations, which are now officially accepted as a general guideline in the Netherlands.Conclusion
In order to optimize the treatment for scoliosis in neuromuscular disorders a Dutch guideline has been composed. This evidence-based, multidisciplinary guideline addresses conservative treatment, the preoperative, perioperative, and postoperative care of scoliosis in neuromuscular disorders. 相似文献99.
Phylogenetic relationships within the Alcidae (Charadriiformes: Aves) inferred from total molecular evidence 总被引:3,自引:1,他引:3
The Alcidae is a unique assemblage of Northern Hemisphere seabirds that
forage by "flying" underwater. Despite obvious affinities among the
species, their evolutionary relationships are unclear. We analyzed
nucleotide sequences of 1,045 base pairs of the mitochondrial cytochrome b
gene and allelic profiles for 37 allozyme loci in all 22 extant species.
Trees were constructed on independent and combined data sets using maximum
parsimony and distance methods that correct for superimposed changes.
Alternative methods of analysis produced only minor differences in
relationships that were supported strongly by bootstrapping or standard
error tests. Combining sequence and allozyme data into a single analysis
provided the greatest number of relationships receiving strong support.
Addition of published morphological and ecological data did not improve
support for any additional relationship. All analyses grouped species into
six distinct lineages: (1) the dovekie (Alle alle) and auks, (2)
guillemots, (3) brachyramphine murrelets, (4) synthliboramphine murrelets,
(5) true auklets, and (6) the rhinoceros auklet (Cerorhinca monocerata) and
puffins. The two murres (genus Uria) were sister taxa, and the black
guillemot (Cepphus grylle) was basal to the other guillemots. The Asian
subspecies of the marbled murrelet (Brachyramphus marmoratus perdix) was
the most divergent brachyramphine murrelet, and two distinct lineages
occurred within the synthliboramphine murrelets. Cassin's auklet
(Ptychoramphus aleuticus) and the rhinoceros auklet were basal to the other
auklets and puffins, respectively, and the Atlantic (Fratercula arctica)
and horned (Fratercula corniculata) puffins were sister taxa. Several
relationships among tribes, among the dovekie and auks, and among the
auklets could not be resolved but resembled "star" phylogenies indicative
of adaptive radiations at different depths within the trees.
相似文献
100.
Both temperature fluctuations and East Asian monsoons have driven plant diversification in the karst ecosystems from southern China 下载免费PDF全文
Hanghui Kong Fabien L. Condamine AJ Harris Junlin Chen Bo Pan Michael Möller Van Sam Hoang Ming Kang 《Molecular ecology》2017,26(22):6414-6429
Karst ecosystems in southern China are species‐rich and have high levels of endemism, yet little is known regarding the evolutionary processes responsible for the origin and diversification of karst biodiversity. The genus Primulina (Gesneriaceae) comprises ca. 170 species endemic to southern China with high levels of ecological (edaphic) specialization, providing an exceptional model to study the plant diversification in karsts. We used molecular data from nine chloroplast and 11 nuclear regions and macroevolutionary analyses to assess the origin and cause of species diversification due to palaeoenvironmental changes and edaphic specialization in Primulina. We found that speciation was positively associated with changes in past temperatures and East Asian monsoons through the evolutionary history of Primulina. Climatic change around the mid‐Miocene triggered an early burst followed by a slowdown of diversification rate towards the present with the climate cooling. We detected different speciation rates among edaphic types, and transitions among soil types were infrequently and did not impact the overall speciation rate. Our findings suggest that both global temperature changes and East Asian monsoons have played crucial roles in floristic diversification within the karst ecosystems in southern China, such that speciation was higher when climate was warmer and wetter. This is the first study to directly demonstrate that past monsoon activity is positively correlated with speciation rate in East Asia. This case study could motivate further investigations to assess the impacts of past environmental changes on the origin and diversification of biodiversity in global karst ecosystems, most of which are under threat. 相似文献