共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary The shallow marine subtropical Northern Bay of Safaga is composed of a complex pattern of sedimentary facies that are generally
rich in molluscs. Thirteen divertaken bulk-samples from various sites (reef slopes, sand between coral patches, muddy sand,
mud, sandy seagrass, muddy seagrass, mangrove channel) at water depths ranging from shallow subtidal to 40m were investigated
with regard to their mollusc fauna >1mm, which was separated into fragments and whole individuals.
Fragments make up more than 88% of the total mollusc remains of the samples, and their proportions correspond to characteristics
of the sedimentary facies. The whole individuals were differentiated into 622 taxa. The most common taxon,Rissoina cerithiiformis, represented more than 5% of the total mollusc content in the samples. The main part of the fauna consists of micromolluscs,
including both small adults and juveniles. Based on the results of cluster-, correspondence-, and factor analyses the fauna
was grouped into several associations, each characterizing a sedimentary facies: (1) “Rhinoclavis sordidula—Corbula erythraeensis-Pseudominolia nedyma association” characterizes mud. (2) “Microcirce sp.—Leptomyaria sp. association” characterizes muddy sand. (3)”Smaragdia spp.-Perrinia stellata—Anachis exilis—assemblage” characterizes sandy seagrass. (4) “Crenella striatissima—Rastafaria calypso—Cardiates-assemblage” characterizes muddy seagrass. (5) “Glycymeris spp.-Parvicardium sueziensis-Diala spp.-assemblage” characterizes sand between coral patches. (6) “Rissoina spp.-Triphoridae —Ostreoidea-assemblage” characterizes reef slopes. (7) “Potamides conicus—Siphonaria sp. 2—assemblage” characterizes the mangrove.
The seagrass fauna is related to those of sand between coral patches and reef slopes with respect to gastropod assemblages,
numbers of taxa and diversity indices, and to the muddy sand fauna on the basis of bivalve assemblages and feeding strategies
of bivalves. The mangrove assemblage is related to those of sand between coral patches and the reef slope with respect to
taxonomic composition and feeding strategies of bivalves, but has a strong relationship to those of the fine-grained sediments
when considering diversity indices. Reef slope assemblages are closely related to that of sand between coral patches in all
respects, except life habits of bivalves, which distincly separates the reef slope facies from all others. 相似文献
2.
Habitat fragmentation is a process involving splitting of continuous habitats into smaller, and more isolated habitat patches.
To assess the effects of small-scale habitat patchiness and isolation without the confounding effect of habitat loss on benthic
macrofauna, two field experiments were conducted in the Archipelago Sea, SW Finland. Using artificial seagrass units (ASUs)
we contrasted continuous patches (“C”) with fragmented patches (“F”) of the same combined area as the continuous patches.
The fragmentation treatment involved two isolation distances (0.5 and 3.0 m) between the ASUs (“F 0.5”) and (“F 3.0”). This
design was repeated in two consecutive experiments where the patch area was 0.25 and 0.0625 m2, respectively. Mobile epifauna were allowed to colonize patches for 12 days in both experiments. In both experiments, the
total epifaunal density was significantly higher in the “F 0.5” treatment than in the “C” treatment, and the three dominant
taxa showed positive or neutral responses to the habitat configuration. No fragmentation effect on the number of species was
detected in either of the experiments, but fragmentation had a negative effect on the epifaunal diversity (Shannon’s H′) in the experiment with the largest patch area. Epifaunal diversity was significantly lower in “F 3.0” treatment than in
“C” or “F 0.5” treatments in the first experiment, indicating stronger effect of isolation instead of fragmentation per se.
Edge effects were indirectly tested by comparing epifaunal densities with patch edge:area ratios. The results suggest that
edge effects may have a more important role than patch size for the total densities of epifaunal taxa, and that small, isolated
patches have equal or higher habitat value compared to larger fragments. 相似文献
3.
Summer phytoplankton blooms on the West Antarctic Peninsula (WAP) shelf result in episodic deposition of labile food material
for benthic detritivores. This summer deposition is thought to enhance benthic recruitment of macro- and megafauna. To explore
seasonality in benthic recruitment, juvenile invertebrates (>100 μm) were collected in a seasonal time series at three stations
on the WAP continental shelf. 4,098 juveniles were collected (average densities 2,000–7,000 m−2), with polychaetes dominant (2,581 individuals). The majority of polychaetes showed evidence of enhanced recruitment prior
to the summer bloom, although patterns varied across stations. Additional taxa showed recruitment peaks in summer, but again,
patterns varied among stations. Based on observed patterns, polychaete taxa are classified as “seasonal”, “marginally seasonal”,
and “non-seasonal” recruiters, with the latter two patterns predominating. The year-round presence of small juveniles in most
taxa suggests that recruitment occurs continuously, with periodic enhancement. Year-round recruitment is consistent with the
presence of a persistent “food bank” of labile organic material in WAP shelf sediments, allowing recruitment to be largely
decoupled from seasonal bloom dynamics. 相似文献
4.
Seventy-five years ago, the geneticist Richard Goldschmidt hypothesized that single mutations affecting development could
result in major phenotypic changes in a single generation to produce unique organisms within animal populations that he called
“hopeful monsters”. Three decades ago, Sarah P. Gibbs proposed that photosynthetic unicellular micro-organisms like euglenoids
and dinoflagellates are the products of a process now called “secondary endosymbiosis” (i.e., the evolution of a chloroplast
surrounded by three or four membranes resulting from the incorporation of a eukaryotic alga by a eukaryotic heterotrophic
host cell). In this article, we explore the evidence for Goldschmidt’s “hopeful monster” concept and expand the scope of this
theory to include the macroevolutionary emergence of organisms like Euglena and Chlorarachnion from secondary endosymbiotic events. We argue that a Neo-Goldschmidtian perspective leads to the conclusion that cell chimeras
such as euglenids and dinoflagellates, which are important groups of phytoplankton in freshwater and marine ecosystems, should
be interpreted as “successful monsters”. In addition, we argue that Charles Darwin had euglenoids (infusoria) in mind when
he speculated on the “primordial intermediate form”, although his Proto-Euglena-hypothesis for the origin of the last common
ancestor of all forms of life is no longer acceptable. 相似文献
5.
Numerical fish-habitat modelling on various scales is considered to be state of the art in river management. However, most
of the concepts applied use steady-state hydraulic parameters such as flow velocity and water depth. Herein we present analysis
and discussion of the possibility of including a drift-feeding parameter (SIF) into habitat evaluations based on multiplying suitability indices. “Sources” and “sinks” of benthic drift were identified
according to both the zero-crossing and hydraulic-threshold methods in an alpine gravel-bed river. Minor differences could
be determined between the two methods in a well-developed riffle–pool section. Macroinvertebrates, used for simulating benthic
drift, were collected by multi-habitat sampling and appraised according to their critical threshold (τ
cr) for motion on the bed surface and sinking velocity (v
s). The findings of the calculation of drift rates using one- (1D) and two-dimensional (2D) hydrodynamic numerical models highlight
a specification of best feeding position for drift-feeding fish (i.e. brown trout, grayling) considering the SIF parameter. Riffle–pool sequences are characteristic of pristine alpine streams; our findings underline their importance as
production (riffles) and consumption areas (pools) in terms of holistic river function. Moreover, the results indicate that
(artificial) lateral obstruction (e.g. dams) may lead to a reduced transport rate of benthic organisms due to low bottom shear
stress (<0.25 N m−2). Thus, deposition of drifting macroinvertebrates occurs in backwaters, with downstream impacts on benthic and fish communities. 相似文献
6.
Masayoshi Maehata 《Ichthyological Research》2001,48(3):283-287
The mating behavior of the rock catfish Silurus lithophilus (Siluriformes: Siluridae), a species endemic to the Lake Biwa system, was observed from May to July in 1989–1994 along the
rocky shore of the lake's outlet, the Seta River. The mating behavior of S. lithophilus involved a certain behavioral sequence: “chasing,”“clinging,” and “enfolding” while “squeezing” by the male; and “circling”
by the spawned pair. The mating behavior of this species was basically similar to that of S. biwaensis, but greatly different from that of S. asotus, which spawns in running water (in ditches). The mating behavior of S. lithophilus (and S. biwaensis) might have developed as an adaptation to lentic environments such as the shores of the large river or the lake.
Received: October 25, 2000 / Revised: February 25, 2001 / Accepted: March 8, 2001 相似文献
7.
Masahiro Horinouchi 《Ichthyological Research》2009,56(2):109-125
Horizontal gradients in fish assemblage structures in and around a seagrass habitat were evaluated by visual observations.
The assemblage structures clearly differed between open microhabitats lacking seagrass, i.e., nearby sand and the area adjoining
the outer margin of the seagrass bed (referred to as “outer gap”), and microhabitats with seagrass within the overall seagrass
bed, although not differing among the latter microhabitats, including both edge and core portions. Such open microhabitats
were found to be not always inferior, but nearly equal to or even sometimes greatly superior in fish species’ diversity and/or
abundance to the microhabitats with seagrass. In particular, the outer gap was always ranked first in total species’ number
and had outstanding abundance in spring. Similar open microhabitats adjoining seagrass walls facing the sand patch within
the seagrass bed (referred to as “inner gap”) in spring were also characterized by higher fish species and individual numbers.
The 11 most abundant fishes showed four discrete distribution patterns (three recognized herein and one implied by precedent
studies), such contributing to a horizontal gradient in the fish assemblage structure. While no fishes showed a preference
for the edge or core of the seagrass bed, group-forming juveniles of several species favored gap microhabitats, suggesting
that, in addition to the traditionally recognized edge and core microhabitats, the concept of gap microhabitats should be
included in seagrass conservation ecology. 相似文献
8.
Céline Labrune Antoine Grémare Jean-Michel Amouroux Rafael Sardá João Gil Sergi Taboada 《Helgoland Marine Research》2008,62(3):201-214
Samples of soft-sediment macrobenthos from 92 sites between 10 and 50 m depth were used to assess (1) the main soft-bottom
macrofauna communities in the Gulf of Lions, (2) the different components of the diversity of benthic macrofauna in this area,
and (3) the relevance of the use of major taxonomic groups as surrogates for the analysis of the structure and diversity of
total macrofauna. Three main communities were identified by cluster analysis and associated procedures. These communities
corresponded well to the assemblages recently identified on the basis of polychaete composition. The α-diversity indices were
in accordance with those reported for similar communities in the Mediterranean. Conversely, the β-diversity value was higher
than the few other data available in the literature for marine soft-bottom macrofauna. The total number of species in the
studied area estimated by the “total species accumulation curve” (TS) method was 2,319, which was only 10% higher than the
number obtained by extrapolation of the species–area curve. The similarity matrix based on polychaetes correlated best with
the one based on total macrofauna. Polychaetes and crustaceans were also the best surrogates of total macrofauna when assessing
α-diversity (except in the case of Δ*). Conversely, molluscs were the best surrogates of total macrofauna β-diversity. Our
results show that the choice of an optimal surrogate for total benthic macrofauna depends on the characteristic of the benthic
macrofauna to be studied. Moreover, this choice is also dependent on the environment to be studied. 相似文献
9.
Linking limitation to species composition: importance of inter- and intra-specific variation in grazing resistance 总被引:1,自引:0,他引:1
Short-term responses of producers highlight that key nutrients (e.g., N, P)—or combinations of these nutrients—limit primary
production in aquatic and terrestrial ecosystems. These discoveries continue to provide highly valuable insights, but it remains
important to ask whether nutrients always predominantly limit producers despite wide variation in nutrient supply and herbivory
among systems. After all, predictions from simple food chain models (derived here) readily predict that limitation by grazers
can exceed that by nutrients, given sufficient enrichment. However, shifts in composition of producers and/or increasing dominance
of invulnerable stages of a producer can, in theory, reduce grazer limitation and retain primacy of nutrient limitation along
nutrient supply gradients. We observed both mechanisms (inter- and intra-species variation in vulnerability to herbivory)
working in a two-part mesocosm experiment. We incubated diverse benthic algal assemblages for several months either in the
presence or absence of benthic macro-grazers in mesocosms that spread a broad range of nutrient supply. We then conducted
short-term assays of nutrient and grazer limitation on these communities. In the “historically grazed” assemblages, we found
shifts from more edible, better competitors to more resistant producers over enrichment gradients (as anticipated by the food
web model built with a tradeoff in resistance vs. competitive abilities). However, contrary to our expectations, “historically
ungrazed” assemblages became dominated by producers with vulnerable juvenile forms but inedible adult forms (long filaments).
Consequently, we observed higher resource limitation rather than grazer limitation over this nutrient supply gradient in both
“historically grazed” (expected) and “historically ungrazed” (not initially expected). Thus, via multiple, general mechanisms
involving resistance to grazing (changes in species composition or variation in stage-structured vulnerability), producer
assemblages should remain more strongly or as strongly limited by nutrients than grazers, even over large enrichment gradients.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Microtubules (MT) are composed of 13 protofilaments, each of which is a series of two-state tubulin dimers. In the MT wall,
these dimers can be pictured as “lattice” sites similar to crystal lattices. Based on the pseudo-spin model, two different
location states of the mobile electron in each dimer are proposed. Accordingly, the MT wall is described as an anisotropic
two-dimensional (2D) pseudo-spin system considering a periodic triangular “lattice”. Because three different “spin-spin” interactions
in each cell exist periodically in the whole MT wall, the system may be shown to be an array of three types of two-pseudo-spin-state
dimers. For the above-mentioned condition, the processing of quantum information is presented by using the scheme developed
by Lloyd. 相似文献
11.
Michael J. Winterbourn Sarah Cadbury Christiane Ilg Alexander M. Milner 《Hydrobiologia》2008,603(1):211-219
In contrast to the northern hemisphere where species of Chironomidae are usually the dominant benthic invertebrates in the
coldest upper reaches of glacial streams, mayflies (Deleatidium spp.: Leptophlebiidae) predominate in equivalent conditions in New Zealand. We examined the life histories and annual production
of Deleatidium spp. at two sites on the Matukituki River (South Island, New Zealand) and at three sites in its glacier-fed tributary, Rob
Roy Stream. Mean annual water temperature at the five sites ranged from 2.1 to 7.0°C. Monthly sampling showed that mayfly
populations were poorly synchronised at all sites but were probably univoltine. The large Deleatidium cornutum was the dominant mayfly species found at the upper sites (Sites 1 and 2) on Rob Roy Stream, whereas above the confluence
with Matukituki River (Site 3) it co-existed with a complex of smaller species we refer to as D. “angustum”. Deleatidium “angustum” also dominated at the Matukituki sites. Deleatidium production calculated for the five sites, assuming an 11-month nymphal life, ranged from 0.48 g dry weight/m2/year (Site 1) to 3.07 g dry weight/m2/year (Site 3). The values for D. cornutum at Sites 2 and 3 are high for a species of Deleatidium and reflect its large size. This species appears to be strongly adapted for growth at low temperatures. Climate change scenarios
for New Zealand predict the gradual and ultimate loss of small South Island glaciers and a consequent warming of streams as
runoff from rainfall and snow melt becomes more dominant in spring. As a result, suitable habitats will be lost for cold-water
specialists such as D. cornutum, and they are likely to suffer reductions in their distributional range and local extinction. In contrast, species such as
those in the D. “angustum” complex may extend their ranges into streams formerly dominated by glacial meltwater.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Handling editor: S. Stendera 相似文献
12.
We studied the community structure and abundance of benthic animals in intertidal seagrass beds in Thailand, where dugongs (Dugong dugon) feed on the seagrass Halophila ovalis. Our objective was to examine whether the benthic community was affected by the foraging activity of the dugongs, which can cause disturbance to the sediment. We collected a total of 4156 benthic animals from three study sites and classified them into 77 different taxa. A lucinid bivalve, Pillucina sp., was the most abundant taxa (approximately 80% of individuals). Taxa richness of the benthic animals was higher in intact H.ovalis vegetation compared to dugong trails at all sites. In general, the densities of five functional groups (classified by position on/in the sediment and motility) and five dominant taxa were higher in intact seagrass vegetation compared to dugong trails, although the magnitude of this difference varied among functional groups and taxa. Densities were at least threefold higher in the seagrass vegetation than in the dugong trails for epifauna and shallow infauna, but were at most twofold higher for deep infauna. Taxa richness and abundance of the benthic animals in the dugong trails were similar between the day following, and 7–9days after, the creation of the trails. Thus, delayed and/or indirect effects of dugong herbivory on benthic communities were not detected in this study. These findings demonstrate that the foraging activity of dugongs in seagrass can have considerable impacts on the abundance and diversity of benthic organisms, although this effect varies among benthic animals with different lifestyles. 相似文献
13.
Inventory, differentiation, and proportional diversity: a consistent terminology for quantifying species diversity 总被引:1,自引:0,他引:1
Almost half a century after Whittaker (Ecol Monogr 30:279–338, 1960) proposed his influential diversity concept, it is time
for a critical reappraisal. Although the terms alpha, beta and gamma diversity introduced by Whittaker have become general textbook knowledge, the concept suffers from several drawbacks. First, alpha
and gamma diversity share the same characteristics and are differentiated only by the scale at which they are applied. However,
as scale is relative––depending on the organism(s) or ecosystems investigated––this is not a meaningful ecological criterion.
Alpha and gamma diversity can instead be grouped together under the term “inventory diversity.” Out of the three levels proposed
by Whittaker, beta diversity is the one which receives the most contradictory comments regarding its usefulness (“key concept”
vs. “abstruse concept”). Obviously beta diversity means different things to different people. Apart from the large variety
of methods used to investigate it, the main reason for this may be different underlying data characteristics. A literature
review reveals that the multitude of measures used to assess beta diversity can be sorted into two conceptually different
groups. The first group directly takes species distinction into account and compares the similarity of sites (similarity indices,
slope of the distance decay relationship, length of the ordination axis, and sum of squares of a species matrix). The second
group relates species richness (or other summary diversity measures) of two (or more) different scales to each other (additive
and multiplicative partitioning). Due to that important distinction, we suggest that beta diversity should be split into two
levels, “differentiation diversity” (first group) and “proportional diversity” (second group). Thus, we propose to use the
terms “inventory diversity” for within-sample diversity, “differentiation diversity” for compositional similarity between
samples, and “proportional diversity” for the comparison of inventory diversity across spatial and temporal scales.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
Amphipod (Gammarus minus) responses to predators and predator impact on amphipod density 总被引:1,自引:0,他引:1
David E. Wooster 《Oecologia》1998,115(1-2):253-259
Recent theoretical work suggests that predator impact on local prey density will be the result of interactions between prey
emigration responses to predators and predator consumption of prey. Whether prey increase or decrease their movement rates
in response to predators will greatly influence the impact that predators have on prey density. In stream systems the type
of predator, benthic versus water-column, is expected to influence whether prey increase or decrease their movement rates.
Experiments were conducted to examine the response of amphipods (Gammarus minus) to benthic and water-column predators and to examine the interplay between amphipod response to predators and predator consumption
of prey in determining prey density. Amphipods did not respond to nor were they consumed by the benthic predator. Thus, this
predator had no impact on amphipod density. In contrast, amphipods did respond to two species of water-column predators (the
predatory fish bluegills, Lepomis macrochirus, and striped shiners, Luxilus chrysocephalus) by decreasing their activity rates. This response led to similar positive effects on amphipod density at night by both species
of predatory fish. However, striped shiners did not consume many amphipods, suggesting their impact on the whole amphipod
“population” was zero. In contrast, bluegills consumed a significant number of amphipods, and thus had a negative impact on
the amphipod “population”. These results lend support to theoretical work which suggests that prey behavioral responses to
predators can mask the true impact that predators have on prey populations when experiments are conducted at small scales.
Received: 21 March 1997 / Accepted: 15 December 1997 相似文献
15.
C. Burger M. J. T. Carrondo H. Cruz M. Cuffe E. Dias J. B. Griffiths K. Hayes H. Hauser D. Looby C. Mielke J.-L. Moreira E. Rieke A. V. Savage G. N. Stacey T. Welge 《Applied microbiology and biotechnology》1999,52(3):345-353
Recombinant fusion proteins offer important new therapeutic approaches for the future. This report describes the use of three
different genetic strategies (i.e. “mono-”, “bi-” and “tri-cistronic” vectors) to achieve stable secretion from BHK cells
of a glycosylated antibody-cytokine fusion protein designed for use in anti-tumour therapy. It describes selection of a robust
and effective production cell line based on stability of secretion of the product, quality of mRNA and protein products and
performance in in vitro bioassays for potency. The data obtained at this stage were utilised in the selection of a suitable
candidate production cell line. The relative productivity and general performance of the cells in stirred tank and fixed bed
culture systems indicated that a variety of cell culture technologies provided robust tools for production of a highly selected
cell clone. Consistency of the product glycosylation was determined by analysis of released oligosaccharides using matrix-assisted
laser desorption ionisation – time of flight mass spectrometry and high-performance anion exchange chromatography. These investigations
showed consistent expression of three glycoforms of the fusion protein which varied in their relative proportions in different
culture systems and at different time points in a fixed bed reactor with continuous perfusion. In conclusion, this study dealt
with a range of important scientific and technical issues which are essential for regulatory approval and commercial success
of a recombinant protein and elucidates some useful markers for process development for similar recombinant biologicals.
Received: 25 March 1999 / Accepted: 23 April 1999 相似文献
16.
Shortage of natural crevice shelters may produce population bottlenecks in juvenile Caribbean spiny lobsters (Panulirus argus), a socially gregarious species. We conducted a field experiment to test enhancement of a local population of juvenile P. argus with the addition of artificial shelters (“casitas”) that mimic large crevices (1.1 m2 in surface area and 3.8 cm in height). Changes in density and biomass of juvenile lobsters 15–50 mm carapace length (CL)
were assessed with a multiple before-after control-impact (MBACI) analysis. Separate analyses were also conducted on small
(15–35 mm CL) and large (35.1–50 mm CL) juveniles to assess size-related effects. First, we carried out 13 lobster surveys
on nine fixed 1-ha sites over a shallow reef lagoon (“before” period). Then, we deployed ten casitas in each of five sites
and left four sites as controls, and conducted 22 further surveys (“after” period). Deployment of casitas resulted in a sixfold
increase in juvenile density (76% contributed by small and 24% by large juveniles) and a sevenfold increase in biomass (40
and 60%, respectively). Capture–recapture results revealed that enhancement was achieved not by promoting individual growth
but by increasing survival, persistence, and foraging ranges of small and large juveniles. Casitas both mitigated shortage
of natural shelter and increased sociality, allowing for cohabitation of smaller, more vulnerable juveniles with larger conspecifics
that have greater defensive abilities. Casitas may help enhance local populations of juvenile P. argus in Caribbean seagrass habitats, typically poor in natural crevice shelters. The use of MBACI and the simultaneous assessment
of multiple interrelated response variables may be a powerful analytical approach to test shelter limitation in other species
and to examine the function of structural habitat in other systems. 相似文献
17.
E. V. Balushkina 《Inland Water Biology》2009,2(4):355-363
In the years 1994–2005, the values of the integrated index IP’ at some stations of the Neva Bay changed from 38.1 to 81.9%, water quality changed from class 3 to class 5, and the states
of some areas of the ecosystem that were evaluated as “tense” went to “catastrophic.” The integrated mean assessment of water
quality according to the IP’ index over the entire Neva Bay throughout 12 years (1994–2005) remained relatively stable, waters were assessed as “polluted”
(fourth class), and the state of the ecosystem was considered “critical.” The state of the eastern part of the Gulf of Finland
in 1994–2005 was less favorable. The species diversity of zoobenthos in the resort zone of the eastern part of the Gulf of
Finland is considerably lower than in the Neva Bay. Waters of the resort zone of the eastern part of the Gulf of Finland in
1994–2005 were assessed as one class lower than in the Neva Bay, i.e., as “polluted-dirty” (fourth-fifth class), and the state
of the ecosystem was assessed as being in a “crisis.” In the resort zone, there was a decline in species diversity and abundance
and biomass of benthic animals; i.e., all characteristics of the degradation of benthic animal communities were observed. 相似文献
18.
In October 1977 an investigation was initiated of the qualitative and quantitative composition of the fauna of the eelgrass
(Zostera marina) beds at Roscoff. Samples were taken in 2 seagrass beds at different tidal levels in order to follow numerical changes in
the course of the year. In March 1978 the area of study was struck by the oil slick of the tanker “Amoco Cadiz ”. For this
reason sampling has been continued at the same frequency. The tabulated results show clearly that the oil slick had a profound
but selective influence on the various animal groups; some of them disappeared while others were apparently unaffected. Rapid
recovery of some species has taken place, but re-establishment of other species, particularly the filter feeders has not been
observed. The very diverse amphipod fauna has disappeared, and has been replaced by a population ofPherusa fucicola andGammarus locusta; the latter was absent in the year before the oil disaster took place. 相似文献
19.
Dionyssis Venieratos 《Bulletin of mathematical biology》1981,43(2):213-232
Two simple models are proposed and analysed, in which it is shown that the formation of a new polymer, resulting from an “error”
in the template action mechanism of production of an old polymer, may compromise the stability of the initial system under
specific conditions, in the context of prebiotic evolution. Autocatalysis is shown to be a “selective advantage”, enabling
the “mutant” to dominate in concentration and even replace the initial polymer. The addition of a third molecule playing the
role of a catalyst causes hysteresis effects. 相似文献
20.
D. L. Nanney R. M. Preparata F. P. Preparata E. B. Meyer E. M. Simon 《Journal of molecular evolution》1989,28(5):451-459
Summary We describe and illustrate a simple heuristic approach to the Sankoff methods for construction of parsimonious evolutionary
trees from nucleotide sequence data. The procedure is intended to permit more valid inferences, particularly from relatively
short sequences, concerning relationships among taxa separated for long time intervals. The procedure is based on the freat
variability of evolutionary plasticity among sites in the molecules and removes from consideration the more highly variable
sites. Editing is accomplished after classifying sites in carefully aligned arrays of sequences. Only “ditypic sites,” i.e.,
sites observed in only two evolutionary states within the array, are used in making phylogenetic inferences. This strategy
makes possible the construction of good approximations to the most parsimonious Steiner strees, by means of efficient programs
that require “dense species arrays,” i.e., species sets that differ from each other by relatively small numbers of differences
in conservative sites. The technique is illustrated with 5S and 5.8S rRNA sequence data from published catalogs. 相似文献