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1.
This work describes stage by stage the biostratigraphy of the Middle to Late Permian in Mexico and Guatemala. Roadian deposits are very poorly represented, as a consequence of tectonic movements at the end of the Kungurian/Leonardian stage. In fact Middle and Late Permian deposits are almost completely lacking in South Mexico and the whole Latin America, due to a probable climatic barrier. The main data concern the Las Delicias sequences from Coahuila, North Mexico, and the Mixteca Terrane, South central Mexico, with some precisions on the Wordian-Capitanian from Los Hornos (Puebla) and from Olinalá, Guerrero, respectively with the discoveries of Parafusulina sellardsi and Polydiexodina capitanensis. New data are provided on Capitanian mudmounds from Olinalá. A hypothetical reconstruction of the different terranes of Mexico at the Pangea stage, is finally presented.  相似文献   

2.
The not yet uploaded Trichoptera World Checklist (TWC) [], as at July 2006, recorded 12,627 species, 610 genera and 46 families of extant and in addition 488 species, 78 genera and 7 families of fossil Trichoptera. An analysis of the 2001 TWC list of present-day Trichoptera diversity at species, generic/subgeneric and family level along the selected Afrotropical, Neotropical, Australian, Oriental, Nearctic and Palaearctic (as a unit or assessed as Eastern and Western) regions reveals uneven distribution patterns. The Oriental and Neotropical are the two most species diverse with 47–77% of the species in widespread genera being recorded in these two regions. Five Trichoptera families comprise 55% of the world’s species and 19 families contain fewer than 30 species per family. Ten out of 620 genera contain 29% of the world’s known species. Considerable underestimates of Trichoptera diversity for certain regions are recognised. Historical processes in Trichoptera evolution dating back to the middle and late Triassic reveal that the major phylogenetic differentiation in Trichoptera had occurred during the Jurrasic and early Cretaceous. The breakup of Gondwana in the Cretaceous led to further isolation and diversification of Trichoptera. High species endemism is noted to be in tropical or mountainous regions correlated with humid or high rainfall conditions. Repetitive patterns of shared taxa between biogeographical regions suggest possible centres of origin, vicariant events or distribution routes. Related taxa associations between different regions suggest that an alternative biogeographical map reflecting Trichoptera distribution patterns different from the Wallace (The Geographical Distribution of Animals: With a Study of the Relations of Living and Extinct Faunas as Elucidating the Past Changes of the Earth’s Surface, Vol. 1, 503 pp., Vol. 2, 607 pp., Macmillan, London, 1876) proposed biogeography patterns should be considered. Anthropogenic development threatens biodiversity and the value of Trichoptera as important functional components of aquatic ecosystems, indicator species of deteriorating conditions and custodians of environmental protection are realised.  相似文献   

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Foraminiferal assemblages have been studied in 33 samples from the Can Gio region to the north of the Mekong Delta and from two regions of the Delta: the Tra Vinh province, in the middle part of the Delta; and the Ca Mau peninsula, to the south. Two plates, including 117 pictures, illustrate the species. These assemblages, either through the nature of the test or through the calculation of the confinement index Ic, clearly indicate differences in the balance between continental and marine influences, the Tra Vinh province being subject to the strongest freshwater influence. The decrease of calcareous specimens and the increase of Ic indicate the impact of deforestation in the Ca Mau peninsula, the influence of organic matter in shrimp ponds, and the impact of pollution in a tidal channel. The distribution of foraminiferal assemblages described in this study should be used as part of a reference point for further observations with a view to assessing environmental impacts of increasing human activities and/or global change.  相似文献   

5.
    
Benthic foraminiferal assemblages are increasingly utilized as indicators of water and sediment quality in coastal-marine environments. Most reef-dwelling foraminifers live on firm substrata such as reef or phytal surfaces, while most assessments have examined assemblages from sediments. This case study compared relative abundances of total foraminiferal-shell assemblages between sediment and phytal/rubble samples collected from one reef within one week. A total of 117 species within 72 genera were identified, with the same taxa in both sample sets in different proportions. Larger benthic foraminifers and some agglutinated taxa were concentrated about 1.5–3 fold in sediment samples, while nearly two-thirds of small, fragile shells were lost. Several common indices were compared, including Taxonomic Richness (number of genera), Shannon (H), Simpson's (D) and Fisher (α) diversity indices, Evenness (E), and the FORAM Index (FI). Highly significant differences (p < 0.001) between shell assemblages from 13 sets of phytal/rubble substrata and sediments were found in mean number (± standard deviation) of genera (49 ± 4 vs. 34 ± 10) and mean FI (5.6 ± 0.8 vs. 3.6 ± 0.4); both reflecting greater relative abundances of smaller foraminifers in the rubble samples. Fisher diversity was marginally significant (p = 0.05); other indices showed no significant differences between sample types. Although assessment of total assemblages is substantially less costly than distinguishing between specimens that were live or dead when collected, many researchers report those distinctions. The results of our study provide insight that can assist interpretations of studies that use live assemblages to calculate the FI, rather than total assemblages for which it was originally developed.  相似文献   

6.
John Tranter of CLEAPSS offers a challenge to biological educators not to let the system grind us down. He concludes by exploding some common myths about health & safety.  相似文献   

7.
The majority of sediment dweller foraminifera are deposit feeders. They use their pseudopodia to gather sediment with associated algae, organic detritus and bacteria. Uptake of bacteria by foraminifera have been observed but rarely quantified. We measured uptake of bacteria by the common foraminifera Ammonia tepida using 15N pre-enriched bacteria as tracers. In intertidal flats, seasonal, tidal and circadian cycles induce strong variations in environmental parameters. Grazing experiments were performed in order to measure effects of abiotic (temperature, salinity and irradiance) and biotic (bacterial and algal abundances) factors on uptake rates of bacteria. In mean conditions, A. tepida grazed 78 pgC ind− 1 h− 1 during the first eight hours of incubation, after which this uptake rate decreased. Uptake of bacteria was optimal at 30 °C, decreased with salinity and was unaffected by light. Above 7 × 108 bacteria ml wt sed− 1, uptake of bacteria remained unchanged when bacterial abundance increased. Algal abundance strongly affected algal uptake but did not affect uptake of bacteria. As uptake of bacteria represented 8 to 19% of microbes (algae plus bacteria) uptake, Ammonia seemed to be mainly dependant on algal resource.  相似文献   

8.
A complex index for comparison of treatment methods effectiveness is proposed. Procedure of the index construction allows the investigator to take into account several particular effectiveness characteristics considering their relative weight in over-all efficiency.  相似文献   

9.
    
Guerrero is one of the most diverse states of Mexico, containing a large number of endemic and endangered amphibian species. However, it is one of the less protected and studied states of the country. Here, we determined the potential distribution of all amphibian species in a risk category present in Guerrero and defined priority areas for amphibian conservation in the state. We modelled the potential distribution of 32 species using the maximum entropy modelling algorithm. These models were used to define priority areas through systematic conservation planning tools. The most important variables explaining species’ potential distribution were measures of climate variability, particularly temperature seasonality. The priority areas for amphibian conservation identified covered a total area of 12,212.72 km2 and contained an important proportion (almost a third) of the cloud mountain forests of the state. The most important planning units for meeting species targets and the most important planning units in terms of biodiversity overlapped in approximately the same planning units, located in the biogeographic regions of the Sierra Madre del Sur and the Pacific Coast. Finally, from the total priority areas identified, only 0.31% (38.17 km2) is currently protected within the existing natural protected areas in Guerrero. Thus, we consider that it is essential to protect additional natural areas in the state. Areas Voluntarily Destined for Conservation (ADVC) may be a good option; however, action must be taken to ensure the legitimacy of the processes by the local people and to avoid privileging only certain members of the community.  相似文献   

10.
Toxoplasma gondii counts among the most consequential food-borne parasites, and although the parasite occurs in a wide range of wild and domesticated animals, farms may constitute a specific and important locus of transmission. If so, parasites in animals that inhabit agricultural habitats might be suspected of harbouring genetically distinct parasite types. To better understand habitat effects pertinent to this parasite’s transmission, we compiled and analysed existing genotypic data of 623 samples from animals across a proximity gradient from areas of human settlement to the wilderness in North America. To facilitate such analysis, T. gondii isolates were divided into three groups: (i) from farm-bound animals (with the most limited home ranges on farms); (ii) from free-roaming animals (with wider home ranges on or near farms); and (iii) from wildlife. In addition, parasite genotype distribution in different animal species was analysed. We observed no absolute limitation of any of five major genotypes to any one habitat; however, the frequency of four genotypes decreased across the gradient from the farm-bound group, to the free-roaming group, then the wildlife, whereas a fifth genotype increased along that gradient. Genetic diversity was greater in free-roaming than in farm-bound animals. The genotypic composition of parasites in wildlife differed from those in farm-bound and free-roaming animals. Furthermore, parasite genotypes differed among host species. We conclude that T. gondii genotype distributions are influenced by the spatial habitat and host species composition, and parasite diversity decreases towards areas of human settlement, elucidating facts which may influence transmission dynamics and zoonotic potential in this ubiquitous but regionally variable parasite.  相似文献   

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Networks tools are being increasingly used in the study of plant-fungus interactions and likely to provide new insights in the way plant-fungus interactions are structured. At the same time, they raise new questions and challenges. Here, I highlight the most important problems and outline how network tools can be effectively used in mycorrhizal ecology. Network-based tools can be used to explore and visualize mycorrhizal interaction patterns: this can pave the way towards further empirical work and hypothesis testing. However, network-based tools cannot, by themselves alone, provide much insight about the ecological mechanisms driving the establishment of mycorrhizal interactions, because many mechanisms can yield a given network-level pattern. They also cannot help predicting the future dynamics of mycorrhizal communities, because modelling studies need to be conducted using parameters and rules that are relevant to the mycorrhizal symbiosis, which is not currently done. Also, drawing analogies between mycorrhizal networks and other types of networks must be made with caution, taking into account all the potential similarities, but also discrepancies, between these kinds of unrelated networks. I think that keeping the above issues in mind will be critical to keep the network-based approach viable and useful in mycorrhizal ecology.  相似文献   

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《Palaeoworld》2020,29(2):325-352
The Mechetlino Quarry section is a potential candidate for the Global Section Stratotype and Point (GSSP) for the base of the Global Kungurian Stage on the International Stratigraphic Chart. In 2017, the Mechetlino Quarry section became the part of the First Geopark in Russia, therefore excavation work was carried out to clear it, a road was laid, and infrastructure was developed. Recent evidence to justify the base Kungurian boundary in the Mechetlino section was obtained. Additional conodonts confirmed the data of V.V. Chernykh on the Artinskian–Kungurian transition. Besides Neostreptognathodus pnevi Kozur and Movshovitsch, the second marker (N. lectulus Chernykh) of the base-Kungurian was established. The Artinskian–Kungurian transition of the Mechetlino Quarry section is characterized by the richest associations of small foraminifers, ammonoids, and other groups. The occurrence of mass Clausiuraloceras above the Kungurian boundary, which changed the representative Artinskian association, was identified. Small foraminifers of the Artinskian–Kungurian transition are numerous and include sufficient species to provide a correlation with Western Tethys, Svalbard and Australia. Data on isotopic ratios of δ13C and δ18O, δ13Corg values and the magnetic susceptibility were obtained for the first time.  相似文献   

15.
赣西北溪流鱼类区系组成及其生物地理学特征分析   总被引:1,自引:1,他引:0       下载免费PDF全文
赣西北地区包括幕阜山脉东南面, 九岭山南北两侧以及鄱阳湖平原之西的广大山区和丘陵地区(图1), 位于E113°55′—116°08′、N28°10′—29°56′。北临湖北、西近湖南、东濒鄱阳湖, 南、北、西三面环山, 中部丘陵起伏。  相似文献   

16.
Several ecological and evolutionary hypotheses are based on the assumption that species reach their highest abundance in the centre of their range and decline in abundance toward the range edges. We reviewed empirical tests of this assumption, which we call the 'abundant centre' hypothesis. We found that of 145 separate tests conducted as part of 22 direct empirical studies, only 56 (39%) support the abundant centre hypothesis. More problematic than the percentage of studies that support the hypothesis is the finding that most studies inadequately sampled the species' ranges. Only two of the studies analysed data that were collected throughout the species' range. The remaining studies relied on data from a small number of points in their analysis, meaning that the range edges were severely under-sampled. Patterns of abundance across the entire range must be known to draw testable hypotheses about the consequences of species' geographical abundance distributions. Indirect tests of the abundant centre hypothesis, in which ecological or evolutionary expectations of abundant centre distributions were examined, did not support or reject the abundant centre hypothesis overall. We conclude that more exploration of species' abundance distributions is necessary and we suggest methods to use in future studies.  相似文献   

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18.
  总被引:1,自引:0,他引:1  
Abstract A most-probable-number technique was used to quantify the abundance of myxomycetes (myxogastrids) in soil samples taken from 23 'Sites of Special Scientific Interest' and one other site in the West of England. Associated organisms and soil conditions were also recorded. Sixteen of the 24 sites yielded myxomycete plasmodium-forming units (PFUs) in numbers averaging 230 cm−3 fresh soil. Where detectable in samples of grassland soil, the numbers ranged from 20–2750 cm−3, in woodland soil from 20–800 cm−3, and in sand dunes from 80–400 cm−3. Repeated sampling revealed changing numbers at single sites. The abundance of PFUs was correlated positively with numbers of soil amoebae, ciliates and nematodes, and with levels of magnesium and soil density, and negatively with organic matter content and levels of NH4-nitrogen and phosphate. Each PFU probably corresponded to one or several uninucleate cells in the soil rather than to a plasmodium.  相似文献   

19.
A survey of foraminiferal microhabitats at several Gulf of Mexico bathyal/abyssal hydrocarbon seeps reveals that many epibenthic species live not on the sediment, but attached to vestimentiferan tubeworms – centimeters to decimeters above the seafloor – thus avoiding the oxygen depletion and H2S toxicity at the sediment–water interface. This observation explains how certain species with a relatively high oxygen requirement (e.g., Cibicides spp.) may become components of foraminiferal death assemblages in seep sediments. Thus, when the sedimentary record of Foraminifera is used to interpret the history of past methane venting, the species from elevated microhabitats cannot be ignored, but they need to be considered separately from the sediment dwellers.  相似文献   

20.
    
Eozoon canadense, 'the dawn animal of Canada', a large foraminifera, was announced in 1864 as the oldest fossil organism known. Camps soon formed into disbelievers of its fossil nature, agnostics, and “Eozoonists”. Eozoon would number among its proponents major figures of the time. The saga of Eozoon, or more precisely the dispute as to its actual nature, spawned hundreds of publications. Here the story is told with a new focus, one on the stature and roles of the major personalities involved, and the evidence they presented. Eozoon is considered to have been 'de-bunked' in the late 19th century. However, it will be shown that it was never indisputably proven to be inorganic. Rather Eozoon simply faded away after its most ardent defenders died. As late as 1947, it was shown as the primordial organism in a biology textbook. The saga of Eozoon remains as a valuable cautionary tale. It is an example of an artifact accepted as fact because it filled a troubling void in knowledge, i.e., at that time, the first traces of life before Cambrian, and it endured because it was promoted by only a few, but powerful, figures in the scientific establishment of the era.  相似文献   

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