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51.
YIT ARN TEH † ERIC A. DUBINSKY WHENDEE L. SILVER CHARLOTTE M. CARLSON†‡ 《Global Change Biology》2008,14(2):413-422
Tropical forests are an important source of atmospheric methane (CH4), and recent work suggests that CH4 fluxes from humid tropical environments are driven by variations in CH4 production, rather than by bacterial CH4 oxidation. Competition for acetate between methanogenic archaea and Fe(III)‐reducing bacteria is one of the principal controls on CH4 flux in many Fe‐rich anoxic environments. Upland humid tropical forests are also abundant in Fe and are characterized by high organic matter inputs, steep soil oxygen (O2) gradients, and fluctuating redox conditions, yielding concomitant methanogenesis and bacterial Fe(III) reduction. However, whether Fe(III)‐reducing bacteria coexist with methanogens or competitively suppress methanogenic acetate use in wet tropical soils is uncertain. To address this question, we conducted a process‐based laboratory experiment to determine if competition for acetate between methanogens and Fe(III)‐reducing bacteria influenced CH4 production and C isotope composition in humid tropical forest soils. We collected soils from a poor to moderately drained upland rain forest and incubated them with combinations of 13C‐bicarbonate, 13C‐methyl labeled acetate (13CH3COO?), poorly crystalline Fe(III), or fluoroacetate. CH4 production showed a greater proportional increase than Fe2+ production after competition for acetate was alleviated, suggesting that Fe(III)‐reducing bacteria were suppressing methanogenesis. Methanogenesis increased by approximately 67 times while Fe2+ production only doubled after the addition of 13CH3COO?. Large increases in both CH4 and Fe2+ production also indicate that the two process were acetate limited, suggesting that acetate may be a key substrate for anoxic carbon (C) metabolism in humid tropical forest soils. C isotope analysis suggests that competition for acetate was not the only factor driving CH4 production, as 13C partitioning did not vary significantly between 13CH3COO? and 13CH3COO?+Fe(III) treatments. This suggests that dissimilatory Fe(III)‐reduction suppressed both hydrogenotrophic and aceticlastic methanogenesis. These findings have implications for understanding the CH4 biogeochemistry of highly weathered wet tropical soils, where CH4 efflux is driven largely by CH4 production. 相似文献
52.
The genus Apalis is a member of the African forest warblers clade of the Cisticolidae. In view of its morphological diversity, it was suggested that this genus needs a taxonomic revaluation. For this, we sequenced a nuclear intron (myoglobin intron 2) and two mitochondrial protein‐coding genes (ND2 and ND3). The 2016 bp of sequence data obtained were aligned and subjected to parsimony, maximum likelihood and Bayesian inference. All three genes strongly reject the monophyly of Apalis but support the placing of all apalises within a broader clade of forest cisticolids which also includes Urolais. Within this forest clade, a subclade is defined which includes the genera Urolais, Schistolais and a well‐supported clade comprising three afromontane species, the Black‐collared Apalis Apalis pulchra, the Ruwenzori Apalis Apalis ruwenzorii and the African Tailorbird Artisornis. This subclade is sister to other members of Apalis, including the type species of the genus the Bar‐throated Apalis Apalis thoracica. A new generic name, Oreolais, is suggested for the Black‐collared and Ruwenzori Apalises. 相似文献
53.
ERIC R. LARSON DANIEL D. MAGOULICK CLINTON TURNER KELLY H. LAYCOCK 《Freshwater Biology》2009,54(9):1899-1908
1. Crayfish are among the most threatened taxa in the world and invasive crayfish are the primary cause of the decline of native crayfish. Most research has emphasised biotic interactions as the mechanism by which native crayfish are displaced by invasives, although crayfish occupy variable environments and the role of disturbance in facilitating crayfish invasion and displacement is understudied. 2. We compared tolerance to a disturbance, stream drying, in a native and invasive crayfish as a potential mechanism to explain their distribution. Our experiments and observations were conducted across scales, from laboratory environmental chambers to stream mesocosms to field sampling. We hypothesised that the invasive crayfish would be more tolerant of desiccation than the native, and that this physiological distinction between the two would be reflected in their distribution in relation to stream drying. 3. In the laboratory, the native crayfish Orconectes eupunctus was less tolerant of desiccation than the invasive Orconectes neglectus chaenodactylus, with all native crayfish dying within 2 days without water, while some of the invasive crayfish survived for nearly 2 weeks. Under simulated stream drying in mesocosms, only the native O. eupunctus survived less well than in a control. Field sampling demonstrated a significant negative relationship between O. eupunctus density and low summer flows, while O. neglectus density was positively associated with low summer flows. The greater resistance of O. neglectus to drying could, through priority effects, inhibit recolonisation by O. eupunctus once flow resumes. 4. Abiotic disturbances are potentially important to the displacement of native by invasive crayfish. Disturbance mediated displacement of aquatic species provides both an opportunity to conserve native species by maintaining or restoring habitat and disturbance regimes and is also a challenge due to increasing human water demand, flow regime alteration and global climate change. 相似文献
54.
ROBERT J. TEN HOVE LISETTE VAN LIESHOUT MIKE B. J. BEADSWORTH M. ARANTZA PEREZ KLAARTJE SPEE ERIC C.J. CLAAS JACO J. VERWEIJ 《The Journal of eukaryotic microbiology》2009,56(4):388-393
ABSTRACT. A retrospective phylogenetic analysis was performed on isolates of Enterocytozoon bieneusi to characterize the genotypes in different patient cohorts. Fifty-seven isolates, collected from patients living in Malawi and the Netherlands, were classified by age and immune status of the hosts. Sequence analysis of the internal transcribed spacer (ITS) region identified 16 genotypes; nine have not previously been described. Genotypes K and D were most prevalent among patient groups, whereas genotype C was restricted to transplantation patients receiving immunosupressives and genotype B showed a predisposition toward patients living with HIV/AIDS. Different genotypes showed more dispersion among isolates from Malawi compared with those from the Netherlands. A constructed map estimating the genealogy of the ITS region reveals a dynamic evolutionary process between the genotypes. 相似文献
55.
ANDREA E. BARBKNECHT W. SUE FAIRBANKS JARED D. ROGERSON ERIC J. MAICHAK LAURA L. MEADOWS 《The Journal of wildlife management》2009,73(1):144-148
ABSTRACT We assessed success of vaginal implant transmitters (VITs), deployed in 198 elk (Cervus elaphus nelsoni), in locating elk calving sites in western Wyoming, USA, in 2006–2007. We identified 60.3% of expelled VIT locations as definite or probable event markers and an additional 21.8% as possible event markers. Failure rate for VITs was 10.6%, and we found an additional 7.3% in improbable or impossible parturition sites. Vaginal implant transmitters were effective in locating calving and abortion sites and will facilitate definition of parturition habitat selection and parturition ranges of specific subpopulations. 相似文献
56.
ERIC PARMENTIER DAVID LECCHINI BRUNO FREDERICH CHRISTOPHE BRIE DAVID MANN 《Biological journal of the Linnean Society. Linnean Society of London》2009,97(4):928-940
Most studies of fish sounds show that the sounds are species-specific, with unique spectral and timing characteristics. This raises the question as to whether these sounds can be used to understand phyletic relationships between species and which acoustic parameters are subject to variation between species. In the present study, 597 sounds (and 2540 pulses) related to signal jumps of four Dascyllus species ( Dascyllus aruanus , Dascyllus trimaculatus , Dascyllus albisella , and Dascyllus flavicaudus ) from different geographic regions (Madagascar, Moorea, Rangiroa, and Hawaii) were analysed. It was possible to discern species-specific sounds, but also variation in sounds between populations. Large variations in sound length were found between Dascyllus species, whereas differences in interpulse duration were found to be variable between populations. In the regions where species live in sympatry, it appears that they restrict the variability in their sounds. This could comprise evidence of adaptation with character displacement of sonic characteristics where different species co-occur. However, sonic characteristics still overlapped substantially between species, suggesting that females would need to sample more than one sound and potentially use other cues to discriminate between species. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 928–940. 相似文献
57.
GLYNIS V. CRON KEVIN BALKWILL ERIC B. KNOX 《Botanical journal of the Linnean Society. Linnean Society of London》2009,160(2):130-148
The biogeography of Cineraria (Asteraceae, Senecioneae) is assessed using a chorological approach in terms of its distribution, centres of diversity and endemism. Rare species are identified and categorised according to Rabinowitz's criteria and causes for rarity in the genus are investigated. The conservation status of the species is assessed according to IUCN criteria for Red List categories and compared to levels of rarity. The main phytogeographic affinity of Cineraria is Afromontane in association with seven recognised centres of endemism in South Africa, four in tropical Africa, in Ethiopia and in Madagascar. Fifteen species are endemic and six are near‐endemic to a specific centre of endemism or mountain range. Seventy four percent of Cineraria spp. are endemic to southern Africa with the centre of diversity in the KwaZulu‐Natal Midlands, South Africa. The rarest species number 11; of these eight are endangered or vulnerable according to IUCN Red Data Criteria and three are data deficient. Causes of rarity in Cineraria are related to narrow habitat specificity, notably soil or rock type and/or altitudinal range. Paired comparisons of the 11 rarest and commonest species reveal no convincing causal links to morphological, reproductive or life history strategy attributes in Cineraria. © 2009 University of the Witwatersrand, Botanical Journal of the Linnean Society, 2009, 160 , 130–148. 相似文献
58.
KEITH H. NISLOW MARK HUDY BENJAMIN H. LETCHER ERIC P. SMITH 《Freshwater Biology》2011,56(10):2135-2144
1. Barriers to immigration, all else being equal, should in principle depress local abundance and reduce local species richness. These issues are particularly relevant to stream‐dwelling species when improperly designed road crossings act as barriers to migration with potential impacts on the viability of upstream populations. However, because abundance and richness are highly spatially and temporally heterogeneous and the relative importance of immigration on demography is uncertain, population‐ and community‐level effects can be difficult to detect. 2. In this study, we tested the effects of potential barriers to upstream movements on the local abundance and species richness of a diverse assemblage of resident stream fishes in the Monongahela National Forest, West Virginia, U.S.A. Fishes were sampled using simple standard techniques above‐ and below road crossings that were either likely or unlikely to be barriers to upstream fish movements (based on physical dimensions of the crossing). We predicted that abundance of resident fishes would be lower in the upstream sections of streams with predicted impassable barriers, that the strength of the effect would vary among species and that variable effects on abundance would translate into lower species richness. 3. Supporting these predictions, the statistical model that best accounted for variation in abundance and species richness included a significant interaction between location (upstream or downstream of crossing) and type (passable or impassable crossing). Stream sections located above predicated impassable culverts had fewer than half the number of species and less than half the total fish abundance, while stream sections above and below passable culverts had essentially equivalent richness and abundance. 4. Our results are consistent with the importance of immigration and population connectivity to local abundance and species richness of stream fishes. In turn, these results suggest that when measured at appropriate scales (multiple streams within catchments), with simple protocols amenable to use by management agencies, differences in local abundance and species richness may serve as indicators of the extent to which road crossings are barriers to fish movement and help determine whether road‐crossing improvements have restored connectivity to stream fish populations and communities. 相似文献
59.
PASCAL MOYAL AHMET BAYRAM MATILDA SAVOPOULOU‐SOULTANI ERIC CONTI MATILDE EIZAGUIRRE BRUNO LE RÜ ARMAN AVAND‐FAGHIH BRIGITTE FRÉROT STEFANOS ANDREADIS 《Biological journal of the Linnean Society. Linnean Society of London》2011,103(4):904-922
The major pest of maize in Mediterranean Europe, the stem borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae), has a fragmented distribution, north and south of the Sahara. The present study aimed: (1) to clarify the uncertain taxonomic status of the Palearctic and sub‐Saharan populations which were first considered as different species and later on as subspecies (Sesamia nonagrioides nonagrioides and Sesamia nonagrioides botanephaga) and (2) to investigate the origin of the Palearctic population which extends from Spain to Iran, outside what is considered typical for this mainly tropical genus. We reconstructed the evolutionary history of both populations using one nuclear and two mitochondrial genes. The sub‐Saharan taxon was fragmented in two isolated populations (West and East) whose mitochondrial genes were distant by 2.3%. The Palearctic population was included in the East African clade and its genes were close or identical to those of a population from Central Ethiopia, where the species was discovered for the first time. Similarly, in Africa, the alleles of the nuclear gene were distributed mainly in two West and East clades, whereas some Palearctic alleles belonged to the West clade. The Palearctic population originated therefore from East and West Africa and is the progeny of the cross between these two African populations. The main species concepts were in agreement, leading to the conclusion that the three populations are still conspecific. In the surveyed regions, the species therefore does not include two subspecies but three isolated populations. The Palearctic population suffered from severe bottlenecks that resulted in the fixation of one East African mitochondrial genome and the large reduction in its genetic diversity compared to the African populations. The data suggest that natural colonization of the Palearctic region was more plausible than human introduction. The allelic distribution of the Palearctic population was similar to that of species that survived the last glaciation. It is concluded that the African populations expanded during the last interglacial, crossed the Sahara and mixed in North Africa where fixation of the East mitochondrial genome occurred. The species then colonized Europe westward through only one eastern entrance. The coalescent‐based estimate of the time to the ancestor of the Palearctic population was 108 000 years, which is consistent with this scenario. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 904–922. 相似文献
60.
ERIC PASQUET 《Ibis》1998,140(1):150-156
A phylogeny of ten species of nuthatch (Sittidae), including the newly described Kabylie Nuthatch Sitta ledanti of North Africa, was constructed using a sequence of 491 bp of the cytochrome-b gene of mtDNA. On the basis of trees derived using parsimony analysis and neighbour-joining methods, and assessments of robustness based on bootstrap analysis, the following phylogenetic relationships were inferred: the five species of the Sitta canadensis group are a monophyletic group, within which S. canadensis, S. whiteheadi and S. villosa form the sister clade of S. krueperi and S. ledanti; the other relations are not so well supported. These phylogenetic relationships are congruent with morphology. Differences in behavioural and ecological characters as well as biogeographic patterns are discussed. 相似文献