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1.
Studies on coccolithophorids in Mexico are rather scarce, probably due to the use of traditional methods for studying marine phytoplankton (e.g. collection, preservation and analysis). This is the first study of the coccolithophorid flora from west coast of Baja California, Mexico. Bottle samples (4 l) were taken at various depths (5, 25 and 50 m), at fixed stations located on perpendicular transects along the west coast of Baja California, considering three different zones: North, Central and South. A total of 32 samples were studied by optical and scanning electron microscopy, yielding 24 taxa identified (17 species and 5 nominal varieties, plus 2 different varieties). The coccolithophorid assemblages are considered subtropical and coastal (with many cosmopolitan taxa). Emiliania huxleyi and Gephyrocapsa oceanica were the most abundant (relative abundance) and widespread species in the study area. We report 15 new records for the Mexican Pacific. The zonal and vertical distribution of some taxa are briefly discussed, as well as the taxonomy of Rhabdosphaera claviger, Helicosphaera carteri, H. hyalina and related taxa.  相似文献   

2.
This paper gives a general overview of the biological conservation problems of Isla de Cedros, off the central part of the Pacific coast of the Baja California peninsula, Mexico. The island's conservation problems can be summarized as: lack of knowledge, habitat degradation, introduction of exotic species, overhunting, and (presumably) commercial capture of reptiles.  相似文献   

3.
Heavy metals were assessed in four species of sea turtles from the Baja California Peninsula, Mexico, representing the first report of heavy metal concentrations in tissues of post-yearling sea turtles from the Eastern Pacific. Concentrations of Cd measured in C. mydas kidney (653 μg/g dry wt) were the highest ever reported for any sea turtle species. Cd accumulated preferentially in kidney and the ratios of kidney to liver Cd in Baja California turtles were among the highest reported for sea turtles globally. Zn, Ni, and Mn concentrations were also significantly higher in kidney than other tissues, while Cu and Fe were greatest in liver, and all metals were lowest in muscle. With the exception of one value (69.9 μg/g in kidney of C. caretta), Pb was low in all tissues from Baja California. In comparisons across species, kidney of C. mydas had greater Zn and Ni concentrations as compared to other species, although there was no difference in liver metal levels among the species. Positive correlations were detected in the concentrations of Cd, Cu and Ni with the straight carapace length of C. caretta.  相似文献   

4.
Microbial communities of stratified phototrophic bacteria in laminated intertidal sediments north of Estuary El Puente, near San Carlos, Baja California Sur, Mexico,‐were studied. This study describes the macroscopic and microscopic characteristics of the mats, including their annual growth. The mats were located in and along meandering mangrove‐lined tidal channels. Their thickness ranged from 0.5 to 25 cm. Square‐meter areas of polygonal mats were detected in several ponds infiltrated by sea water. The principal microbial community of the upper surface of various morphotypes of microbial mats was identified as cyanobacteria belonging to the genera Microcoleus, Lyngbya, Phormidium, and Oscillatoria. Other cyanobacte‐rial genera such as Pseudanabaena, Spirulina, Synechococcus, and Gloeocapsa, as well as many unidentified diatoms, were also present but at lower population densities. The second inward reddish layers of the microbial mats contained similar cyano‐bacterial genera plus anoxygenic phototrophic bacteria belonging to the genera Chloroflexus, Thiocapsa, Chromatium, Prosthecochloris, Rhodopseudomonas, and Chlorobium, as well as several unidentified bacteria. In situ measurements on the growth of the mats, from intermittent tide sites, showed an annual buildup of two layers: green and reddish. These layers corresponded to a vertical growth of 1.4 ± 0.27 mm/year. Permanently submerged mats did not show vertical growth during the same period of time.  相似文献   

5.
Abstract Aims Ants (Hymenoptera: Formicidae) of the Baja California peninsula are poorly known, with information based largely on scattered museum and literature records. We provide the first comprehensive account of ant species occurring on the peninsula, we examine distribution patterns, and we assess the ‘peninsular effect’ which predicts that species richness declines from the base to the tip of a peninsula. Location Peninsula of Baja California, Mexico. Methods Data collection involved examining, identifying and recording label data from c. 2350 series of ants. These records provide a provisional, if incomplete, species list. We applied the incidence‐based estimator, Chao‐2, to our data base of specimen records to estimate the total number of ant species on the peninsula. We assessed endemism by comparing our peninsular species list to those from adjacent states. The peninsular effect was tested by comparing genus and species level richness between the two states of Baja California, and across five latitudinal blocks. Results We document 170 native ant species in thirty‐three genera, plus six non‐native species, in Baja California. It seems likely that additional species remain to be discovered: the Chao‐2 estimator of species richness, at 206.0 species, is about 20% higher than our observed species richness. About 30% of the species and 20% of the genera are restricted within Baja California to the relatively mesic California Floristic Province of north‐western Baja California. Nearly all of these species also occur in California. Forty‐seven species (27.6%) are peninsula endemics. Using our entire data set, the peninsular effect appears to be strong, with about twice as many species in the northern state of Baja California than are recorded from the southern state of Baja California Sur; the ratio of genera is 33 to 24. However, this effect becomes weak at the species level and absent at the genus level when minimizing habitat effects by omitting species restricted to the California Floristic Province. At a finer scale, across latitudinal blocks of about 1.9°, the number of species declines towards central portions of the peninsula and then increases in the Cape Region. Nine ant species display strongly disjunct distributions, and these occur in two general patterns: peninsula disjuncts and peninsula–mainland disjuncts. Main conclusions The Baja California peninsula supports a diverse and distinctive ant fauna, with the proportion of endemic species similar to that displayed by plants. Patterns of species and genus richness across the five latitudinal blocks provide poor support for the peninsular effect. Moreover, habitat diversity, especially that related to topographic relief, appears to be the most important factor affecting the gradient of ant species richness in Baja California. Additional collections are needed to develop a more complete species list and to determine the boundaries and status of many species. Nevertheless, the present data base provides a useful starting point for understanding the evolution of ant assemblages in Baja California and for comparison with peninsular patterns in other taxa.  相似文献   

6.
The Sierra de La Laguna, in the southern part of the state of Baja California Sur, Mexico, was decreed a biosphere reserve in 1994. It harbors relict plant communities with a high level of endemism. Floristic research has established that the two main communities, the oak–pine woodland (OPW) and the dry tropical forest (TDF), harbor 43 and 33 endemic species, respectively. We segregate the reserve surface into seven major habitats and each endemic species were assigned a hierarchic value into an abundance-distribution scale, useful as dominance ranking. Using such scale, we found that almost half of the species are in the lowest rank (low abundance and aggregate distribution). Using GIS, we obtain the surface for each habitat, where mountainsides represent the largest in the reserve area. We obtained an index of importance from the proportion of endemic species by habitat and its surface occupied, founding that, in spite of the small and fragmented nature of the upland riparian habitats, they have the greatest index value. Consequently, for future conservation plans in the reserve, these habitats should be considered remarkable sites, meriting better attention to ensure endemic plant preservation. Also, since 86% of the endemic species appear in one, two or three habitats, a high dependency on particular environmental conditions is suggested for them.  相似文献   

7.
This study deals with the cyanobacterial composition, and the nitrogen fixation of four members, of cryptobiotic crusts collected from eroded soils in a transitional area between arid and tropical climatic environments. Identification was based on microscopic analyses. Morphotypes were identified directly from reactivated natural crusts and from cultured strains. The identified morphotypes were Scytonema cf. ocellatum, Scytonema sp., Microcoleus cf. paludosus, M. cf. sociatus, Calothrix cf. elenkinii, C. cf. marchica, Nostoc cf. microscopicum, and Phormidium sp. Results show that the cyanobacterial composition of the microbiotic crusts studied is different from those in warmer and cooler deserts, particularly the absence of Microcoleus cf. vaginatus and Nostoc cf. commune in our samples. Such differences could be caused by the transitional character of the area. The results of the acetylene reduction assay show that the capacity of nitrogen fixation of some morphotypes is limited to the heterocyst-forming morphotypes.  相似文献   

8.
Aim We studied the relationship between the size and isolation of islands and bat species richness in a near‐shore archipelago to determine whether communities of vagile mammals conform to predictions of island biogeography theory. We compared patterns of species richness in two subarchipelagos to determine whether area per se or differences in habitat diversity explain variations in bat species richness. Location Islands in the Gulf of California and adjacent coastal habitats on the Baja California peninsula in northwest Mexico. Methods Presence–absence surveys for bats were conducted on 32 islands in the Gulf of California using acoustic and mist‐net surveys. We sampled for bats in coastal habitats of four regions of the Baja peninsula to characterize the source pool of potential colonizing species. We fitted a semi‐log model of species richness and multiple linear regression and used Akaike information criterion model selection to assess the possible influence of log10 area, isolation, and island group (two subarchipelagos) on the species richness of bats. We compared the species richness of bats on islands with greater vegetation densities in the southern gulf (n = 20) with that on drier islands with less vegetation in the northern gulf (n = 12) to investigate the relationship between habitat diversity and the species richness of bats. Results Twelve species of bats were detected on islands in the Gulf of California, and 15 species were detected in coastal habitats on the Baja peninsula. Bat species richness was related to both area and isolation of islands, and was higher in the southern subarchipelago, which has denser vegetation. Log10 area was positively related to bat species richness, which increased by one species for every 5.4‐fold increase in island area. On average, richness declined by one species per 6.25 km increase in isolation from the Baja peninsula. Main conclusions Our results demonstrate that patterns of bat species richness in a near‐shore archipelago are consistent with patterns predicted by the equilibrium theory of island biogeography. Despite their vagility, bats may be more sensitive to moderate levels of isolation than previously expected in near‐shore archipelagos. Differences in vegetation and habitat xericity appear to be associated with richness of bat communities in this desert ecosystem. Although observed patterns of species richness were consistent with those predicted by the equilibrium theory, similar relationships between species richness and size and isolation of islands may arise from patch‐use decision making by individuals (optimal foraging strategies).  相似文献   

9.
Abstract. An ordination analysis of vegetation and flora of Los Cabos Region, Baja California Peninsula, Mexico and its relationships with their environment and geomorphic characteristics was studied at 38 sites, selected based on ecoregion mapping units (EMU) previously delineated for the study area. Multivariate methods were used to analyse the relationship between physical characteristics of the environment and the two primary vegetation types, the Dry tropical forest (DTF) and the Xerophilous scrubland (XS), which together represent 83% of the vegetation cover in the study area. Sites were grouped based on both physical characteristics and relative abundance of plant species. The results of the statistical analysis suggest that altitude, rainfall, temperature, and lithology can help explaining differences between these important vegetation types. In the case of XS, the morpho‐physiognomic characteristics of vegetation in each site discriminated between two scrub types.  相似文献   

10.
Marina victoriae andM. brevis are newly described species from the southern Baja California peninsula, Mexico. The former is a perennial herb locally abundant in the eroded hillsides at the foothills of Sierra de la Victoria, where an oak woodland and a dry tropical forest meet. The latter is an elusive ephemeral inhabiting a narrow strip of land between the mangroves and the desert scrub on an island in the Gulf of California. These two new species belong to the seriesChrysorrhizae, a group native to the Gulf of California basin.  相似文献   

11.
Aim To analyse the distributional patterns of the Baja California Peninsula's resident avifauna, and to generate a regionalization based on a method that uses a parsimony analysis (parsimony analysis of endemicity, PAE) of point data and modelled potential distributions. Location The Baja California Peninsula, Mexico. Methods A data base was constructed containing records of 113 species of resident terrestrial birds present in the Baja California Peninsula. Records and localities were obtained from the literature and from specimens housed in scientific collections world‐wide. Raw data points and potential distribution maps obtained using the software Genetic Algorithms for Rule‐set Prediction (GARP), were analysed with PAE. Results The data base consisted of 4164 unique records (only one combination of species/locality) belonging to 113 terrestrial resident bird species, in a total of 809 localities. From the point distribution matrix, the analysis generated 500 equally parsimonious trees, from which a strict consensus cladogram with 967 steps was obtained. The cladogram shows a basal polytomy and some geographical correspondence of a few resolved groups obtained in the analysis. These results do not allow the recognition of areas defined by avifaunistic associations. From the potential distribution matrix, the analysis generated 501 equally parsimonious trees, and a strict consensus cladogram of 516 steps was obtained. The cladogram shows a higher resolution because of the number of resolved groups with better geographical correspondence and therefore regions are well‐defined. Main conclusions The correspondence of some groupings of species suggest their validity as areas with biogeographical (historical and/or ecological) meaning. This regionalization in the Baja California avifauna seems to be consistent with previous regionalizations for other groups. Hence, PAE is a useful tool for area categorization if reliable point records and prediction tools are available. Our results suggest that the geographical definition is much better using potential data generated by GARP, particularly when they are contrasted with the results from point data. Thus, this is an excellent alternative for developing biogeographical studies, as well as for improving the use of data from scientific collections and other sources of biodiversity information.  相似文献   

12.
A new species of the genusSanicula (sect.Sanicoria) endemic to the southern Sierra Juárez of Baja California, Mexico, is described and illustrated.Sanicula moranii resemblesS. deserticola andS. bipinnatifida, but has thicker basal leaves, with broader petioles and rachises, and shorter fruit prickles that are confined to the apical part of the mericarps. The taxonomic relationships of these species are discussed, along with aspects of their distribution and habitat.
Resumen  Una neuva especie del géneroSanicula (secciónSanicoria) endémica de la Sierra Juárez de Baja California, México, es descrita e ilustrada.Sanicula moranii presenta similitud conS. deserticola yS. bipinnatifida, no obstante tiene gruesas hojas basales con pecíolos y raquis anchos, y espínulas del fruto más cortas que se distribuyen únicamente en la parte apical de los mericarpos. Además, se comentan las relaciones taxonómicas de las tres especies, así como algunos aspectos de sus distribuciones y hábitats.
  相似文献   

13.
Mielke  Wolfgang 《Hydrobiologia》2001,445(1-3):77-83
Loureirophonte psammophila n. sp. was collected from coarse sediments of a beach near La Paz, Baja California, Mexico. The species belongs to the subterranea-group as defined by Fiers (1993). It differs from the other representative of the group, L. subterranea (Lang, 1965) in the presence of an outer dentiform process on 2nd segment of the antennula, the chaetotaxy of P.2–P.5 and the 1-segmented male endopodite P.4. A map with the distribution of the eleven species known so far is provided.  相似文献   

14.
Reliable plans for desert bird conservation will depend on accurate prediction of habitat change effects on their distribution and abundance patterns. Predictive models can help highlight relationships between human‐related and other environmental variables and the presence of desert bird species. Presence/absence of 30 desert bird species of Baja California peninsula was modelled on the basis of explanatory variables taken from the field, maps, and digital imagery. Generalized linear models were fit to each bird species using both variables representing human activity and other environmental factors as predictors that might influence distribution. Probability of species presence was used as a habitat suitability index to evaluate the effect of human activity when the model contained a significant human activity variable. No differences were found in bird species richness between natural sites and those transformed by agriculture or urbanization. Of 59 bird species recorded in surveys, 34% were positively or negatively associated with human‐transformed habitats. Fourteen species seem to benefit from transformation of natural vegetation by agriculture or urbanization, while six were negatively affected. Sensitivity analyses of final models indicated all were robust. Results suggest that the occurrence of a large percentage of bird species inhabiting scrub habitats is sensitive to human habitat transformation. This finding has important conservation implications at regional scale as fragmentation and conversion of desert ecosystems into agricultural and urban areas affect the distribution of species that are highly selective for scrub habitat. Land use and anthropogenic activities seem to change ecological patterns at large spatial scales, but other factors could drive species richness distribution too (i.e. individual species response, species–energy relationships). The spatial modelling approach at regional scale used in this study can be useful for designing natural resource management plans in the Sonoran desert scrub.  相似文献   

15.
Macrocystis pyrifera (L.) Ag.frond elongation rates were measured during autumn-winter, spring and summer in a shallow water (7.5 m depth) kelp bed in Bahía Papalote, northern Baja California. Frond elongation was maximum during spring and minimum during winter. Frond growth was significantly correlated with solar radiation, and was highest in the smallest size fronds (0–2 m). Average frond elongation rate varied between 0.3–11% d–1 during the study period. The relationship between average frond length and elongation rate followed an exponential curve with a negative slope during autumn-winter and summer, but was best described by a straight line during spring. Standard growth rates were obtained by a graphic method. Standard growth rates had intermediate values between those reported for southern California and southern Baja California.M. pyrifera growth cycle shows a different trend from what has been previously reported.  相似文献   

16.

Aim

Desert springs or oases are the only permanent mesic environments in highly water-limited arid regions. Oases have immense cultural, evolutionary and ecological importance for people and a high number of endemic and relic species. Nevertheless, they are also highly vulnerable ecosystems, with invasive species, overexploitation and climate change being the primary threats. We used the arthropod communities' spatiotemporal diversity and distribution patterns as a proxy to understand biodiversity dynamics in two geographically close but ecologically contrasting and highly threatened ecosystems: deserts and oases.

Location

Baja California Peninsula, Mexico.

Methods

Arthropod communities at five oases and surrounding desert scrub areas were sampled in two seasons. Using DNA metabarcoding and traditional taxonomic surveys, we tried to identify what biotic and abiotic characteristics of the habitat are important drivers of arthropod diversity and how these characteristics can change across spatial and temporal scales.

Results

Over 6200 individuals representing 23 orders were collected. In oasis samples, the community composition fluctuated more in space (i.e. among sites) than in time (i.e. seasons). Thus, seasonal changes did not affect oasis community diversity and composition, but the dissimilarity among sites increased with geographic distance. Moreover, anthropic activities negatively correlated with arthropod diversity in oases. On the other hand, the season, geography (e.g. latitude) and biotic characteristics of the habitat (e.g. sampled scrub species) significantly affected the diversity and composition of the desert arthropod communities.

Main Conclusions

Neutral dynamics (e.g. historical climatic events, dispersal limitation and spatial component) and human impact significantly influenced the biodiversity patterns of each oasis. In contrast, the habitat's seasonal variation and biotic characteristics were the most important variables influencing the diversity of the desert communities. Baja California oases harbour distinct invertebrate communities; therefore, each oasis should be conserved individually to preserve these unique assemblages.  相似文献   

17.
Cyanobacteria are important primary producers, and many are able to fix atmospheric nitrogen playing a key role in the marine environment. However, not much is known about the diversity of cyanobacteria in Portuguese marine waters. This paper describes the diversity of 60 strains isolated from benthic habitats in 9 sites (intertidal zones) on the Portuguese South and West coasts. The strains were characterized by a morphological study (light and electron microscopy) and by a molecular characterization (partial 16S rRNA, nifH, nifK, mcyA, mcyE/ndaF, sxtI genes). The morphological analyses revealed 35 morphotypes (15 genera and 16 species) belonging to 4 cyanobacterial Orders/Subsections. The dominant groups among the isolates were the Oscillatoriales. There is a broad congruence between morphological and molecular assignments. The 16S rRNA gene sequences of 9 strains have less than 97% similarity compared to the sequences in the databases, revealing novel cyanobacterial diversity. Phylogenetic analysis, based on partial 16S rRNA gene sequences showed at least 12 clusters. One-third of the isolates are potential N(2)-fixers, as they exhibit heterocysts or the presence of nif genes was demonstrated by PCR. Additionally, no conventional freshwater toxins genes were detected by PCR screening.  相似文献   

18.
La Paz Bay and La Paz Lagoon are water bodies of the Gulf of California that are influenced by waste water discharges from the City of La Paz and from activities of the phosphorite mining company “Rofomex”. Because seaweeds concentrate elements from the water and are used as effective indicators of contamination by metals, we investigated their usefulness in this region. Concentrations of certain major elements (Ca, Fe, K and Na) and trace elements (As, Ba, Co, Cr, Cs, Hf, Rb, Sb, Sc, Se, Sr, Ta, Th, U, Zn and Zr) were determined in 12 species of seaweeds from La Paz Bay and La Paz Lagoon using instrumental neutron activation analysis. The contents of trace elements of environmental importance (As, Co, Cr, Fe, Sb, Se and Zn) in all studied samples are within the range of typical levels for a pristine environment not subjected to anthropogenic impact. Somewhat higher concentrations of Cr (81mg kg−1), Hf (4mg kg−1), Rb (48mg kg−1), Sc (6.3mg kg−1), Ta (0.95mg kg−1), Th (6.8mg kg−1), U (33mg kg−1) and Zn (90mg kg−1) were found in the green seaweed species Ulva (formerly Enteromorpha) intestinalis, whereas such elements as As (77mg kg−1), Sb (1.4mg kg−1) and Se (1.8mg kg−1) were mainly concentrated in the species Sargassum sinicola, Codium cuneatum and Padina mexicana respectively. Because of their higher abundance and heterogeneity in elemental composition the seaweeds species Ulva intestinalis and Caulerpa sertularioides seem to be more suitable for further biomonitoring of heavy metal pollution of the coastal waters in this zone.  相似文献   

19.
Solar salterns are extreme hypersaline environments that are five to ten times saltier than seawater (150–300 g L−1 salt concentration) and typically contain high numbers of halophiles adapted to tolerate such extreme hypersalinity. Thirty-five halophile cultures of both Bacteria and Archaea were isolated from the Exportadora de Sal saltworks in Guerrero Negro, Baja California, Mexico. 16S rRNA sequence analysis showed that these cultured isolates included members belonging to the Halorubrum, Haloarcula, Halomonas, Halovibrio, Salicola, and Salinibacter genera and what may represent a new archaeal genus. For the first time, metabolic substrate usage of halophile isolates was evaluated using the non-colorimetric BIOLOG Phenotype MicroArray™ plates. Unique carbon substrate usage profiles were observed, even for closely related Halorubrum species, with bacterial isolates using more substrates than archaeal cultures. Characterization of these isolates also included morphology and pigmentation analyses, as well as salinity tolerance over a range of 50–300 g L−1 salt concentration. Salinity optima varied between 50 and 250 g L−1 and doubling times varied between 1 and 12 h. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

20.
The Baja California Peninsula and surrounding landmasses harbor an abundant flora in an otherwise harsh and arid environment. Of the many plant groups native to this peninsular and insular region, passionflowers (Passiflora, Passifloraceae) are represented by several conspicuous taxa that all belong to a single lineage, section Dysosmia. Basic questions remain regarding this group, particularly the taxonomic status among the Passiflora arida complex. Therefore, we investigated the claims of endemism, habitat characteristics, and taxon boundaries with in section Dysosmia in the Baja California region using extensive sampling of herbarium specimens and iNaturalist observations. We confirmed that only one of the native Passiflora taxa (P. fruticosa) was endemic to the Baja California Peninsula, with an additional taxon (P. palmeri) considered near‐endemic. Environmental data revealed significant distinctions between the habitats of many of the native taxa as well as within the P. arida complex, especially with respect to precipitation and temperature tolerances. Geometric morphometric analyses of leaf shape were largely not successful at separating taxa, indicating leaf shape may not be a good indicator of taxon identity in this particular group. Based on ecological differences and discrete macro‐ and micromorphological features, a varietal name is here synonymized and a new combination is proposed: Passiflora pentaschista.  相似文献   

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