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  • 1
    ISSN: 1432-1939
    Keywords: Larrea tridentata ; Mexico ; Deserts ; Canopy architecture ; Foliole movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The creosote bush (Larrea tridentata) is a common desert perennial with bifoliate, amphistomatic, divaricate leaves. The leaves can vertically close their folioles and vary their profile with respect to direct solar radiation. Field data from different Mexican deserts showed a significant correlation between foliole aperture and mean foliole inclination: in plants in which folioles were more open, the foliole surfaces were less vertical. In a series of field experiments in the Chihuahuan Desert, foliole aperture varied significantly with the water-status of the plant and the hour of the day. In moist plants, folioles opened in the early morning and closed in the afternoon. Water-stressed plants showed significantly lower foliole apertures. A simulation of the light interception patterns of the plants showed that foliole closure in water-stressed individuals reduces direct radiation interception by around 24%. Most (64%) of the reduction in interception was due to the vertical inclination of the photosynthetic surfaces induced by foliole closure in the water-stressed plants. The rest (36%) of the reduction in interception was due to differential self-shading between foliole pairs, which was higher in the closed folioles of the water-stressed plants, but operated more towards the early hours of the day.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Dunes ; Germination ; Mexico ; Ecophysiology ; Neotropic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study describes the germination responses of ten tropical dune species to several factors to which their seeds are exposed in the field. Species studied were: three sand dune endemics (Amaranthus greggii, Palafoxia lindenii, and Trachypogon gouini), three pantropical coastal species (Sesuvium portulacastrum, Sporobolus virginicus and Ipomoea stolonifera) and four cosmopolitan grasses also found inland (Panicum repens, Panicum maximum, Pappophorum vaginatum and Andropogon glomeratus). Six species germinated when exposed to different constant temperatures. Four required temperature fluctuation (S. portulacastrum, P. lindenii, S. virginicus, P. repens). Light promoted germination of three species (S. Portulacastrum, P. vaginatum, P. lindenii). Species varied in their degree of sensitivity to salinity. Seeds of T. gouini, I. stolonifera, S. portulacastrum, P. repens, P. Maximum and P. vaginatum were able to germinate under some of the salinity concentrations. Not all species were able to recover after being transferred to distilled water. Seedling emergence was inhibited when seeds were buried. This response was related to depth and to seed size. S. portulacastrum and S. virginicus were the most affected. Nitrates only affected germination response of two species. Seed age promoted germination under a wider range of conditions. P. lindenii showed very heterogeneous responses depending on seed cohort. No dormancy mechanisms were found, other than a thermoperiod and/or light requirement for some of the species. Cosmopolitan grasses tolerated both sand burial and salinity, although the endemics were the most successful in emerging from sand burial; coastal pantropicals were very tolerant to high saline concentrations and recovered completely.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 212 (1991), S. 209-219 
    ISSN: 1573-5117
    Keywords: Anostraca ; Notostraca ; Spinicaudata ; Laevicaudata ; Branchiopoda ; Mexico ; distribution ; conchostracan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We inventorize the known distribution of the species of Anostraca, Notostraca, Spinicaudata, and Laevicaudata present in Mexico. Determinations of the species and their distribution involved: 1) Examination of Mexican collections of phyllopods, 2) Extensive sampling in 17 states, and 3) Study of laboratory cultures. The number of phyllopod species known to occur in Mexico is 27: 14 of Anostraca, including three undescribed species, 1 of Notostraca, 10 of Spinicaudata, and 2 of Laevicaudata. These results also include 44 new state records. The records of Branchinecta packardi are the first for Mexico. Some species have extensive distributions, not limited to Mexico: Streptocephalus mackini, S. texanus, Thamnocephalus platyurus, Triops longicaudatus and Leptestheria compleximanus. The species known only from Mexico are Streptocephalus kargesi, S. moorei, Paralimnetis mapimi, two undescribed species of Branchinecta, and an undescribed species of Streptocephalus. The largest number of species found to occur in the same pond at one time was eight.
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  • 4
    ISSN: 1573-5117
    Keywords: Branchinecta ; Branchiopoda ; Anostraca ; Mexico ; hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A new fairy shrimp,Branchinecta belki n.sp., endemic to the south of Coahuila state is described and figured. A total of nine species of phyllopods, including the new species, occur in ponds in the type area. The laboratory hybridization ofB. belki andB. packardi through ‘no-choice’ mating tests in reciprocal crosses is discussed. A mixture of characteristics of parental species is present in male F1 and F2 hybrids. This may provide a biological tool, or ‘search image’ (sensu Wiman, 1979a), for detecting male hybrids, should such exist, between theBranchinecta species of this study in nature. In addition to the reported interspecific hybridizations inStreptocephalus (Wiman, 1979a & 1979b) and inArtemia (Bowenet al., 1985) under laboratory conditions, the new evidence inBranchinecta suggests that absence of efficient premating mechanisms may be common in Anostraca.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 255-256 (1993), S. 467-474 
    ISSN: 1573-5117
    Keywords: Rotifera ; zoogeography ; Mexico
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This faunistic survey of Mexican Rotifera, covering 32 localities, mostly in Central Mexico, has yielded 96 taxa of which 41 are new to Mexican fauna. The zoogeographic status of the rotifer fauna of Mexico was reevaluated on the basis of the present data.
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