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121.
Beyond floricentrism: The pollination function of inflorescences 总被引:9,自引:0,他引:9
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The kinematics of tongue projection by terrestrial adult California newts, Taricha torosa (Rathke, 1833), are described based upon high-speed cinematography. Tongue projection results from coupled anterior movements of the ceratohyals and branchial arches. Four distinct periods are defined during a projection sequence: preparation, tongue projection, tongue recovery and mouth closing. Key anatomical correlates of projection are described, with special emphasis on the mobility of the hyoid arch. Adult Taricha (Gray, 1850) have lost the mandibulo-hyoid ligament and reduced additional connective tissues present in larvae. These changes decouple the hyoid arch from mouth opening and release the ceratohyals to participate in a tongue projection system distinct from those of ambystomatids and plethodontids. These phylogenetic differences pose questions about the evolution of tongue projection systems in terrestrial urodeles. Currently available data are consistent with the interpretation that terrestrial urodeles have independently evolved specialized tongue projection systems at least twice: the ceratohyal-stable mode of plethodontids and the ceratohyal-mobile system of newts. In all cases, an essential underlying (= plesiomorphic) feature is the presence of the depressor mandibulae muscle. We regard this pathway for mouth opening as a prerequisite which liberated the hyobranchium for alternative function. Comprehensive studies of the mandibulo-hyoid ligament and depressor mandibulae will be vital to modelling the evolution of specialized tongue projection systems of urodeles. 相似文献
125.
IAIN. M. YOUNG ERIC. BLANCHART† CLAIRE CHENU‡ MARK. DANGERFIELD§ CARLOS FRAGOSO¶ MICHEL GRIMALDI‡ JOHN. INGRAM LUCILE JOCTEUR MONROZIER†† 《Global Change Biology》1998,4(7):703-712
The structural framework of soil mediates all soil processes, at all relevant scales. The spatio-temporal heterogeneity prevalent in most soils underpins the majority of biological diversity in soil, providing refuge sites for prey against predator, flow paths for biota to move, or be moved, and localized pools of substrate for biota to multiply. Just as importantly, soil biota play a crucial role in mediating soil structure: bacteria and fungi aggregate and stabilize structure at small scales (μm–cm) and earthworms and termites stabilize and create larger-scale structures (mm–m). The stability of this two-way interaction of structure and biota relations is crucial to the sustainability of the ecosystem. Soil is constantly reacting to changes in microclimates, and many of the soil–plant–microbe processes rely on the functioning of subtle chemical and physical gradients. The effect of global change on soil structure–biota interactions may be significant, through alterations in precipitation, temperature events, or land-use. Nonetheless, because of the complexity and the ubiquitous heterogeneity of these interactions, it is difficult to extrapolate from general qualitative predictions of the effects of perturbations to specific reactions. This paper reviews some of the main soil structure–biota interactions, particularly focusing on soil stability, and the role of biota mediating soil structures. The effect of alterations in climate and land-use on these interactions is investigated. Several case studies of the effect of land-use change are presented. 相似文献
126.
SYNOPSIS. This paper develops a model based on egg-laying ratesand female oviposition temperature preferences in two speciesof cicada, Cacama valvata and Tibicen bifidus, from a centralNew Mexico desert grassland habitat. Output from the model indicatesthat C. valvata achieves maximal daily egg production (eggsfemale1 day1) on days when maximum shade ambienttemperatures reach 41°C; the corresponding value for T.bifidus is 33°C. These differences correlate with the thermalregime experienced by each species in its respective typicalhabitat. Simulations of the effects of variation in mean habitatambient temperature on egg production demonstrated that knowndistributional limits for T. bifidus correspond to thermal conditionsthat reduce daily egg production by only about 510% relativeto long-term means at the study site. The same is true for C.valvata only in lower-ambient temperature habitats. In higher-temperaturehabitats, C. valvata exhibits an unusual plasticity in the timingof adult activity and reproduction that allows it to occupya much wider geographic range than T. bifidus. Contrary to expectations,frequency distributions of predicted daily egg production rateswere negatively skewed in each species' respective typicalhabitat, and Gaussian only in thermally marginal habitats.The findings are discussed in the context of attempts to modelpopulation- and community-level effects of climatic change. 相似文献
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DAVID J. DAVIES ERIC N. POWELL ROBERT J. STANTON JR. 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1989,22(2):207-212
Rates of shell production rarely exceed 500 g CaCO3 .m-2 yr-1 in clastic sediments. Loss of shell carbonate by dissolution greatly exceeds loss by bioerosion and abrasion in most habitats. Rates of shell dissolution in modern sediments, estimated from rates of organic carbon degradation or measured directly, usually exceed 1000 g CaCo3 .M-2 yr-1 . This taphonomic loss is concentrated at or just below the sediment-water interface in the taphonomically-active zone (TAZ). Consequently, except where rates of shell production are very high or rates of organic carbon degradation very low, shells cannot permanently accumulate on the sea floor. Preservation requires rapid burial, usually by physical 'event' processes, to slow down taphonomic loss. Only near the base of the TAZ does the long-term sedimentation rate become an effective mediator of shell preservation as sediment accumulation gradually removes buried shell material from the taphonomically-active zone. 相似文献
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ERIC A. COLHOUN GUUS VAN DE GEER ROBERT S. HILL TREVOR BIRD 《The New phytologist》1989,111(3):531-548
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JOSEPH DONALD SMITH JEFFERY C. KING ERIC C. HOLLAND 《The Journal of eukaryotic microbiology》1982,29(1):103-105
The antiviral agent phosphonoacetic acid inhibits growth of Tetrahymena thermophila at concentrations comparable to those inhibiting growth of other eukaryotic cells, with 50% inhibition at 0.5 mM phosphonoacetic acid. The compound is cytotoxk to Tetrahymena at concentrations greater than 2.0 mM. When a culture of Tetrahymena the growth of which was totally inhibited by 2.0 mM phosphonoacetic acid was diluted with fresh medium, growth resumed in an exponential, rather than synchronous, fashion. [2–14C]phosphonoacetic acid is not metabolized by Tetrahymena. 相似文献
130.