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1.
Regulation of Apical Dominance by Ethephon, Irradiance and CO2 总被引：2，自引：0，他引：2
A. SKYTT ANDERSEN 《Physiologia plantarum》1976,37(4):303-308
Apical dominance of intact pea plants (Pisum sativum L. cv. Alaska) was found to be diminished by high irradiance and by increasing the CO2 content of the air. Ethephon treatment of young plants resulted in an outgrowth of laterals, but this was significant only when the apical dominance already was weakened by high irradiance and/or CO2. 相似文献
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PIERRE-OLIVIER ANTOINE LEVENT KARADENIZLI GERÇEK SARAÇ SEVKET SEN 《Zoological Journal of the Linnean Society》2008,152(3):581-592
A giant rhinocerotoid is described for the first time south of the Black Sea, in Turkey. The single specimen, a fragmentary radius referred to Paraceratherium sp., originates from conglomerates nearby at Gözükizilli, in the Çankiri–Çorum Tertiary basin. These layers correspond to the Lower member of the Kizilirmak Formation. The same locality (Gözükizilli-2) yields also the small rhinocerotid Protaceratherium sp., cf. P. albigense (Roman, 1912). Three other mammal localities (Gözükizilli-1, in the Lower Member of the formation, with several rodent species; Tepe 641 and Kizilirmak, in the Upper Member, with a diversified micro- and macro-mammal fauna) allow us to refer the Kizilirmak Formation as a whole to the Late Oligocene. All the observed taxa have strong Asian and/or European affinities, which precludes any geographical insulation for this part of Anatolia during the Late Oligocene. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 152 , 581–592. 相似文献
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The immediate effects of a high intensity wildfire on the ant communities of a heath and a mallee site in semi-arid north-western Victoria are reported. Following fire the number of species trapped on the ground doubled (to ca. 80 each site), total ant abundance decreased by half (due to the demise of previously dominant species), surface activity of reproductive castes increased, and dramatic changes in species relative abundance (including shifts toward greater equitability) occurred. These changes are interpreted in terms of fire-induced simplification of the habitat and release from competition with dominant species. The results appear to illustrate the importance of interspecific competition in structuring foraging activity in mallee ant communities. Observations are also reported on seed-harvesting by ants, including changes in harvester ant abundance, germination from within-nest seed storage, and the first record of Heteroponera removing seeds. 相似文献
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Niche theory predicts that few closely related species can co‐occur because such species tend to be ecologically similar and niche differentiation is required to avoid competitive exclusion. We analyse the co‐occurrence of a remarkable 10–15 species of the ant genus Monomorium occurring within single 10 × 10 m plots in a tropical savanna of northern Australia. Most of the species are undescribed, so we use genetic analysis to validate our species demarcations. We document nest dispersion patterns, and investigate differentiation in the three primary niche dimensions: space, time and food. We also examine species differences in competitive abilities, by describing rates of foraging activity, foraging ranges, worker aggression, and levels of behavioural dominance. Analyses of nest and forager distributions showed very limited evidence of spatial segregation within plots. The great majority of species foraged either exclusively or primarily during daylight hours. Body size and isotopic analyses indicated very limited dietary differentiation. Such limited niche partitioning occurred despite the species differing markedly in their competitive abilities as measured by rates of resource discovery, recruitment and monopolization. Our findings defy the traditional assumption that multiple closely related and ecologically similar species of highly interactive taxa cannot co‐occur. It seems very likely that species coexistence in our study system is determined to a very large degree by stochastic processes relating to dispersal and establishment, as predicted by neutral theory. However, neutral theory assumes competitive equivalence, whereas we found very marked differences in the competitive abilities of our co‐occurring species. We suggest that competitive exclusion is prevented by the modular nature of ant colonies, with competition limiting colony performance but not preventing occurrence. We conclude that other factors that allow species persistence, and not just competitive equivalence, can allow dispersal and establishment processes to drive species coexistence. 相似文献
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ABSTRACT Red-shouldered hawks (Buteo lineatus) are a species of special conservation concern in much of the Great Lakes region, and apparent population declines are thought to be primarily due to habitat loss and alteration. To evaluate red-shouldered hawk-habitat associations during the nesting season and at the landscape scale, we conducted repeated call-broadcast surveys in central Minnesota, USA, across 3 landscapes that represented a range of landscape conditions as a result of differing management practices. In 2004, we conducted repeated call-broadcast surveys at 131 locations in 2 study areas, and in 2005, we surveyed 238 locations in 3 study areas. We developed models relating habitat characteristics at 2 spatial scales to red-shouldered hawk occupancy and assessed support for these models in an information-theoretic framework. Overall, a small proportion of nonforest (grass, clear-cut area, forest <5 yr old), and a large proportion of mature deciduous forest (>40 yr old), had the strongest association with red-shouldered hawk occupancy (proportion of sites occupied) at both spatial scales. The landscape conditions we examined appeared to contain a habitat transition important to red-shouldered hawks. We found, in predominately forest landscapes, the amount of open habitat was most strongly associated with red-shouldered hawk occupancy, but in landscapes that included slightly less mature forest and more extensive open habitats, the extent of mature deciduous forest was most strongly associated with red-shouldered hawk occupancy. Our results suggested that relatively small (<5 ha) patches of open habitat (clear-cuts) in otherwise forested landscapes did not appear to influence red-shouldered hawk occupancy. Whereas, in an otherwise similar landscape, with smaller amounts of mature deciduous forest and larger (>15 ha) patches of open habitat, red-shouldered hawk occupancy decreased, suggesting a threshold in landscape composition, based on both the amount of mature forest and open area, is important in managing forest landscapes for red-shouldered hawks. Our results show that during the nesting season, red-shouldered hawks in central Minnesota occupy at similar rates landscapes with different habitat compositions resulting from different management strategies and that management strategies that create small openings may not negatively affect red-shouldered hawk occupancy. 相似文献
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