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STOMATAL-DEPENDENT AND STOMATAL-INDEPENDENT UPTAKE OF NOx 总被引:2,自引:2,他引:0
HENRIK SAXE 《The New phytologist》1986,103(1):199-205
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JOHN KANOWSKI CARLA P. CATTERALL STEPHEN G. MCKENNA RIGEL JENSEN 《Austral ecology》2008,33(4):485-494
Abstract We examined the impact of severe cyclone ‘Larry’ on the vegetation structure of monoculture and mixed species timber plantations, restoration plantings and reference sites in upland rainforests on the Atherton Tableland, north Queensland, Australia. Sites were initially assessed in 2000 and resurveyed in 2006, 6–8 months after the cyclone traversed the region. In both surveys, timber plantations had a relatively open canopy, grassy understorey and few shrubs or small‐sized trees; whereas restoration plantings had a relatively closed canopy, an understorey of bare ground, leaf litter and rainforest seedlings, a high density of small‐diameter trees and a moderate representation of special life forms characteristic of rainforest. Cyclone damage varied with tree size, site type, proximity to the cyclone and stem density. First, the proportion of trees that were severely damaged by the cyclone (major branches broken, stem snapped or pushed over) increased with the diameter of trees across all site types. Second, damage to larger‐sized trees (>10 cm d.b.h., >20 cm d.b.h.) was proportionally highest in monoculture plantations, intermediate in mixed species plantations and rainforest, and lowest in restoration plantings. Third, within site types, damage levels decreased with distance from the cyclone track and with stem density. There was no evidence that topographical position influenced damage levels, at least for timber plantations. We tentatively attribute the high levels of damage experienced by timber plantations to their relatively open structure and the large size of stems in plantations. Restoration plantings generally escaped severe damage by the cyclone, but their continued development towards rainforest conditions may require a coordinated monitoring and maintenance programme to address the potential threat of weed invasion. 相似文献
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Echolocation constraints of Daubenton's Bat foraging over water 总被引:2,自引:0,他引:2
1. Daubenton's Bats ( Myotis daubentonii ) foraging over a stream concentrated their activity over calm surfaces, avoiding an adjacent area with small ripples (< 3 cm high). Aerial insects were most abundant over the ripples, so insect distribution could not explain why the bats avoided this area.
2. The bats flew low over water and always ( N = 22) directed the head forwards, presumably emitting the echolocation beam parallel to the surface, thus minimizing clutter. At an angle of incidence of 30° there was significantly more clutter from the rippled water.
3. The ripples produced ultrasonic noises in the form of transient pulses at an average rate of 6·2 per second. In the present case, such pulses were common enough potentially to interfere with target detection by the bats. Transient noises and echo clutter from moving ripples may be the principal reason why bats generally avoid foraging low over turbulent water.
4. The target strength of a potential insect prey at the water surface and the source levels of the bats' searching signals were measured to use in estimating the echo level at the bat when it detects the prey. The echo level at detection (+ 38 dB sound pressure level) was about the same as the clutter level extrapolated to the detection distance. This suggests that Daubenton's Bat operates at very low signal-to-noise ratios when foraging for insects near the water surface. 相似文献
2. The bats flew low over water and always ( N = 22) directed the head forwards, presumably emitting the echolocation beam parallel to the surface, thus minimizing clutter. At an angle of incidence of 30° there was significantly more clutter from the rippled water.
3. The ripples produced ultrasonic noises in the form of transient pulses at an average rate of 6·2 per second. In the present case, such pulses were common enough potentially to interfere with target detection by the bats. Transient noises and echo clutter from moving ripples may be the principal reason why bats generally avoid foraging low over turbulent water.
4. The target strength of a potential insect prey at the water surface and the source levels of the bats' searching signals were measured to use in estimating the echo level at the bat when it detects the prey. The echo level at detection (+ 38 dB sound pressure level) was about the same as the clutter level extrapolated to the detection distance. This suggests that Daubenton's Bat operates at very low signal-to-noise ratios when foraging for insects near the water surface. 相似文献
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ISABEL SANMARTÍN HENRIK ENGHOFF FREDRIK RONQUIST 《Biological journal of the Linnean Society. Linnean Society of London》2001,73(4):345-390
We analysed patterns of animal dispersal, vicariance and diversification in the Holarctic based on complete phylogenies of 57 extant non‐marine taxa, together comprising 770 species, documenting biogeographic events from the Late Mesozoic to the present. Four major areas, each corresponding to a historically persistent landmass, were used in the analyses: eastern Nearctic (EN), western Nearctic (WN), eastern Palaeoarctic (EP) and western Palaeoarctic (WP). Parsimony‐based tree fitting showed that there is no significantly supported general area cladogram for the dataset. Yet, distributions are strongly phylogenetically conserved, as revealed by dispersal‐vicariance analysis (DIVA). DIVA‐based permutation tests were used to pinpoint phylogenetically determined biogeographic patterns. Consistent with expectations, continental dispersals (WP?EP and WN?EN) are significantly more common than palaeocontinental dispersals (WN?EP and EN?WP), which in turn are more common than disjunct dispersals (EN?EP and WN?WP). There is significant dispersal asymmetry both within the Nearctic (WN→EN more common than EN→WN) and the Palaeoarctic (EP→WP more common than WP→EP). Cross‐Beringian faunal connections have traditionally been emphasized but are not more important than cross‐Atlantic connections in our data set. To analyse changes over time, we sorted biogeographic events into four major time periods using fossil, biogeographic and molecular evidence combined with a ‘branching clock’. These analyses show that trans‐Atlantic distributions (EN‐WP) were common in the Early‐Mid Tertiary (70‐20 Myr), whereas trans‐Beringian distributions (WN‐EP) were rare in that period. Most EN‐EP disjunctions date back to the Early Tertiary (70‐45 Myr), suggesting that they resulted from division of cross‐Atlantic rather than cross‐Beringian distributions. Diversification in WN and WP increased in the Quaternary (< 3 Myr), whereas in EP and EN it decreased from a maximum in the Early‐Mid Tertiary. 相似文献
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