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151.
Regulation of Crustacean Molting: A Multi-Hormonal System 总被引:5,自引:3,他引:2
CHANG ERNEST S.; BRUCE MARILYN J.; TAMONE SHERRY L. 《Integrative and comparative biology》1993,33(3):324-329
SYNOPSIS. In order to increase in size, arthropods must firstmolt (shed) their confining exoskeleton. This molting processis under the immediate control of the steroid molting hormone20-hydroxyecdysone (20-HE). Both the initial rise in circulatinghormone concentration and a coordinated decline are necessaryfor successful molting. Synthesis and/or release of ecdysone,the precursor to 20-HE, is regulated by the neuropeptide molt-inhibitinghormone (MIH). We have determined the primary amino acid sequenceof MIH in the lobster, Homarus americanus. This peptide hasa high degree of identity with the lobster hyperglycemic hormone.Another endocrine factor that appears to be involved in moltingis the juvenile hormone-like terpenoid methyl farnesoate (MF).We have characterized hemolymph MF binding proteins during themolt cycle. In addition, recent data indicate that MF may stimulatethe secretion of 20-HE in vivo and in vitro. 相似文献
152.
Abstract Two sets of data were used to evaluate the procedure for rapid assessment of rivers described by Chessman (1995): (i) 72 samples from four habitats at 27 sites on the Nepean River and tributaries; and (ii) 41 riffle samples from the Blue Mountains. In the Nepean system all the sites had moderate anthropogenic disturbance but none had gross organic pollution. There were, however, conductivity differences related to mixed sandstone and shale lithology. The sites differed widely in natural physical attributes such as stream order (2–6) and altitude (40–600 m). The Blue Mountains data included sites with little or no anthropogenic disturbance and sites greatly affected by organic pollution. There was again a wide range of altitudes (15–1000 m) but stream orders were more restricted (1–4). The occurrence of macroinvertebrate families was analysed using cluster analysis (TWINSPAN) and ordination (semi-strong hybrid multidimensional scaling). Relationships between the patterns observed, the SIGNAL biotic index, and physical and chemical data were investigated. The Nepean data showed that the sample size of 100 animals used in the rapid procedure was sufficient to reveal natural distribution patterns in the communities, and that SIGNAL was essentially independent of these patterns. In the Blue Mountains, water pollution had a greater effect on macroinvertebrate communities than the physical habitat, and SIGNAL distinguished sites with differing levels of pollution. 相似文献
153.
A modification of the Rayleigh test for vector data 总被引:2,自引:0,他引:2
154.
CHRISTOPHER N. JACQUES JONATHAN A. JENKS CHRISTOPHER S. DEPERNO JARET D. SIEVERS TROY W. GROVENBURG TODD J. BRINKMAN CHRISTOPHER C. SWANSON BRUCE A. STILLINGS 《The Journal of wildlife management》2009,73(8):1282-1291
ABSTRACT Ungulate mortality from capture-related injuries is a recurring concern for researchers and game managers throughout North America and elsewhere. We evaluated effects of 7 variables to determine whether ungulate mortality could be reduced by modifying capture and handling procedures during helicopter net-gunning. During winter 2001–2006, we captured 208 white-tailed deer (Odocoileus virginianus) and 281 pronghorn (Antilocapra Americana) by helicopter net-gunning throughout the Northern Great Plains. Of 281 pronghorn, 25 (8.9%) died from capture-related injuries; 12 were from direct injuries during capture, and 13 occurred postrelease. Of 208 deer, 3 (1.4%) died from injuries sustained during helicopter captures, with no mortalities documented postrelease. We used logistic regression to evaluate the probability that ungulates would die of injuries associated with helicopter net-gun captures by analyzing effects of snow depth, transport distance, ambient and rectal temperatures, pursuit and handling times, and whether individuals were transported to processing sites. The probability of capture-related mortality postrelease decreased 58% when transport distance was reduced from 14.5 km to 0 km and by 69% when pursuit time decreased from 9 minutes to <1 minute. Wildlife managers and researchers using helicopter capture services in landscapes of the Midwest should limit pursuit time and eliminate animal transport during pronghorn and white-tailed deer capture operations to minimize mortality rates postrelease. 相似文献
155.
PETER STILING DANIEL MOON† ANTHONY ROSSI† BRUCE A. HUNGATE‡ BERT DRAKE§ 《Global Change Biology》2009,15(8):1895-1902
The effects of elevated CO2 on plant growth and insect herbivory have been frequently investigated over the past 20 years. Most studies have shown an increase in plant growth, a decrease in plant nitrogen concentration, an increase in plant secondary metabolites and a decrease in herbivory. However, such studies have generally overlooked the fact that increases in plant production could cause increases of herbivores per unit area of habitat. Our study investigated leaf production, herbivory levels and herbivore abundance per unit area of leaf litter in a scrub‐oak system at Kennedy Space Center, Florida, under conditions of ambient and elevated CO2, over an 11‐year period, from 1996 to 2007. In every year, herbivory, that is leafminer and leaftier abundance per 200 leaves, was lower under elevated CO2 than ambient CO2 for each of three species of oaks, Quercus myrtifolia, Quercus chapmanii and Quercus geminata. However, leaf litter production per 0.1143 m2 was greater under elevated CO2 than ambient CO2 for Q. myrtifolia and Q. chapmanii, and this difference increased over the 11 years of the study. Leaf production of Q. geminata under elevated CO2 did not increase. Leafminer densities per 0.1143 m2 of litterfall for Q. myrtifolia and Q. chapmanii were initially lower under elevated CO2. However, shortly after canopy closure in 2001, leafminer densities per 0.1143 m2 of litter fall became higher under elevated CO2 and remained higher for the remainder of the experiment. Leaftier densities per 0.1143 m2 were also higher under elevated CO2 for Q. myrtifolia and Q. chapmanii over the last 6 years of the experiment. There were no differences in leafminer or leaftier densities per 0.1143 m2 of litter for Q. geminata. These results show three phenomena. First, they show that elevated CO2 decreases herbivory on all oak species in the Florida scrub‐oak system. Second, despite lower numbers of herbivores per 200 leaves in elevated CO2, increased leaf production resulted in higher herbivore densities per unit area of leaf litter for two oak species. Third, they corroborate other studies which suggest that the effects of elevated CO2 on herbivores are species specific, meaning they depend on the particular plant species involved. Two oak species showed increases in leaf production and herbivore densities per 0.1143 m2 in elevated CO2 over time while another oak species did not. Our results point to a future world of elevated CO2 where, despite lower plant herbivory, some insect herbivores may become more common. 相似文献
156.
CAIYUN LUO GUANGPING XU ZENGGUO CHAO SHIPING WANG XINGWU LIN YIGANG HU ZHENHUA ZHANG JICHUANG DUAN XIAOFENG CHANG AILING SU YINGNIAN LI XINQUAN ZHAO MINGYUAN DU YANGHONG TANG BRUCE KIMBALL 《Global Change Biology》2010,16(5):1606-1617
Knowledge about the role of litter and dung decomposition in nutrient cycling and response to climate change and grazing in alpine ecosystems is still rudimentary. We conducted two separate studies to assess the relative role of warming and grazing on litter mass loss and on the temperature sensitivity of litter and dung mass loss. Experiments were conducted for 1–2 years under a controlled warming–grazing system and along an elevation gradient from 3200 to 3800 m. A free‐air temperature enhancement system (FATE) using infrared heaters and grazing significantly increased soil temperatures (average 0.5–1.6 °C) from 0 to 40 cm depth, but neither warming nor grazing affected soil moisture except early in the growing seasons at 30 cm soil depth. Heaters caused greater soil warming at night‐time compared with daytime, but grazing resulted in greater soil warming during daytime compared with night‐time. Annual average values of the soil temperature at 5 cm were 3.2, 2.4 and 0.3 °C at 3200, 3600 and 3800 m, respectively. Neither warming nor grazing caused changes of litter quality for the first year of the controlled warming–grazing experiment. The effects of warming and grazing on litter mass losses were additive, increasing litter mass losses by about 19.3% and 8.3%, respectively, for the 2‐year decomposition periods. The temperature sensitivity of litter mass losses was approximately 11% °C?1 based on the controlled warming–grazing experiment. The annual cumulative litter mass loss was approximately 2.5 times that of dung along the elevation gradient. However, the temperature sensitivity (about 18% °C?1) of the dung mass loss was about three times that of the litter mass loss. These results suggest greater warming at night‐time compared with daytime may accelerate litter mass loss, and grazing will enhance carbon loss to atmosphere in the region through a decrease of litter biomass and an increase of dung production with an increase of stocking rate in future warmer conditions. 相似文献
157.
MERRILL NICOLAS BRUCE S. RUBIDGE 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2010,43(1):45-59
Nicolas, M. & Rubidge, B.S. 2010: Changes in Permo-Triassic terrestrial tetrapod ecological representation in the Beaufort Group (Karoo Supergroup) of South Africa. Lethaia, Vol. 43, pp. 45–59.
For more than a century, large collections of fossils from the Beaufort Group have been built up at various museums in South Africa and have been handled as separate databases in the individual museums. Because of the unique time-extensive record of continental vertebrate biodiversity represented by the fossils of the Beaufort Group, a single standardized database has been compiled for the fossils collected from the Beaufort Group housed in South African museums. This unique data set has enabled the determination of terrestrial tetrapod ecological representation from the Middle Permian to Middle Triassic Beaufort Group of South Africa. □ Beaufort Group , biodiversity , ecology , Permo-Triassic . 相似文献
For more than a century, large collections of fossils from the Beaufort Group have been built up at various museums in South Africa and have been handled as separate databases in the individual museums. Because of the unique time-extensive record of continental vertebrate biodiversity represented by the fossils of the Beaufort Group, a single standardized database has been compiled for the fossils collected from the Beaufort Group housed in South African museums. This unique data set has enabled the determination of terrestrial tetrapod ecological representation from the Middle Permian to Middle Triassic Beaufort Group of South Africa. □ Beaufort Group , biodiversity , ecology , Permo-Triassic . 相似文献
158.
Comparison of ecosystem water-use efficiency among Douglas-fir forest, aspen forest and grassland using eddy covariance and carbon isotope techniques 总被引:13,自引:0,他引:13
STÉPHANE PONTON LAWRENCE B. FLANAGAN KARRIN P. ALSTAD BRUCE G. JOHNSON KAI MORGENSTERN† NATASCHA KLJUN† T. ANDREW BLACK† ALAN G. BARR‡ 《Global Change Biology》2006,12(2):294-310
Comparisons were made among Douglas‐fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C3) grassland for ecosystem‐level water‐use efficiency (WUE). WUE was defined as the ratio of photosynthetic CO2 assimilation rate and evapotranspiration (ET) rate. The ET data measured by eddy covariance were screened so that they overwhelmingly represented transpiration. The three sites used in this comparison spanned a range of vegetation (plant functional) types and environmental conditions within western Canada. When compared in the relative order Douglas‐fir (located on Vancouver Island, BC), aspen (northern Saskatchewan), grassland (southern Alberta), the sites demonstrated a progressive decline in precipitation and a general increase in maximum air temperature and atmospheric saturation deficit (Dmax) during the mid‐summer. The average (±SD) WUE at the grassland site was 2.6±0.7 mmol mol?1, which was much lower than the average values observed for the two other sites (aspen: 5.4±2.3, Douglas‐fir: 8.1±2.4). The differences in WUE among sites were primarily because of variation in ET. The highest maximum ET rates were approximately 5, 3.2 and 2.7 mm day?1 for the grassland, aspen and Douglas‐fir sites, respectively. There was a strong negative correlation between WUE and Dmax for all sites. We also made seasonal measurements of the carbon isotope ratio of ecosystem respired CO2 (δR) in order to test for the expected correlation between shifts in environmental conditions and changes to the ecosystem‐integrated ratio of leaf intercellular to ambient CO2 concentration (ci/ca). There was a consistent increase in δR values in the grassland, aspen forest and Douglas‐fir forest associated with a seasonal reduction in soil moisture. Comparisons were made between WUE measured using eddy covariance with that calculated based on D and δR measurements. There was excellent agreement between WUE values calculated using the two techniques. Our δR measurements indicated that ci/ca values were quite similar among the Douglas‐fir, aspen and grassland sites, despite large variation in environmental conditions among sites. This implied that the shorter‐lived grass species had relatively high ci/ca values for the D of their habitat. By contrast, the longer‐lived Douglas‐fir trees were more conservative in water‐use with lower ci/ca values relative to their habitat D. This illustrates the interaction between biological and environmental characteristics influencing ecosystem‐level WUE. The strong correlation we observed between the two independent measurements of WUE, indicates that the stable isotope composition of respired CO2 is a useful ecosystem‐scale tool to help study constraints to photosynthesis and acclimation of ecosystems to environmental stress. 相似文献
159.
BRUCE J. TURNER DAVID D. DUVERNELL THOMAS. M. BUNT MICHAEL G. BARTON 《Biological journal of the Linnean Society. Linnean Society of London》2008,95(3):566-582
Three pupfish (Cyprinodon) morphotypes (two endemic) occur in some of the young (6000 ypb) saline lakes on the Bahamian island of San Salvador. The ‘normal’ morph, a detritivore/omnivore, is not different in its general features from Cyprinodon variegatus from other Bahamian islands. ‘Bulldog’ is a scale‐eater/piscivore that preys upon normal pupfish, and ‘bozo’ is a specialized molluskivore. Reproductive isolation among these morphs is not predicted by the evolutionary biology of congeneric species because sympatry of even morphogically and ecologically quite divergent pupfishes has usually resulted in hybridization/introgression. Survey of variation at eight microsatellite loci reveals that sympatric normal and bulldog populations are genetically distinctive by several criteria, and are therefore likely reproductively isolated. The bulldog morph in Crescent Pond is markedly divergent from those in Little Lake and Osprey Lake, a finding consistent with, although it does not prove, separate parallel origins of this morphotype. The data also suggest that the bulldogs in the latter two lakes did not evolve by intralacustrine speciation from the current sympatric normal populations. Some of the genetic data suggest that the bozo morph may also be reproductively isolated from the other two pupfishes, but only a small, pooled sample of this rare morphotype was available, and the issue is not resolved. Isolating mechanisms between bulldog and normal morphs are of special interest because of the possibility that they arose as a consequence of a predator–prey relationship. A strong correlation between reproductive isolation and predator–prey interactions could provide an important example of ecological speciation via direct selection against heterotypic interactions. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 566–582. 相似文献
160.
Abstract: Isopod crustaceans are rarely preserved in the fossil record. Herein, an appraisal of the fossil record for the cirolanid isopods is presented. Five genera are briefly discussed, including Bathynomus, Brunnaega, Palaega, Pseudopalaega and Cirolana. A key for the cirolanid genera known to date from the fossil record is provided based mostly on pleotelson characters. From the early Miocene of the Slovak part of the Vienna Basin, Cirolana feldmanni sp. nov. is described being only the fifth fossil Cirolana species known to date and one of the few with preserved appendages. The material exhibits preservation suggesting biphasic moulting; the mode of preservation suggests a rather short time between shedding the posterior and anterior parts of the exoskeleton instead of hours or even days known in extant taxa. As no subsequent transport or physical disturbance was inferred, the specimens can be stated as in situ preservation. From the palaeoecological point of view, it is concluded that Cirolana feldmanni sp. nov. is the first unequivocal fossil deep‐water Cirolana as suggested by the accompanied fauna. 相似文献