Search Results - (Author, Cooperation:C. N. Johnson)

2012-03-24

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Ascomycota ; Biomass ; Charcoal ; Climate Change ; *Ecosystem ; *Extinction, Biological ; Fires ; Fossils ; Herbivory ; Humans ; Plants ; Population Dynamics ; Queensland ; Time ; Trees ; *Vertebrates

2018-05-23

The American Society for Microbiology (ASM)

0019-9567

1098-5522

Medicine

2015-09-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Biodiversity ; DNA, Fungal/analysis ; *Ecosystem ; Environment ; Humans ; *Mycorrhizae/genetics/isolation & purification/physiology ; Phylogeny ; Phylogeography ; Plant Roots/*microbiology ; *Symbiosis ; Water ; Wind

2015-06-26

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

*Air Movements ; Arctic Regions ; Asia ; Cluster Analysis ; Europe ; Freezing ; Global Warming/*statistics & numerical data ; Ice Cover ; North America ; Seasons ; *Temperature ; Thermodynamics

1089-7550

AIP Digital Archive

Physics

High quality YBa2Cu3O7−∂ (YBCO) thin films that combine good electrical properties and smooth surfaces without particles are important for many future applications. Today most films with good electrical properties have secondary phases in the form of copper-rich surface particles and small Y2O3 inclusions in the film. This work investigates how the surface particle coverage and superconducting properties of dc-magnetron sputtered thin films change as a function of target stoichiometry and the use of Ar:O2 or Ar:O2:N2O as sputtering gases. In an attempt to eliminate the copper-rich surface particles, sputtering was performed using targets deficient in copper (by up to 28%). However, only a small reduction in the number of the surface particles was achieved with an Ar:O2 sputtering gas mixture and little change in the superconducting properties was found. No new secondary phases could be detected. When nitrous oxide (N2O) was added to the sputtering gas, the superconducting properties deteriorated and Ba2CuO3 precipitates formed. To compensate for the usual Y2O3 formation in YBCO, yttrium-rich targets were also investigated. A significant reduction in the number of copper-rich surface particles was achieved when an Ar:O2 sputtering gas mixture was used and an yttrium-rich phase (possibly Y2BaCuO5) was detected. By incorporating N2O in the sputtering gas, the formation of copper-rich surface particles and the precipitates of the yttrium-rich phase was avoided and hence smooth films were deposited. No deterioration of the superconducting properties was observed in this case. It is concluded that the use of yttrium-rich targets and N2O in the sputtering gas may be a reliable way to achieve smooth films without surface particles and with satisfactory superconducting properties. It appears that the excess yttrium in the target compensates for the usual formation of Y2O3 inclusions and the N2O is needed to avoid barium desorption. © 1995 American Institute of Physics.

Electronic Resource

1442-9993

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract   There has been debate over the cause of the extinction of ‘megafauna’ species during the late Pleistocene of Australia. One view is that environmental change, either natural or human-induced, was the main factor in the extinctions. Some support for this comes from the observation that, among herbivores, most of the species that went extinct were apparently browsers rather than grazers. Browsers would presumably have been more dependent on shrubland and woodland habitats than grazers, and it has been argued that such habitats might have contracted in response to aridity or changed fire regimes in the late Pleistocene. Here, we test this idea by comparing extinction rates of browsers and grazers in the late Pleistocene, controlling for body mass in both groups. We show that in both browsers and grazers the probability of extinction was very strongly related to body mass, and the body mass at which extinction became likely was similar in the two groups. It is true that more browsers than grazers went extinct, but this is largely because most very large herbivores in the late Pleistocene were browsers, not because large browsers were more likely to go extinct than similarly sized grazers. This result provides evidence against some forms of environmental change as a cause of the extinctions.

Electronic Resource

1442-9993

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract  Many species of herbivorous mammals declined to extinction following European settlement of inland Australia. The rufous bettong, Aepyprymnus rufescens (a macropodoid marsupial), is ecologically similar to many of these species. We used analysis of microsatellite markers to determine dispersal patterns and mating system characteristics in a cluster of local populations of A. rufescens, with the aim of gaining a better understanding of regional population dynamics in such species. Particularly, we asked whether the rufous bettong showed source-sink dynamics, as Morton (1990) hypothesized that many mammals may have been made vulnerable to extinction through such processes. We compared populations separated by distances of up to 12 km, and detected significant genetic differentiation among local populations (FST = 0.016). Females displayed greater genetic structuring than males, suggesting that females dispersed over shorter distances or less frequently than males. Geographic distance was weakly related to genetic distance between populations suggesting some gene flow at this scale, and paternity assignment indicated that dispersal can occur over distances of up to 6.5 km. Our study populations varied widely in density, but density did not explain the pattern of genetic differentiation observed. These findings of significant structure among populations, some influence of distance on genetic divergence and that density explains little of the divergence among populations, suggested that source-sink dynamics did not play a large role among these populations. Variance in male mating success was low (maximum assigned paternity for an individual male was 14% of offspring). While data on multiple maternity were limited, roughly half of repeat maternity was assigned to the same male, suggesting that the mating system of the rufous bettong is not purely promiscuous.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Within taxonomic groups, there is almost always a positive relationship between the size of geographic range and the local abundance of species. This pattern has attracted much interest, and several ecological mechanisms have been proposed as causes of it. However, these hypotheses do not ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The reproductive success of females in several species of primates is limited by the availability of food4, and the observation that reproductive success generally declines with group size suggests that females in groups compete with one another for access to resources5'6. The regression ...

Electronic Resource

1432-1939

Bettongia gaimardi ; Mesophellia ; Spore dispersal ; Ectomycorrhizae ; Fire

Springer Online Journal Archives 1860-2000

Biology

Abstract Several species of marsupials in Eucalyptus forests in Australia feed predominantly on the sporocarps of hypogeous fungi. This feeding is apparently beneficial to the fungi as it results in dispersal of spores. As these fungi are in almost all cases ectomycorrhiza-forming species, mycophagy by mammals may play an important role in the maintenance of mycorrhizal symbiosis in Eucalyptus forests. Fire is frequent and a dominant ecological factor in these forests, and this study tested the hypothesis that fire triggers both increased sporocarp production by some hypogeous ectomycorrhizal fungi associated with eucalypts, and increased mycophagy by mammals. Three experimental burns were set in E. tenuiramus forest in southeastern Tasmania. Digging activity (which reflects feeding on hypogeous fungi) by a mycophagous marsupial, the Tasmanian bettong Bettongia gaimardi, increased up to ten-fold after fire, with a peak about 1 month post-fire. This was associated with a similar pattern of increase in sporocarp production, which was due to species in the family Mesophelliaceae (especially Castoreum tasmanicum and Mesophellia spp.). This family appears to have radiated in association with eucalypts and has an exclusively Australasian distribution, unlike many of the other ectomycorrhizal fungi collected in this study which are cosmopolitan and have broad host ranges. No B. gaimardi were killed by fire, and there was no increase in mortality following fire. Population density increased after fire as a result of immigration of adult males. However, body condition and fecundity of individual B. gaimardi were maintained at pre-fire levels. This suggests that the availability of energy to B. gaimardi increased as a result of fire, and the fact that the contribution of fungus to the diet of B. gaimardi was high on burnt relative to control sites suggests further that this increase in energy availability was provided by hypogeous fungi. Effects of fire on hypogeous fungi and B. gaimardi were short-lived; all measured variables returned to control values about 4 months after fire. The capacity of B. gaimardi to survive fire and to harvest the increased sporocarp production triggered by fire provides a mechanism for the rapid dispersal of spores after fire. This should result in the establishment of ectomycorrhizae very early in post-fire succession. Because only some species of ectomycorrhizal fungi fruited in response to burning, fire probably has a strong influence on community structure among ectomycorrhizal fungi.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Electronic Resource

1432-0762

Springer Online Journal Archives 1860-2000

Biology

Summary Female red-necked wallabies settle within their mothers' home ranges, apparently for life, while males disperse at about two years of age. However, sons spend much more time with their mothers before dispersing than do daughters of similar ages. Females who associate regularly with their subadult offspring are less likely to reproduce successfully at their next breeding attempt than are females who spend little time with their subadults, and sons therefore impose greater short-term reproductive costs on their mothers than do daughters. Females who are generally gregarious also suffer reduced reproductive success, even though reproductive success is independent of local density. It is suggested that the reproductive costs to females of associating with their subadult offspring, and other relatives, are incurred through tolerance of ecological competition from those kin, and therefore reflect a form of prolonged maternal investment, which is initially heaviest in sons but is sustained for longer periods in daughters. Females produce equal numbers of male and female offspring, and spend equal amounts of time suckling them in infancy.

Electronic Resource