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41.
Abstract ‘Alpine grazing reduces blazing’ is a widely and strongly held view concerning the effects of livestock grazing on fuels, and therefore fire behaviour and impact, in Australia's high country landscapes. As a test of this hypothesis, we examined the patterns of burning across the alpine (treeless) landscapes of the Bogong High Plains in Victoria, following the extensive fires of January 2003. Data were collected from multiple transects, each 3–5 km long, with survey points located randomly at either 50, 200 or 500 m intervals. The transects traversed the major regions of the Bogong High Plains, both grazed and ungrazed. At each point, we recorded whether the point was burnt or unburnt, the vegetation type (closed‐heath, open‐heath, grassland or herbfield), the estimated prefire shrub cover, slope, aspect, and a GPS location. At burnt heathland sites, we recorded the minimum twig diameter (an a posteriori measure of fire severity) in a sample of common shrubs. In total, there were 108 km of transect lines, 419 survey points and 4050 twig measurements, with sample points equally distributed across grazed and ungrazed country. The occurrence of fire (i.e. burnt or unburnt) in grazed and ungrazed areas was analysed by logistic regression; the variation in twig diameters by anova . Approximately half of all points were burnt. There was no statistically significant difference between grazed and ungrazed areas in the proportion of points burnt. Fire occurrence was determined primarily by vegetation type, with the proportion burnt being 0.87 for closed‐heath, 0.59 for open‐heath, and 0.13 for grassland and all snow‐patch herbfield points unburnt. In both closed‐heath and open‐heath, grazing did not significantly lower the severity of fire, as measured by the diameter of burnt twigs. We interpret the lack of a grazing effect in terms of shrub dynamics (little or no grazing effect on long‐term cover of taller shrubs), diet and behaviour of cattle (herbs and dwarf shrubs eaten; tall shrubs not eaten and closed‐heath vegetation generally avoided), and fuel flammability (shrubs more flammable than grass). Whatever effects livestock grazing may have on vegetation cover, and therefore fuels in alpine landscapes, they are likely to be highly localized, with such effects unlikely to translate into landscape‐scale reduction of fire occurrence or severity. The use of livestock grazing in Australian alpine environments as a fire abatement practice is not justified on scientific grounds.  相似文献   
42.
Using ancient DNA sequences of subfossil European pond turtles ( Emys orbicularis ) from Britain, Central and North Europe and accelerator mass spectrometry radiocarbon dating for turtle remains from most Swedish sites, we provide evidence for a Holocene range expansion of the pond turtle from the southeastern Balkans into Britain, Central Europe and Scandinavia, according to the 'grasshopper pattern' of Hewitt. Northeastern Europe and adjacent Asia were colonized from another refuge located further east. With increasing annual mean temperatures, pond turtles reached southern Sweden approximately 9800 years ago. Until approximately 5500 years ago, rising temperatures facilitated a further range expansion up to Östergötland, Sweden (approximately 58°30'N). However, around 5500 years ago pond turtle records suddenly terminate in Sweden, some 1500 years before the Holocene thermal maximum ended in Scandinavia and distinctly earlier than previously thought. This extinction coincides with a temporary cooling oscillation during the Holocene thermal maximum and is likely related to lower summer temperatures deteriorating reproductive success. Although climatic conditions improved later again, recolonization of Sweden from southern source populations was prevented by the Holocene submergence of the previous land connection via the Danish Straits that occurred approximately 8500 years ago.  相似文献   
43.
1. Variation and control of nutritional input is an important selective force in the evolution of mutualistic interactions and may significantly affect coevolutionary modifications in partner species. 2. The attine fungus‐growing ants are a tribe of more than 230 described species (12 genera) that use a variety of different substrates to manure the symbiotic fungus they cultivate inside the nest. Common ‘wisdom’ is that the conspicuous leaf‐cutting ants primarily use freshly cut plant material, whereas most of the other attine species use dry and partly degraded plant material such as leaf litter and caterpillar frass, but systematic comparative studies of actual resource acquisition across the attine ants have not been done. 3. Here we review 179 literature records of diet composition across the extant genera of fungus‐growing ants. The records confirm the dependence of leaf‐cutting ants on fresh vegetation but find that flowers, dry plant debris, seeds (husks), and insect frass are used by all genera, whereas other substrates such as nectar and insect carcasses are only used by some. 4. Diet composition was significantly correlated with ant substrate preparation behaviours before adding forage to the fungus garden, indicating that diet composition and farming practices have co‐evolved. Neither diet nor preparation behaviours changed when a clade within the paleoattine genus Apterostigma shifted from rearing leucocoprinous fungi to cultivating pterulaceous fungi, but the evolutionary derived transition to yeast growing in the Cyphomyrmex rimosus group, which relies almost exclusively on nectar and insect frass, was associated with specific changes in diet composition. 5. The co‐evolutionary transitions in diet composition across the genera of attine ants indicate that fungus‐farming insect societies have the possibility to obtain more optimal fungal crops via artificial selection, analogous to documented practice in human subsistence farming.  相似文献   
44.
Induced herbivore resistance in seaweeds: a meta-analysis   总被引:3,自引:0,他引:3  
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45.
Serradium semiaquaticum sp. n. is described from several North Italian caves. The new species is very similar to, and probably the closest relative of S. hirsutipes Verhoeff, 1941, which lives in the same caves as S. semiaquaticum but has a wider distribution. Serradium hirsutipes is redescribed and newly recorded from several caves. Serradium semiaquaticum is remarkable by its semiaquatic habits and correspondingly modified spiracles and mouthparts, whereas S. hirsutipes is normal in these respects. The genus Serradium is reviewed, and a key to the known species is given. Serradium as currently defined may not be a monophyletic group. Serradium semiaquaticum and S. hirsutipes show strong gonopodal similarity (synapomorphy?) with species of Polydesmus, subgenus Acanthotarsius.  相似文献   
46.
A STATIC NON-OVERLOAD POLLEN COLLECTOR   总被引:5,自引:1,他引:4  
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47.
This paper analyses ethical issues in forensic psychiatric research on mentally disordered offenders, especially those detained in the psychiatric treatment system. The idea of a 'dual role' dilemma afflicting forensic psychiatry is more complicated than acknowledged. Our suggestion acknowledges the good of criminal law and crime prevention as a part that should be balanced against familiar research ethical considerations. Research aiming at improvements of criminal justice and treatment is a societal priority, and the total benefit of studies has to be balanced against the risks for research subjects inferred by almost all systematic studies. Direct substantial risks must be balanced by health benefits, and normal informed consent requirements apply. When direct risks are slight, as in register-based epidemiology, lack of consent may be counter-balanced by special measures to protect integrity and the general benefit of better understanding of susceptibility, treatment and prevention. Special requirements on consent procedures in the forensic psychiatric context are suggested, and the issue of the relation between decision competence and legal accountability is found to be in need of further study. The major ethical hazard in forensic psychiatric research connects to the role of researchers as assessors and consultants in a society entertaining strong prejudices against mentally disordered offenders.  相似文献   
48.
Storm's Stork Ciconia stormi is one of the rarest of the storks, regarded as globally endangered and found only in parts of western Indonesia, Malaysia and Brunei. Prior to this study, its breeding biology was unknown and the population status in Indonesia was not well understood. Its breeding habitat, prey, behaviour, voice, eggs and the development of the young are described here for the first time. Breeding biology was studied in 1989 at a nest in south Sumatra, Indonesia. The nest was in the transition zone between mangrove and freshwater swamp forest. Incubation took less than 29 days, and two eggs hatched. Fish 2–7 cm long comprised 67% of the prey for feeding young. The chick was fully feathered at 52–57 days and was seen flying when 57–62 days old. The species is rare in south Sumatra. It occurs in low numbers and flocks of up to seven birds were observed. The density is estimated at 20–40 birds within 110,000 ha of primary swamp forest. At this density, the population would be below 100 birds in south Sumatra and between 100 and 300 in Indonesia. The species is threatened by development and conversion of primary swamp forest.  相似文献   
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