ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01512.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractStrong tidal currents flowing over mobile sediment give rise to migrating bedforms termed megaripples and sandwaves. For colonizing epifauna a megaripple field is a habitat subject to repeated disturbance as advancing megaripples bury all epifauna in their path. Eight epifaunal species occur in a megaripple field in tipper Spencer Gulf, South Australia. The stalked bryozoanLanceopora obliquais an r‐strategist and occurs patchily in high densities. An ascidianPolycarpa pedunculata, probably a K‐strategist, and a group of four species of articulated bryozoans, have much lower population densities which are predictable according to the frequency of disturbance. Other species occur in low, but variable densities. Some species show adaptations in morphology, behaviour or life history patterns which favour survival in this unusual environm

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01513.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThe value of cattle dung as a food resource for the bush flyMusca vetustissima(Walker) in the winter rainfall agricultural region of southwestern Australia was assessed by bioassay in the laboratory. The size (headwidth) of adult females was measured from flies reared on different samples of dung. Variation in size correlated with seasonal patterns of pasture growth, larger flies being produced during the growing season from autumn to spring. Size declined with senescence of annual pastures in late spring and early summer, occurring later in southern areas where the growing season was longer. After pasture senescence, dung from shorter growing season areas usually produced larger flies, apparently a result of the inverse relationship between digestibility of feed and length of growing season. Dung from irrigated perennial pastures never produced flies as large as that from annual pastures but generally high values were sustained during summer. Grazing of cereal stubble and feeding of hay in annual pasture areas during summer usually caused some increase in fly size. A spontaneous resurgence in the size of flies often occurred several weeks after pasture senescence and was attributed to more thorough digestion as a result of reduced intake of less palatable dry pasture.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01514.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractSeveral leaf characteristics, including toughness and total phenols and condensed tannins, were measured in Australian rain forest leaves of different ages and related to observed herbivory rates. In most cases, toughness and chemical toxicity increased as leaves aged, and corresponding insect grazing decreased. Herbivory losses ranged from 4.8% to 32.5% leaf area losses, and were more positively correlated with toughness than with phenolics. It is suggested that a suite of factors, including physical and chemical characteristics of leaves as well as spatial and temporal factors, interact to create variation in grazing intensities.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01515.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractWater stress, concentrations of foliar nutrients and damage of foliage by insects were studied over an eleven month period, for eight dieback eucalypts and eight closely matched healthy trees growing in close association on two grazing properties near Brisbane. Four healthy eucalypts in a neighbouring State Forest were also studied. The study region had suffered severe climatic stress between 1972 and 1976 when dieback was first observed by residents and when high populations of defoliating insects were observed. Dieback trees had a higher proportion of foliage damaged by insects and higher concentrations of foliar nutrients than did matched healthy trees. The study period was one of low climatic stress during which dieback and healthy trees followed similar seasonal patterns of predawn xylem pressure potential. Dieback trees developed lower daytime minimum xylem pressure potentials than did matched healthy trees, and differed in their stomatal responses. A model of initiation and development of rural eucalypt dieback is proposed. This may have general application to many non‐specific rural diebacks in which heavy insect damage is implicated. The balance between rural eucalypts and their insect herbivores is precarious. Any factor capable of causing extensive defoliation, or an increase in foliar nitrogen, or an increase in populations of insect herbivores may upset this balance. A positive feedback loop may be activated, whereby the production of nitrogen rich epicormic foliage enhances a build up of insect populations. Repeated insect defoliation leads to tree dieback. Evidence in the literature supporting the model is reviewed and aspects requiring further research are outline

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01516.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractCover and abundance of all understorey vascular plant species were studied on permanent plots on two areas (Maramingo and Reedy Creek) in the foothill forests of East Gippsland, eastern Victoria. The areas were harvested for sawlogs and pulpwood in 1976, and parts were burned to assist regeneration. Plots were assessed before harvesting and at intervals until 1980. Changes in total species composition were minimal, although there were many positive and negative changes in crown cover and abundance of individual species. Total cover of understorey vegetation was reduced initially but recovered well on both areas. By 1980, cover at Maramingo was slightly greater than the low levels before harvesting. Some species there were favoured by burning while others were not. At Reedy Creek the original dense understorey had not regenerated fully by 1980. Snig tracks had revegetated to 60% of original average cover but log landings were slower to revegetate. Introduced species were initially a very minor component of the vegetation on both areas: they remained so at Reedy Creek (confined mainly to tracks) but at Maramingo three species proliferated along with other small herbaceous plants.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01517.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractTransects across the margins of rainforests with eucalypt forests at two sites in New South Wales are described. At Girard State Forest along ten transects it was consistently found that pure rainforest occurs where there is no evidence of past burning; and that rainforest tree species appear to be invading and replacing eucalypt forest through a formerly burned ecotone area. A similar pattern was found at Barrington Tops. It is suggested that adaptations shown by species of tall open forests which enable them to regenerate rapidly after burning may have evolved initially in a fire free, prehuman rainforest environment in response to other types of disturbance.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01518.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractKwongan is an important vegetation type in southwestern Australia. It occurs in small patches throughout Tutanning Nature Reserve. Eleven patches, totalling 64 ha, were found to contain 315 vascular plant species: over half the total species recorded for the whole reserve. The patches were floristically heterotoneous (cf. Westhoff&van der Maarel 1973) but could be grouped according to three major soil types. The richest kwongan was on pockets of shallow duplex soil occurring midway down the landscape profile. Species richness appears to decline only slightly with increasing time since fire. Presence of emergentBanksia attenuataat one site did not influence the overall speciesrichness of that area.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractIndirect evidence provides additional support for the hypothesis that the level of available nitrogenous food is the major limiting influence in the abundance of the koala. It appears that koalas may select for low fibre content which is usually correlated with high nitrogen levels of leaves.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractMature plants of species which characteristically occupy the mobile crests and upper slopes of the central Australian sandridges are more tolerant of sand burial or undercutting than those of the lower slopes and swales. Seedlings growing on the mobile crest areas are susceptible to sand burial, even during wet years. The young shoots of vegetatively spreading species are less susceptible than individual seedlings of the same size.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1983.tb01521.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY