ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01536.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe indigenous arid zone shrub Acacia victoriae grows rapidly and is relatively shortlived. The relationship between population structure, growth and mortality was examined by annual monitoring of over 1200 plants at twenty sites from 1978 to 1981. Sites were reassessed in 1992. Plants of similar size varied greatly in growth rate. Annual mortality ranged up to 16%. Of 752 plants alive in 1981, 206 (27%) survived until 1992. A transition matrix model, based on growth and mortality over the 3 year period, predicted a size‐class frequency distribution after 12 years that was significantly different from the one observed in 1992. The proportion of large plants present in 1992 was higher than predicted. The model's prediction that a large proportion of plants would remain in the lower size‐classes was reliable. We concluded that size is not a good indicator of age and that it is unreliable to identify cohorts of this species by examining size‐class frequency distribu

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01537.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe heat‐pulse method was used to estimate transpiration rates continuously for periods up to 2 years in mature trees of Eucalyptus wandoo and Eucalyptus salmonophloia at two topographic locations in a remnant native woodland in the Western Australian wheatbelt. Annual transpiration per tree ranged from about 11400 to 18000 L per tree. Highest transpiration rates occurred in late spring or early summer, depending on rainfall distribution. The trees were able to rapidly utilize water following heavy rain outside the agricultural growing season. Extrapolating transpiration rates from single trees to an area of woodland showed that annual transpiration at the ridge site was 150 mm and 168 mm at a site alongside a drainage line. Scaling up transpiration from individual trees requires caution and should allow for variability in trees and soils. The role of trees in curtailing salinization is discusse

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01538.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the field, the population density (n) of crowded, living ramets of Salvinia molesta ranged from 2500 m−2in nutrient‐poor water to more than 30 000 m−2in nutrient‐rich water. Biomass of living shoots (B) in some localities exceeded 600 gm−2dry weight (150 tonnes ha−1fresh weight) and shoots plus roots of living and floating dead material exceeded 1600 gm−2dry weight (400 tonnes ha−1fresh weight). The ultimate limit B= 105n0.5suggested by previous authors was not exceeded. The highest n and smallest ramets occurred in nutrient‐rich water and B was a linear function of n. Field experiments confirmed no effect of n, but a strong effect of nutrient availability, on ramet weight.In a glasshouse experiment, ramet populations did not ‘self‐thin’ along the log log B‐n trajectory of slope ‐0.5, which has been suggested for aclonal plants, but followed trajectories having slopes closer to +1.0 before halting at the ambient B‐n limit. Nutrient concentrations in the plants increased during the experiment, causing ramet size to decrease and slopes of log log B‐n trajectories to depart from +1.0 by amounts which reflected the degree to which nutrient concentration had changed. Under constant conditions, mean ramet size is expected to remain constant and log log B‐n trajectories to travel in a straight line of slope +1.0 to the ambient B‐n limit. This behaviour of salvinia, whose ramets consist of a single structural module, is contrasted with that expected of clonal plants whose ramets are made up of multiple structural modules.A logistic model explained the increases in n and biomass of living and dead ramets when ramets were assumed to have constant longevity, constant time to decay, and when both the B‐n limit and size of ramets were dependent on nitrogen content of the plant. There was no indication that physiological integration within phenets halted production of new ramets when carrying capacity was reached and new ramets continued to be produced on top of older ramets. Rates of ramet mortality were equal to, and

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01539.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractPopulations of the morphologically defined taxon Trissolcus basalis (Wollaston) from two major hosts (Nezara viridula [L.] and Agonoscelis rutila [F.]) were tested, using biological criteria, to determine whether they represented populations of one genetical species, or whether they represented populations of two host‐associated sibling species. Individuals from both hosts exhibited no obvious courtship differences and they selected mates at random in mate‐choice experiments. In addition, female wasps produced offspring of both sexes after mating with a male from either population. We conclude that the individuals of the two populations tested constitute a single genetical spec

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01540.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe growth of saplings of Atherosperma moschatum within a Tasmanian forest during 1987/88 was negatively correlated with canopy closure. The dry weights and specific leaf weights of new leaves were also negatively correlated with canopy closure, but leaf areas showed a maximum at an intermediate canopy closure. Leaf chlorophyll concentration was positively correlated with canopy closure. Internode length was not correlated with canopy closure, but the ratio of leaf dry weight to internode length was negatively correlated with canopy closure. These results indicate that the load of photosynthetically active radiation may be a major determinant of the variation in plant development.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01541.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractStony downs consist of grassy areas that alternate with areas that have a substantial stone cover. The stone‐covered areas are impermeable, and most rain falling on them runs off, substantially increasing the effective rainfall in adjacent grassy areas. As a result, 20–25 mm of rain on stony downs wetted the soil around the grass to a depth of 140–170 mm and allowed sustained grass response. This is much less than the 35–40 mm of rain required for the same response on red clay or grey clay plains.Grasses respond very rapidly after rain. Some have green shoots the day after rain, and all have responded by the second day. Ephemerals dry off in 4–6 weeks, but most tussock grasses still have some green foliage 8–10 weeks after rain. Deeper rooted tussock grasses remain green for so long because most of the moisture that reaches deeper roots after rain remains there. Most moisture loss is through the soil surface and is recognizable as a drying front that descends through the soil profile. Soil above the drying front is nearly air dry (<5% moisture) while soil below the front has substantial moisture (14–16%). By about a month after rain in summer, the drying front is at a depth of about 80–120 mm. This is near the tips of the roots of ephemeral grasses and the ephemerals then dry off rapidly. Only the tips of the leaves of deep rooted grasses like Mitchell grass (Astrebla spp.) dry off. Their leaves continue to remain mostly green during most of the second month after rain and they do not dry off completely until the third month when the drying front reaches the bottom of the m

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01542.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractDiaspore (seed and/or fruit) survivorship of 12 species of North Queensland rainforest trees was monitored over a 4 week period in two rainforests on the Atherton Tableland, north Queensland, Australia, with replicated sites in forest interiors, canopy gaps, forest edges and adjacent pastures. General linear modelling was used to estimate the relative importance of forest site, habitat, species and diaspore type on survival.The probability of survival varied significantly among species, between habitat, forest and diaspore types. Survival averaged 41.2% at day 28, was greater in one forest (Curtain Fig, 56.1%) than the other (Lamins Hill, 25.3%) and was apparently inversely related to the abundance of rodents. In both forests, survival declined in the order: pasture ≥ forest edge ≥ forest interior = canopy gap. A lack of significant difference between the forest interior and canopy gap is consistent with findings in other rainforest sites within Australia, but contrasts with most results from other continents. The study also indicated that diaspore weight was an important intrinsic variable affecting survival, the predators (mostly rodents) taking small to moderately large diaspores rather than the very large o

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01543.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe present paper examines patterns of termite eating in Australian mammals and lizards (total numbers of species, volume percentage of diet) relative to climate (arid, semi‐arid, temperate‐mesic). Most termite eaters in arid and semi‐arid Australia are lizards. Termite consumptio as a proportion of total lizard diet decreases from arid to mesic climates. More mammal species are relatively termite specialized (>50%) in arid than in semi‐arid and mesic regions. Termite consumption in echidnas resembles that of the lizards: relatively high in the arid and relatively low in the mesic zone. For the Dasyuridae, termites comprise only a minor fraction (<10%) in their diet, irrespective of climate. It is argued that the climatic peculiarities of inland Australia (scant and variable rainfall) cause marked seasonality in termite availability, supporting specialized termite eaters in only the most energy‐frugal forms (lizards, echidnas). Areas of future research are i

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01544.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn a ‘restinga’ habitat of southeastern Brazil, we studied the food habits and the microhabitat use of two lizards with distinct foraging modes: the tropidurid Tropidurus torquatus, a sit‐and‐wait predator, and the teiid Cnemidophorus ocellifer, a wide forager. The diet of the two species differed strongly, indicating a low level of similarity in their trophic niche. The sit‐and‐wait predator fed mainly on mobile prey, whereas the wide forager fed mainly on sedentary prey (larvae). The spatial niche breadth of T. torquatus was larger than that of C. ocellifer. Despite interspecific differences, the two species overlapped greatly in micro‐habitat use. The data indicate that at Linhares the two lizard species differed more in food resources than in microhabitat, and that most of the food differences reflect the foraging patterns o

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1994.tb01545.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY