Using single- and multi-target regression trees and ensembles to model a compound index of vegetation condition

An important consideration in conservation and biodiversity planning is an appreciation of the condition or integrity of ecosystems. In this study, we have applied various machine learning methods to the problem of predicting the condition or quality of the remnant indigenous vegetation across an extensive area of south-eastern Australia—the state of Victoria. The field data were obtained using the ‘habitat hectares’ approach. This rapid assessment technique produces multiple scores that describe the condition of various attributes of the vegetation at a given site. Multiple sites were assessed and subsequently circumscribed with GIS and remote-sensed data.     

NUTRIENT LOAD CHARACTERIZATION FROM INTEGRATED SOURCE DATA FOR THE LOWER MISSISSIPPI RWER1

ABSTRACT: Nutrient data from all available sources for the lower Mississippi River were examined for potential differences among sampling agencies and geographic locations for the period between 1960 and 1998. Monthly means grouped by parameter, sampling location and agency, were calculated and compared as paired sets, excluding those months where data were not available for both sets. Some significant differences were found between various agencies collecting nutrient data on the river, as well as between various stretches of river, especially in the case of phosphorus nutrient data. Results were used to synthesize data sets from which a history of nutrient loading in the Mississippi River was determined. General trends in nitrate+nitrite, total Kjeldahl nitrogen, orthophosphate, total phosphorus and silica loads, as well as changes in nutrient proportions and the specific limiting nutrient (by month) are reported. This study provides a useful summary of contemporary and historical nutrient data that may assist in the evaluation of Mississippi River water quality and its potential effect on the Gulf of Mexico.     

The dynamics of arsenic in four paddy fields in the Bengal delta

Irrigation with arsenic contaminated groundwater in the Bengal Delta may lead to As accumulation in the soil and rice grain. The dynamics of As concentration and speciation in paddy fields during dry season (boro) rice cultivation were investigated at 4 sites in Bangladesh and West Bengal, India. Three sites which were irrigated with high As groundwater had elevated As concentrations in the soils, showing a significant gradient from the irrigation inlet across the field. Arsenic concentration and speciation in soil pore water varied temporally and spatially; higher As concentrations were associated with an increasing percentage of arsenite, indicating a reductive mobilization. Concentrations of As in rice grain varied by 2-7 fold within individual fields and were poorly related with the soil As concentration. A field site employing alternating flooded-dry irrigation produced the lowest range of grain As concentration, suggesting a lower soil As availability caused by periodic aerobic conditions.     

Specialisations of swimming muscles in the pelagic antarctic fish Pleuragramma antarcticum

The distribution and ultrastructure of muscle-fibre types has been investigated in adult and juvenile specimens of the pelagic high-antarctic silverfish Pleuragramma antarcticum Boulenger, 1902 collected from the South Shetland Islands during the winter of 1984/1985. Two main fibre-types were identified in araldite-embedded material. The axial musculature was mainly composed of poorly vascularised, largediameter muscle fibres which were densely packed with myofibrils (volume density 81 and 72% for adults and juveniles, respectively). These ultrastructural characteristics are typical of fast-twitch fibres. The number of capillaries ner unit cross-sectional area and the volume density of mito     

The encrusting spongeHalisarca laxus: population genetics and association with the ascidianPyura spinifera

The encrusting spongeHalisarca laxus forms a seemingly obligate association with the stalked solitary ascidianPyura spinifera. In 1991 we examined spatial variation and short-term temporal variation in this association at three neighbouring sites in southeastern Australia. This sponge dominated the surface of almost all the 500 individual ascidians examined, with mean cover usually exceeding 90%. This pattern was consistent among sites and throughout the year of the study. The domination of a small isolated patch of habitable substratum by a sponge is most unusual, given that they are regarded as relatively poor recruiters. To understand how this association might be maintained, we determined the underlying genotypic diversity of the sponge population using starch-gel electrophoresis.P. spinifera is a clump-forming ascidian and usually occurs in clumps of up to 22 individuals. Electrophoretic surveys, based on six variable allozyme loci, revealed that at a total of five plots within three neighbouring New South Wales populations, single sponge genotypes may cover entire ascidian clumps; although a clump sometimes played host to more than one sponge clone. Allele frequencies (averaged across four loci that appear to conform to Mendelian inheritance) showed little variation among populations (standardised genetic variance,F _ST=0.013). Nevertheless, sponge populations were genotypically diverse, with samples from 63 of 172 individual clumps displaying unique clonal genotypes. Moreover, multi-locus genotypic diversity within all sites approached the level expected for sexual reproduction with random mating. Taken together, these data imply thatH. laxus produces sexually-derived larvae that are at least moderately widelly dispersed. Given the relatively small size of the patches that this sponge inhabits, we also conclude that these larvae are good colonists and good spatial competitors on their ascidian hosts.     

Cross-hybridization of the chromosome 13/21 alpha satellite DNA probe to chromosome 22 in the prenatal screening of common chromosomal aneuploidies by fish

In a routine application of commercially available centromeric DNA probes for the prenatal screening of common trisomies involving the autosomes 13, 18, and 21, and sex chromosomes, four cases of discrepancy between fluorescence in situ hybridization (FISH) results and follow-up cytogenetic analysis were observed from a total of 516 cases of amniocentesis. In three of these cases, the results were false negative, and in one false positive. In this case, amniocentesis was performed because of a positive triple test in a 34-year-old woman with previous infertility treatment. The alpha satellite DNA probe for chromosomes 13/21 revealed five signals in 50 per cent of uncultured amniocytes, while standard cytogenetic analysis showed a normal karyotype. FISH analysis on metaphase chromosomes demonstrated the location of the additional signal in the centromeric region of chromosome 22. This additional signal was also present in the centromeric region of chromosome 22 of the mother, providing evidence for a possible inherited polymorphism in chromosome 22 responsible for unspecific hybridization with the alpha satellite probe for chromosomes 13/21 in this case. The observed polymorphism in centromeric regions may contribute to unreliability of the use of the 13/21 alpha satellite probe for prenatal screening by FISH.     

Size and age compositions and reproductive biology of the nervous shark Carcharhinus cautus in a large subtropical embayment, including an analysis of growth during pre- and postnatal life

The lengths-at-age of individuals of the nervous shark Carcharhinus cautus in Shark Bay, Western Australia, have been determined and used to explore the types of situation when it might be advisable to shift from employing a von Bertalanffy equation to a more complex equation for describing the growth of this species and of elasmobranchs in general. The reproductive biology of C. cautus was also examined in order to construct curves for describing growth throughout life from conception as well as from parturition. The presence, in November and early December, of fresh bite marks on the sides of mature females and of a very high proportion of spent individuals among mature males indicate that C. cautus copulates in late October/early November. Ovulation and conception occur in late November/early December and parturition takes place approximately 11 months later. Since mature non-pregnant females contain vitellogenic ova for 12-13 months, i.e. from November or December to the following December, and mature pregnant females contain embryos for 11 months, i.e. from December to October, C. cautus has a biennial reproductive cycle. By parturition, the females and males of C. cautus had reached ~28% and 32% of their lengths at their maximum observed ages, respectively. The maximum recorded total lengths and ages of females and males of C. cautus were 133 cm and 16 years and 111 cm and 12 years, respectively. Females and males reached maturity at ~101 and ~91 cm, respectively, and at least 50% of females and males had become mature by the end of their sixth and fourth years of life after parturition, respectively. The three-parameter, von Bertalanffy growth curves provided reasonably good fits to the lengths-at-age of females and males of C. cautus during just postnatal life and throughout the whole of pre- and postnatal life. While the four-parameter, Schnute growth curve significantly improved the fit to these data for both females and males from conception and for females from parturition, it was recognised that the likelihood ratio test is very sensitive when, as in these cases, there are a large number of data points. A number of interrelated factors were thus taken into account when discussing circumstances when it might be appropriate to switch from using a von Bertalanffy growth curve to the more complex Schnute growth curve.     

Distribution of Trypetesa lampas (Cirripedia,Acrothoracica) in various gastropod shells

The distribution of Trypetesa lampas (Hanoock) and its rates of infection of different species of gastropod shells in the waters of Anglesey were studied. T. lampas was found in depths from 3 to at least 25 fathoms (5 to 46 m). It infected dead shells, mainly of Buccinum undatum L., Colus gracilis (da Costa), Neptunea antiqua (L.) and Natica alderi (Forbes); it was absent from shells occupied by hermit crabs in the intertidal zone. Significantly more B. undatum shells were infected than shells of N. antiqua and Natica alderi, and more of both C. gracilis and N. antiqua than of Natica alderi. Larger shells of B. undatum were more likely to be infected than were the smaller ones. The number of females per shell varied with the shell length raised to the power 2.39 instead of as expected with the square of the length.