Добірка наукової літератури з теми "Biotic communities Victoria"

The habitats of existing populations of Thelymitra epipactoides in Victoria, Australia, are described according to the physical and biotic environments. The orchid is confined to a range of heathland communities usually near the coast. The species seems to prefer the more open, previously disturbed sites within the community. Following a discussion of the particular habitat requirements of T. epipactoides, some guidelines for the conservation management of the species are outlined.

Laser-based Fourier-Transform Raman spectroscopy (FTRS) has been used to identify in situ compounds of ecophysiological significance in diverse field-fresh Antarctic cryptoendolithic microbial communities. FTRS does not disrupt the community and permits characterization of visible and invisible compounds in their natural configuration within cells and their current or former microhabitat. The small “footprint” of the microscopic laser beam permits accurate analysis of discrete zones of compounds produced by extant or degraded micro-organisms with minimum destruction of the biota. This spatial chemical analysis is applicable to any translucent or exposed habitat or biotic assemblage. Two hydrated forms of biodegradative calcium oxalate were differentiated in black-pigmented and hyaline lichen zones of endolithic communities. The oxalate was restricted to zones containing fungi. Communities dominated by cyanobacteria at Battleship Promontory (77°S) and a newly discovered site at Timber Peak (74°S) contrasted chemically with those dominated by eukaryotic algae at East Beacon (78°S). FTRS also showed the zonation of pigments including chlorophyll and UV-protective carotenoids in situ. At extreme sites on the polar plateau, it revealed the presence of “fossil” endolithics where detrimental climatic changes had made the microbes non-viable or amorphous, being represented solely by their residual bio-molecules. The technique has potential for past or present life-detection anywhere in the world without destruction of the microniche.

AbstractBiotic communities in Antarctic terrestrial ecosystems are relatively simple and often lack higher trophic levels (e.g. predators); thus, it is often assumed that species’ distributions are mainly affected by abiotic factors such as climatic conditions, which change with increasing latitude, altitude and/or distance from the coast. However, it is becoming increasingly apparent that factors other than geographical gradients affect the distribution of organisms with low dispersal capability such as the terrestrial arthropods. In Victoria Land (East Antarctica) the distribution of springtail (Collembola) and mite (Acari) species vary at scales that range from a few square centimetres to regional and continental. Different species show different scales of variation that relate to factors such as local geological and glaciological history, and biotic interactions, but only weakly with latitudinal/altitudinal gradients. Here, we review the relevant literature and outline more appropriate sampling designs as well as suitable modelling techniques (e.g. linear mixed models and eigenvector mapping), that will more adequately address and identify the range of factors responsible for the distribution of terrestrial arthropods in Antarctica.

ABSTRACT The Dry Valleys of Antarctica are a unique ecosystem of simple trophic structure, where the abiotic factors that influence soil bacterial communities can be resolved in the absence of extensive biotic interactions. This study evaluated the degree to which aspects of topographic, physicochemical and spatial variation explain patterns of bacterial richness and community composition in 471 soil samples collected across a 220 square kilometer landscape in Southern Victoria Land. Richness was most strongly influenced by physicochemical soil properties, particularly soil conductivity, though significant trends with several topographic and spatial variables were also observed. Structural equation modeling (SEM) supported a final model in which variation in community composition was best explained by physicochemical variables, particularly soil water content, and where the effects of topographic variation were largely mediated through their influence on physicochemical variables. Community dissimilarity increased with distance between samples, and though most of this variation was explained by topographic and physicochemical variation, a small but significant relationship remained after controlling for this environmental variation. As the largest survey of terrestrial bacterial communities of Antarctica completed to date, this work provides fundamental knowledge of the Dry Valleys ecosystem, and has implications globally for understanding environmental factors that influence bacterial distributions.

Streams and rivers are globally threatened ecosystems because of increasing levels of exploitation, habitat degradation and other anthropogenic pressures. In the Lake Victoria Basin (LVB) in East Africa, these threats are mostly caused by unsustainable land use; however, the monitoring of ecological integrity of river systems has been hampered by a lack of locally developed indices. This study assessed the health of four rivers (Nzoia, Nyando, Sondu–Miriu and Mara) on the Kenyan side of the LVB using physicochemical water quality parameters and a fish-based index of biotic integrity (IBI). Fish tolerance ranking was derived from principal component analysis of water quality parameters, and the concept of niche breadth (NB). The relationship between fish species and water quality parameters was examined with canonical correspondence analysis, whereas community metrics and stressors were evaluated through Pearson network correlation analysis. Fish species richness, trophic structures, taxonomic composition and species tolerance were used to generate the metrics for fish-based IBI. NB showed that most of the fish species were moderately tolerant to poor water. Moderately tolerant and intolerant fish species were negatively correlated with a high level of organic loading in the Mara River. Fish-based IBI scores for the rivers ranged from 26 to 34, with Sondu–Miriu scoring the lowest. Our results show that the cumulative effect of stressors can adequately rank fish species tolerance according to the disturbance gradients and further develop regional metrics to assess river health. Despite the fact that fish communities are declining, continual management and enforcement of environmental regulations are important, with conservation and management of headwaters and low-order streams being essential while they are still species rich.