Showing papers on "Biodiversity published in 1981"

Dynamics of some Western Australian ligneous formations with special reference to the invasion of exotic species

Abstract: Invasion of natural vegetation in Australia by exotic species has become pronounced in the last 150 years of European settlement. Changes in the frequency and type of fire have been a major disturbance to the dynamics of natural vegetation, and this disturbance has allowed rapid spread of exotics, particularly in urban and semi-rural regions. Less obvious disturbances include changes in nutrient levels and hydrological regimes, which also allow exotic species to establish and spread, at the expense of native species. Permanent plots established in various vegetation types show a decline in diversity which is associated with an increase in invasion by exotic species. Possible management strategies, designed to maintain the natural vegetation, which can be postulated include control and change of fire regime, removal of exotic species before seed-set, and the active introduction of native plants adapted to disturbance.

Bird Distributions on Small Rainforest Remnants in New South Wales.

Abstract: We studied bird distributions on 15 small patches of subtropical rainforest, ranging from 0.08 to 2.5 ha, in north-eastern New South Wales. Three-quarters of the bird species found in an extensive area of nearby rainforest were recorded in one or more of these isolated patches. Species that were not recorded, generally were rare in the extensive forest or are characterized by large home ranges. Several species more typical of open country were also found in the isolated patches. The number of resident species per patch ranged from one to 19; these were added in a rather predictable order from small to larger areas. Additional species observed in the patches either were transient or had home ranges encompassing several discontinuous areas. Although area is the best single predictor of species richness, isolation, disturbance by livestock and distance from water all tend to reduce the number of resident bird species. We propose that high dispersal abilities of rainforest birds near Dorrigo reflect the geographical and palaeogeographical distribution of Australian rainforest. The small total area and discontinuity of original tracts of rainforest, perhaps accentuated during the Pleistocene, have generally prevented persistence or colonization of highly sedentary, specialized bird species.

Plant communities and species distribution of low alpine Betula nana heaths in Northernmost Sweden

Abstract: Low alpine Betula nana heaths were studied with regard to plant communities, species distribution, and environmental conditions. It is clear from cluster analyses and PCA-ordinations that the distribution of winter snow is the most important factor for the composition of plant communities and the distribution of most plant populations. Under deep snow conditions soil instability is also important as a differentiating factor. The numerical treatment of data gives a phytosociological grouping in eoncordance with earlier opinions based on stand tabulations. The cluster analysis group the species into chionophobous, chionophilous, moderate snow bed species, and an additional group of wide snow depth amplitude. Only a few species remain unclassified. The ecological species groups are readily identified also in PCA-ordinations. They are independent of differences in species numbers and combinations.

Habitat distribution and species diversity of small mammals in South-East Queensland in relation to vegetation structure

Abstract: Two measures of vegetation structure and density failed to show any relationship ta species diversity of small mammals in a series of south-east Queensland coastal habitats. However, the distribution of some species appears to be related to the responses of the animals to vegetation density. Two groups of small mammal species, a rainforest group and a heathland group, are evident. The distribution of these groups is discussed in relation to the habitat responses of the constituent species.