Proportion Of Rare Species Research Articles

Species number, species abundance and body length of arboreal arthropods associated with an Australian rainforest tree

Abstract. The species number, the abundance per species and the body length of arthropods foraging within the crowns of an over‐storey rainforest tree from Australia, Argyrodendron actinophyllum (Sterculiaceae), were investigated by interception trap sampling and restricted canopy fogging. Emphasis was placed upon the interpretation of trap data. Arthropods were trapped continuously day and night, over a 2‐year period and the final analyses examined the attributes of 759 species which represented 20,500 individuals. The proportion of‘rare’species (Le. collected once) intercepted was high (35.7%), although lower than in other similar rainforest surveys. Neither the α log‐series nor the log‐normal distribution could be fitted to the relationship between number of species and number of individuals, since the number of rare species was much higher than predicted and the mode of the distribution could not be identified. The proportion of rare species was higher in fogging collections (452%) than in trap collections. The data are compared with a study of Bornean arboreal beetles, obtained by fogging trees during a single sampling event. Several patterns were common to both data sets. However, the three‐dimensional plot of the variables describing the structure of the arthropod community showed a notably rougher surface than in the case of Bornean beetles. Although several factors may complicate the interpretation of the three‐dimensional plots, long‐term and continuous sampling may alter our perception of complex arthropod communities. This methodology is imperative for a proper understanding of arthropod community structure in rain forests.

Species Richness, Species Rarity and Conservation Evaluation of Rich-Fen Vegetation in Lowland England and Wales

(1) The botanical resource of rich-fen sites in England and Wales is analysed, based on a survey between 1972-85 of most known sites. The 464 plant species recorded in the survey are segregated into those (153) for which fens are a major habitat (principal fen species), those (203) that are as well or better represented in other habitats as in fens (affiliated species) and those (108) essentially atypical of fens (accidental species). (2) The occurrence of principal fen species of low frequency (occurring in < 5% of samples) (i.e. rare species) is analysed from 2900 quadrats from herbaceous and wooded fen vegetation. Many rare species occur mainly in just a few distinctive herbaceous vegetation types of low crop mass. Most do not occur at all in fen carr. (3) Variation in species richness (number of species 100 m-2) in 2100 samples of herbaceous fen vegetation is analysed. Very species-rich stands are infrequent and referable to just a few vegetation types. These are the ones that also contain most rare species. (4) Individual fen plant species (principal and affiliated species) occupy a discrete range of vegetation species-richness (the 'associated-richness') in herbaceous fen vegetation samples. Those species which show only small variation in the associated-richness values (interquartile range <50% median associated-richness value) are 'richness indicator species' and their occurrence can be used to predict the species-richness of herbaceous fen vegetation. (5) Regressions of total number of species and number of common species against number of rare species within vegetation samples both show a strong (P < 0 0001) positive relationship. The proportion of rare species within the vegetation also increases with increasing species richness. (6) The present infrequency of species-rich vegetation (and its associated rare species) in undrained fens is probably mainly due to increase in vegetation crop mass at many sites, caused by the abandonment of traditional management regimes perhaps exacerbated by increased net productivity caused by fertilizer run-off from the catchments. (7) A few rare species are most characteristic of comparatively species-poor vegetation of fairly high crop-mass. The reasons for their current rarity are not known. (8) The data on species-richness and rarity provide a basis for conservation priorities in rich-fens. Four possible indices, based on richness and rarity, for the evaluation of fen sites for conservation are proposed and fifteen sites are evaluated using these.

Accuracy of species and abundance minimal areas determined by similarity area curves

A new method for estimating the accuracy of a representative ecological sample (species minimal area and abundance minimal area determined by similarity area curves) is presented. Formulas are derived to calculate the adequate similarity level (IS, respectively IK) in relation to the desired accuracy of the sample: IS=2 w/1+w for qualitative similarity and ≧K=2 x/(1+x)(1+y) for quantitative similarity, where w=desired qualitative accuracy of the sample, x=desired quantitative accuracy of the sample, y=abundance proportion of rare species. Based on samples from a low diversity environment in the supralittoral fringe of rocky shores (“black zone”), the new approach was tested and led to the following results: (1) Similarity area curves are an objective method to calculate the minimal area and to test the accuracy of the sample size chosen. (2) A large presample is necessary to calculate the minimal area. (3) The size of minimal area is subject to seasonal and regional variations. (4) Incidental species lead to an overestimation of the species minimal area. (5) Highly dominant species lead to an underestimation of the abundance minimal area.

Commonness and rarity in plants with special reference to the Sheffield flora part II: The relative importance of climate, soils and land use

Although the flora of the Sheffield region was initially shaped by climatic and edaphic forces, at this present time land use appears to be by far the most significant determinant of the commonness and rarity of individual species. Differences between major habitats of the region with respect to their proportion of rare species (aquatic > mire > woodland > grassland > open habitats > arable) can be attributed simply to differences in the vulnerability of the vegetation of the various habitats to changing patterns of land use. The greater levels of fertility and disturbance associated with modern land use is resulting in the creation of a new flora with the replacement of communities of stress-tolerant species ( sensu Grime, 1974) by those with competitive or ruderal strategies. These changes, apparent in the Sheffield region, are probably an accurate reflection of those which are occurring within Britain as a whole.

Patterns of initial saprophytic fungal colonization of grass roots from two severely disturbed soils

Development of the root-surface fungal assemblages of Agropyron trachycaulum grown on amended oil-sands tailings and a subalpine coal-mine spoil from Alberta (Canada) was followed over one growing season. Fungi were isolated, using a root-washing procedure, from the region of main seminal and nodal roots 4 cm from the root–hypocotyl axis. Fungal colonization of the root surfaces was rapid, with equilibrium numbers of species reached 2 weeks after plant emergence. Although the application of either fertilizer, peat, or sewage sludge to these spoils had no effect on the general form of the colonization curve, peat amendation did result in significantly higher numbers of species on the root surfaces. Species turnover within all assemblages was high throughout the growing season. The amount of species replacement ranged from a low of 67% to a high of 91% between consecutive 4-week sampling periods. Thus, although the number of species was relatively constant, species composition changed considerably. The structure of the root-surface fungal assemblages was characterized by a large proportion of rare species. The species abundance distributions were essentially negative exponential. Neither time nor amendation had any significant effect on these distributions. The large incidence of rare species within the assemblages suggests that these root surfaces represent nonequilibrium systems with respect to species occurrences.