Showing papers on "Diversity index published in 1992"

The use of Rarefaction Analysis for Estimating Palynological Richness from Quaternary Pollen-Analytical Data

Abstract: Reconstructing temporal changes in diversity from pollen assemblages is potentially important both palaeoecologically and ecologically because community diversity may, in part, result from historical processes. The use of diversity indices such as Shannon's information index or Simpson's index is not appropriate with pollen percentage data because such indices consider both the numbers of different taxa and their relative frequencies or representation. The latter aspect in pollen data is inevitably influenced by inherent differences in pollen production and dispersal. The total number of taxa present in a sample is a robust and useful measure of palynological richness if, and only if, all the pollen counts are standardized to a fixed number of grains. Rarefaction analysis implements such a standardization and provides minimum variance unbiased estimates of the expected number of taxa (t) in a random sample of n individuals taken from a larger collection of N individuals containing T taxa. The underlying m...

Análise comparativa da florística e fitossociologia da vegetação arbórea do cerrado sensu stricto na Chapada Pratinha, DF - Brasil

Abstract: Six sites were surveyed at Chapada Pratinha in Brazil (15-20o S e 46-49o W). Three of them were localized in conservation units in the Federal District and the others were in Silvania-GO, Paracatu-MG e Patroci'nio-MG. Ten plots of 1000 m2 (20x50m) were sampled in each site. The minimum diameter for measurement of the woody plants was 5 cm at 0.30 m from the ground level. Floristic composition, importance value index and Shannon's diversity index were analyzed for each area. Sorense's and Morisita's similarity indices were used to compare the six sites. There were 139 species belonging to 42 families. Of these, only 22 species were common to all areas. Only Leguminosae and Vochysiaceac had high importance values for all areas. The number of trees/ha ranged from 664 to 1396. Shannon's diversity index ranged from 3.11 to 3.56. Similarities were high for Sorense's index but low when Paracatu and Patroci'nio were compared to the other areas using Morisita's index. The existing conservation units do not include all structural and floristic diversity of the region, and therefore, the creation of new units in the last two areas is suggested.

Biological diversity of a temporary pond herpetofauna in north Florida sandhills

Abstract: From 1985 through 1990, the herpetofauna of a temporary pond in an uplands longleaf pine sandhills community in north-central Florida was monitored. A drift fence completely encircled the pond. Animals were captured in pitfall traps and marked as they entered and exited the pond basin. I captured 16 155 individuals of 42 species (16 amphibians, 26 reptiles). The species richness, diversity (using Margalef's Diversity Index) and dominance (using the Berger-Parker Index) varied among years. Between 62.5% and 87.5% of the amphibian species and 65% to 81% of the reptile species were captured in any one year. Daily amphibian capture was positively correlated with rainfall, whereas reptile capture was either not correlated or weakly negatively correlated with rainfall. Hydroperiod duration was not correlated with the numbers of either amphibians or reptiles captured. Neither the amphibian nor the reptile community showed any trends in diversity or dominance indices during the course of the study, although both communities were dominated by a few species. However, the species responsible for community dominance changed somewhat as the study progressed. Assessing the results of this study is hampered by the lack of comparable studies elsewhere, expected natural fluctuations of amphibian populations, and a prolonged drought, especially during the latter stages of the study. The herpetological community at Breezeway Pond does not appear to follow theoretical predictions of community response to stress. Temporary ponds are important centres of herpetofaunal biodiversity in uplands sandhills communities. Long-term studies are needed to monitor the composition, structure, and functional interactions of their resident species.

A comparison of sampling techniques and summary indices for assessment of water quality in the Yamaska River, Québec, based on benthic macroinvertebrates

Abstract: The Yamaska River drainage basin in Quebec, Canada, is intensively farmed and heavily polluted with poorly treated domestic and industrial wastes. We investigated the responses of the resident and colonizing components of the benthic macroinvertebrate community to municipal/industrial versus agricultural pollution in the basin, and evaluated the performances of seven diversity and biotic indices for assessing water quality. Samples of riffle-dwelling, infaunal and colonizing invertebrates were collected from 13 stations representing a wide range of types and degrees of pollution using Surber, scoop and artificial substrate samplers. The data were summarized using the indices S (number of taxa), N (number of individuals), H' (Shannon-Wiener's diversity index), D (Simpson's diversity index), BBI (Belgian Biotic Index), TBI (a modification of Hilsenhoff's Biotic Index), % CHIR (percentage of arthropods consisting of Chironomidae) and %OLIGO (percentage of total organisms consisting of Oligochaeta). Different components of the community generated somewhat different assessments and were, therefore, complementary. Community composition, expressed as the percentage of individuals contributed by major taxonomic groups, reflected the kinds of stresses at a station more consistently than did any of the indices. S and TBI came closest to ranking control, agricultural and municipal/industrial sites in accordance with our a priori classification, both between months and among sampling methods. %OLIGO usually separated municipal/industrial sites from control sites. Other indices were found to be less sensitive, accurate or temporally stable, or were otherwise inappropriate for use with certain sampling methods or for certain types of pollution. With most of our samples, all of the summary indices suggested that the impact of agricultural practices on stream ecosystems may be as severe as the impacts of municipal and industrial wastes.

Gradients in butterfly species diversity in an urban area in brazil

Abstract: The diversity (Shannon-Weaver) of butterflies throughout the urbanized area of Porto Alegre, Brazil, was analyzed using 109 sampling areas within three char­ acteristic zones of urbanization: buildings (B), houses and buildings (HB), and houses (H). Highest diversity was found in the periphery of the houses zone (H) one to two kilometers beyond the perimeter of the houses and bUildings zone (HB). From zone H to zone HB we observed a significant decrease in diversity and a small overlap in community com­ position (Renkonen's PS). From zone HB to a central zone of buildings (B), there was a relatively small change in community composition demonstrated by statistically similar diversity indices and a high species similarity. These findings suggest the existence of two macrohabitats for butterflies in the city: 1) B + HB and 2) H. Samples from areas within the same urbanized zone showed the highest degree of similarity. Diversity decreased in the B + HB macrohabitat mainly owing to a reduction in species richness (S). Biotic and abiotic factors that may be involved in this reduction are discussed. For late spring and midsummer samples, nearly 50% of the variation in diversity was explained by vegetation cover and distance from the city center. This value rises to 63% for the total diversity and 70% for the log transformation of species richness. These high proportions emphasize the importance of regional urban environmental conditions for butterfly diversity. In the winter, only vegetation cover presented a partial regression coefficient that was significant, accounting for less than 20% of the variation in diversity. Also, a scattered distribution of areas with high butterfly diversity associated with high vegetation cover was observed during the winter.

Temporal and spatial variations in dominance, diversity and biotic indices along a limestone stream receiving a trout farm effluent

Abstract: Benthic macroinvertebrate response to organic pollution generated by a trout farm, located in the upper Rio Tajuna (Central Spain), was evaluated by calculating Whittaker's and Camargo's dominance indices; Margalef s, Menhinick's, Camargo's, Shannon's and MacArthur's diversity indices; and several biotic indices, including the Trent Biotic Index (TBI), the Chandler Biotic Score (CBS), the Biological Monitoring Working Party (BMWP), the Average Score Per Taxon (ASPT) and the Overall Quality Rating (OQR). An upstream sampling site (S-1) and three downstream stations placed 10 (S-2), 150 (S-3) and 1000 (S-4) m below the fish farm outlet were selected along the study area. Site S-3 was situated just below a man-made waterfall (1.8 m in height). Winter, spring and summer macrobenthic surveys were conducted during 1986. Plecopterans, ephemeropterans, coleopterans, trichopterans, amphipods and planarians decreased in abundance or were basent at downstream sampling sites, whereas simuliids, leeches, chironomids and tubificid worms increased in abundance. All diversity and biotic indices had highest and lowest values at S-1 and S-2, respectively, and higher values at S-3 (below the waterfall) than at S-4. However, Shannon's and MacArthur's diversity indices and the TBI were less effective in quantifying differences among sampling sites, exhibiting the lowest positive coefficients of linear correlation with species richness and other diversity and biotic indices. Both dominance indices had highest values at S-2, but similar values at S-1, S-3 and S-4. Biotic indices (except the TBI) and Margalef s, Menhinick's and Camargo's diversity indices appear to be the most sensitive measures for assessing macroinvertebrate response to changes in environmental conditions downstream from the fish farm. In addition, temporal variation in species richness, Margalef s index and biotic indices was similar, exhibiting their highest coefficients of variation at S-4. It is concluded that small waterfalls may improve the streamns self-purification of organic pollution generated by trout farms.

Diversity and seasonality of Leiodid beetles (Coleoptera : Leiodidae) in an old-growth and a 40-year-old forest in New Hampshire

Abstract: The seasonality and diversity of members of the beetle family Leiodidae were determined for an old-growth and a 40-yr-old forest in New Hampshire. Thirty-four species were found at each site for a combined total of 39 species. Diversity was calculated using log series index α, Shannon-Wiener index, coefficient of community, and percent similarity. Seasonality is lengthily unimodal for the Cholevinae, which feed on carrion and fungi. The Leiodinae feed on slime molds and fungi and are more narrowly unimodal. Anisotoma spp. exhibit broadly overlapping abundance peaks, whereas some members of Agathidium and Leiodes have abundance peaks at different times, indicating the possibility of resource partitioning. The greater leaf litter depilis and amount of woody debris at the old-growth site are presumed to lead to the production of more food resources for the leiodids. The difference in forest ages and the disturbance by selective cutting has not lowered species richness, but the diversity indices used reflect a difference between the sites based on greater abundance in the old-growth forest. The dispersal ability of leiodids is presumed to lead to rapid recolonization of the younger forest as food sources become available. Anisotoma inops Brown is a potential indicator species for old-growth forests in northeastern North America.

Diversity and evenness of Hemiptera communities on naturally vegetated derelict land in NW England

Abstract: Samples of Hemiptera were collected at sixteen naturally vegetated derelict sites using both suction apparatus and beating bags Sample sites were chosen to provide a broad range of vegetation types, representing changes in successional stage and soil pH Hemipteran diversity indices were significantly correlated with site area, but not with soil pH or site age Vegetation species diversity and evenness indices were not significantly correlated with site age, area or soil pH Hemipteran and vegetation evenness (using both Shannon evenness, J, and Heip's evenness, F10) were significantly correlated Similar evenness correlations were found when sub-order Homoptera and vegetation were compared No significant correlations were found between the diversities of sub-order Heteroptera and vegetation Factors determining Hemiptera and vegetation diversity on these sites are discussed It is suggested that rare plant species are of importance in determining the presence of rare species of Hemiptera on the sites It is proposed that diversity as a concept is of most value in ecological studies when its two components, species richness and evenness are considered separately

The Concept of Seasonal Succession Theory Applied to Phytoplankton Through the Coupling Use of Diversity Index and Rank‐Frequencies Diagrams in a Eutrophic Ecosystem

Abstract: Seasonal succession of phytoplankton was studied in a eutrophic lake (Lake Aydat, Massif Central, France), from March to November 1985. An attempt is made to check the succession stages of the concept of ecological succession theory using either the H-diversity index of SHANNON and WEAVER or the FRONTIER'S rank-frequencies diagrams. A description of a stage 3 community was only possible through the use of the latter diagrams.