scholarly journals Intercontinental comparison of ferns community assemblages in Malaysian and Nigerian tropical forests

2021 ◽  
Author(s):  
Gbenga Festus Akomolafe ◽  
Rusly Binti Rosazlina ◽  
Zakaria Rahmad ◽  
Fatai Oloyede
Keyword(s):  
Species Richness ◽  
Tropical Forests ◽  
Diversity Indices ◽  
Life Forms ◽  
Taxonomic Composition ◽  
Shannon Index ◽  
The Other ◽  
Significant Difference ◽  
Fern Species ◽  
Community Assemblages

Research on ferns ecology has gained attention in the last decade, yet there is paucity of information on the intercontinental comparison of ferns community across two continents. This study focused on comparing the ferns community assemblages in tropical forests of Malaysia and Nigeria, thereby assessing the patterns of the species richness and diversity across the two continents. The diversity and taxonomic compositions of ferns were assessed using 180 plots of size 10 m x 10 m in each country. The species richness and other diversity indices were determined using the combined forests data for each country and for the individual forests. The observed and rarefied–extrapolated fern species richness are significantly higher in Malaysian forests than Nigerian forests. Also, the other diversity indices (Simpson index, Margalef index, and Fisher’s alpha) are significantly higher in Malaysian forests except Shannon index which showed no significant difference between the two biogeographic regions. There is a very low similarity in the taxonomic composition of ferns between the two biogeographic areas, although the similarity in composition increased with increasing taxonomic levels (genus and family levels). Terrestrial and epiphytic ferns are more dominant than the other life forms in the two countries. Since the two countries receive varying degrees of environmental factors, we then hypothesize that these observed differences are due to climatic differences as well as historical and evolutionary processes.

scholarly journals Floristic composition of the Montane Forest in the Almadina-Barro Preto axis, Southern Bahia, Brazil

2014 ◽  
Vol 14 (1) ◽  
Author(s):  
Macielle Macedo Coelho ◽  
André Márcio Amorim
Keyword(s):  
Species Richness ◽  
Tropical Forests ◽  
Atlantic Forest ◽  
Floristic Composition ◽  
Woody Species ◽  
Life Forms ◽  
Montane Forest ◽  
Forest Remnants ◽  
Southern Bahia ◽  
Arboreal Habit

The aim of this study is to survey the angiosperms of two montane forest remnants in the southern Bahia, Brazil: Corcovado (SCO) and Pedra Lascada (SPL). Both fragments are located in the municipality of Almadina and Barro Preto, respectively, and are 18 km distant from each other. We sampled 899 species of angiosperms distributed in 437 genera and 116 families. The SCO was the richest area with 678 species, distributed in 367 genera and 100 families. SPL showed 466 species in 269 genera and 88 families. The percentage of species identified was 85.8% and of this total, 37.7% are endemic to the Atlantic Forest, 11.2% are endemic to southern Bahia and northern Espírito Santo and 7% are disjunct between the Atlantic Forest and Amazon. The remaining percentages (44.3%) were of species widely distributed. The richest families in the two areas were Orchidaceae (10%), Rubiaceae (7%), Bromeliaceae (5.5%), Melastomataceae (4.2%) and Poaceae (4%). The richest genera were Psychotria (2%),Piper (1.8%), Ocotea (1.6%),Vriesea (1.5%) and Peperomia (1.4%). More than half of the recorded species showed non-arboreal habit, regarding life forms documented. That comes against the assertion that many authors in the tropical forests, where species richness in angiosperms is expected for non-woody species, especially in montane forests. Twelve species have been identified as new, but seven others already described from collections previously obtained in these two areas. Orchidaceae, Rubiaceae, Poaceae and Bromeliaceae showed significant richness in this study these families are commonly reported as the richest in other inventories in the Atlantic Forest in southern Bahia reinforcing their importance to the regional flora. The high levels of richness, endemism, and the growing numbers of new taxonomic discoveries from the SPL and SCO sites indicate the biological importance of these two forest remnants. The implementation of parks or other protected environmental reserves would be essential to the conservation of its species.

scholarly journals The microbial diversity and structure in peat land forest in Indonesia

2019 ◽  
Vol 5 (1) ◽  
pp. 133-144
Author(s):  
MJH Talukder ◽  
Hui Sun
Keyword(s):  
Species Richness ◽  
Peat Soil ◽  
Bacterial Species ◽  
Mineral Soil ◽  
The Other ◽  
Swamp Forest ◽  
Peat Swamp Forest ◽  
Soil P ◽  
Peat Swamp ◽  
Significant Difference

Soil of tropical forest ecosystem plays very crucial part in controlling the universal carbon cycle. The isolation of microorganisms and their identification are important for understanding their vital role on transformation of organic matter of this ecosystem. Soil storage maximum microbial genetic diversity because of it’s a multilayered environment. No complete methods were discovered yet to cultivate majority of soil microorganisms. A little is known about microbial structure and their essentiality in tropical peat lands compared to most other terrestrial and oceanic habitats. In providing insight to the impacts of land-use of peat land on microbes in Central Kalimantan, Borneo Indonesia, we examined the community structure and diversity of bacteria and fungi in different peat forest soil including: i) natural peat swamp forest (well mixed swamp forest type); ii) disturbed peat soil and iii) mineral soils by using 454 pyrosequencing technology. The results showed that no significant difference was found for diversity and evenness among the sites of fungal community. However, natural peat swamp forest had the highest species richness (Chao1), which was significantly higher than the other two sites (P<0.05 and P<0.05). According to the OTUs analysis four fungi phyla were obtained of which 45 species were classified. The Ascomycota was the most abundant phylum, followed by Basidiomycota, Zygomycota and Glomeromycota. The natural peat swamp forest and disturbed peat soil harbored the maximum number Ascomycota. On the other hand, mineral soil and natural peat soil contained the highest number of Basidiomycota. The top species in natural peat swamp forest included Sugiyamaella paludigena, Polyancora globosa and Ganoderma gibbosum. The mineral soil enriched the abundance of Penicillium herquei, Sugiyamaella paludigena and the disturbed peat soil contained the highest frequency of Polyancora globosa, Gymnopilus lepidotus. According to the PCoA analysis, the community structure of fungus in natural peat soil differed significantly from mineral soil (P=0.04) and disturbed peat soil (P=0.039). No significant difference was found for bacterial species richness (Chao1) among the sites. The diversity of bacteria in disturbed peat soil significantly differed from the other sites (P<0.05 and P<0.05). eleven bacterial phyla and 53 genera were examined. All of the three sites contained the similar abundance of Proteobacteria. The natural peat swamp forest and disturbed peat soil harbored the most abundant Acidobactria. Genera Mycobacterium, Gp1, Gp13, Gp2, Burkholderia, Actinospica, Aciditerrimonas were found in all the sites. Genera Granulibacter, Gp4, Acidisoma, Clostridium_sensu, Clostridium_ XI were only observed in natural peat swamp forest. Genera Rudaea, Rhodopila, Streptomycetes were found only mineral soil. The PCoA analysis showed that the structure of bacteria in natural peat swamp forest significantly differed from the disturbed peat soil (P=0.045). Overall, the bacterial species richness and diversity are more among the sites than of the fungi. J. Biodivers. Conserv. Bioresour. Manag. 2019, 5(1): 133-144

scholarly journals Floristic composition, diversity and structure of Khaya senegalensis stands in Benue Department, Cameroon

2021 ◽  
Vol 8 (1) ◽  
pp. 60-68
Author(s):  
Awé Djongmo Victor ◽  
Noiha Noumi Valery Valery ◽  
Madou Chantal Chantal ◽  
Zapfack Louis
Keyword(s):  
Species Richness ◽  
Diversity Index ◽  
Basal Area ◽  
Shannon Index ◽  
Simpson Index ◽  
Importance Value Index ◽  
Importance Value ◽  
Acacia Senegal ◽  
Significant Difference ◽  
Khaya Senegalensis

The present work has been done to provide basic data for a better conservation and valorization ofKhaya senegalensis stands in Sudano-Sahelian zone of Cameroon. A 100 m x 50 m transectmethod was undertaken to measure floristic diversity through the use of species richness,Shannon index, Pielou equitability, Simpson index, importance value index and importance valuefamily. The vegetation structure is determined by density, basal area and biovolume. Theinventory included trees with a dbh ?10 cm on an area of 1 ha per plot. A total of 6743individuals distributed in 24 families, 33 genera and 54 species were inventoried in all Khayasenegalensis stands studied. Statistical analysis showed significant differences, Shannon index,Simpson index, Pielou equitability, density, basal area, biovolume, species richness, heights class,diameters class, circumferences class but does not certify a significant difference of importancevalue index among in the villages. The undergrowth of Khaya senegalensis stands is more diverseat Bamé with a Shannon diversity index (ISH=5.87 ± 0.12 bit). The greatest of Pielou equitabilityis observed at Bamé (EQ=0.80 ± 0.01). The largest of Simpson index is recorded at Bamé(D=0.098 ± 0.001). Khaya senegalensis Stands are denser at Bamé (194 ± 3.12 individuals/ha).The basal area and biovolume of Khaya senegalensis stands are very high at Bamé (BA=25.87 ±0.06 m2/ha and Biovolume =15.32 ± 0.012 m3/ha). The species importance value is maximal in allthe studied villages (SIV=300 ± 71.45). The importance value index of species revealed a cleardominance in the undergrowth of Khaya senegalensis stands are Combretum adenogonium;Acacia senegal; Terminalia laxiflora; Guiera senegalensis; Acacia nilotica; Entada Africana.The vertical structure has three aspects, like the L (Dbh), asymmetric (height) and dissymmetrical(circumference) structures attesting to a strong regeneration of the understory ligneous woods ofKhaya senegalensis stands studied.

scholarly journals Sponge-Associated Amphipod Communities as Bioindicators for Pollution

2021 ◽  
Author(s):  
◽  
Ronja Hauke
Keyword(s):  
Species Richness ◽  
Community Structure ◽  
Sex Ratios ◽  
Diversity Indices ◽  
Life Cycle Stage ◽  
Sponge Species ◽  
Pollution Level ◽  
Sponge Tissue ◽  
Pollution Levels ◽  
Significant Difference

<p>Pollution negatively impacts organisms across all marine ecosystems. Coastal areas are particularly vulnerable to pollution due to their proximity to human settlements. Amphipods are commonly used as bioindicators to monitor pollution burdens, due to their high sensitivities and their ubiquity. Pollution can reduce amphipod abundance, species richness, evenness and diversity. Community structure, proportionality of adults to juveniles and sex ratios may also be affected. Sponges often harbour high densities of amphipods, offering food, refuge and nurseries to their symbionts. Sponge-associated amphipods differ in their level of specialization on their host. This study provides first insights into the usefulness of sponge-associated amphipod communities as bioindicators. For this, it hypothesized that amphipod densities, species diversity, community structure, sex ratio and age proportionality will differ according to pollution levels.  To test this, sponges were collected from three sites with varying degrees of pollution in Wellington Harbour. The sponges were weighed, and their volume was measured. They were dissected and their amphipods were identified to species level, counted, measured (length) and their sex and life cycle stage (adult or juvenile) were recorded. From this data, amphipod densities, species richness, evenness and Shannon-Wiener diversity indices were calculated and compared among pollution levels. Community structure was also compared between sites and sponge species. Pollution level significantly affected species richness, evenness, diversity and community structure. The highest values for species richness, evenness and diversity were found in sponges from the least polluted. The lowest levels of these factors were found in sponges from the most polluted site. Sponges from the intermediate site generally harboured moderate richness, evenness and diversity compared to the other sites. Community composition was significantly affected by pollution, although effect sizes differed between sponge species. Higher pollution levels seemed to favour dominance of species that are better adapted to living in sponges. Generalists seemed to thrive in low to intermediate pollution levels. The majority of sex ratios measured had a female bias, which appeared to increase with increasing pollution although the difference was not statistically significant. The proportion of adults also showed a non-significant increase with pollution level. There was no significant difference in amphipod abundance per litre of sponge tissue between pollution levels, possibly because pollution levels may have been too low to cause a reduction in amphipod density. These results show that sponge-associated amphipod communities are useful as bioindicators, as amphipod diversity, richness and evenness were significantly reduced by pollution and the sponge association allows for these community-scale comparisons to be made within an easily measurable framework. Species evenness in particular provided an accurate indication of different pollution levels.</p>

scholarly journals Sponge-Associated Amphipod Communities as Bioindicators for Pollution

2021 ◽  
Author(s):  
◽  
Ronja Hauke
Keyword(s):  
Species Richness ◽  
Community Structure ◽  
Sex Ratios ◽  
Diversity Indices ◽  
Life Cycle Stage ◽  
Sponge Species ◽  
Pollution Level ◽  
Sponge Tissue ◽  
Pollution Levels ◽  
Significant Difference

<p>Pollution negatively impacts organisms across all marine ecosystems. Coastal areas are particularly vulnerable to pollution due to their proximity to human settlements. Amphipods are commonly used as bioindicators to monitor pollution burdens, due to their high sensitivities and their ubiquity. Pollution can reduce amphipod abundance, species richness, evenness and diversity. Community structure, proportionality of adults to juveniles and sex ratios may also be affected. Sponges often harbour high densities of amphipods, offering food, refuge and nurseries to their symbionts. Sponge-associated amphipods differ in their level of specialization on their host. This study provides first insights into the usefulness of sponge-associated amphipod communities as bioindicators. For this, it hypothesized that amphipod densities, species diversity, community structure, sex ratio and age proportionality will differ according to pollution levels.  To test this, sponges were collected from three sites with varying degrees of pollution in Wellington Harbour. The sponges were weighed, and their volume was measured. They were dissected and their amphipods were identified to species level, counted, measured (length) and their sex and life cycle stage (adult or juvenile) were recorded. From this data, amphipod densities, species richness, evenness and Shannon-Wiener diversity indices were calculated and compared among pollution levels. Community structure was also compared between sites and sponge species. Pollution level significantly affected species richness, evenness, diversity and community structure. The highest values for species richness, evenness and diversity were found in sponges from the least polluted. The lowest levels of these factors were found in sponges from the most polluted site. Sponges from the intermediate site generally harboured moderate richness, evenness and diversity compared to the other sites. Community composition was significantly affected by pollution, although effect sizes differed between sponge species. Higher pollution levels seemed to favour dominance of species that are better adapted to living in sponges. Generalists seemed to thrive in low to intermediate pollution levels. The majority of sex ratios measured had a female bias, which appeared to increase with increasing pollution although the difference was not statistically significant. The proportion of adults also showed a non-significant increase with pollution level. There was no significant difference in amphipod abundance per litre of sponge tissue between pollution levels, possibly because pollution levels may have been too low to cause a reduction in amphipod density. These results show that sponge-associated amphipod communities are useful as bioindicators, as amphipod diversity, richness and evenness were significantly reduced by pollution and the sponge association allows for these community-scale comparisons to be made within an easily measurable framework. Species evenness in particular provided an accurate indication of different pollution levels.</p>

scholarly journals Mineral Fertilizers Influence the Macrofauna of Soils Under Cocoa Trees in the South-Western Côte d’Ivoire

2021 ◽  
Vol 13 (2) ◽  
pp. 32
Author(s):  
Hypolith K. Kouadio ◽  
Alain Jacques A. Kotaix ◽  
Sydiki Bakayoko ◽  
Emmanuel K. Kassin ◽  
Aïdara Sékou ◽  
...  
Keyword(s):  
Species Richness ◽  
Functional Groups ◽  
Diversity Indices ◽  
Living Environment ◽  
Mineral Fertilizers ◽  
First Year ◽  
Mineral Fertilization ◽  
Soil Macrofauna ◽  
Significant Difference ◽  
Soil Monolith

A study on mineral fertilization of soils was carried out for two years in three cocoa farms in the Nawa region of south-western C&ocirc;te d&rsquo;Ivoire. The aim of this study was to evaluate the effects of mineral fertilizers on soil macrofauna. The experimental design was Fisher block with four treatment with three repetitions. The treatments were control without fertilizer (T0), NPK 0-23-19 fertilizer (T1), NPK 0-15-15 + 17 CaO + 5 MgO + 1 B2O3 + 0.5 Zn (T2) and NPK 4-10-10 + 19 CaO + 4 MgO + 0.8 B2O3 + 0.3 Zn (T3). Twelve soil monoliths were made per treatment and per site, to count the macrofauna of the soil. Each soil monolith was subdivided into three strata 0-10 cm, 10-20 cm and 20-30 cm. The organisms were counted and classified into functional groups. The abundance, species richness and diversity indices of Shannon-weaver and Pi&eacute;lou were determined. The analysis of variance of the numbers of individuals in the macrofauna did not show a significant difference between the treatments on different strata of the monoliths during the second year of the trial. However, during the first year, all the treatments with fertilizer in the 0-10 cm stratum had a more abundant macrofauna than that of the control without fertilizer at Soubr&eacute; and Mayo. Multivariate analyses (AFC) showed links between functional groups of organisms and treatments. Myriapods and earthworms were linked to the T2 and T3 treatments, microarthropods to T1 and other organisms to T0. As for macrofauna diversity, the highest value of species richness (7 species), Shannon-weaver (2) and Pi&eacute;lou (1) indices were found in the fertilized treatments. Mineral fertilizers thus presented better conditions for the expansion of macrofauna. A reasoned application of mineral fertilizers creates a favourable living environment for certain soil organisms.

scholarly journals The gut microbiome in pancreatogenic diabetes differs from that of Type 1 and Type 2 diabetes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rupjyoti Talukdar ◽  
Priyanka Sarkar ◽  
Aparna Jakkampudi ◽  
Subhaleena Sarkar ◽  
Mohsin Aslam ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Gut Microbiome ◽  
Bacterial Species ◽  
Diversity Indices ◽  
The Other ◽  
Cross Sectional ◽  
Significant Difference ◽  
Patients With Diabetes

AbstractWe hypothesized that the gut microbiome in patients with diabetes secondary to chronic pancreatitis (Type 3c) is different from those with Type 1 and Type 2 diabetes. This was a cross-sectional preliminary study that included 8 patients with Type 1, 10 with Type 2, 17 with Type 3c diabetes and 9 healthy controls. Demographic, clinical, biochemical, imaging and treatment data were recorded and sequencing of the V3–V4 region of the bacterial 16SrRNA was done on fecal samples. Bioinformatics and statistical analyses was performed to evaluate the differences in the diversity indices, distance matrices, relative abundances and uniqueness of organisms between the types of diabetes. There was significant difference in the species richness. Beta diversity was significantly different between patients with Type 3c diabetes and the other groups. 31 genera were common to all the three types of diabetes. There was significant differences in the species level taxa between Type 3c diabetes and the other groups. The unique bacterial species signature in Type 3c diabetes compared to Type 1 and Type 2 diabetes included Nesterenkonia sp. AN1, Clostridium magnum, Acinetobacter lwoffii, Clostridium septicum, Porphyromonas somerae, Terrabacter tumescens, and Synechococus sp.

scholarly journals Evaluating Multi-Sensors Spectral and Spatial Resolutions for Tree Species Diversity Prediction

2021 ◽  
Vol 13 (5) ◽  
pp. 1033
Author(s):  
Enoch Gyamfi-Ampadu ◽  
Michael Gebreslasie ◽  
Alma Mendoza-Ponce
Keyword(s):  
Species Richness ◽  
Species Diversity ◽  
Tree Species ◽  
Diversity Index ◽  
Diversity Indices ◽  
Shannon Index ◽  
Coefficient Of Determination ◽  
Landsat 8 ◽  
Tree Species Diversity ◽  
Sentinel 2

Forests contribute significantly to terrestrial biodiversity conservation. Monitoring of tree species diversity is vital due to climate change factors. Remote sensing imagery is a means of data collection for predicting diversity of tree species. Since various sensors have different spectral and spatial resolutions, it is worth comparing them to ascertain which could influence the accuracy of prediction of tree species diversity. Hence, this study evaluated the influence of the spectral and spatial resolutions of PlanetScope, RapidEye, Sentinel 2 and Landsat 8 images in diversity prediction based on the Shannon diversity index (H′), Simpson diversity Index (D1) and Species richness (S). The Random Forest regression was applied for the prediction using the spectral bands of the sensors as variables. The Sentinel 2 was the best image, producing the highest coefficient of determination (R2) under both the Shannon Index (R2 = 0.926) and the Species richness (R2 = 0.923). Both the Sentinel and RapidEye produced comparable higher accuracy for the Simpson Index (R2 = 0.917 and R2 = 0.915, respectively). The PlanetScope was the second-accurate for the Species richness (R2 = 0.90), whiles the Landsat 8 was the least accurate for the three diversity indices. The outcomes of this study suggest that both the spectral and spatial resolutions influence prediction accuracies of satellite imagery.

Avian monitoring – comparing structured and unstructured citizen science

2018 ◽  
Vol 45 (2) ◽  
pp. 176 ◽  
Author(s):  
Corey T. Callaghan ◽  
John M. Martin ◽  
Richard E. Major ◽  
Richard T. Kingsford
Keyword(s):  
Species Richness ◽  
Citizen Science ◽  
Community Composition ◽  
Urban Areas ◽  
Diversity Indices ◽  
Urban Greenspace ◽  
Shannon Diversity ◽  
Spatial Coverage ◽  
Significant Difference ◽  
Urban Greenspaces

Context Citizen science is increasingly used to collect biodiversity data to inform conservation management, but its validity within urban greenspaces remains largely unresolved. Aims To assess the validity of eBird data for generating biodiversity estimates within an urban greenspace. Methods We compared data from structured avian surveys with eBird data at an urban greenspace in Sydney during 2012–16, using species richness and Shannon diversity indices. We also compared community composition, using non-metric multidimensional scaling (NMDS) and dissimilarities using non-parametric MANOVA. Key results Structured surveys had a lower overall species richness (80 versus 116) and Shannon diversity (3.64 versus 3.94) than eBird data, but we found no significant differences when using years as replicates. After standardising the richness and diversity indices by time spent surveying in a given year, structured surveys produced significantly higher biodiversity estimates. Further, when grouped into species occupying different broad habitats, there were no significant differences in waterbird or landbird species richness, or in Shannon diversity between data sources. Conclusions The most likely explanation for the larger magnitudes of the biodiversity indices from the eBird data is the increase in effort manifested in the number of observers, time spent surveying and spatial coverage. This resulted in increased detection of uncommon species, which in turn accounted for a significant difference (R2 = 0.21, P = 0.015) in overall community composition measured by the two methods. Implications Our results highlight the opportunities provided by eBird data as a useful tool for land managers for monitoring avian communities in urban areas.

scholarly journals Ranking the Biases: The Choice of OTUs vs. ASVs in 16S rRNA Amplicon Data Analysis Has Stronger Effects On Diversity Measures Than Rarefaction and Similarity Threshold

2021 ◽  
Author(s):  
Marlène Chiarello ◽  
Mark McCauley ◽  
Sébastien Villéger ◽  
Colin R Jackson
Keyword(s):  
16S Rrna ◽  
Beta Diversity ◽  
Alpha Diversity ◽  
Diversity Indices ◽  
Taxonomic Composition ◽  
Shannon Index ◽  
Minimal Impact ◽  
Alpha And Beta Diversity ◽  
Methodological Choices ◽  
Similarity Threshold

Abstract BackgroundAdvances in the analysis of amplicon sequence datasets have introduced a methodological shift in how research teams investigate microbial biodiversity, away from the classification and downstream analyses of traditional operational taxonomic units (OTUs), and towards the usage of amplicon sequence variants (ASVs). While ASVs have several inherent properties that make them desirable compared to OTUs, questions remain as to the influence that these pipelines have on the ecological patterns being assessed, especially when compared to other methodological choices made when processing data (e.g. rarefaction) and computing diversity indices. ResultsWe compared the respective influences of using ASVs vs. OTU-based pipelines, rarefaction of the community table, and OTU similarity threshold (97% vs. 99%) on the ecological signals detected in freshwater invertebrate and environmental (sediment, seston) 16S rRNA data sets, determining the effects on alpha diversity, beta diversity and taxonomic composition. While the choice of OTU vs. ASV pipeline significantly influenced unweighted alpha and beta diversities and changed the ecological signal detected, weighted indices such as the Shannon index, Bray-Curtis dissimilarity, and weighted Unifrac scores were not impacted by the pipeline followed. By comparison, OTU threshold and rarefaction had a minimal impact effect on all measurements, although rarefaction improved overall signals, especially in OTU-based datasets. The identification of major classes and genera identified revealed significant discrepancies across methodologies. ConclusionWe provide a list of recommendations for the analysis of 16S rRNA amplicon data. We notably recommend the use of ASVs when analyzing alpha-diversity patterns, especially in species-rich or environmental samples. Abundance weighted alpha- and beta-diversity indices should also be preferred compared to ones based on the presence-absence of biological units.

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