View source for Species Richness vs. Evenness

{{#seo:

|title=Species Richness vs. Evenness: Understanding Biodiversity and Ecological Diversity

|description=Explore the difference between species richness and species evenness, how ecologists measure biodiversity, and why abundance, dominance, sampling scale, ecosystem function, and community structure matter for conservation.

|keywords=species richness, species evenness, biodiversity, ecological diversity, diversity indices, Shannon diversity, Simpson diversity, Hill numbers, species abundance, community structure, rank abundance, ecosystem function, biodiversity conservation, ecological monitoring

|image=File:Placeholder.png

|image_width=300

|image_height=200

|type=article}}

[[Category:Biodiversity]]
[[Category:Ecology]]
[[Category:Species Diversity]]
[[Category:Community Ecology]]
[[Category:Conservation Biology]]
[[Category:Ecological Monitoring]]

__NOTOC__

== Species Richness vs. Evenness ==

Species richness and species evenness are two fundamental but distinct dimensions of biodiversity. Species richness describes the number of species present in a community, while species evenness describes how evenly individuals are distributed among those species. Two ecological communities can therefore contain the same number of species while differing substantially in their overall diversity because one community may be dominated by a few species and the other may have a much more balanced distribution of abundance.

Research on biodiversity measurement shows that richness and evenness should not automatically be treated as interchangeable indicators of ecological condition. Their relationship varies among ecosystems, spatial scales, environmental gradients, and taxonomic groups. In some communities richness and evenness increase together, while in others they may be weakly related, independent, or negatively related. Measuring both can consequently provide information that would be lost if biodiversity were represented only by a species count or a single composite diversity index.

=== Measuring Species Richness and Evenness ===

Species richness is conceptually straightforward: it is the number of species detected within a defined community, sample, or geographic area. In practice, however, observed richness depends strongly on sampling effort. Larger samples generally detect more species, particularly rare species, making direct comparisons between surveys potentially misleading when sampling intensity differs.

Ecologists use methods such as rarefaction, extrapolation, species-accumulation curves, and richness estimators to improve comparisons among samples. These approaches attempt to distinguish genuine ecological differences from differences caused simply by the number of individuals, sites, or samples examined.

Evenness instead concerns the distribution of abundance among species. A highly even community has relatively similar abundances among its species. A community with low evenness is dominated by one or a few species while the remaining species are comparatively rare.

Rank-abundance curves provide a useful visual representation of both properties. The length of the curve reflects richness, while its slope provides information about evenness and dominance.

=== Diversity Indices ===

Many biodiversity indices combine information about richness and relative abundance. Shannon diversity and Simpson diversity are among the most widely used examples, but they place different amounts of emphasis on common and rare species.

Hill numbers provide a framework connecting several commonly used diversity measures. At one end, diversity can essentially represent species richness. Increasing the weighting given to abundance progressively emphasizes common or dominant species. Expressing diversity as an effective number of species can also make comparisons more intuitive than interpreting entropy values directly.

This distinction matters because identical values of a composite diversity index can sometimes result from substantially different combinations of richness and evenness. Reporting the underlying components alongside composite diversity measures can therefore provide a clearer description of community structure.

=== Richness-Evenness Relationships and Community Structure ===

Ecological research does not support a single universal relationship between richness and evenness. Studies across terrestrial, aquatic, forest, grassland, microbial, bird, and other communities demonstrate that the two variables can respond differently to environmental conditions.

A community can gain species while becoming increasingly dominated by a small number of organisms. Conversely, evenness can increase without a corresponding increase in the total number of species.

Dominance and rarity are therefore central to interpreting biodiversity. Communities frequently contain a relatively small number of common species and many uncommon or rare species. Because richness gives equal weight to every detected species, it can be strongly influenced by the presence or absence of rare organisms.

Evenness provides complementary information by revealing whether ecological abundance is concentrated among a few dominant species or distributed more broadly throughout the community.

=== Sampling, Scale, and Detection ===

Richness and evenness are both influenced by how ecological communities are sampled. Observed richness generally rises as sampling effort or sampled area increases because additional sampling detects increasingly rare species.

Evenness and spatial aggregation can also affect species-accumulation patterns. If individuals are strongly concentrated among a small number of species or spatial locations, substantially more sampling may be required to detect uncommon organisms.

Observer differences, survey methodology, laboratory procedures, and analytical techniques can further influence biodiversity estimates. These problems are particularly important in microbial ecology, where enormous numbers of rare taxa can make estimates of total richness difficult.

Consequently, biodiversity comparisons should account for sampling effort, spatial scale, detection probability, and methodological differences whenever possible.

=== Forests, Grasslands, and Plant Communities ===

Plant communities provide numerous examples of richness and evenness responding independently. Forest management, land-use history, succession, habitat edges, elevation, disturbance, and environmental gradients can alter the number of plant species without producing equivalent changes in their relative abundance.

Grassland studies similarly demonstrate that communities containing comparable numbers of species can differ substantially in dominance structure. In some cases, relatively stable richness can occur alongside declining evenness, indicating that a community is becoming increasingly dominated by fewer species even though species have not yet disappeared.

Such patterns demonstrate why monitoring species counts alone can overlook important ecological changes.

=== Birds and Terrestrial Vertebrates ===

Bird and mammal communities also demonstrate the distinction between richness and evenness. Habitat structure, urbanization, agriculture, forest conditions, and environmental gradients can influence the number of species and their relative abundances differently.

An area containing many bird species, for example, is not necessarily characterized by an evenly distributed bird community. A handful of adaptable species may become extremely abundant while many others persist at low population levels.

For wildlife monitoring, combining richness with abundance distributions and community composition can therefore provide a more informative assessment of ecological condition.

=== Aquatic and Marine Communities ===

Marine and freshwater research similarly distinguishes species counts from abundance structure. Studies of phytoplankton, diatoms, fish, benthic organisms, and deep-sea communities have examined richness and evenness as separate predictors of ecological processes.

Environmental variables such as nutrient availability, salinity, temperature, habitat structure, and disturbance can affect these biodiversity components differently. Marine protected areas and other conservation interventions may likewise influence richness, abundance, and community composition in different ways.

Aquatic biodiversity assessment consequently benefits from measuring several dimensions of diversity rather than assuming that greater species richness necessarily represents improved ecosystem condition.

=== Microbial Richness and Evenness ===

Microbial communities illustrate some of the greatest challenges associated with biodiversity measurement. Microbial ecosystems can contain extremely large numbers of taxa, including a substantial "rare biosphere" that is difficult to detect completely.

Because unseen rare taxa strongly influence estimates of total richness, microbial richness can be particularly sensitive to sequencing depth, laboratory methodology, sampling effort, and statistical estimation.

Shannon and Simpson diversity measures may sometimes be more robust because they give less weight to extremely rare taxa. Evenness-richness plots have also been proposed as a way of displaying both dimensions simultaneously rather than reducing microbial community structure to a single diversity statistic.

Research across soil, freshwater, and other microbial systems shows that richness and evenness can respond differently to climate, elevation, environmental conditions, and ecological disturbance.

=== Ecosystem Function and Productivity ===

Richness and evenness can influence ecosystem processes through different mechanisms. Greater richness may increase the range of ecological functions represented within a community, while greater evenness can increase the contribution of species that would otherwise remain relatively uncommon.

Experimental and observational studies have investigated relationships between richness, evenness, productivity, biomass, decomposition, invasion resistance, multifunctionality, and ecological stability.

Some research indicates that abundance distributions can substantially modify relationships that initially appear to be driven by richness. Communities containing identical numbers of species may function differently when one is dominated by a few organisms and another distributes abundance more evenly.

Abundance-sensitive diversity measures can therefore sometimes explain ecosystem functioning better than richness considered alone.

=== Stability and Resilience ===

Biodiversity is frequently associated with ecosystem stability and resilience, but the underlying relationship involves more than simply counting species.

Evenness can affect how strongly an ecosystem depends on dominant species. When most individuals belong to only one or two species, environmental changes affecting those species can produce substantial changes in community structure and ecosystem processes.

More even communities distribute abundance among a larger proportion of their species, potentially changing their response to disturbance. However, ecological stability also depends on species identity, functional traits, environmental conditions, spatial structure, and interactions among organisms.

Richness and evenness should therefore be interpreted as complementary components of a broader multidimensional biodiversity framework.

=== Conservation and Ecological Monitoring ===

The distinction between richness and evenness has important implications for conservation. A habitat may retain approximately the same number of species while undergoing substantial ecological degradation if formerly uncommon or moderately abundant species decline and a few disturbance-tolerant species become dominant.

Conversely, local richness can sometimes increase through species introductions even while native community composition is substantially altered. An increase in the raw number of species therefore does not automatically indicate ecological improvement.

Effective biodiversity monitoring can combine species richness with evenness, abundance, dominance, species composition, functional diversity, phylogenetic diversity, and other ecological indicators.

Tracking several dimensions helps distinguish between communities that merely contain similar numbers of species and communities that retain similar ecological structure and function.

=== Why Richness and Evenness Should Be Reported Separately ===

Species richness answers the question: "How many species are present?"

Species evenness answers a different question: "How evenly are individuals distributed among those species?"

Neither question alone completely describes biodiversity. A community with twenty species dominated almost entirely by one species is ecologically different from a twenty-species community in which abundance is distributed relatively evenly.

Composite diversity indices can summarize these differences, but summaries can sometimes conceal the mechanism producing a change. A declining diversity index, for example, might result from species loss, increasing dominance, declining evenness, or some combination of these processes.

Reporting richness and evenness separately therefore makes biodiversity changes easier to interpret.

=== Conclusion ===

Species richness and species evenness represent complementary dimensions of ecological diversity. Richness measures how many species occur within a community, whereas evenness describes how abundance is distributed among those species. Decades of ecological research demonstrate that these dimensions do not necessarily move together and can respond independently to disturbance, environmental gradients, management, sampling scale, and ecological change.

Measures such as Shannon diversity, Simpson diversity, Hill numbers, rank-abundance distributions, rarefaction, and species-accumulation curves provide different ways of examining these patterns. No single metric captures every important feature of biodiversity.

For ecological research, conservation, and environmental monitoring, the most informative approach is therefore generally multidimensional. Species richness remains an essential measure, but interpreting it alongside evenness, abundance, dominance, composition, functional diversity, and other ecological characteristics provides a more complete picture of how biological communities are structured and how they are changing.

__TOC__




=== Core Concepts and Biodiversity Measurement ===

[https://www.sciencedirect.com/science/article/pii/S0304380025004259 | S. Pavoine | Ecological Modelling | 2026]
 Parametric formulas for guiding through biodiversity indices. Reviews species richness and abundance-sensitive diversity measures and provides a framework for understanding relationships among biodiversity indices.

[https://www.sciencedirect.com/science/article/pii/S1439179126000332 | R. Warren II | Basic and Applied Ecology | 2026]
 The evenness illusion. Reassesses how ecological evenness is conceptualized and measured and cautions against assuming that every mathematical evenness index represents the same biological property.

[https://www.nature.com/nature-index/topics/l4/biodiversity-measurement-and-estimation-techniques | Nature Portfolio | Nature Index | 2026]
 Biodiversity measurement and estimation techniques. Introduces alpha diversity, richness, abundance, evenness, Hill numbers, and related techniques for comparing ecological communities.

[https://www.davidzeleny.net/anadat-r/doku.php/en:div-ind | David Zelený | Analysis of Community Ecology Data in R | 2026]
 Indices of diversity and evenness. Introduces species richness, Shannon and Simpson indices, evenness measures, effective numbers of species, and Hill numbers for ecological community analysis.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC11470763/ | Various Authors | Ecology and Evolution | 2024]
 Dynamic perspectives on biodiversity quantification. Reviews richness, Shannon diversity, Simpson diversity, and modern biodiversity metrics and stresses that different measures answer different ecological questions.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC11420109/ | T. O. Kvålseth | Ecology and Evolution | 2024]
 Diversity analysis: Richness versus evenness. Explains why richness and evenness are distinct components of biodiversity and uses graphical methods to demonstrate tradeoffs between them when comparing ecological communities.

[https://www.sciencedirect.com/science/article/pii/S1470160X2400428X | C. Ricotta | Ecological Indicators | 2024]
 Hill numbers everywhere: does it make ecological sense? Critically evaluates Hill-number approaches and how increasing weight on abundant species changes the interpretation of biodiversity.

[https://onlinelibrary.wiley.com/doi/10.1111/oik.07202 | M. Roswell, J. Dushoff, and R. Winfree | Oikos | 2021]
 A conceptual guide to measuring species diversity. Compares species richness, Shannon diversity, and Simpson diversity and explains how increasing emphasis on abundance changes the ecological meaning of a diversity measurement.

[https://journals.asm.org/doi/10.1128/msphere.01019-20 | J. Gauthier et al. | mSphere | 2021]
 Evenness-Richness Scatter Plots: a visual and insightful representation of Shannon entropy measurements for ecological community analysis. Shows how separating richness from evenness reveals patterns hidden by a single Shannon-diversity value.

[https://www.sciencedirect.com/science/article/abs/pii/S1470160X17303047 | C. Guisande et al. | Ecological Indicators | 2017]
 DER: An algorithm for comparing species diversity between communities. Discusses biodiversity measurement using species richness, relative abundance, and heterogeneity rather than treating them as interchangeable concepts.

[https://www.sciencedirect.com/science/article/abs/pii/S1470160X16301479 | W. L. Strong | Ecological Indicators | 2016]
 Biased richness and evenness relationships within Shannon-Wiener index values. Demonstrates mathematically that identical Shannon values can result from different combinations of richness and evenness.

[https://arxiv.org/abs/1602.04005 | C. Palaghianu | Computational Ecology | 2016]
 A tool for computing diversity and consideration on differences between diversity indices. Compares Shannon, Simpson, Pielou, Margalef, Menhinick, Berger-Parker, and other measures and shows that indices emphasize different aspects of community structure.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC4224527/ | E. K. Morris et al. | Ecology and Evolution | 2014]
 Choosing and using diversity indices: insights for ecological applications from the German Biodiversity Exploratories. Reviews commonly used biodiversity measures and explains how species richness, dominance, and evenness contribute differently to diversity indices.

[https://pubmed.ncbi.nlm.nih.gov/22210185/ | J. Soininen et al. | Oikos | 2012]
 The relationship between species richness and evenness: a meta-analysis of studies across aquatic and terrestrial ecosystems. Finds that richness-evenness relationships vary substantially among ecological communities rather than following a universal pattern.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC3494667/ | H. Zhang et al. | PLOS ONE | 2012]
 The relationship between species richness and evenness in plant communities along a successional gradient. Shows that richness and evenness can be negatively related and that their relationship changes with spatial scale.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0049024 | H. Zhang et al. | PLOS ONE | 2012]
 Examines subalpine meadow succession on the Qinghai-Tibetan Plateau and demonstrates why richness and evenness should often be analyzed independently rather than collapsed into one index.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC3130435/ | C. Spellerberg and P. Fedor | Journal of Ecology and Environment | 2011]
 Reviews long-standing challenges in using species diversity for ecological assessment, including confusion between richness, evenness, abundance, and composite diversity indices.

[https://www.nature.com/scitable/knowledge/library/characterizing-communities-13241173/ | Nature Education | Scitable by Nature Education | 2010]
 Characterizing communities. Explains species richness as the number of species present and species evenness as the similarity of their relative abundances, illustrating why communities with identical richness can have very different diversity structures.

[https://royalsocietypublishing.org/doi/10.1098/rsbl.2006.0550 | L. Jost | Biology Letters | 2007]
 Partitioning diversity into independent alpha and beta components. Develops the effective-number approach to diversity and clarifies problems that occur when entropy values are interpreted directly as biological diversity.

[https://pdodds.w3.uvm.edu/research/papers/others/2006/jost2006a.pdf | L. Jost | Oikos | 2006]
 Entropy and diversity. Argues that Shannon entropy and related indices should be converted into effective numbers of species so biodiversity values have an intuitive biological interpretation.

[https://academic.oup.com/femsec/article/43/1/1/509981 | T. C. J. Hill et al. | FEMS Microbiology Ecology | 2003]
 Using ecological diversity measures with bacterial communities. Discusses richness, Shannon diversity, Simpson diversity, and evenness and how each metric responds differently to common and rare organisms.

[https://link.springer.com/article/10.1556/ComEc.4.2003.1.2 | R. A. Laird and B. S. Schamp | Community Ecology | 2003]
 Species evenness, not richness, has a consistent relationship with productivity in old-field vegetation. Finds productivity relationships with evenness that were not consistently present for species richness.

[https://link.springer.com/article/10.1556/ComEc.2.2001.2.7 | F. Gosselin | Community Ecology | 2001]
 Lorenz partial order: the best known logical framework to define evenness indices. Examines the theoretical requirement that evenness should represent an aspect of diversity independent of species richness.

[https://link.springer.com/article/10.1023/A%3A1009626406418 | R. Rousseau, P. Van Hecke, D. Nijssen et al. | Environmental and Ecological Statistics | 1999]
 The relationship between diversity profiles, evenness and species richness based on partial ordering. Develops mathematical methods for distinguishing changes in richness from changes in abundance distribution.

[https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1934352 | M. O. Hill | Ecology | 1973]
 Diversity and evenness: a unifying notation and its consequences. Introduces the influential Hill-number framework, allowing diversity measures to be interpreted as effective numbers of species while varying sensitivity to relative abundance.

[https://www.jstor.org/stable/1934352 | M. O. Hill | Ecology | 1973]
 Hill's diversity numbers provide a continuum from simple species richness to diversity measures increasingly dominated by common species, illustrating how richness and evenness contribute differently.

[https://www.jstor.org/stable/1932409 | E. C. Pielou | Journal of Theoretical Biology | 1966]
 The measurement of diversity in different types of biological collections. Helped establish mathematical approaches for comparing ecological diversity and provided foundations for measures of community evenness.

[https://www.forestresearch.gov.uk/tools-and-resources/fthr/species-diversity/ | Forest Research | Forest Research, UK Government | Current resource]
 Species diversity. Provides an accessible explanation that species diversity reflects both how many species occur in a community and how evenly abundance is distributed among them.

=== Richness-Evenness Relationships and Community Structure ===

[https://pmc.ncbi.nlm.nih.gov/articles/PMC12285210/ | Various Authors | Ecology and Evolution | 2025]
 Does evenness even exist? Reexamines the conceptual foundations of ecological evenness and asks whether supposedly simple evenness indices capture a single biological property.

[https://www.frontiersin.org/journals/conservation-science/articles/10.3389/fcosc.2025.1552578/full | G. Tavilla et al. | Frontiers in Conservation Science | 2025]
 Assessing plant species diversity in Maltese rocky cliffs. Finds relatively stable species richness alongside declining evenness and increasing dominance, illustrating biodiversity change that simple species counts would overlook.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2656.14136 | L. Sandal et al. | Journal of Animal Ecology | 2024]
 Species richness and evenness of European bird communities. Finds that evenness in species abundance was largely independent of species richness, demonstrating that the two dimensions can follow different geographical patterns.

[https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1338596/full | L. Meng et al. | Frontiers in Plant Science | 2024]
 Variations in species diversity patterns and community structure. Uses rank-abundance distributions to show richness through curve length and evenness through its slope.

[https://academic.oup.com/jpe/article/16/1/rtac040/6561790 | R. M. Tiwari et al. | Journal of Plant Ecology | 2023]
 Decoupling the impact of biodiversity and environmental factors on ecosystem functioning. Reports a strong negative correlation between species richness and evenness in studied plant communities.

[https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2023.1108739/full | H. Yan et al. | Frontiers in Ecology and Evolution | 2023]
 Diminishing influence of the negative relationship between richness and evenness on estimates of alpha diversity. Examines how interactions between richness and evenness affect conclusions drawn from biodiversity metrics.

[https://www.sciencedirect.com/science/article/pii/S1439179123000117 | F. Leroy et al. | Basic and Applied Ecology | 2023]
 How has bird biodiversity changed over time? Reviews evidence that changes in species richness can differ substantially depending on spatial scale and may not parallel changes in other biodiversity dimensions.

[https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2022.971585/full | Z. Zhao et al. | Frontiers in Ecology and Evolution | 2022]
 Assessing tree species diversity in forest ecosystems. Describes richness and evenness as fundamental but distinct biodiversity properties and proposes a method for evaluating them independently.

[https://public-pages-files-2025.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2022.971585/pdf | Z. Zhao et al. | Frontiers in Ecology and Evolution | 2022]
 Presents the DRE diversity measure, designed to retain separate information about species richness and evenness rather than allowing one component to obscure the other.

[https://academic.oup.com/book/39450/chapter/339204935 | Oxford Academic | Oxford University Press | 2021]
 Species richness, diversity, and packing. Reviews richness, evenness, alpha diversity, beta diversity, and gamma diversity and their application to ecological inventories.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC7900956/ | J. A. Myers et al. | Ecology | 2021]
 A multiscale framework for disentangling the roles of evenness, density, and aggregation in species richness patterns. Shows that richness patterns can arise partly from how individuals are distributed among species and across space.

[https://www.nature.com/articles/s41598-020-58202-4 | H. M. Tu et al. | Scientific Reports | 2020]
 Different habitat types affect bird richness and evenness. Finds that natural and agricultural habitats can influence species richness and evenness differently across landscapes.

[https://link.springer.com/article/10.1134/S1067413618040021 | V. V. Akatov et al. | Russian Journal of Ecology | 2018]
 The relationship of dominance and evenness with species richness. Shows that richness-evenness relationships differ among competitive, stress-tolerant, and ruderal plant communities.

[https://arxiv.org/abs/1802.09425 | N. DeMalach et al. | Global Ecology and Biogeography | 2018]
 Plant species accumulation curves are determined by evenness and spatial aggregation in drylands worldwide. Demonstrates that evenness helps determine the shape of species-accumulation curves.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0200191 | D. Hattermann et al. | PLOS ONE | 2018]
 New insights into island vegetation composition and species diversity. Emphasizes that either richness or evenness alone can provide a misleading description of biodiversity.

[https://www.pnas.org/doi/10.1073/pnas.1521291113 | K. J. Locey and J. T. Lennon | Proceedings of the National Academy of Sciences | 2016]
 Scaling laws predict global microbial diversity. Analyzes richness, abundance, rarity, and evenness across microbial communities and highlights the enormous contribution of rare taxa to total richness.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC3871376/ | Various Authors | PLOS ONE | 2014]
 Relationship between evenness and body size in species-rich assemblages. Examines biological factors affecting the relative-abundance structure of ecological communities.

[https://www.sciencedirect.com/science/article/abs/pii/S0006320708004904 | T. Reitalu et al. | Biological Conservation | 2009]
 Small-scale plant species richness and evenness in semi-natural grasslands. Finds that richness and evenness can respond differently to management and landscape history, supporting their separate use in biodiversity monitoring.

[https://www.lunduniversity.lu.se/publication/f234bd5e-89e1-4e6f-9917-a37f05b6b8da | T. Reitalu et al. | Lund University / Biological Conservation | 2009]
 Examines grassland richness and evenness across management and landscape contexts and argues that conservation assessments should measure both rather than richness alone.

[https://esajournals.onlinelibrary.wiley.com/doi/10.1890/06-1751 | B. J. Wilsey and H. W. Polley | Ecology | 2007]
 Relationships among species richness, evenness, and abundance in grassland communities. Investigates whether changes in richness correspond to changes in evenness and total abundance.

[https://dr.lib.iastate.edu/handle/20.500.12876/23350 | B. Wilsey et al. | Ecology | 2005]
 Relationships among indices suggest that richness is an incomplete surrogate for grassland biodiversity. Demonstrates that communities having similar species counts can differ substantially in abundance distribution.

[https://www.science.org/doi/10.1126/science.147.3655.250 | R. H. Whittaker | Science | 1965]
 Dominance and diversity in land plant communities. A foundational treatment of species abundance distributions showing how dominance and relative abundance contribute to ecological diversity.

[https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1944002 | F. W. Preston | Ecology | 1962]
 The canonical distribution of commonness and rarity. Explores statistical patterns in species abundance that influence observed richness and community evenness.

[https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1932766 | R. H. Whittaker | Ecological Monographs | 1960]
 Vegetation of the Siskiyou Mountains, Oregon and California. Influential community-ecology research illustrating how species composition, dominance, and richness change across environmental gradients.

[https://www.nature.com/articles/163688a0 | F. W. Preston | Nature | 1948]
 The commonness, and rarity, of species. Introduces influential ideas about species-abundance distributions and why ecological communities typically contain both common and rare species.

=== Sampling, Scale, and Detection ===

[https://onlinelibrary.wiley.com/doi/abs/10.1002/ece3.10594 | Z. Huang et al. | Ecology and Evolution | 2023]
 Elevational patterns of microbial species richness and evenness. Shows that richness-evenness relationships can vary among bacteria, fungi, taxonomic groups, climatic zones, and elevation.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC10560872/ | Z. Huang et al. | Ecology and Evolution | 2023]
 Examines forest-soil microbial communities across tropical, subtropical, and cold-temperate elevation gradients and finds differing patterns for richness and evenness.

[https://academic.oup.com/jpe/article/16/4/rtad002/6995394 | L. W. Morrison et al. | Journal of Plant Ecology | 2023]
 Observer error in grassland vegetation surveys. Compares observer effects on richness, Shannon diversity, Shannon evenness, and Simpson diversity.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/2041-210X.12613 | T. C. Hsieh, K. H. Ma, and A. Chao | Methods in Ecology and Evolution | 2016]
 iNEXT: an R package for rarefaction and extrapolation of species diversity. Allows standardized comparisons using Hill numbers representing richness, Shannon diversity, and Simpson diversity.

[https://esajournals.onlinelibrary.wiley.com/doi/10.1890/13-0133.1 | A. Chao et al. | Ecological Monographs | 2014]
 Rarefaction and extrapolation with Hill numbers. Provides a unified framework for comparing richness and abundance-sensitive diversity across samples with unequal sampling effort.

[https://link.springer.com/article/10.1556/ComEc.9.2008.1.14 | A. Chiarucci et al. | Community Ecology | 2008]
 Discovering and rediscovering sample-based rarefaction. Reviews rarefaction as a technique for comparing species richness across unequal sampling efforts.

[https://esajournals.onlinelibrary.wiley.com/doi/10.1890/0012-9658(2001)082%5B2626:EBFFIS%5D2.0.CO;2 | N. J. Gotelli and R. K. Colwell | Ecology | 2001]
 Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness. Explains why raw species counts depend strongly on sampling effort.

[https://royalsocietypublishing.org/doi/10.1098/rstb.1994.0091 | R. K. Colwell and J. A. Coddington | Philosophical Transactions of the Royal Society B | 1994]
 Estimating terrestrial biodiversity through extrapolation. A foundational review of methods for estimating total species richness when ecological surveys detect only a fraction of the species present.

[https://www.jstor.org/stable/1932766 | R. H. Whittaker | Ecological Monographs | 1960]
 Demonstrates the importance of spatial gradients and community composition when interpreting local species counts and abundance distributions.

=== Forests, Grasslands, and Plant Communities ===

[https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2025.1688827/full | Y. Wang et al. | Frontiers in Plant Science | 2025]
 Functional diversity of plant communities and species succession. Investigates changes in richness and several dimensions of diversity as vegetation succession progresses.

[https://royalsocietypublishing.org/rspb/article/292/2050/20250496/234697/ | Various Authors | Proceedings of the Royal Society B | 2025]
 Tests species richness, evenness, and their interaction when examining productivity and invasion, illustrating that the two components can have different ecological effects.

[https://nsojournals.onlinelibrary.wiley.com/doi/10.1002/ecog.08309 | N. Rondeau et al. | Ecography | 2025]
 Maximising trait evenness promotes recovery of plant species richness in managed grasslands. Connects even trait distributions with restoration of species-rich plant communities.

[https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2025.1487582/full | J. Che et al. | Frontiers in Plant Science | 2025]
 Elevation gradient effects on grassland species diversity. Measures species richness, Shannon diversity, Simpson diversity, dominance, and Pielou evenness along mountain gradients.

[https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2024.1291252/full | S. M. D. Kinnoumè et al. | Frontiers in Forests and Global Change | 2024]
 Tree diversity and ecosystem functioning in riparian corridors. Examines species richness together with phylogenetic and functional dimensions of biodiversity.

[https://edepot.wur.nl/675180 | K. Andraczek et al. | Ecology | 2024]
 Weak reciprocal relationships between productivity and plant diversity. Quantifies grassland biodiversity using species richness, evenness, and Shannon diversity rather than relying on a single measure.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0268018 | P. Kumar et al. | PLOS ONE | 2022]
 Calculating forest species diversity with information-theory methods. Compares species richness, Shannon diversity, and evenness across forest transects.

[https://academic.oup.com/jpe/article/15/2/413/6364142 | G. Valadi et al. | Journal of Plant Ecology | 2022]
 Edge influence on herbaceous plant richness, diversity, and evenness. Finds changes in all three properties between forest-fragment edges and interiors.

[https://journals.plos.org/plosone/article/asset?id=10.1371/journal.pone.0139031.PDF | Y. Kouba et al. | PLOS ONE | 2015]
 Effects of previous land use on plant species composition and diversity. Measures richness and evenness separately across forest stands with different management histories.

[https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002324 | G. Yvon-Durocher et al. | PLOS Biology | 2015]
 Five years of experimental warming increases phytoplankton richness and alters relative abundance. Demonstrates that environmental change can affect richness and evenness simultaneously but not identically.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0109261 | J. Lemieux and M. Cusson | PLOS ONE | 2014]
 Effects of habitat-forming species richness, evenness, identity, and abundance on benthic communities. Separates richness and evenness experimentally when studying community structure.

[https://academic.oup.com/jpe/article/3/2/71/906849 | P. G. Dimitrakopoulos | Journal of Plant Ecology | 2010]
 Influence of evenness on the litter-species richness–decomposition relationship. Demonstrates that the relative abundance of plant species can alter ecosystem processes independently of richness.

=== Birds and Terrestrial Vertebrates ===

[https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2024.1387879/full | T. Shaw et al. | Frontiers in Ecology and Evolution | 2024]
 Forest structural heterogeneity positively affects bird diversity. Examines how vegetation structure and forest conditions influence species richness and community composition.

[https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2024.1302002/full | M. W. D. McCloy et al. | Frontiers in Ecology and Evolution | 2024]
 Promoting urban ecological resilience through avian biodiversity. Discusses management practices capable of increasing local bird richness and other biodiversity dimensions.

[https://www.sciencedirect.com/science/article/pii/S1470160X24007234 | L. M. Berman et al. | Ecological Indicators | 2024]
 Fractional Richness: an index for camera-trap networks. Develops a richness measure incorporating abundance information to provide more information than simple species counts.

[https://www.nature.com/scitable/knowledge/library/sampling-biological-communities-23676556/ | Nature Education | Scitable | 2011]
 Sampling biological communities. Uses rank-abundance curves to illustrate communities with contrasting richness and evenness and explains how sampling reveals these differences.

=== Aquatic and Marine Communities ===

[https://www.frontiersin.org/journals/water/articles/10.3389/frwa.2025.1678547/full | P. S. Samuel et al. | Frontiers in Water | 2025]
 Diversity fluctuations of a freshwater microbial community. Finds strong relationships between Microcystis dominance and reduced species evenness.

[https://www.gmri.org/stories/gulf-of-maine-explained-marine-biodiversity/ | Gulf of Maine Research Institute | GMRI | 2024]
 Marine biodiversity overview discussing long-term changes in richness and evenness detected through fisheries and ecosystem monitoring.

[https://www.frontiersin.org/research-topics/47880/freshwater-biodiversity-and-ecosystem-functioning-novel-ideas-and-approaches/magazine | Frontiers Editors | Frontiers | 2023]
 Freshwater biodiversity and ecosystem functioning. Collects research examining multiple dimensions of biodiversity rather than equating biodiversity solely with the number of species.

[https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2023.1150001/full | C. Liu et al. | Frontiers in Ecology and Evolution | 2023]
 Disentangling multiple relationships of species diversity and community biomass. Tests whether diatom richness and evenness independently influence biomass.

[https://www.sciencedirect.com/science/article/pii/S1470160X21009791 | W. Zhang et al. | Ecological Indicators | 2021]
 Ecosystem functioning is linked to microbial evenness and community composition. Illustrates why abundance distribution can sometimes be more informative than species count alone.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.13549 | S. A. Blowes et al. | Journal of Applied Ecology | 2020]
 Mediterranean marine protected areas and biodiversity. Uses species richness, rarefied richness, abundance structure, and other biodiversity measurements to evaluate protection effects.

[https://royalsocietypublishing.org/rspb/article/286/1906/20191189/85163/ | Various Authors | Proceedings of the Royal Society B | 2019]
 Biodiversity–ecosystem functioning relationships in fish communities. Tests richness, evenness, and biomass simultaneously to determine how different dimensions of biodiversity relate to ecosystem functioning.

[https://nora.nerc.ac.uk/id/eprint/526523/1/Ashford_et_al-2019-Ecology_and_Evolution.pdf | O. S. Ashford et al. | Ecology and Evolution | 2019]
 Seafloor biodiversity study using taxonomic, phylogenetic, and functional richness and evenness metrics to compare deep-sea crustacean assemblages.

[https://www.sciencedirect.com/science/article/abs/pii/S1385110114001609 | M. Cusson et al. | Journal of Experimental Marine Biology and Ecology | 2015]
 Relationships between biodiversity and stability of marine benthic assemblages. Examines how species richness and evenness relate to temporal ecological variability.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0084568 | R. M. Pendleton et al. | PLOS ONE | 2014]
 Loss of rare fish species from tropical floodplain food webs. Shows that species richness can affect ecosystem functioning even when the lost organisms are relatively rare.

[https://research-portal.st-andrews.ac.uk/en/publications/relationships-between-biodiversity-and-the-stability-of-marine-ec/ | M. Cusson et al. | University of St Andrews | 2014]
 European-scale analysis showing that richness, evenness, abundance, and community composition can exhibit different relationships with ecological stability.

[https://academic.oup.com/plankt/article-abstract/35/5/1154/1536665 | C. A. Larson and G. E. Belovsky | Journal of Plankton Research | 2013]
 Salinity and nutrients influence species richness and evenness of phytoplankton communities. Experimental study showing different responses of richness and evenness to environmental conditions.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0011832 | R. Danovaro et al. | PLOS ONE | 2010]
 Deep-sea biodiversity in the Mediterranean Sea. Reports differences in species richness, evenness, and total diversity among benthic environments.

=== Microbial Richness and Evenness ===

[https://www.nature.com/articles/s41598-024-77864-y | I. Cassol et al. | Scientific Reports | 2025]
 Key features and guidelines for microbial diversity analysis. Distinguishes richness-based alpha-diversity measures from metrics incorporating relative abundance and evenness.

[https://arxiv.org/abs/1302.3753 | B. Haegeman et al. | ISME Journal | 2013]
 Robust estimation of microbial diversity in theory and practice. Shows why estimated microbial species richness is highly sensitive to unseen rare taxa and argues that Shannon and Simpson diversity can sometimes be estimated more reliably.

[https://pure.manchester.ac.uk/ws/files/19594100/PRE-PEER-REVIEW.PDF | B. Haegeman et al. | University of Manchester / ISME Journal | 2013]
 Explains how microbial communities with long tails of rare taxa make true richness difficult to estimate while abundance-weighted diversity measures remain more robust.

[https://www.nature.com/articles/ismej2009153 | A. Engelbrektson et al. | ISME Journal | 2010]
 Experimental factors affecting PCR-based estimates of microbial diversity. Shows that laboratory methodology can alter estimates of both species richness and evenness.

[https://www.cd-genomics.com/microbioseq/the-use-and-types-of-alpha-diversity-metrics-in-microbial-ngs.html | CD Genomics | MicrobioSeq | Current resource]
 Overview of microbial alpha-diversity measurements including observed richness, Chao estimators, Shannon diversity, Simpson diversity, evenness, and rank-abundance curves.

=== Ecosystem Function, Productivity, and Stability ===

[https://www.sciencedirect.com/science/article/pii/S219756202600045X | Y. Xu et al. | Forest Ecosystems | 2026]
 The role of species evenness in a subtropical forest. Examines how abundance distribution interacts with richness and environmental conditions in determining forest ecological processes.

[https://www.nature.com/nature-index/topics/l4/species-abundance-and-community-structure-in-ecology | Nature Portfolio | Nature Index | 2026]
 Species abundance and community structure in ecology. Reviews research connecting species richness, evenness, dominance, community assembly, and environmental heterogeneity.

[https://academic.oup.com/jpe/article/19/3/rtaf205/8364808 | G. Hou et al. | Journal of Plant Ecology | 2026]
 Initial species evenness modulates divergent stability responses. Investigates how initial abundance distribution affects community responses and stability under environmental change.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC12371026/ | Various Authors | Nature Communications | 2025]
 Species abundances surpass richness effects in biodiversity–ecosystem functioning relationships. Finds that abundance-weighted Hill diversity can explain biomass patterns better than richness or evenness considered independently.

[https://pmc.ncbi.nlm.nih.gov/articles/PMC13103429/ | Various Authors | Ecology Letters | 2025]
 Even evenness is important. Examines direct and indirect pathways through which the distribution of abundance among species influences ecological processes.

[https://www.nature.com/articles/s41467-025-63210-x | H. F. Yan et al. | Nature Communications | 2025]
 Species abundances surpass richness effects in the biodiversity–ecosystem functioning relationship. Finds abundance-sensitive Hill diversity can outperform richness and evenness individually in predicting reef-fish biomass production.

[https://www.sciencedirect.com/science/article/pii/S2666683923000305 | R. Zhang et al. | Biological Conservation | 2023]
 Critical role of multidimensional biodiversity in ecosystem functioning. Argues that conservation and ecological assessment should move beyond species richness toward multidimensional biodiversity measures.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/2041-210X.14158 | R. A. Moral et al. | Methods in Ecology and Evolution | 2023]
 Going beyond richness: modelling biodiversity–ecosystem-function relationships. Develops analytical approaches that incorporate species identities and relative abundances rather than richness alone.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.14098 | I. Hordijk et al. | Journal of Ecology | 2023]
 Evenness mediates the global relationship between forest productivity and species diversity. Shows that richness-related productivity gains may become constrained when increasing richness is associated with lower evenness.

[https://academic.oup.com/jpe/article/15/2/385/6372391 | W. Miao et al. | Journal of Plant Ecology | 2022]
 Effects of biodiversity, stand factors, and functional identity on forest biomass and productivity. Compares species diversity with functional richness, evenness, and dispersion.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.13345 | Y. Cao et al. | Journal of Applied Ecology | 2019]
 Weighting effective numbers of species for ecological assessment. Recommends reporting species richness, evenness, and species composition rather than reducing biodiversity to one statistic.

[https://www.nature.com/articles/ismej2017160 | S. Fontana et al. | ISME Journal | 2018]
 Individual-level trait diversity predicts phytoplankton community properties better than species richness or evenness. Demonstrates that richness and evenness are informative but do not capture every dimension of community structure.

[https://www.nature.com/articles/srep39325 | D. Wohlgemuth et al. | Scientific Reports | 2016]
 Specific arrangements of species dominance can be more influential than evenness. Investigates how community dominance structure can alter biodiversity–ecosystem-function relationships.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2011.01944.x | Y. Zhang, H. Y. H. Chen, and P. B. Reich | Journal of Ecology | 2012]
 Forest productivity increases with evenness, species richness and trait variation. Meta-analysis identifies distinct contributions of richness and evenness to forest productivity.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0050152 | J. Sircely and S. Naeem | PLOS ONE | 2012]
 Biodiversity and ecosystem multifunctionality in western Kenyan fallows. Investigates whether species-rich plant communities support multiple ecosystem processes more effectively.

[https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2011.01918.x | F. T. Maestre et al. | Journal of Ecology | 2012]
 Species richness effects on ecosystem multifunctionality depend on evenness, composition and spatial pattern. Demonstrates that richness effects cannot always be separated from relative abundance and spatial organization.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052821 | C. M. Clark et al. | PLOS ONE | 2012]
 Testing the link between functional diversity and ecosystem functioning. Distinguishes functional richness from functional evenness and demonstrates why diversity has multiple independent dimensions.

[https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2656.2011.01857.x | J. Reiss et al. | Journal of Animal Ecology | 2011]
 Testing effects of consumer richness, evenness and body size on ecosystem functioning. Separates effects of consumer richness from relative abundance in experimental food webs.

=== Conservation, Monitoring, and Applied Biodiversity ===

[https://www.nature.com/articles/s41467-026-73613-z | H. Saeedi et al. | Nature Communications | 2026]
 Gaps and drivers of global marine animal biodiversity. Uses richness estimators and inverse Simpson diversity, allowing comparisons between raw species counts and abundance-weighted biodiversity.

[https://www.coastalwiki.org/wiki/Disturbances,_biodiversity_changes_and_ecosystem_stability | Coastal Wiki Contributors | Coastal Wiki | 2026]
 Disturbances, biodiversity changes and ecosystem stability. Reviews evidence showing that richness alone may be an insufficient indicator when species identity, dominance, evenness, and turnover are changing.

[https://academic.oup.com/icb/article/65/2/392/8161038 | Y. X. G. Wang et al. | Integrative and Comparative Biology | 2025]
 Beyond species richness: the importance of phylogenetic and functional biodiversity. Reviews evidence that ecological outcomes can depend on evenness and functional diversity rather than simple species counts.

[https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2024.1447694/full | M. A. Sial et al. | Frontiers in Ecology and Evolution | 2024]
 Diversity, evenness, and richness of wild mammals along environmental gradients. Uses separate metrics to characterize wildlife community structure and ecological condition.

[https://academic.oup.com/jue/article/8/1/juac017/6711445 | R. Thompson et al. | Journal of Urban Ecology | 2022]
 Urban bird diversity: does abundance and richness vary with urbanization? Demonstrates how species richness and total abundance can show contrasting responses to urban development.

[https://academic.oup.com/book/35382/chapter/301337498 | Oxford University Press | Oxford Academic | 2020]
 Biodiversity and invasive species. Explains how invasion and disturbance can change richness, dominance, evenness, functional composition, and resilience in different ways.

[https://link.springer.com/article/10.1007/s10980-018-0742-9 | E. Aggemyr et al. | Landscape Ecology | 2018]
 Species richness and composition differ in response to landscape conditions. Argues that patches having equal species richness can contain completely different communities and that ecological analysis should move beyond simple richness.

[https://academic.oup.com/jinsectscience/article/13/1/79/1075847 | J. Majumder et al. | Journal of Insect Science | 2013]
 Butterfly species richness and diversity in Trishna Wildlife Sanctuary. Applies richness and diversity indices to conservation assessment of tropical insect communities.

[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0030535 | E. C. Ellis et al. | PLOS ONE | 2012]
 All is not loss: plant biodiversity in the Anthropocene. Argues that species richness alone provides an incomplete picture because human activities can increase local species counts while profoundly altering composition and evenness.