Does Evenness Even Exist?

Area of Science:

• Ecology
• Biodiversity Science
• Community Ecology

Background:

• The concept of ecological diversity is traditionally defined by species richness and evenness.
• Evenness indices and related metrics like Hill numbers are widely used to quantify biodiversity.
• These metrics are often computed independently or in conjunction with richness measures.

Purpose of the Study:

• To critically evaluate the utility and limitations of evenness indices and Hill numbers in ecological research.
• To propose an alternative approach for understanding community structure and assembly.
• To highlight the operational problems associated with the abstraction of evenness.

Main Methods:

• Analysis of the sensitivity and replicability of evenness indices and Hill numbers using empirical data.
• Examination of the relationship between these metrics and parameters of theoretical count distribution models.
• Simulation studies to assess the variability of these metrics under controlled conditions.

Main Results:

• Evenness indices and Hill numbers demonstrate high sensitivity to dominant species abundance.
• These metrics exhibit poor within-community replicability and high variability among similar communities.
• Their relationship with underlying model parameters is inconsistent, and they are weak indicators of biodiversity trends.

Conclusions:

• Evenness is an abstraction that poses operational challenges in ecological studies.
• Ecologists should prioritize fitting theoretical models to empirical count distributions.
• Utilizing estimated model parameters offers a more reliable method for understanding community structure and assembly.