The Rate of Species Diversification is Calculated as the

Calculate the net diversification rate based on species richness and time.

Usually 1 if starting from a common ancestor, or 2 for a crown group.

The total number of species currently existing in the clade.

Time elapsed in Million Years (Ma).

How the Rate of Species Diversification is Calculated

In evolutionary biology and phylogenetics, the rate of species diversification is calculated as the net difference between the speciation rate and the extinction rate. It represents how rapidly new species are accumulating within a specific clade or geographic region over geological time.

The Mathematical Formula

While the theoretical definition is r = λ – μ (where λ is speciation and μ is extinction), we often cannot observe these rates directly in the fossil record or molecular phylogenies. Instead, we calculate the average net diversification rate using the change in species counts over time:

r = [ ln(Nₜ) – ln(N₀) ] / t

• r: Net diversification rate (species per million years).
• ln: Natural logarithm.
• Nₜ: Number of species at the end of the time period (Current richness).
• N₀: Number of species at the beginning (Initial richness).
• t: Time interval (usually measured in Millions of Years, Ma).

Understanding the Variables

Initial Species (N₀): When analyzing a specific clade that originated from a single common ancestor (stem group), this value is typically set to 1. If the analysis begins after the first divergence (crown group), it may be set to 2.

Current Species (Nₜ): This is the extant diversity—the number of living species currently described within the group being analyzed.

Time (t): The age of the clade, determined through fossil dating or molecular clock analysis.

Example Calculation

Consider a genus of flowering plants that originated 10 million years ago from a single ancestor and now consists of 500 species.

• N₀ = 1
• Nₜ = 500
• t = 10 Ma

The calculation would be:

r = (ln(500) – ln(1)) / 10 = (6.21 – 0) / 10 = 0.621 species/Ma

This result implies a rapid radiation event compared to background rates often observed in other lineages.

Speciation vs. Extinction

It is crucial to remember that this calculator provides the net rate. A clade could have a high diversification rate because speciation is extremely high (even if extinction is moderate), or because extinction is extremely low. Conversely, if the rate is negative, it indicates that the extinction rate exceeds the speciation rate, and the clade is in decline.