Biodiversity Indices: Measuring Ecological Diversity

• Biodiversity indices are tools to measure and interpret diversity in ecological communities
• They provide understanding into ecosystem health, conservation, and resource management
• Each index gives a unique perspective on the different aspects of biodiversity, including species richness, evenness, and ecological dominance
• Understanding biodiversity indices helps assess species diversity, detect changes over time and compare ecological communities

Significance

• Higher values in indices usually point to more diverse and healthier ecosystems
• Lower values might mean ecological stress or dominance by a few species
• Indices range from 0 (no diversity) to higher values (increasing diversity)

Abundance

• The total number of individuals of all species in an area
• Calculation: Sum of all the individuals counted
• Formula: N equals the total individuals

Relative Abundance

• The proportion of each species relative to the total number of individuals
• Calculation: Count individuals of the species and divide by total abundance for each species
• Formula: Relative Abundance = Individuals of Species / N

Density

• The number of individuals per unit area
• Calculation: Total individuals divided by the area surveyed
• Formula: D = N/A, where A equals the area surveyed

Relative Density

• The proportion of a species' density to the total density
• Calculation: Determine density for each species, then compute proportion
• Formula: Relative Density = Density of Species / Total Density

Frequency

• The number of times a species is found in sampled plots
• Calculation: Count plots where each species occurs, then divide by total plots sampled
• Formula: F = (Number of plots with species / Total plots sampled) X 100

Relative Frequency

• The proportion of each species' frequency relative to the total frequency of all species
• Calculation: Calculate the frequency for each species, then divide by total frequency
• Formula: Relative Frequency = Frequency of Species / Total Frequency

Importance Value (IV)

• A measure that combines density, frequency, and dominance
• Calculation: Compute the relative density, relative frequency, plus relative basal area/cover (if relevant), and sum
• Formula: IV = Relative Density + Relative Frequency + Relative Dominance

Species Richness

• Total number of different species in a given area
• Calculation: Simply count the number of different species
• Formula: R = S, where S is the total number of species

Evenness

• The degree to which species' abundances are distributed evenly across species
• Calculation: Equates to comparing observed diversity to maximum possible diversity

Qualitative Measurement

• Evenness measures how similar the abundance of different species/categories are in a community and ranges from zero to one
• When evenness is close to zero, most individuals belong to one or a few species/categories
• When evenness is close to one, each species/category has the same number of individuals
• Evenness measures the relative abundance of different species

Simpson's Index (D)

• Measures the probability that two individuals randomly selected will belong to the same species
• Formula: D=(n/N)2 or D= Σn(n-1) / N(N-1)
• n = the total number of organisms of a particular species
• N = the total number of organisms of all species
• The value ranges between 0 and 1
• 1 = No Diversity
• 0 = Infinite diversity

Shannon Diversity Index (H)

• Used to describe species diversity in a community while accounting for the abundance and evenness of the species
• Typical values are between 1.5 and 3.5
• Rare to be greater than 4
• Increases as richness and evenness of the community increase

Shannon-Wiener Index Calculation

• Formula: H' = -Σpi log pi from i=1 to S
• H' = the value of the diversity index
• pi = the proportion of the ith species
• loge = the natural logarithm of pi
• S = the number of species in the community