Alpha diversity refers to the mean diversity of species within individual sites or ecosystems at a local scale. It is measured by counting the number of distinct taxa like species, genera, or families within an ecosystem. Alpha diversity, along with beta diversity (diversity between habitats along environmental gradients) and gamma diversity (overall diversity in a region), were concepts introduced by R.H. Whittaker to describe biodiversity at different scales.

1. Alpha diversity
In ecology, alpha diversity (α-diversity)
is the mean species diversity in sites
or habitats at a local scale.

2. Alpha diversity
• Alpha diversity (α-diversity) is expressed in terms
species richness or number of species in an
ecosystem. It defines the biological diversity
within an ecosystem, community or simply in a
particular habitat.
• The alpha diversity can be measured by counting
the distinct group of organisms such as different
species, genera, and families or number of
taxonomic entities (number of taxa) within the
ecosystem.

3. • The term was introduced by R. H. Whittaker
• Whittaker's idea was that the total species
diversity in a landscape is determined by two
different things,
• the mean species diversity in sites or habitats
at a more local scale (alpha diversity)
• and the differentiation among those habitats
(beta diversity).

5. Diversity of Diversities
• Difference between the diversities is usually one
of relative emphasis of two main envir. aspects
• Two key features
– Richness
– Abundance – our emphasis today
• Each index differs in the mathematical method of
relating these features
– One is often given greater prominence than the other
– Formulae significantly differ between indices

6. Alpha Diversity Indices
• “Heterogeneity Indices”
– Consider both evenness AND richness
– Species abundance models only consider evenness
• No assumptions made about species abundance
distributions
– Cause of distribution
– Shape of curve
• “Non-parametric”
– Free of assumptions of normality

7. Beta diversity
Beta Diversity (between habitat
diversity along environment gradient)

8. Beta diversity
• Beta diversity (β-diversity) is defined as the
quantitative measurement of diversity of
communities along environmental gradients.
• The species diversity that experience changing
environment between ecosystems is
compared to measure the beta diversity.
• It is given as the rate of change in species
composition among communities or across
different ecological habitat.

9. Conti…
• In ecology, beta diversity (β-diversity or true
beta diversity) is the ratio between regional
and local species diversity. The term was
introduced by R. H. Whittaker together with
the terms alpha diversity (α-diversity)
and gamma diversity (γ-diversity).

10. Gamma diversity
• Gamma diversity (γ-diversity) is defined as the
species richness or total number of species
over a large region (ecological, units).
• Gamma diversity also called as large-scale
landscape diversity, within a region is given by
the quantitative measurement of overall
diversity for different ecosystems.
• It is often expressed as the species richness of
component communities.