Kerala 27. Uttar Pradesh

Alpha diversity is characterised by several widespread patterns that are characteristic of most taxa and are strongly correlated with physical environmental gradients. For example,

• Marine and terrestrial environments in tropical regions have more species of higher taxonomic groups than those in higher latitude communities. • Richness of species in terms of most taxa is positively correlated with habitat structural complexity. • Structurally simple habitats like open oceans, grasslands, etc. generally support fewer species than structurally complex communities such as forests and coral reefs. In the open oceans maximum richness of most groups is found at depths between 2000-4000 m. In contrast coral species richness peaks at depths between 15-30 m because corals obtain their energy from photosynthetic organisms embedded in their tissues, and are thus confined to the photic zone. • Island communities are poor in species than comparable mainland communities.

Beta (β) richness refers to the rate of change in species composition across habitats and β diversity refers to diversity between the ecosystems.

Gamma (γ) richness refers to the rate of change across larger landscape gradients and gamma diversity is a measure of the overall diversity for different ecosystems in a region. Hunter defines gamma diversity as “geographic-scale species diversity”. Let us make this concept more clear to you by giving an example. Suppose we want to compare diversity of hypothetical species in different ecosystems say I, II and III (Table 5.1).

We can walk a transect in each of these three ecosystems and count the number of species we see, this gives us the alpha diversity for each ecosystem, e.g. α diversity of ecosystem I, II and III is 10,7, and 3 reap. Now, if we examine the change in species diversity between these ecosystems then we are measuring the β diversity, e.g. beta diversity between I and II is 7(representing 5 found in ecosystem I but not in ecosystem II plus 2 species found in ecosystem II but not in I), similarly β diversity between ecosystem II and III is 8 and between ecosystem I and III is 13. The total number of species for the three ecosystems is 14, which represents the gamma diversity.

Table 5.1: Alpha, beta and gamma diversity for hypothetical species in three different ecosystems

Hypothetical species Ecosystem-I Ecosystem-II Ecosystem-III

A B C D E F G H I J K X X X X X X X X X X X X X X X X

L X X

M N

X X Alpha diversity 10 7 3

Beta diversity I vs. II (7) II vs. III (8) I vs. III (13) Gamma diversity 14

Introduction to Biodiversity