Alpha, Beta & Gamma Diversity – Definitions, Examples, Formula & NEET MCQs

Introduction to Biodiversity Measures

Biodiversity is the sum of the different species and the diversity that occurs within a particular area, region, or on Earth. It is the entire array of life forms from the microbes to the plants and animals and is found at all levels of biological organisation. It is estimated by the Convention on Biological Diversity (CBD) that there exist around 8.7 million species on our planet, though not more than 1.5 million have been taxonomically described.

Not only does biodiversity sustain ecosystem productivity and stability, but it also provides essential services such as food, medicine, and clean water. Biodiversity loss due to habitat destruction, pollution, and climate change is seriously threatening ecological balance and human health.

Alpha Diversity – Definition, Measurement & Examples

Alpha diversity is a description of species richness and evenness in a specific habitat or ecosystem. It quantifies how many species there are and how evenly individuals are distributed across those species. Alpha diversity is typically measured through the use of indices such as the Shannon Index and Simpson's Index.

For example, a coral reef community is able to support more than 1,000 fish species within one reef location, exhibiting high alpha diversity. Diversity helps in making ecosystems more resilient because greater alpha diversity generally increases productivity, stability, and ecological interactions.

Indices for Alpha Diversity

• Species Richness: The first basic, which is most often used and shows the overall quantity of various species in a certain region.

• Shannon Index (H): These are responsible for giving an account of the number of species in a given ecosystem and also their distribution.

• Simpson Index (D): Looks at the chance of the occurrence whereby two people chosen randomly from a sample are from the same species.

Factors Influencing Alpha Diversity

• Habitat Complexity: Complex structures can also accommodate more species as they result in different niches for the species to live in.

• Productivity: The areas of higher primary productivity are characterised by higher species diversity because a large amount of energy is accumulated for various species.

• Disturbances: Moderate disturbance will promote diversity because competitors will not be able to entirely take over and dominate the region, high or very low levels of disturbance will reduce it.

Beta Diversity – Definition, Measurement & Examples

Beta diversity is the difference in species composition across various ecosystems, also referred to as between-community diversity. It indicates the amount of change or turnover in species from one ecosystem or community to another. This also covers in situ and ex-situ conservation of biodiversity of the area. Beta diversity helps us understand regional patterns of biodiversity and locate areas with characteristic species assemblages.

For Example, research in the Amazon lowlands has demonstrated great beta diversity among patches of forests isolated by rivers, and in some areas, species turnover has been more than 60%. Quantifying beta diversity helps ecologists to evaluate habitat fragmentation, ecosystem integrity, and how environmental conditions affect the distribution of species.

Indices for Beta Diversity

• Jaccard Index: It is a measure of similarity between two communities.

• Sorensen Index (Dice coefficient): Similar to the Jaccard Index, but gives more weight to shared species.

Factors Influencing Beta Diversity

• Environmental Gradients: Changes in environmental conditions (e.g., temperature, moisture, soil type) across a landscape can lead to variations in species composition between communities.

• Geographical Barriers: Physical barriers such as mountains, rivers, and oceans can limit the movement of species, resulting in different communities on either side of the barrier.

Gamma Diversity – Definition, Factors & Examples

Gamma diversity is the overall species diversity in a wide geographic area, including several ecosystems and communities. It is the summation result of alpha diversity (species richness in individual habitats) and beta diversity (species turnover among habitats) and is an integrated assessment of regional biodiversity.

For example, India's Western Ghats, an identified hotspot of biodiversity, have extremely high gamma diversity, with more than 7,400 plant species, approximately 25% of which occur only in the area. Gamma diversity is very important for wide-scale planning for conservation as well as managing ecosystems, as it captures the general richness and patterning of life forms on different habitats.

Indices for Gamma Diversity

• Total Species Richness: It is an index of total diversity in a large region or landscape combining richness from all communities.

• Whittaker's Gamma Diversity: It measures the overall species diversity in a landscape or ecosystem, without regard to how species are distributed within local communities.

Factors Influencing Gamma Diversity

• Landscape Heterogeneity: Fragile areas containing different sorts of biotopes and micro-climatic conditions have a level next to gamma diversity due to the presence of a much higher number of special and specific species and groups.

• Regional Processes: Some factors like climate patterns, geological history, and evolutionary processes afford a region’s variety on a much bigger scale.

Relationship Between Alpha, Beta, and Gamma Diversity

Alpha, Beta, and Gamma diversity are interconnected measures that jointly help ecologists in understanding biodiversity at various spatial scales.

• Alpha Diversity is used to describe the species richness of a specific location or ecosystem (local diversity). It quantifies the variety of species within a particular, relatively homogenous location.

• Beta Diversity contrasts the diversity among ecosystems. It quantifies the change or turnover in species from one to another within a region. It connects local diversity (alpha) to regional diversity (gamma).

• Gamma Diversity is the overall species diversity throughout all the ecosystems of a larger region (landscape or regional diversity).

Relationship: All three levels of biodiversity are mathematically related as:

Gamma Diversity = Alpha Diversity × Beta Diversity

Some basic similarities about Alpha, Beta, and Gamma diversity are discussed below in the table below:

Alpha, Beta, and Gamma Diversity NEET MCQs

Q1. In the context of diversity patterns of species, which one of the following statements is incorrect?

1. Alpha diversity is diversity within a single community.

2. Beta diversity is a measure of the change in species composition from one community or habitat to another.

3. Alpha diversity is the regional diversity found among a range of communities in a geographical region.

4. Gamma diversity is the regional diversity found among a range of communities/habitats in a geographical region.

Correct answer: 3) Alpha diversity is the regional diversity found among a range of communities in a geographical region.

Explanation:

The incorrect statement regarding diversity patterns of species is Alpha diversity is the regional diversity found among a range of communities in a geographical region. However, the correct statement should be Alpha diversity is diversity within a single community. Alpha diversity refers to the diversity of species within a single community or habitat. It is a measure of species richness and/or species evenness within a specific area or ecosystem.

Hence, the correct answer is option 3) Alpha diversity is the regional diversity found among a range of communities in a geographical region.

Q2. What does gamma diversity measure?

1. The overall number of species within a region or continent

2. The richness of species within a single habitat or region

3. The turnover of species between habitats or regions

4. The variety of ecosystems, habitats, and ecological communities on Earth

Correct answer: 1) The overall number of species within a region or continent

Explanation:

Gamma diversity measures the total number of species within a larger region or area and can reflect differences in environmental conditions or historical factors such as biogeographic history. It measures the overall number of species within a region or continent. Hence option A is the correct answer.

Option(2) The richness of species within a single habitat or region is not measured by gamma diversity. Hence option B is incorrect.

Option(3) The turnover of species between habitats or regions is not measured by gamma diversity. Hence option C is incorrect.

Option(4) The variety of ecosystems, habitats, and ecological communities on Earth is not measured by gamma diversity. Hence option D is incorrect.

Hence the correct answer is Option 1) The overall number of species within a region or continent.

Q3. What does beta diversity measure?

1. The richness of species within a single habitat or region

2. The overall number of species within a region or continent

3. The turnover of species between habitats or regions

4. The variety of ecosystems, habitats, and ecological communities on Earth

Correct answer: 3) The turnover of species between habitats or region

Explanation:

Beta diversity refers to the turnover of species between habitats or regions, measuring the degree of change in species composition across different environments. It highlights how distinct or similar species communities are in different areas and reflects ecological variation driven by environmental conditions, habitat types, or historical factors like biogeographic barriers. A high beta diversity indicates significant differences in species composition between regions, often due to varying environmental gradients or isolation, while low beta diversity suggests similar species assemblages across habitats.

Hence the correct answer is option 3, The turnover of species between habitats or regions

Also Read:

• MCQs on Difference between Alpha, Beta, and Gamma Diversity

• Biosphere Reserves

• Types of Pollution

FAQs on Alpha, Beta, and Gamma Diversity

What is alpha diversity?

Alpha diversity describes the species diversity within a specific habitat, ecosystem, or sampling area. It measures the number of species and distribution of individuals among species within that location. A higher alpha diversity means the ecosystem supports more species in a relatively small area.

Example: Counting the number of plant species in a 1 m² quadrat of a grassland or fish species in a single pond.

What is beta diversity?

Beta diversity refers to the variation in species composition between two habitats or ecosystems. It shows the turnover of species from one habitat to another and helps understand how different two communities are. Higher beta diversity means the two areas share fewer species.

Example: Comparing species between a deciduous forest and an adjacent grassland; many species will differ between the two habitats.

What is gamma diversity?

Gamma diversity represents the overall diversity for a large geographical area that includes multiple habitats or ecosystems. It combines the alpha and beta diversity to give a regional diversity estimate.

Example: Measuring the total species diversity in the entire Western Ghats, which includes forests, grasslands, rivers, and wetlands.

What is the formula linking alpha, beta, and gamma diversity?

The relationship of alpha, beta, and gamma diversity can be expressed as:

Gamma Diversity = Alpha Diversity × Beta Diversity

• Alpha diversity = diversity within a specific area/habitat.

• Gamma diversity = total diversity across a region.

• Beta diversity = change or turnover in species between habitats.
  
  

This formula helps ecologists compare biodiversity patterns at local, habitat, and regional scales.

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