Alpha, Beta and Gamma Diversity: Definition, Importance, Examples, Types

Biodiversity is the range of organisms, their interactions, and the ecological processes that conserve them. It is responsible for maintaining healthy ecosystems through functions such as pollination, nutrient cycling, and climate control. The IPBES (2019) report warns that approximately 1 million species are at risk of extinction because of human actions. Biodiversity is examined using three major components, which are alpha, beta, and gamma diversity, a term coined by R.H. Whittaker in 1972. These are used to measure diversity at local, habitat, and regional levels.

This Story also Contains

1. Biodiversity
2. Alpha Diversity: Definition, Measurement Methods, and Examples
3. Beta Diversity: Definition, Measurement Methods, and Examples
4. Gamma Diversity: Factors and Examples
5. How Alpha, Beta, and Gamma Diversity Are Connected in Biodiversity?

Alpha diversity indicates species richness within a habitat. Tropical rainforests can have 300+ tree species per hectare. Beta diversity records the difference in species between habitats, and gamma diversity accounts for overall diversity in an area. For example, the Western Ghats in India have more than 7,400 plant species, with 1,800 endemics. The relationship is usually stated as: Gamma = Alpha × Beta Diversity. All these are basic principles of the Biodiversity and Conservation chapter of Biology.

Biodiversity

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 up to the plants and animals and is found at all levels of biological organisation, from genetic diversity, species diversity, and ecosystem diversity. 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 Methods, and Examples

Alpha diversity is a description of species richness and evenness in a specific habitat or ecosystem, alternatively referred to as within-community diversity. Alpha diversity 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.

Measurement of 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 production 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.

Examples of Alpha Diversity

Tropical Rainforests: These habitats are found to have incredibly high alpha diversity based on their multi-layered complex forest structure, warm, stable climate, and high primary productivity. The Amazon rainforest alone harbours more than 390 billion individual trees of some 16,000 species, and it is the most species-rich terrestrial ecosystem on earth. This Biosphere Reserves has high levels of support for many mammals, birds, insects, and microorganisms, as well as being crucial for carbon sequestration and oxygen production.

Coral Reefs: With their unusually high species richness, coral reefs such as the Great Barrier Reef are home to over 1,500 fish species, more than 400 species of coral, and a rich diversity of marine invertebrates, including molluscs and crustaceans. The three-dimensional reef structure provides diverse microhabitats, adding to overall marine diversity. Coral reefs provide critical coastal protection, fisheries, and productivity to the marine ecosystem, but they are under threat from climate change and ocean acidification.

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Beta Diversity: Definition, Measurement Methods, and Examples

Beta diversity is the difference in species composition across various ecosystems or communities, also referred to as between-community diversity. It indicates the amount of change or turnover in species from one ecosystem or community to another, with a focus on differences in species composition along landscapes. 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.

Measurement of 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.

Examples of Beta Diversity

• Mountain Ranges: The Andes Mountains show high beta diversity due to varying altitudes and climate conditions, resulting in different species assemblages at different elevations.
• River Systems: The Amazon River creates distinct habitats on its banks and islands, leading to differences in species composition across the river and contributing to high beta diversity in the region.

Gamma Diversity: Factors and Examples

Gamma diversity is the overall Species Diversity noted 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.

Measurement of 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.

Examples of Gamma Diversity

• Biomes: The Amazon Basin is a tropical rainforest biome and has high gamma diversity through the diverse habitats such as the river, wetland, and forest types that comprise and support a broad array of species and communities.
• Ecoregions: The Mediterranean Basin, with a distinct climatic zone and heterogeneity of the environment, being coastal, mountainous, and forest, has high gamma diversity. This region is home to various plant and animals, which forms part of the biome system depending on the climatic conditions of the region.

Also Read:

• Biodiversity: Definition, Types, Importance, Facts
• Biodiversity Pattern Species
• Biodiversity Loss and Causes

How Alpha, Beta, and Gamma Diversity Are Connected in Biodiversity?

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:

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