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# Species Diversity

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The Earth is home to many life forms; from glowing mushrooms to flying lemurs. How do we describe the range of different species in a particular habitat? Here, we will discuss species diversity: what it means, what are some examples, how it is determined, and why it is important.

• First, we will talk about the definition of species diversity.
• Then, we will learn the different calculations related to species diversity.
• After, we will look at some examples of places with lowest/highest species diversity.
• Then, we will go over the difference between genetic and ecosystem diversity.
• Lastly, we will talk about the importance of species diversity.

## Species Diversity Definition

Let's start by looking at the definition of species diversity.

Species diversity is the number and relative abundance of different species occupying a specific area (this could be a habitat, a biome, or the biosphere as a whole).

Species diversity has two major components:

• Species richness: The number of different species that live in an area.

• Species evenness (or relative abundance): The representation of each species relative to the total number of individuals in an area (Fig. 1).

It is important to note that two areas with similar species richness do not necessarily have the same species evenness.

## Species Diversity Calculation

Let’s say there are two forest communities each with four tree species. We’ll call them species A, B, C, and D. The distribution of the tree species in our hypothetical forest communities are as follows:

 A B C D Community 1 25 25 25 25 Community 2 60 10 10 20

In this example, species richness is equal for both communities because they both have four tree species, but their relative abundance differs. Imagine what these two communities would look like. It would be easy to notice that there are four different species of trees in Community 1 because they are all well-represented.

On the other hand, it would be harder to notice the different species in Community 2 because of how abundant species A is relative to the other species. Just by visualizing these communities, we can intuitively say that Community 1 is more diverse than Community 2.

### Species Diversity Calculation Using the Shannon diversity (H) Index

While we can intuitively describe the species diversity of a community, there are tools used to calculate diversity using species richness and relative abundance. One of these tools is called the Shannon diversity (H) index.

The Shannon diversity index measures the diversity through the variety and abundance of species in a community.

The Shannon diversity index can be calculated using the following equation:

 $H\mathit{=}\mathit{-}\mathit{\left(}{\mathit{p}}_{\mathit{A}}\mathit{ln}\left({p}_{A}\right)\mathit{+}{\mathit{p}}_{\mathit{B}}\mathit{l}\mathit{n}\mathit{\left(}{\mathit{p}}_{\mathit{B}}\mathit{\right)}\mathit{+}{\mathit{p}}_{\mathit{C}}\mathit{l}\mathit{n}\mathit{\left(}{\mathit{p}}_{\mathit{C}}\mathit{\right)}\mathit{+}\mathit{.}\mathit{.}\mathit{.}\mathit{\right)}$ Where,A, B, C . . . are the species in the communityp is the relative abundance of each speciesln is the natural logarithm

We can determine the ln of each value of p using the “ln” function in a scientific calculator. The higher the value of H, the more diverse the community is.

Let’s try calculating the Shannon diversity index of the two forest communities in the previous example.

 Community 1 Community 2 H = -(0.25 ln 0.25 + 0.25 ln 0.25 + 0.25 ln 0.25 + 0.25 ln 0.25) Therefore, H = 1.39 H = -(0.6 ln 0.6 + 0.1 ln 0.1 + 0.1 ln 0.1 + 0.2 ln 0.2)Therefore, H = 1.09

These calculations show that–as we had thought intuitively–Community 1 is more diverse than Community 2.

### Species Diversity Calculation using Simpson's diversity (D) Index

Another tool used to describe species diversity is Simpson's diversity index.

Simpson's diversity index represents the probability that any two individuals that are randomly picked from a large would belong to the same species. It shows the number of different types of species in a community as well as how evenly dispersed each species' population is.

Simpson's diversity index can be calculated using the following equation:

 D = Σ(ni(ni - 1)) / (N(N - 1)) Where:n is the number of each speciesN is the total number of individuals

Let's try calculating Simpson's diversity index of the two forest communities in the previous example. Note that the lower the value of D, the more diverse the community is.

 Community 1 Community 2 D = (25 (25-1) +25 (25-1) + 25 (25-1) + 25 (25-1)) / 100 (100-1)Therefore, D = 0.24 D = (60 (60-1) + 10 (10-1) + 10 (10-1) + 20 (20-1)) / 100 (100-1)Therefore, D = 0.41

Again, as we have intuited, Community 1 is more diverse than Community 2.

The two indices can be used to calculate species diversity but are slightly different: the Shannon diversity index measures species diversity with the assumption that all species are represented in the sample and that they are randomly sampled, while Simpson's diversity index gives more weight to dominant or common species.

### Limitations and Challenges in Calculating species diversity

It can be challenging to determine the number and relative abundance of species in a community for several reasons:

1. There are many species that are quite rare, making it hard to come up with a sample big enough to represent them.

2. Some species are difficult to identify based only on morphology; scientists may compare its DNA sequence to other DNA sequences in a database, but it is a more expensive procedure.

3. Species that are more mobile or less visible–for example, nocturnal species, deep-sea creatures, and microorganisms–may also be difficult to census.

## Examples of places with the lowest and highest species diversity

The glaciers of Antarctica have a harsh, inhospitable environment, making it low in species diversity. The Lesser Sunda Islands in Indonesia is relatively new, so there are not many species that have colonized it, also making it species-poor.

But, as with other species-poor areas, the few species that are able to inhabit it can proliferate because it does not have many other species to compete with for resources like food.

On the other hand, areas near the equator–such as the Amazon Rainforest–tend to have higher species diversity. There are many explanations as to why this is the case. One explanation is that there are more diverse habitats and ecological niches towards the equator. Another explanation points to the higher amount of energy at the equator, this is known as the latitudinal diversity gradient (Fig. 2).

Latitudinal diversity gradient refers to a pattern observed in the natural world in which species richness increases towards the equator. This trend holds true for both northern and southern hemispheres as well as both marine and terrestrial species. Latitude characterizes the input of solar energy, with the equator receiving the most energy input.

## How is species diversity different from genetic diversity and ecosystem diversity?

Species diversity is one out of three levels of biodiversity, the total variety of life on Earth. The two other levels of diversity are genetic diversity and ecosystem diversity.

Genetic diversity is the number of different inherited traits of a species. It can be observed within a species: for example, human populations have different inherited traits (e.g., eye color, height, complexion, and even diseases) that reflect their genetic diversity.

On the other hand, ecosystem diversity refers to the number of different ecosystems in a particular area. For example, a marine ecosystem contains other subgroups including coral reefs, mangrove systems, saltwater estuaries, and the ocean floor.

## What is the relationship between species diversity and stability?

There are multiple relationships between species diversity and stability.

If we are talking about stability at the ecosystem-level, then species diversity can stabilize ecosystem processes provided that the species have different responses to changes in the environment such that when one species increases in number it can compensate for the decrease of another.

Higher species and genetic diversity can also translate to a higher chance of individuals having traits that would enable them to adapt to changes in the environment.

On the other hand, if we are talking about stability at the species level, then higher species diversity can actually lead to less species-level stability. This is because the number of individuals that can be packed into a community has a limit, therefore as the number of species in the community increases, the average population sizes of the species in the community decrease. With the decrease in population size, there is a higher risk of local extinction.

## Why is species diversity important?

Species diversity is important for biological, economic, and cultural reasons.

Healthy ecosystems have a diverse range of species, each of which plays a part in the functioning of the ecosystem. Species interact in ways that affect each other’s survival and reproduction. For example, most flowering plants are pollinated by animals such as birds and insects. This interaction helps flowering plants to reproduce and diversify. On the other hand, pollinators get to eat pollen or nectar. If pollinators such as bees disappeared in one area, it would threaten the survival of flowering plants that depend on them and create an imbalance in the ecosystem.

Species diversity is also important for economic and cultural reasons. The food we eat, the clothes we wear, and even the houses we live in–much of what we use and consume in our everyday lives are derived from nature. Even many medications come from compounds naturally produced by a diverse group of organisms. For example, most antibiotics are produced by fungi and bacteria. Humans from different social and cultural backgrounds also use various species of plants for their medicinal properties.

Unfortunately, because of their value, species diversity is threatened by habitat loss and overexploitation (including hunting, fishing, and extraction) by humans. This is why it is essential for natural resources to be managed and protected by individuals and institutions alike.

## Species Diversity - Key takeaways

• Species diversity is the number and relative abundance of different species occupying a specific area.
• Species diversity has two major components: species richness (the number of different species that live in an area) and species evenness (the representation of each species relative to the total number of individuals in an area).
• We can calculate species diversity using the Shannon diversity (H) and Simpson's diversity index (D).

• Species diversity is one out of three levels of biodiversity, the total variety of life on Earth. The other two levels are: genetic diversity (number of different inherited traits of a species) and ecosystem diversity (number of different ecosystems in a particular area).

• Species diversity is important for biological, economic, and cultural reasons.

## References

1. Mittelbach, Gary G., et al. “Evolution and the Latitudinal Diversity Gradient: Speciation, Extinction and Biogeography.” Ecology Letters, vol. 10, Blackwell Publishing, 2007, https://doi.org/10.1111/j.1461-0248.2007.01020.x.
2. Kaufman, Dawn M. “The Latitudinal Gradient of Diversity: Synthesis of Pattern and Process.” National Center for Ecological Analysis and Synthesis, www.nceas.ucsb.edu/projects/2084/proposal.pdf. Accessed 24 Aug. 2022.
3. Ha, Melissa, and Rachel Schleiger. “9.2: Species Diversity - Biology LibreTexts.” Biology LibreTexts, bio.libretexts.org, 25 July 2020, bio.libretexts.org/Bookshelves/Ecology/Environmental_Science_(Ha_and_Schleiger)/03%3A_Conservation/3.01%3A_The_Value_of_Biodiversity/3.1.02%3A_Species_Diversity.
4. “What Is Biodiversity? | eAtlas.” What Is Biodiversity? | eAtlas, eatlas.org.au, eatlas.org.au/content/what-biodiversity. Accessed 24 Aug. 2022.
5. Zedalis, Julianne, et al. Advanced Placement Biology for AP Courses Textbook. Texas Education Agency.
6. Reece, Jane B., et al. Campbell Biology. Eleventh ed., Pearson Higher Education, 2016.
7. Biodiversity and Ecosystem Stability | Learn Science at Scitable.” Biodiversity and Ecosystem Stability | Learn Science at Scitable, www.nature.com, www.nature.com/scitable/knowledge/library/biodiversity-and-ecosystem-stability-17059965. Accessed 24 Aug. 2022.
8. Singh, Purnima. “Simpson’s Diversity Index Calculator.” Simpson’s Diversity Index Calculator, www.omnicalculator.com, 6 Apr. 2022, www.omnicalculator.com/statistics/simpsons-diversity-index
9. “Student Handout 1A: How to Calculate Biodiversity.” Entomology and Nematology Department - University of Florida, Institute of Food and Agricultural Sciences, entnemdept.ufl.edu/hodges/protectus/lp_webfolder/9_12_grade/student_handout_1a.pdf. Accessed 24 Aug. 2022.

Species diversity is important for biological, economic, and cultural reasons. Healthy ecosystems have a diverse range of species, each of which plays a part in the functioning of the ecosystem. Species interact in ways that affect each other’s survival and reproduction. Additionally, much of what we use and consume in our everyday lives are derived from different organisms.

Species diversity is the number and relative abundance of different species occupying a specific area

Species diversity can be caused by different processes including mutation and natural selection.

Species diversity is the number and relative abundance of different species occupying a specific area. On the other hand, genetic diversity is the number of different inherited traits of a species.

There are three types of biodiversity: genetic, species, and ecosystem diversity.

## Species Diversity Quiz - Teste dein Wissen

Question

The keystone species concept was first proposed by ___________ in ______.

Robert T. Paine; 1969

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Question

What are the three different groups of keystone species?

Predators

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Question

Apex predators are...

Predatory species at the highest trophic level.

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Question

Which is an example of an apex predator?

Orca

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Question

Which is an example of an ecosystem engineer?

Beaver

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Question

Which is an example of a mutualism?

Ants and aphids

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Question

How do bees benefit flowers?

By spreading their genetic material, pollen.

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Question

How do flowers benefit bees?

They provide food, in the form of nectar.

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Question

What does a trophic cascade refer to?

The cascading affects from the removal of a important organisms from the highest trophic levels, particularly apex predators.

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Question

Which is an example of a foundation species?

Coral

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Question

True or False: A foundation species can also be a keystone species.

True

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Question

True or False: Foundation species are dependent on interactions between species at different trophic levels.

False

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Question

True or False: Foundation and keystone species are synonyms, referring to the same species.

False

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Question

Which keystone species were once widespread in the United States, but are now restricted to smaller areas or extinct entirely?

Brown bear

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Question

Which of these species expanded its range following the disappearance of keystone species?

Coyote

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Question

What level of biodiversity is defined by the

number of different inherited traits of a species?

Genetic diversity

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Question

What level of biodiversity is defined by the

number of different ecosystems in a particular area?

Ecosystem diversity

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Question

What level of biodiversity is defined by the number and relative abundance of different species occupying a specific area?

Species diversity

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Question

What are the two major components of species diversity?

Species richness and relative abundance

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Question

What component of species diversity refers to the number of different species that live in an area?

Species richness

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Question

What component of species diversity refers to the representation of each species relative to the total number of individuals in an area?

Relative abundance

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Question

How can we use the Shannon diversity (H) index in determining species diversity?

The higher the value of H, the more diverse the community is.

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Question

True or false: two areas with similar species richness will always have the same species evenness.

False. Two areas with similar species richness do not necessarily have the same species evenness.

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Question

True or false. Areas near the equator tend to have higher species diversity, while areas near the poles tend to have lower species diversity.

True. There are many explanations as to why this is the case. One explanation is that there are more diverse habitats and ecological niches towards the equator. Another explanation points to the higher amount of energy at the equator.

Show question

Question

What is the relationship between species diversity and ecosystem stability?

Species diversity can stabilize ecosystem processes provided that the species have different responses to changes in the environment such that when one species increases in number it can compensate for the decrease of another.

Higher species and genetic diversity can also translate to a higher chance of individuals having traits that would enable them to adapt to changes in the environment.

Show question

Question

What is the relationship between species diversity and species stability?

Higher species diversity can actually lead to less species-level stability. This is because the number of individuals that can be packed into a community has a limit, therefore as the number of species in the community increases, the average population sizes of the species in the community decrease. With the decrease in population size, there is a higher risk of local extinction.

Show question

Question

What characteristics of a species might make it challenging for scientists to determine their species diversity?

Species that are quite rare, difficult to identify based on morphology, mobile, and/or less visible can be challenging to census.

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Question

Why is it possible for some species to proliferate in species-poor areas?

The few species that are able to inhabit species-poor areas can proliferate because they do not have many other species to compete with for resources like food.

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Question

The Lesser Sunda Islands are found close to the equator yet are species-poor. Why is this the case?

The Lesser Sunda Islands in Indonesia is relatively new, so there are not many species that have colonized it, also making it species-poor.

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Question

Why do the glaciers of Antarctica have low species diversity?

The glaciers of Antarctica have a harsh, inhospitable environment, making it low in species diversity.

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Question

What are endemic species?

Endemic species are species that naturally occur in a particular geographic territory with a limited range.

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Question

Species can be endemic to ____.

all of the above

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Question

True or false. All endemic species are endangered.

False. Not all endemic species are endangered.

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What is the difference between endemic and endangered?

Endemic species are species that naturally occur in a particular geographic territory with a limited range. On the other hand, endangered refers to the conservation status of a species or group. It falls under the "threatened" category set by the IUCN. Not all endangered species are endemic, and not all endemic species are endangered.

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Question

Which of the statements below is false?

An exotic species naturally occurs in the specific areas it inhabits.

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Question

True or false. All endemic species are native species.

True. Endemic species is a subcategory of native species.

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Question

True or false. All native species are endemic species.

False. Not all native species are endemic species.

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Why are endemic species more vulnerable to extinction?

Because threats to species tend to be localized, species that inhabit larger geographic areas have a higher chance of survival even if some populations are threatened in certain areas. Additionally, endemic species that have small populations can be vulnerable due to genetic factors including inbreeding and genetic drift.

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Question

What is a biodiversity hotspot?

A relatively small geographic area with a lot of endemic species that are endangered

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Why is it important to conserve and protect biodiversity hotspots?

When a biodiversity hotspot is threatened, there is a risk of losing a massive amount of species diversity.

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How does inbreeding increase the risk of extinction?

Inbreeding is when closely-related individuals reproduce. Offspring produced through inbreeding have little genetic variation, making them more prone to diseases and defects.

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How does genetic drift increase the risk of extinction?

Genetic drift is when chance events cause changes in allele frequencies. Genetic drift causes allele frequencies to change at random, so succeeding generations may inherit unfavorable traits.

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Question

Species that are not endemic are called ___.

Generalists

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Question

What characterizes areas that tend to have higher occurrence of endemic species?

Geographic isolation

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Question

Why is it difficult for some endemic species to survive in other areas?

Endemic species may be adapted to the unique conditions of their habitat, making it difficult for them to survive in other environmental conditions.

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