WEC - Species richness (CH10)

What are some caveats when counting species richness?

Uncertainty in identifying species and the possibility of missing rare species

What is a rarefaction curve used for?

It shows the increase in species richness as sampling effort increases.

Where on the rarefaction curve would you ideally stop sampling?

Ideally, sampling would continue until 100% of the community is sampled, but practical constraints limit sampling to a range between B and C on the curve.

What is species evenness?

It refers to the abundance distribution of different species in a community.

What are the commonly used diversity indices?

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The Shannon index and the Simpson index.

How is the Shannon index calculated?

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It combines species richness and evenness based on information theory principles.

How is the Simpson index calculated?

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It emphasizes species evenness and is derived from ecological principles.

What happens to diversity indices in an uneven community?

Both the Shannon and Simpson indices decrease.

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What happens to diversity indices in an even community?

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The indices approach their maximum possible values.

What happens to diversity indices when a species is removed?

\: Both the calculated index value and the maximum possible value decrease.

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What are some questions to explore using the diversity indices?

The effects of making the community even or uneven and the impact of removing a species

Shannon Diversity Index

A measure of diversity that focuses more on species evenness rather than richness.

Rank Abundance Graph

A graph that represents the distribution of species abundance in a community.

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Relative Abundance

The proportion of individuals belonging to a particular species relative to the total number of individuals.

Resource Continuum

The range of different resources available in an ecosystem.

Niche Breadth

The range of resources or environmental conditions a species can utilize or tolerate.

Niche Overlap

The extent to which the niches of different species overlap.

Carrying Capacity

The maximum population size that an environment can sustain indefinitely.

Alpha, Beta, Gamma Diversity

Alpha = The diversity of species within a local habitat or community

Beta = The difference in species composition between different local habitats or communities.

Gamma = The total number of species in a defined region or area.

Rarefaction Curve

A graph that shows how species richness increases with increased sampling effort or sample size.

Subsampling

The process of selecting a subset of individuals or data from a larger population or dataset.

Sampling Effort

The amount of time, resources, or effort dedicated to collecting samples or data.

Significant difference

A statistically significant difference that indicates a meaningful distinction between two or more groups or conditions.

What type of graphs are ordination plots?

Ordination plots are multi-dimensional graphs where two dimensions are plotted to analyze patterns and differences in communities.

How do reefs and jars compare in terms of alpha diversity?

Reefs and jars have the same alpha diversity, but they are represented by different species, making their communities diverse.

How do coastal locations differ from each other in terms of species representation?

Coastal locations are more spread out, indicating that each location is represented by different species, unlike the clustered communities in reefs.

What factors can explain the differences between coastal locations and reefs?

Factors such as salinity, human impacts, and temperature can help explain the differences in species composition between coastal locations and reefs

What factors influence species richness in spatially varying environments?

Productivity, energy, predation, heterogeneity, and harshness are spatially varying factors that can influence species richness.

How does productivity affect species richness?

Higher productivity usually leads to increased species richness because more resources are available for different species to utilize.

What is the relationship between predation intensity and species richness?

Predation intensity follows a hump-shaped relationship with species richness, where an optimal level of predation leads to higher diversity.

How does spatial heterogeneity influence species richness?

More complex and spatially heterogeneous areas tend to support higher species richness due to the availability of different niches and hiding spots.

What effect does environmental harshness have on species richness?

Harsh environments, such as extreme temperatures or pH levels, generally have lower species richness as only certain species can tolerate those conditions.

What are some spatially varying factors that influence species richness?

Productivity, energy, predation, heterogeneity, and harshness are all spatially varying factors that can affect species richness.

What is the definition of harshness in relation to species richness?

Harshness refers to environmental conditions that only certain species can tolerate, resulting in lower species richness.

2. What are the two different aspects of temporal variation?

* Predictable
* Unpredictable

4. What factors influence species richness in island biogeography

* Immigration
* Extinction
* Island size
* Island location

5. How does island size affect species richness?

* Large islands have higher species richness due to higher immigration rates and lower extinction rates.
* Small islands have lower species richness due to lower immigration rates and higher extinction rates.

6. How does island location affect species richness?

* Islands close to the mainland have higher species richness due to higher immigration rates and lower extinction rates.
* Islands far from the mainland have lower species richness due to lower immigration rates and higher extinction rates

7. What is the equilibrium in island biogeography?

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The intersection of the number of species incoming and the number of species leaving the island, which indicates the species richness of the island.

8. How is island biogeography important in conservation biology?

* It helps determine the number of species saved by a reserve, the extinction rate for a single species, and the optimal structure of a reserve.
* It aids in the development of wildlife corridors for the movement of animals between habitats

When is a community usually most diverse?

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In the early stages of community succession.

Counting species richness

* Caveats to counting species are that you may not be certain of species identity or that you miss species by only taking a sample of the community.
* You will likely count common species, but rare species may be more difficult to find.
* You can draw a rarefaction curve to see how your sampling effort relates to the number of species

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Species evenness

* The evenness of a community refers to how close in abundance each species is.
* If a community consists of one dominant species that has high abundance and low \n abundances of other (rare) species, it is considered less diverse, even if richness is the \n same.

Determining species diversity

• Diversity indices take both species richness and species evenness into account. \n • There are a bunch of indices out there, with two of the most used being the Shannon \n index and the Simpson index. They differ in the weight they put on species richness or \n evenness

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Shannon diversity

* Derived from information theory and represents the uncertainty with which we can predict randomly selected individuals from a community.
* Puts more weight on abundance than evenness.
* Varies between 0 and approximately 4.

Simpson diversity

* Derived from ecology. It is the probability that two randomly selected individuals are of the same species.
* Puts more weight on species evenness than richness
* Varies between 0 and approximately 1.

Shannon versus Simpson indices

In case of a perfectly even community, the Simpson index increases much faster with \n increasing richness than the Shannon diversity index.

Rank-abundance graphs

Rank-abundance graphs give a more complete picture of distribution of species \n abundance, instead of condensing community diversity into a single value

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Species richness and resources

* However, species richness may be enough to suit many \n purposes.
* Simple model where resources are depicted with R, niche \n breadth with n, and overlap between niches with o.
* Species interactions have an influence on this model.
* Interspecific competition likely allows for resources to be fully \n utilized, and richness will depend on range of resources, \n extent of specialism, and permitted niche overlap.
* Predation can exclude species from the community, and \n reduce richness, but it may stimulate richness by reducing \n interspecific competition and thus allow more niche overlap.

Energy

Energy can be thought of most simply as \n temperature, as high temperatures \n generally lead to higher metabolism of \n species, or as potential evapotranspiration \n (PET).

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Effects of energy and productivity \n can be difficult to disentangle. It is \n also again dependent on spatial \n scale.

Predation intensity Predation

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Predation can decrease richness \n through driving certain species \n towards extinction, but it may also \n increase richness through predator- \n mediated coexistence.

Spatial heterogeneity

\n • Extra species can be accommodated by spatially heterogeneous sites, as they provide \n more microhabitats and microclimates, thus increasing niche space and resource \n continuum. \n • Heterogeneity can have an abiotic and/or a \n biotic component.

Climatic variation and its absence

Temporal variation can be predictable or unpredictable within the generation time of \n a species. \n • Predictable seasonal environments may have higher species richness as different \n species may be adapted to different conditions throughout the year. \n • Predictable unseasonal (stable) environments may \n allow for more specialization and thus higher \n species richness.

Disturbance

Unpredictable temporal variation is considered a disturbance. \n • The intermediate disturbance \n hypothesis states that very \n frequent disturbance and very \n rare disturbance both have \n lower species richness than \n intermediate disturbance

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Environmental age: evolutionary time

Disturbances also act on very long evolutionary time scales. \n • Communities closer to equilibrium and saturation have higher species richness. \n • Depending on the disturbances in their distant past, some communities may be closer \n to saturation than others.

Species-area relationship

• Species richness increases as island area increases. \n • Larger areas likely contain more habitats and thus increase the resource continuum. \n • Larger areas also provide a larger ‘target’ for colonization.

Time and adaptive radiation on islands

• Time since island origin plays affects species \n richness observed simply because species may \n not have had enough time to colonize an island. \n • On isolated islands, evolution may cause \n species to arise faster than immigration.