The course presents an overview of the theory behind biological diversity evolution and dynamics and of methods for diversity calculation and estimation. We will become familiar with the major alpha, beta, and gamma diversity estimation techniques.
Understanding how biodiversity evolved and is evolving on Earth and how to correctly use and interpret biodiversity data is important for all students interested in conservation biology and ecology, whether they pursue careers in academia or as policy makers and other professionals (students graduating from our programs do both). Academics need to be able to use the theories and indices correctly, whereas policy makers must be able to understand and interpret the conclusions offered by the academics.
The course has the following expectations and results:
- covering the theoretical and practical issues involved in biodiversity theory,
- conducting surveys and inventories of biodiversity,
- analyzing the information gathered,
- and applying their analysis to ecological and conservation problems.
Needed Learner Background:
- basics of Ecology and Calculus
- good understanding of English

À partir de la leçon

Species-abundance distributions and comparisons

In this module we will talk about the most common species-abundance distribution models and I will show you how to compare different communities and samples in order to achieve a quantitative and statistical measure of the changes in biological diversity due to treatments.
I will explain some Evenness measures and how to represent them in form of curves of biodiversity. This will help to discriminate communities’ diversity and to better analyse the anthropogenic impacts on biodiversity.

Ph.D., Associate Professor in Ecology and Biodiversity Biological Diversity and Ecology Laboratory, Bio-Clim-Land Centre of Excellence, Biological Institute

[MUSIC]

Hi guys.

Welcome to the 20th lecture of the course Biological Diversity Theories,

Measures and Other Sampling Techniques.

Today we will see how to analyze an tropogenic impacts on biodiversity.

What are tropogenic impacts on biodiversity.

For instance we have deforestation, that's a very big problem.

We have over fishing, pollution, water pollution, garbage pollution.

So a different way to impact biological diversity.

To analyze this impact, we have different methods.

There are some methods that are based on univariate measures.

For instance, indexes that are based on species richness.

So the effect of disturbance is more evident on abundances.

There are indexes based on species evenness

that is better response to disturbance.

And we can use different way to measure this.

For instance, we can use the Simpson Index,

Caramago Index, Smith-Wilson Index, and the Q evenness.

The higher is the evenness, the healthier is the area.

Indexes that are based on species diversity are also used, but

are difficult to evaluate if you want to compare these impacts we need to

provide good information or real good information of the difference.

And we use different diversity that includes both information from richness

and evenness.

These can be confounding.

Also the indexes based on taxonomical or functional diversity.

That we will see next lecture, they are very useful to understand this

univariate measure of the impacts of biodiversity.

We have also admitted that our basis on species abundance distribution.

This methods try to assess the impacts of biodiversity,

that moves from log-normal, that is, a kind of proxy of undisturbed size,

to geometrical series, that mean that size are very disturbed.

If you remember from the last lectures, we have different ways to

show all the abnormalities distributed inside the species.

So log-normal is the best way because it means that community is healthy.

And it means that inside is undisturbed.

Geometrical series is why we have big domicile species

kind of synonym of disturbance.

The best approach is to fit our data to a geometrical series and

then calculate the slope m or the slope of rank abundance distribution regression.

In this way we analyze if the site is very disturbed or not so much disturbed or

completely undisturbed comparing the slope and the regression of the RAD.

Low slope means that there is more evenness and

so that the side that we are analyzing is undisturbed.

High slope means that the evenness is very low and

in this case the side is disturbed because there is dominance of species.

To avoid the influence of the richness we can use, the evenness of Smith-Wilson.

That's very useful in these cases when we want to analyze the impacts of

biodiversity.

Another way, another meter of species distribution to analyze the impacts

of biodiversity Is the ECDF, the empirical cumulative distribution function,

or the K-dominance curves.

And the last way is a new system, a new graph,

that I want to show you to analyze the impact that is ABC curves.

ABC curves are curves that are based on the distribution of abundances

and biomass.

So we use ABC curve to analyze the effect of impacts of biodiversity,

because biomass grow in a different way with respect to biodiversity

when the site is disturbed or not.

So do you remember from the last lectures that we

started to analyze what is an ECD curve.

So empirical cumulative distribution function curve.

The empirical cumulative distribution function is a powerful graph

to understand what are the impacts, or topogenic impacts on biodiversity.

For instance in this example you will find three curves.

And the highest one is the undisturbed forest, the intermediate one is

a disturbed forest, and the lowest one is an agricultural field.

You see the agricultural field, for instance,

as the intermediate part of the cube that is quite parallel or

more parallel to the epsilon axis if compared to undisturbed forest.

Moreover, the undisturbed forest is the left low part

that is higher than the other two groups.

This means that the number of rare species in the undisturbed forest is higher than

the other two.

Another way to analyze impacts on biodiversity is K-dominance curves.

You see in this example there are two curves, and the highest one means that

the community in that case has more biological diversity, is more diverse,

than the second one.

So the curve that's placed itself on top of the graph is more diverse,

and the curve that is below the others is the lower diverse.

A third interesting way to analyze the affect of anthropogenic impacts

on biodiversity is the Abundance Biomass Curves, the ABC curves.

From these curves you can monitor what are the effects.

In this example you will see three different communities.

One is undisturbed, the second one is moderately disturbed,

the third on is highly disturbed.

If you put on the x axis the species rank in a log, and on the epsilon axis,

the biomass or the abundance cumulative of each species, you will see that

in undisturbed places, biomass curve is always over the abundance curve.

It means that the biomass of the system is higher than single number of species.

In the intermediate disturbance side instead

you will see that the two curves cross many times.

It means that abundance can be sometimes higher than biomass and this is because

some species grow faster than the other because the site is disturbed.

For instance, by other species,

is that this is condition that you can see that on the disturbed side,

the number of individuals is very high because there are pioneer or

invasive species that can arrive in and then can grow fast, but they can

not accumulate much biomass, so Analyzing these two codes and the behavior.

So when you see that biomass is higher than abundance,

then you can understand that the site is undisturbed.

When they cross many times, that's moderately disturbed.

And when the abundance curve is higher than

the biomass curve can understand the society's highly disturbed.

There is also a mathematical way that is used for

statistics to calculate from the ABC queues, the effects on diversity.

And this is called W index.

And W index is very simple, because it's just the sum of Bi- Ai/50,

multiplied by the number of species in the system.

Bi is simply the biomass of each species of the rank i.

And Ai is the number of individuals of each species of rank i.

You just need to mind that Ai and Bi can refer to different species

of different ranks, because they rank differently.

They are according to biomass or according to biodiversity.

Anyway, from more disturbed sites, you have

an index that is higher positive to zero that is moderately disturbed side,

to negative indexes that are disturbed side.

So If your value that you obtain from the W statistic called W index

is a positive, you can say that this side is undisturbed.

If it's around 0, the side is moderately disturbed.

And if it's negative, it's sure that it's highly disturbed.

The third way to assess the impact

on biodiversity are methods based on multivariate measures.

These offerings as principal components analysis or so

called PCA or coordinate analysis but sometimes they are of limited use.

Is it better to use beta-diversity index for

instance if we want to use multivariate measure.

We can use Sorensen or Jaccard or even better Bray-Curtis or

Chao-Sorensen, Chao-Jaccard to evaluate the effect of disturbance on community.

Because these indexes are influenced by the most abundant species,

it's very important to increase the number of replicates for each treatment.

For instance, the disturbed and not disturbed side.

And utilize both incidents, the indexes, for instance,

presence, the hub sense data, and abundance in indexes.

Also it's possible to calculate some kind of index of disturbance of the community

or IDC or index of biotic integrity that is called IBI.

To compare standard level of beta diversity to close not-disturbed areas

to those of disturbed sites.

So we can have a different comparison to understand how

big is the impact on the biodiversity of the community.

So thanks for your attention, and see you at the next lecture.

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