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Hi students.

Welcome to the third lecture of my course in biological diversity theories,

measures and data sampling techniques.

Today I will tell you about the evolution of biological diversity.

First of all we need to clarify the rule of predators and

parasites on the evolution of biological diversity.

Speciation takes a very important rule of course in the evolution.

Predators may have played a very big role in shaping biological diversity.

They can really push the speciation events

with an effect that is called top-down effect.

So we have these two type of effects, the top-down and bottom-up.

Top-down effect is the effect played by predators,

which shape the lower level of the food chain.

And bottom-up effects is that side that is playing in the opposite side.

Bottom-up effect is called controlled by resources.

For instance light, food, energy.

And this effect is from the bottom-level towards the upper level.

So it starts from primary producer to herbivores towards predators.

These effects are very important because they move up and

down along the food chain.

Another important element in the evolution of biodiversity is parasite.

Parasites plays very important role in speciation.

They can address the speciation events just by

managing the population abundances.

In this case they manage host abundances.

So for instance,

the sickle cell anemia shaped human evolution because some population,

[INAUDIBLE] population has different blood cells so as this kind of sickle cell.

And in this case, they can prevent the attack of parasites for

instance, mosquito carriers.

So, parasites also plays very important role in evolution of biodiversity.

In 2009 a paper published in Nature by two authors, Levin Ale,

Reese Lambert argued that niches are very important in maintenance of

biological diversity, also in species diversity.

In this way, they challenged the neutral theory of biodiversity.

This study, like many others,

does not take into account the effect of history on biological diversity.

To have a better picture and to understand the evolutionary dynamics of biodiversity,

we need to consider the biogeographic and phylogenetic approaches.

So geological, evolutional, and ecological dynamics in the context of natural

history are very important to understand how biological diversity can be created.

This study in nature suggested that niche differences,

including variation in the rooting that cause

species to limit their own individuals more than they limit the competitors.

Another important point in the evolution of biodiversity is the debate about

the gradualism against punctuated equilibrium.

Stephen J Gould and Niles Eldredge suggested that evolution moves

according to punctuated equilibriums.

It means that there is nothing gradual in the pattern of evolution and

speciation, but species evolve in a jump.

So they just evolve after stable point, stable periods.

Once species appear in the fossil records,

they can stay in a stable equilibrium for long time.

It means that we can have two different speciation types.

The first one is gradual movement towards the evolution and

the second one is jump over the evolution.

According to Gladwell's model, species descends from a common ancestral and

gradually diverge more and

more in their morphology as they acquire unique adaptations.

Instead, the punctuated equilibrium proposed by Stephen Jay Gould and

Niles Eldredge, say that a new species change most as it pass from the parent

species, and then change little for the rest of their existence.

So we have this kind of jump in the evolution.

Is something that Darwin already proposed in his famous picture in his notebook.

Two other very important mechanisms in the evolution of biodiversity are phenotypic

plasticity and character displacement.

Phenotypic plasticity is the ability of the genotype to produce more than

one phenotype when exposed to different environments.

It's that character displacement is something that has been started since

the time of Darwin.

For instance,

David Black used data collected by Darwin about finches in Galapagos Islands and

he understood that these differences in beak shape make differences in behavior.

It means that these species on each island can change their behavior.

In this way, they can select different food resources and this way they speciate.

Endosymbiosis was proposed as important mechanism in the evolution of species

diversity.

The endosymbiotic theory was firstly articulated

by the Russian botanist Konstantin Mereschkowski.

And then was again proposed by another botanist, a Russian botanist,

Boris Kozo-Polyansky.

The endosymbiotic theory was advanced and then substantiated with microbiological

evidence by Lynn Margulis in 1967 paper titled On the Origin of Mitosis Cells.

In her work published in 1981, titled Symbiosis in Cell Evolution,

she argued that akaryotic cell originated as communities of interacting entities,

including endosymbiotic that developed into flagella and.

I recently suggested that, apart from endosymbiosis,

another mechanism is very important.

That is called symbiosis, it means that genes carriers can introduce

inside the cell, it can integrate completely in the genome of these cell.

So in this way, they share part of their own genetic material.

Different kind of speciation are being recognized.

The first one, allopatric speciation takes place when the barrier grow for

instance rivers, mountain chain.

And they split to population into meta population that can evolve just

because of this allopatric differences.

So they are in two different place,

they are isolated and they can evolve in this way.

Peripatric speciation is a different kind of speciation that takes place

when this simple meta-population move in another niche.

So in this way, this population is isolated from the original population,

but, they have kind of contact until they completely split.

The parapatric speciation instead

continues to keep these two populations in contact.

So it means that there is a kind of gene flow between them.

The sympatric speciation instead is a kind of speciation where the population

evolve insulated, but together in the same place, in the same environment.

So there is not a physical barrier that divides them.

Not a special division, but this population can completely divide in

two different species even if they live in the same environment.

In this speciation process, different elements plays key role.

Founder effect is the effect when few individuals of one population move

in another empty space.

So they just move in a completely isolated space.

In this case, they can evolve a new species.

So just slightly increasing differences in characters.

Bottleneck effect happens when there is a catastrophic reduction in a population.

It means that genetic viability is reduced.

And the resulting population has less viability in their genotypes.

This is a genetic drift.

In this case, the reduction of population, so

the number of individuals in the resulting population, is very low.

So it is the number of gene.

There are prezygotic and postzygotic barriers that divide species.

Prezygotic barriers prevent species for interbreeding for each other.

And postzygotic barriers happen when species are able to reproduce but

they produce offspring that are not fertile,

that cannot be selected by natural selection.

An important mechanism in shaping biological diversity is

the avoidance of competition.

An empty space due to cyclic variation of population around the carrying capacity is

filled by individuals of the same species with mutation that allow them to adapt,

but not evolve in different species.

But with endosymbiosis and symbiosis and phenotypic plasticity,

some polymorphic metapopulation can evolve in different

species following the principle of the avoidance of competition.

All these process are summarized in the idea of facilitation.

Facilitation is something that was suggested by many authors and

I recently suggest in the biodiversity related niches differentiation theory.

As suggested by this theory, the exploitation of 3D space and

the species facilitation allow the increase of niche.

And in this way,

this niche space enhance the number of species that can fill the ecosystem.

So co-evolution is the evolution of

one species triggered by the evolution of the associated species.

For instance, Darwin noticed that an orchid in the tropic as this very long and

he suggested there would be a moth with a very long tube

that can fertilize this species.

So this is a kind of co-evolution, so

it's one species that pushed the other to evolve.

Parallel evolution is something very similar but it means that species,

even if they are in different space,

in different region of the world, evolve in the same way.

So this is because they adapt to very similar conditions.

Scientists try to understand the evolution of biodiversity adopting different

systems.

For instance, they try to model the evolution of bio diversity.

They even adopt the game theory.

In this system, there are two different species, one that is very strong, and

another one that is weak.

So one that is competing species, and another one that is cooperating species.

So we have recipient and donor.

And another system the scientist adopt in the game theory to understand

the evolution of species was this couple system of two species, hawk, dove.

And they understood then species diversity can evolve when this system is stable.

It means that there are evolutionary stable strategies

that allow two species to coexist in the same environment.

So that's all for this lecture.

See you in the next one.

1.3. The evolution of biodiversity

Biological Diversity (Theories, Measures and Data sampling techniques)

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