These resources are available to all the organisms of that species.
So does biodiversity come from competition?
We know that the Interspecific competition reduced
the number of species because of competitive exclusion.
But at the same time, Intraspecific competition increased
the number of species because of carrying capacity.
This also happens to human beings.
In an attempt to clarify competition, Vito Volterra,
James Lotka developed the model of Competition.
This model asks two questions but this very simple model is oversimplified.
These are linear module, it accounts only for two species but
nature is much more complicated.
Not convinced by the competitive principle,
in 1961 ecologist Hutchinson suggested the paradox principle.
The problem, he wrote, that is presented by the phytoplankton is essentially
how it is possible for a number of species to coexist in a relatively isotropic or
unstructured environment all competing for the same sort of materials.
Species are filed under different sets of environmental condition.
This is why if the environment changed sufficiently during time,
no competitor can remain superior to exclude the other species for a long time.
And what happens if environment doesn't change?
Two mechanisms allow to reduce competition and
at the same time guarantee the co-existence of species.
This mechanism is special distribution and biological history.
Dispersal and migration liabilities reduce the competition for space and resources.
And at the same time, the rule and
the niche of a species come from the past interactions.
Even if competition is the most studied interaction in ecology,
models are too simple.
And no real species as unique realize in niche.
We have no proof of competition now, and in the past.
Therefore, we need to move behind extreme line model or competition.
There are some neglected points.
Heterogeneity and environmental variability do matter.
Avoiding the competition in the past allowed the coexistence in the present.
And character displacement amplifies small phenotypic differences during time.
In 2001, Stephen Hubbell proposed the neutral theory
of biodiversity with random vat, speciation, and dispersal.
In this theory, the essential feature is that species are considered all equal or
identical and they have all the same fitness.
Anyway, as the equilibrium theory of island biogeography
proposed by MacArthur Wilson, our both neutral theory
as the main word to have increased the importance of species' niches.
We will discuss it in more detail during next lecture.