EESA01H3 Lecture Notes - Lecture 8: Allopatric Speciation, Binomial Nomenclature, Ecosystem Diversity

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EESA01H3 F: Lecture 8 - Biodiversity and Conservation. October 31th, 2016.
Natural Selection:
Evolution: results from random genetic changes across generations, which may
proceed randomly or be influenced by natural selection.
Natural selection: is the process by which traits that enhance survival and reproduction
are passed on more frequently to future generations, altering the genetic makeup of
populations of organisms over time.
This is based on an organism’s ability to adapt, due to their mutations being
either selected for or selected against.
Directional selection: is when the extreme phenotypes are favored over other
phenotypes. This causes the allele frequency to shift frequently over time in the direction
of that extreme phenotype.
Thick snail shells are favored over thin shells.
Stabilizing selection: is a form of natural selection where genetic diversity decreases
and the population mean stabilizes on a particular trait value.
Shells that are too thin break and those that are too thick are heavy. This means
that intermediate shells are preferred.
Disruptive selection: is when extreme phenotypes are favored over intermediate
phenotypes. This means that the variance of the trait increases and the population
becomes divided into two distinct groups.
Each of the extreme shell cases are better suited than the compromise.
Environmental Conditions Influence Adaptation & Evolution:
Divergent evolutions: individuals living in different environments experience different
selective pressures and eventually diverge in their traits.
Convergent evolution: is unrelated species may develop similar traits because of
adaptations to pressures in similar environments.
What is Biodiversity?:
Biodiversity: is the total variety of all organisms in an area.
This takes into account the diversity of species, their genes, their populations, habitats,
and communities.
Scientists have described about 1.8 million species.
How do Species Become Diverse?:
Speciation: is the process by which a new species comes to be.
Allopatric speciation: is speciation as a result of the physical separation of populations
over some geographic distance.
These separations needs to be for a very long time, 1000’s of generations.
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Speciation is clear once reproduction is no longer possible between the newly
differentiated species.
How Can this Separation Occur?:
The uplift of mountains that separate two areas.
The movement of massive ice sheets or changes in the course of major rivers that break
up different areas on a continent.
Sea levels rise, which create isolated islands.
Drier climates, which may divide a lake into several smaller, isolated lakes.
Formation of new islands in the oceans from volcanic activity.
Changes in ocean currents.
Figure 1: Divergence of Organisms Through History.
Classification of Organisms:
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