Biology Lecture No. 16: Species And Speciation
(Monday, November 7, 2011)
-Microevolution describes the changes in allele frequency from generation to generation.
-Macroevolution describes the creation of new species from generation to generation.
Methods Of Defining Species:
-Species can be identified, determined, distinguished, and overall, defined using either the
Morphological Species Concept (MSC), Biological Species Concept (BSC), and/or the Phylogenetic
Species Concept (PSC).
Forms And Processes Of Speciation:
- Three processes from which speciation may occur include: isolation (reproductive segregation of
species population), convergence (Similarities which have arisen independently in two or more
organisms that are not closely related), and secondary contact (determines degree of divergence).
Applications Of Defining Species And It’s Importance:
-It is essential for the purpose of conserving certain species that endangered or close to extinction. E.g.
forest-dwelling Indian elephants are distinct than savannah dwelling African elephants in social structure
and require different necessities form the environment in which they inhabit.
Morphological Species Concept (MSC):
-MSC is the method of identifying species by similarity in traits of individuals of the studied population.
According to this concept, if one looks at enough distinct phenotypic traits, one can eventually separate
individuals into their own distinct species.
Problems Associated With The Morphological Species Concept (MSC):
-Some populations of the same species show a tremendous amount of variation in phenotype
(divergence). E.g. canis familiaris individuals are all in the same species, yet there are so many
-Many birds are dimorphic, and males are phenotypically diverse when compared to females of the
- In contrast, there can be a lot of similarity in phenotypes of individuals of different species
(convergence). Biological Species Concept (BSC):
-BSC, used by zoologists, defines species not by how similar they look, but rather if the members of a
species are able to interbreed with the members of another species.
-Provides an explanation for why individuals in a species resemble each other (because they all share a
common gene pool).
-Tends to be very objectively testable than MSC. If mating between population A and population B
occurs and offspring are fertile, than population A and population B are the same species.
-E.g. Ligers and Zorses are sterile therefore Lions & Tigers not same species and Zebras & Horses not
Prezygotic Isolating Mechanisms:
-When no gene flow is present, a zygote is not formed regardless the circumstances.
-Temporal Isolating Mechanisms occur when species cannot interbreed due to difference in mating time
period. E.g. Eastern spotted skunks never breed with western spotted skunks as both skunks have
different reproduction periods.
-Habitual Isolating Mechanisms occur when species cannot interbreed due to differences in habitat
preference. E.g. American toads prefer more moist habitats as opposed to Fowler’s toads which prefer
drier habitats, therefore they do not interbreed.