Slide
1
In this tutorial - we are talking about speciation. Speciation is
the process of creating a new species. But before we can talk about
speciation - we need to talk about the definition of a species.
There are many definitions of a species - we will talk about three examples: the morphological species concept, the evolutionary species concept, and the Biological species concept.
Slide 2
The morphological species
concept states that a species is a group of individuals with shared
morphologies or appearances.
This definition makes sense - it is probably no surprise to learn that the Blackburnian warbler is a distinct and separate species from the Chestnut-sided warbler. They look different from each other.
Slide 3
This definition does not always work,
however, For a long time it was thought that these two parrots are from
different species because they look so different from each other. In
fact, they are the male and female of the same species - sexual dimorphism can
make the morphological species concept difficult to use.
Also, look at these ants - they look very different from each other. But in fact they are sisters - ants are an example of what are known as eusocial insects and each ant in the colony has a very specific role or job. Even genetically very similar individuals can look quite different depending upon their job. Again, the morphological species concept is difficult to use with these ants.
Slide 4
The morphological species concept is also difficult to
use when different species look very similar. This is the case with
Eastern and Western Meadowlarks. It is challenging for even a seasoned
ornithologist to tell these species apart by simply looking at them.
They are, however, considered distinct species because they have very
different songs and do not usually mate with each other.
Slide 5
The
Evolutionary species concept groups organisms together based on shared
evolutionary history. This can be a useful definition but it also has
limitations - specifically because we usually do not know the full
evolutionary history of a species.
Slide 6
The Biological
Species Concept is the definition that is used the most by biologists.
It describes a species as a group of potentially interbreeding
individuals that can produce fertile offspring. The limitations of this
definition is that it cannot be used to describe asexual and extinct species.
Also, sometimes different species do interbreed and produce hybrids -
often, however, these hybrids are not fertile.
An example of this is a mating between a horse and donkey to produce a mule. Horses and donkeys are considered distinct species because mules are sterile.
Slide 7
Regardless
of the definition that is used to define a species - we know that the number
of species has been steadily increasing since the evolution of life on earth.
While there have been periods of mass extinction - such as at the end of
the Cretaceous 65 million years ago. It is not the biggest extinction
but it is the most famous because it ended the age of dinosaurs and made way
for mammals and birds. During this event, 50% of the known genera (a
genus is a level of organization just above a species) - went extinct.
Despite these mass extinctions, the number of different types of organisms has been increasing. Some biologists estimate that there may be 150 million different species on earth.
Slide 8
The definition that is used
to define a species has more than just biological implications. It can
have politcal implications as well.
For example, the Endangered Species Act is some of the strongest environmental legislation that exists in the United States. This legislation was enacted to save species from going extinct as a result of human activity.
The endangered species act uses the Biological Species Concept to define a species. This has implications for organisms like the Red Wolf - Canis rufus.
The Red Wolf used to range through out the southeastern US (and even into central Pennsylvania) but it became extinct in the wild in 1980. In 1987 it was reintroduced into North Carolina in efforts to reestablish a wild population. These efforts have been successful but controversial. Red wolves and gray wolves can interbreed and produce fertile offspring - so people have argued about the validity of giving the red wolf distinct species status. The Fish and Wildlife Service considers the matter settled and supports the idea that the red wolf is a separate species from the gray wolf and deserves protection under the endangered species act.