Biological- A group of organisms that can breed and produce viable and fertile offspring
Morphological- A group of organisms that has similar body shape and other structures
Ecological- A group of organisms that reacts in the same way to their environment, basically eats the same foods and resides in the same habitat
Phylogenetic- The smallest group of organisms that share a common ancestor (new branch on tree of life)
In the Biological species concept what barriers can separate different species?
The barriers that separate species in this concept are reproductive things that keep them from producing viable fertile offspring these are separated into two groups prezygotic (prevent a zygote from even being formed) and Postzygotic (keep the offspring from meeting the criteria of being viable and fertile.
Prezygotic:
Habitat isolation- organisms live in different habitats and therefore rarely come in contact with each other
Temporal isolation- Mating habits vary in time of day or time of year
Behavioral isolation- certain mating behaviors are specific to the group so they don’t attract members from the other group
Mechanical isolation- the organisms’ reproductive parts don’t fit together properly
Gamete isolation- fusing of the sperm and egg is unable to occur
Postzygotic-
Reduced hybrid viability- The new organism is less suited for the environment than either parent and will therefore be naturally selected against
Reduced hybrid fertility- The hybrid is sterile and therefore genes cannot flow between the two species keeping them isolated
Hybrid Breakdown- The first generation of the hybrid may be successful but when they breed with either parent species their offspring is not
What is the difference between allopatric and sympatric speciation?
Allopatric speciation occurs when a geographical barrier such as a canyon arises between to species. Over time the species evolve separately and once some type of reproductive isolation arises so that even if they were put into they same environment again they couldn’t reproduce new species have been formed
Sympatric speciation is more rare but it occurs within a population. This can happen when gene flow is reduced between certain sects of a population due to habitat differentiation, sexually selective behaviors, or polyploidy. Polyploidy is most common within plants where often times once they have an off number of chromosomes they cannot reproduce with either parent species but they can fertilize themselves. Speciation within a population can also occur when certain genetic traits allows some of the organisms to utilize a different food group or environmental resource creating habitat isolation. When mates are chosen for certain traits (sexual selection) species can faction off as well.
Facts:
-A hybrid zone is a region where different species overlap and mate producing hybrid offspring
-If the offspring in the hybrid zone are in some way less “fit” than the parent species over time reproductive barriers with strengthen this is called reinforcement
-If the hybrids are successful the opposite can happen and reproductive barriers may be reduced possibly eventually even leader to reverse speciation
-There are two patterns for the course of speciation in the fossil record punctuated equilibrium (stays the same for a very long time and then rapidly changes) Gradualism (long periods of time show small but consistent change which eventually constituted new species.
-In some cases speciation can occur from a change in a single gene such as with Japanese snails.
This is an example of sympatric speciation these two species of flies are not separated geographically at all but they have form different species because they both utilize a different food source and have therefore created a habitat isolation between themselves.
Summary: For the purpose of this book and the study of evolution the biological species concept was used, which is that, species are different if they cannot produce viable fertile offspring. Speciation can occur either because of a geographical separation (allopathic) or with the same geographical area due to polyploidy, sexual selection, or habitat shift. Hybrid zones are sometimes formed where two different species habitats overlap the offspring being unsuccessful can create more reproductive barriers but successful hybrids can reduce them. Speciation can occur at different rates sometimes even within one generation as is the case with autoplyoidy. Study of genetics has shown that as little as one gene difference can separate a species.
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