• These meadowlarks look very similar yet they are not the same species.
Definition of Species
• A species is a group of interbreeding organisms that produce viable, fertile offspring in nature. • Members of a species will interbreed with one another but not other organisms outside of the species. (At least most of the time!)
Macroevolution vs. Microevolution
• Macroevolution is evolution on a scale of separated gene pools. • Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population.
Macroevolution Part II: Allopatric Speciation
• By contrast, these brittle stars look very different from one another, but they are the same species.
Asexual Species Even though asexual groups do not exchange genes, they do form recognizable groups. Most have evolved from a sexual species. Only those whose phenotype is best adapted to the environment, will continue to survive. However, it makes them less adapted to environmental change. Dandelions are asexual. The pollen is sterile and the egg is diploid. 5
• A ring species is a connected series of neighboring populations, each of which can interbreed with closely sited related populations, but for which there exist at least two "end" populations in the series. • These end populations are too distantly related to interbreed, though there is a potential gene flow between each "linked" species. • Such non-breeding, though genetically connected, "end" populations may coexist in the same region thus closing a "ring". 6
• Ensatina escholtzi is a salamander ring species that has a range along the coast and inside range of California. • All along this range, the salamanders interbreed, but the salamanders on the ends of the ring do not interbreed. • Their groupings are called subspecies. 7
• The blue zones represent where interbreeding is occurring. • So are there is gene flow all along the salamander’s range, yet the ends of the rings do not interbreed. Are they the same species? 8
• Each Canis species will interbreed with the domestic dog but not readily with one another. • This is true, even when given the opportunity to do so. Thus, they are not the same species since they do not interbreed in nature.
• Tigers and lions will interbreed in captivity, but they do not interbreed in nature. • Lions form groups or prides and live in the grasslands. • Tigers are more solitary and live in the forests. • Tiglon are products of male tigers and female lions. • Ligers are the opposite cross. I.
Cladogenesis vs. Anagenesis
Anagenesis- is the accumulation of changes in one species that leads to another species. It is the lineage of a species. Over time a species may accumulate enough changes that it is considered a species that differs from the ancestral species.
II. Cladogenesis- is the budding of one or more new species from an ancesteral species that continues to exists. This results in biological diversity. 10 11 12
Allopatric vs. Sympatric Speciation
Allopatric speciationSpeciation occurs because a given group has been separated from the parent group, usually because of a geographic separation as time goes by.
• First, geographic isolation occurs. This is an extrinsic isolating mechanism. • The two populations must become isolated geographically from one another. • If the groups become sympatric again one of two things result…
1. They become separate species, as evidenced by the fact they can no longer interbreed. 2. They can still interbreed, thus they remain the same species.
Why does speciation occur after geographic isolation?
1. The population that...