BIOl 152 1st Edition Lecture 6 Outline of Last Lecture I Types of Selection II Preservation of Genetic Variation III Barriers isolating gene pools Outline of Current Lecture I Post zygotic barriers II Limitations of Biological Species Concept III Other Species concepts IV Modes of Speciation Current Lecture I Post zygotic barriers There are several post zygotic barriers that assure that interbreeding between two species is not successful by maintaining that the embryo does not develop These barriers are reduced hybrid viability reduced hybrid fertility and hybrid breakdown Reduced hybrid viability occurs when embryonic development is sustained to a point and then the embryo dies Reduced hybrid fertility occurs when the embryo survives but is sterile or unable to reproduce Hybrid breakdown is more common in plants and is when hybridization occurs resulting in a new species but by the second generation the species is unable to reproduce These barriers aid in assuring that different species cannot produce viable offspring II Limitations of the Biological Species concept The Biological Species concept is helpful in describing how groups of actually or potentially interbreeding populations maintain their unique identities with closed gene pools However this concept does not include asexual species or extinct species and does not explain the implications of hybridization and ring species III Other Species Concepts There are other species concepts that attempt to cover the factors that the Biological Species concept excludes These concepts are the morph species concept the ecological species concept the evolutionary concept and the phylogenetic concept The morph These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute species concept is like referring to a field guide to identify a species in a population An ecological species concept emphasizes the role a species has on its environment Evolutionary species concept emphasizes common ancestry among different species and therefore accounts for the extinct animals The Phylogenetic species concept emphasizes recent common ancestry between populations to understand the differences and why they developed that way IV Modes of speciation Speciation refers to the origin of new species and species are the fundamental unit of biodiversity and evolution There are two modes of speciation allopatric speciation and sympatric speciation Allopatric speciation describes speciation that occurs when a species is separated by some physical barrier Vicariance occurs when a physical barrier such as a river or canyon separates a population This separates a population and closes the gene pool allowing for the populations to evolve differently from each other Another possibility is dispersal or when some of a population moves to another area and are separated from the larger population and develop differently Sympatric speciation is similar to allopatric except it describes geographically overlapping populations The mechanisms in play are isolating mechanisms and habitat differentiation These mechanisms separate species because each species has its preferred habitat and times for breeding Another mechanism for sympatric speciation is instantaneous speciation and shows up as errors during cell division and does not allow the offspring generation to interbreed with the parent population