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Lecture 19

Biology 1001A Lecture 19.pdf

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Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 19 Species & Speciation –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– - if there were no speciation, we could still have evolution, but there would only be one species present on the Earth today - speciation marks the interface between micro-evolution (change within a single lineage) and macro-evolution (large scale evolutionary patterns) Morphological Species Concept - identifies species based on whether they look similar to each other - using the morphological species concept, the spiders would be classified as being of four different species and the birds would be classified as being of the same species - it is difficult to apply the morphological species concept to species where there is sexual dimorphism because the males and females tend to look very different from each other and could therefore be incorrectly classified as belonging to separate species Biological Species Concept - species are defined as an interbreeding (or potentially interbreeding) group of individuals that are reproductively isolated from other such groups - if the biological species concept is used, the spiders above would be of the same species because they are not reproductively isolated and are capable of mating with each other, whereas the birds would not be considered to be of the same species because they are reproductively isolated and do not mate - the offspring produced by mates of a different species represent an evolutionary dead- end because they are usually sterile - limitations to biological species concept - it is difficult to see if the populations are of the same species when they are geographically isolated because their lack of contact doesn’t allow them to mate naturally - if a species is extinct and fossil records are all that is known about them, then the morphological species concept is the only concept that can be applied to estimate whether they are of the same species - the biological species concept cannot be applied when organisms reproduce asexually because they are all reproductively isolated - hybridization is a grey area for the biological species concept One Species or Two? Biology 1001A | 2012 - it depends greatly on the species concept that you are using - using the morphological species concept, these two birds are from different species because they are different in appearance - using the biological species concept, these two birds are of the same species because they are not reproductively isolated and will produce fertile offspring together - whether the individuals are of the same species depends greatly on the concept used Achieving Reproduction Isolation - prezygotic isolating mechanisms - prezygotic means occurring before the formation of a zygote - temporal isolated is the mechanism by which different species do not mate because their mating seasons differ - the reproductive habitat can be different for two similar species, therefore they will not mate - behavioural or courtship isolation is the mechanism where mating displays by some species are not attractive to other species, therefore mating will not occur - mechanical isolation is when the sexual organs of one species do not fit with those of another species, therefore mating cannot occur - postzygotic isolating mechanisms - inviability in hybrid offspring (offspring dies) - sterility in the hybrid offspring Allopatry - most speciation occurs in allopatry, which is the
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