Flashcards in 02 Origin of Species Deck (20)
Who first classified organisms into hierarchies, the precursor to our modern day system?
When did Linnaeus develop his concept of a species, and how did he classify them?
1730s, by structural (morphological) features
what is the biological species concept, and how is this an improvement over Linnaeus' original system?
A biological species is a population or group of populations whose members have the potential to interbreed with one another in nature to produce fertile offspring, but cannot successfully interbreed with other members of other populations.
This expanded concept allows us to include physiological, biochemical and genetic similarities as criteria, not just Linnaean morphology.
what implicant assumptions does the biological species concept make?
• The same species will share common characteristics (which is also possible between two closely related species)
• Genetic compatibility within members of the same species ("potential to interbreed with one another")
• This inbreeding occurs naturally (without human intervention)
• Sexual reproduction
explain why classifying a unicellular organism using the biological species concept is problematic
The biological species concept assumes sexual reproduction, not binary fusion, which is asexual ("interbreeding"
give two examples of where the biological species concept breaks down
asexually reproducing and extinct species
what is a subspecies?
organisms belonging to different subspecies of the same species are capable of interbreeding and producing fertile offspring, but they do not interbreed in nature due to geographic isolation or other factors. The differences between subspecies are usually less distinct than the differences between species.
what would happen if gene flow stopped between two subspecies?
they would be considered distinct species
give an example of a sexually reproducing species that does not fit the biological species concept
a hybrid that is fertile, like the red wolf; this is an example of the trickle effect: gene flow keeps morphologically and behaviourally distinct populations from becoming reproductively isolated.
What are the general differences between the biological species concept and other definitions of species?
other concepts of species focus on similarities between members instead of the separateness of other species, this allows them to be applied to asexually reproducing organisms, extinct species, and ambiguous members like fertile hybrids.
ecological species concept
The ecological species concept views a species in terms of its ecological niche. A niche is the total resources available for use by an organism. The more that niches overlap the more competition there is for resources. The natural tendency is for the divergence of species to reduce this competition. It applies to sexual and asexual species and emphasizes the role of disruptive selection.
phylogenetic species concept
phylogenetic species concept defines a species as the smallest group of individuals on a phylogenetic tree. A phylogenetic tree is one hypothesis of the evolutionary history of a group of organisms. It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species.
list all the mechanisms that can change allele frequency, thus altering the gene pool, and identify which one works to decrease the differences between different populations of one species
natural selection, mutation, genetic drift, and gene flow all serve to change allele frequency, but of these only gene flow can decrease the differences between different populations
what are the two main types of reproductive isolation?
prezygotic and postzygotic isolation
what are the main types of prezygotic isolation?
behavioural, mechanical, temporal, and gametic isolation; most (behavioural, mechanical, and temporal) prevent mating, all prevent fertilisation.
behavioural isolation, define and specify whether it is considered prezygotic or postzygotic
prezyogtic, prevents mating/fertilisation because the activities or behaviors of different species do not attract other species (ex. incompatible bird songs or other mating ritual, think worst-case sexual selection)
mechanical isolation, define and specify whether it is considered prezygotic or postzygotic
prezygotic, prevents mating/fertilisation due to morphological constraints (gametes cannot physically become fertilised)
temporal isolation, define and specify whether it is considered prezygotic or postzygotic
prezygotic, prevents mating/fertilisation due to a separation of their reproductive timing (ex. bloom time in flowers)
gametic isolation, define and specify whether it is considered prezygotic or postzygotic
prezygotic, does not prevent mating but does prevent fertilisation due to gametic incompatibility (ex. different species have different surface proteins and receptors in their gametes)