BISC 102 Lecture Notes - Lecture 12: External Fertilization, Sympatric Speciation, Meiosis

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Morphological Species Concept: Just like humans, there are small differences among
individuals, but need to look closely
Species are discrete groups of organisms, defined by unique reliable
morphological characteristics that separate them from other species.” BUT:
This is a simple concept, but some species are diverse in morphology, or cryptic
(differences are not morphological).
Advantages
Traditional, simple (Linnaean concept)
Applicable for living and extinct groups
Applicable for asexual and sexual groups (all life forms)
Disadvantages
Doesn’t resolve cryptic groups (2 groups that look the same, but don’t
interbreed): also called “sibling species”
Confounded by morphs (interbreeding populations with different phenotypes,
such as geographic varieties)
It is not very useful for studying speciation
Biological Species Concept (BSC): Species or groups of actually or potentially
interbreeding natural populations that are reproductively isolated from other such groups
Emphasizes reproductive isolation (Example: Animal gene flow among species).
● Advantage
Most useful for studying speciation.
● Disadvantage
Cannot be applied to extinct species, asexual species, or prokaryotes.
Problem of scale: how much hybridization and gene flow is too much?
Cannot be applied to fossils or asexual organisms (including all prokaryotes)
Phylogenetic species concept (PSC): Smallest diagnosable group of organisms that form
an unbroken lineage on a phylogeny (i.e., line between 2 nodes, or line between node and a
tip).
● Advantages
Can us genetic and/or morphological data.
Applicable to living and extinct groups.
Applicable to asexual and sexual groups.
● Disadvantages
Species status changes with changing phylogeny.
Trivial characteristics can define unique species.
Note: This concept has implications for conservation biology.
Ecological species concept (ESC): A species is a set of organisms occupying a single
niche, including a unique habitat and resources (food, predator, parasites).
● Advantages
Applicable to asexual and sexual groups.
● Disadvantages
Can’t be applied to extinct groups.
Trivial characteristics can define unique species.
● Note: This concept emphasizes the role of natural selection.
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