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BIOL 1407 Instructor: Mr. Sanregret Review Sheet Chapter 24
1) Biological species concept was the earliest scientific concept of species: a species is a group or groups
of individuals within which breeding and producing viable, fertile offspring is possible. Species =
reproductive isolation.
2) There are two main categoies of reproductive isolation: prezygotic and postzygotic. Prezygotic
barriers include habitat, temporal, behavioral, mechanical, and gametic isolation. Postzygotic barrier
allow the generation of a hybrid zygote, the passing on of genes is prevented because the hybrid zygote
is either not viable or not fertile. Some plant hybrids are viable and fertile, but over generations the
hybrids become progressively less healthy.
3) The flaws in this concept are a) hard to test (e.g. fossils, organisms that don’t breed in captivity, etc.);
b) doesn’t apply to asexual organisms; c) sometimes groups that appear to be distinctly different types
can interbreed to produce viable, fertile offspring (e.g. dogs and wolves, red and yellow flickers).
4) Alternative species concepts: Ecological species concept: one niche = one species. A niche consists
of all the resources an organism uses and how they use them. No two species can share a single niche
because one will always be a little better than the other and out-compete them. E.g. Barnacles of
species A out-compete barnacles of species B when side by side. However, species B can survive in
air longer so it’s niche is higher in tidal zone.
5) Morphological species and paleontological species concepts: Species are identified by anatomy,
known either from live specimens or fossils. This is not so much a definition of species, but rather the
most practical way to distinguish different species.
6) Phylogenetic species concept: Species are defined based on common ancestry.
7) Two modes of speciation: allopatric speciation, where a geographic boundary exists between two
populations that become separate species; and sympatric speciation, where no geographic barrier
exists between populations that become new species.
8) In allopatric speciation, a geographic boundary may be due to a geological change, or due to a group
from the parent population traveling and colonizing a distant location. In either case, the barrier to
gene flow between the two populations facilitates the evolution of reproductive isolation.
9) When subgroups of one population each adapt to a variety of different unoccupied niches, forming a
new species for each niche, it is called adaptive radiation. A major example of adaptive radiation
was the adaptive radiation of mammals following the extinction of the dinosaurs.
10) One way in which sympatric speciation occurs is why plants become polyploid. This may happen
when meiotic errors result in 2N gametes producing 4N offspring (autopolyploidy). It may also occur
when two plant species hybridize. The resulting offspring have complete sets of both parent species
chromosomes (allopolyploidy). In both cases, the offspring are capable of self fertilizing, or crossing
with other similar individuals, but not with the parent species.
11) Sympatric speciation may occur in animals if an individual exploits resources not used by the parent
population. An example of this would be a fruit parasite fly that lays its eggs in a different species of
fruit than the parent population. Non-random mating may also result in sympatric speciation. For
example, if female fish of a certain genotype prefer red males, while female fish of another genotype
prefer silver males, this may result in a lack of gene flow between the two genotypes, facilitating
reproductive isolation.
12) Fossil evidence suggests that when a new species forms, most of the changes from the parent species
that occur early in the “lifespan” of the species (maybe the first 1% of the species’ duration on Earth).
During the rest of a species’ time it stay relatively the same. This model is sometimes called
“punctuated equilibrium.” This is in contrast to gradualism, where species slowly and continually
grow more different after they diverge.