BIOL 1543 Lecture Notes - Lecture 18: Reproductive Isolation, Microevolution, Masked Booby
23 Aug 2016
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DOWNLOAD 18 - ORIGIN OF SPECIES
textbook reading: 14:1-4, 7-8, 11, 14-17
SPECIATION
many species of cormorants around the world can fly
cormorants on the Galapagos Islands cannot fly
how did these flightless cormorants get to the Galapagos Islands?
why are these flightless cormorants found nowhere else in the world?
an ancestral cormorant species is thought to have flown from the Americas to
the Galapagos Islands more than 3 million years ago
terrestrial mammals could not make the trip over the wide distance, and no
predatory mammals naturally occur on these islands today
without predators, the environment of these cormorants favored birds with
smaller wings, perhaps channeling resources to the production of offspring
ORIGIN OF SPECIES
origin of species the source of biological diversity
microevolution the change in the gene pool of a population from one generation
to the next
speciation the process by which one species splits into two or more species
every time speciation occurs, the diversity of life increases
the many millions of species on Earth have all arisen from an ancestral life
form that lived around 3.5 billion years ago
DEFINING A SPECIES
although the basic idea of species as distinct life-forms seems intuitive, devising a more
formal definition is not easy and raises questions
how similar are members of the same species?
what keeps one species distinct from others?
variation within parameters?
biological species concept defines a species as:
a group of populations
members who have the potential to interbreed in nature
produce fertile offspring
therefore, members of a species are similar because they reproduce with each other
reproductive isolation (no gene flow)
prevents members of different species from mating with each other
prevents gene flow between species
maintains separate species
therefore, species are distinct from each other because they do not share the same
gene pool
can be problematic
some pairs of clearly distinct species occasionally interbreed and produce
hybrids
for example, grizzly bears and polar bears may interbreed and
produce hybrids called grolar bears
melting sea ice may bring these two bear species together more
frequently and produce more hybrids in the wild
cannot usually be determined for extinct organisms known only from fossils
does not apply to prokaryotes or other organisms that reproduce only asexually
therefore, alternate species concepts can be useful
morphological species concept
classifies organisms based on observable physical traits and can be applied to:
asexual organisms
fossils
there is some subjectivity in deciding which traits to use
example: if two plants share most traits but have different flower color, are
they different species?
ecological species concept
defines a species by its ecological role or niche
focuses on unique adaptations to particular roles in a biological community
for example:
two species may be similar in appearance but distinguishable based on:
what they eat
where they live
some African Cichlids that are morphologically identical are
different species due to habitat
phylogenetic species concept
