24.3 Isolation and Divergence in Sympatry
Ð When populations or species live in the same
geographic area, or close enough to one another to
make interbreeding possible, biologists say that
they live in sympatry ("together- homeland").
Paragraph 2
Ð Recently, a number of studies have countered this
prediction. Sympatric speciation--speciation that
occurs even though populations live within the
same geographical area (Figure 24.7)-can indeed
occur, and serves as a source of new branches on
the tree of life. How does it work?
Paragraph 3
Ð Two types of factors can initiate the process of
sympatric speciation: (1) extrinsic (external) factors,
such as disruptive selection for extreme
phenotypes based on different ecological niches
and/or mate preferences; and
Ð (2) intrinsic (internal) factors, such as chromosomal
mutations. Let's consider an example of each of
these factors in turn.
Sympatric Speciation by Disruptive Selection
Ð Disruptive selection (sometimes called divergent
selection PROCES! once populations have
separated) can act on diverse types of traits
ranging from morphology to behaviors. Further,
disruptive selection can involve the survival of
, organisms in their environment (ecological
selection) and/or their ability to attract mates
(sexual selection).
Disruptive selection for ecological niche in killer whales
Ð One of the first patterns Bigg noticed was that killer
whales tend to occur in two kinds of groups in the
coastal waters of British Columbia: larger groups of
10-25 individuals that he 3. Genetic divergence
occurs as mutation, genetic drift, and selection
increase the differences between populations over
time. called resident groups, and smaller, traveling
groups of 2-6 individuals that he called transient
groups. Bigg used these names because he
thought the transients were moving from one
resident group to another. But he soon discovered
that he was wrong: the transient killer whales
looked different from the resident killer whales. For
example, the transients were larger, on average,
and had pointier dorsal fins than the residents
(Table 24.3). The two so-called ecotypes were not
mixing.
Ð Biologists use the term niche (pronounced nitch) to
describe the range of ecological reasources that a
species can use and the range of conditions that It
can tolerate (Ch. 52, Section 52.1). It turn out that
the two ecotypes of killer whales occupy different
niches within the same area of ocean:
Ð Resident ecotype cats Ish, especially salmon (never
Ð When populations or species live in the same
geographic area, or close enough to one another to
make interbreeding possible, biologists say that
they live in sympatry ("together- homeland").
Paragraph 2
Ð Recently, a number of studies have countered this
prediction. Sympatric speciation--speciation that
occurs even though populations live within the
same geographical area (Figure 24.7)-can indeed
occur, and serves as a source of new branches on
the tree of life. How does it work?
Paragraph 3
Ð Two types of factors can initiate the process of
sympatric speciation: (1) extrinsic (external) factors,
such as disruptive selection for extreme
phenotypes based on different ecological niches
and/or mate preferences; and
Ð (2) intrinsic (internal) factors, such as chromosomal
mutations. Let's consider an example of each of
these factors in turn.
Sympatric Speciation by Disruptive Selection
Ð Disruptive selection (sometimes called divergent
selection PROCES! once populations have
separated) can act on diverse types of traits
ranging from morphology to behaviors. Further,
disruptive selection can involve the survival of
, organisms in their environment (ecological
selection) and/or their ability to attract mates
(sexual selection).
Disruptive selection for ecological niche in killer whales
Ð One of the first patterns Bigg noticed was that killer
whales tend to occur in two kinds of groups in the
coastal waters of British Columbia: larger groups of
10-25 individuals that he 3. Genetic divergence
occurs as mutation, genetic drift, and selection
increase the differences between populations over
time. called resident groups, and smaller, traveling
groups of 2-6 individuals that he called transient
groups. Bigg used these names because he
thought the transients were moving from one
resident group to another. But he soon discovered
that he was wrong: the transient killer whales
looked different from the resident killer whales. For
example, the transients were larger, on average,
and had pointier dorsal fins than the residents
(Table 24.3). The two so-called ecotypes were not
mixing.
Ð Biologists use the term niche (pronounced nitch) to
describe the range of ecological reasources that a
species can use and the range of conditions that It
can tolerate (Ch. 52, Section 52.1). It turn out that
the two ecotypes of killer whales occupy different
niches within the same area of ocean:
Ð Resident ecotype cats Ish, especially salmon (never
