Speciation:
A Diagram Book
By Adam Rothstein
For Bordertown
Speciation:
A Diagram Book
Welcome to the Speciation Diagram Book!
Speciation is the evolutionary process by which species
derive. This crucial theory to the spread of new species is a
little tricky, however. This handbook has been designed to
illustrate the concepts of speciation, by animating the
interactions of animal populations in low-tech, flipbook
style diagrams.
All theories of speciation, in that they represent
' cladogenesis' or the 'cleaving' of species into separate
lineages, rather than ' anagenesis', or evolution within
lineages, occur in relation to a topological boundary. The
diagrams in this book are tripartite: there is a left portion, a
right portion, and a center portion. The center denotes a
' species border'. Whether geographic, topological, or
behaviorially reified, this border is the splitting point. It is
the point at which individuals are forced to make their
mating choices, and the point at which the gene pool of
species has a change to mimic this boundary line.
Watch this space. New borders are evolving all around us,
and life evolves along with it.
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First, let's talk about...
Genetic Drift
Although the exact role played by genetic drift in speciation
is uncertain, it is a potential explanation for how
cladogenesis speciation occurs rapidly, whereas anagenesis
is a much slower process.
Natural selection is a well-known means of evolution. Over
time, improvements in individuals' genetic fitness increase
the prevelance of certain traits, as those individuals more
successful at breeding contribute their genetic makeup to
the total population.
Genetic drift, on the other hand, can potentially effect large
changes in the gene pool much quicker than otherwise
would happen naturally, due to random sampling.
The gene pool is only defined by those individuals in the
population that interbreed. A rare characteristic can
become more common quickly, if random sampling gives
that characteristic a larger than average chance at being
represented within the breeding population.
1
First, let's talk about...
Genetic Drift
Although the exact role played by genetic drift in speciation
is uncertain, it is a potential explanation for how
cladogenesis speciation occurs rapidly, whereas anagenesis
is a much slower process.
Natural selection is a well-known means of evolution. Over
time, improvements in individuals' genetic fitness increase
the prevelance of certain traits, as those individuals more
successful at breeding contribute their genetic makeup to
the total population.
Genetic drift, on the other hand, can potentially effect large
changes in the gene pool much quicker than otherwise
would happen naturally, due to random sampling.
The gene pool is only defined by those individuals in the
population that interbreed. A rare characteristic can
become more common quickly, if random sampling gives
that characteristic a larger than average chance at being
represented within the breeding population.
A sudden die-off, a splitting of one herd or flock into two, or
any other separation that results into one large breeding
group dividng into multiple smaller breeding groups can
result in an individual or individuals with a particular trait
formerly in the minority suddenly becoming much more
representative throughout the population. What was
previously rare in terms of the whole, is now more common.
Individuals with that rare trait might have previously
fought a hard fight to breed and continue adding the
trait to that population's gene pool. But now, with
competitors reduced or new territory available, they
might find it easier to breed, and so their minority
increases in number relative to the whole.
A sudden die-off, a splitting of one herd or flock into two, or
any other separation that results into one large breeding
group dividng into multiple smaller breeding groups can
result in an individual or individuals with a particular trait
formerly in the minority suddenly becoming much more
representative throughout the population. What was
previously rare in terms of the whole, is now more common.
Individuals with that rare trait might have previously
fought a hard fight to breed and continue adding the
trait to that population's gene pool. But now, with
competitors reduced or new territory available, they
might find it easier to breed, and so their minority
increases in number relative to the whole.
Perhaps, once there is a more sizeable number of
individuals expressing that trait, the trait's
improvements to the genetic fitness of the individuals
begin to take hold. Maybe animals with improved speed
hunt better together, whereas a single faster individual
only made better escapes from predators. What
genetic drift started, natural selection continues, until
the minority trait is found in a majority of the
population.
Additionally, competition with the individuals bearing
the new trait might make life harder for those without
it, who survived fine previously, but now struggle
against the up-and-comers. Perhaps the trait is a new
marking pattern, or significantly better survival
behavior that leaves the other individuals more
exposed to predators. In a sense, these "obsolete"
individuals are at the mercy of the same curve from
which they previously reaped the reward at the
expense of others. Evolution is about competition, and
competition itself is a state that begets multiples in
benefits for winners and hazards for losers.
Perhaps, once there is a more sizeable number of
individuals expressing that trait, the trait's
improvements to the genetic fitness of the individuals
begin to take hold. Maybe animals with improved speed
hunt better together, whereas a single faster individual
only made better escapes from predators. What
genetic drift started, natural selection continues, until
the minority trait is found in a majority of the
population.
Additionally, competition with the individuals bearing
the new trait might make life harder for those without
it, who survived fine previously, but now struggle
against the up-and-comers. Perhaps the trait is a new
marking pattern, or significantly better survival
behavior that leaves the other individuals more
exposed to predators. In a sense, these "obsolete"
individuals are at the mercy of the same curve from
which they previously reaped the reward at the
expense of others. Evolution is about competition, and
competition itself is a state that begets multiples in
benefits for winners and hazards for losers.
Individuals of a species are always competing, not just
against other species for habitat and resources, but
against the members of their own species, even as
they work together to breed and continue their
population.
Eventually, the prior trait may be wiped out of
existence. The random sampling of genetic drift
promotes traits by simply increasing their relative
odds. After that point, natural selection runs its course,
but with a different beginning point than might
otherwise have been. Both genetic drift and natural
selection play into the evolution of species, but as we
will see, geographic speciation creates conditions
under which genetic drift is likely to occur, accelerating
the rise of new mutations to the top of the
expressionary gene pool heap.
Individuals of a species are always competing, not just
against other species for habitat and resources, but
against the members of their own species, even as
they work together to breed and continue their
population.
Theories ofSpeciation....
Allopatric
Speciation
Allopatric speciation (from the ancient Greek allos, "other"
+ Greek patra, "fatherland") occurs when a population is
split into two geographically isolated populations, such that
they are able to interbreed freely within these populations,
but not across these populations.
2
Individuals,
Assemble!
Theories ofSpeciation....
Allopatric
Speciation
Allopatric speciation (from the ancient Greek allos, "other"
+ Greek patra, "fatherland") occurs when a population is
split into two geographically isolated populations, such that
they are able to interbreed freely within these populations,
but not across these populations.
Populations often exist across separate territories or
distributed across the extent of their habitat. But, they
can consistently interbreed by either traveling between
territories or by meeting up with members of other
territories during yearly migration. By continuing to
interbreed, the gene pool maintains a spread consistency,
and evolution occurs only as traits are naturally selected
across the entirety of the population.
2
Populations often exist across separate territories or
distributed across the extent of their habitat. But, they
can consistently interbreed by either traveling between
territories or by meeting up with members of other
territories during yearly migration. By continuing to
interbreed, the gene pool maintains a spread consistency,
and evolution occurs only as traits are naturally selected
across the entirety of the population.
But the face of the earth is always changing. Depending
on the species and its territory, a toplogical shift such as
a river swinging its course, the rise of a mountain range,
climate shift such that a species depended on for food or
other resources splits its own territory, or any other
spontaneous reallignment of biome and geography could
potentially rend a population into two halves, which are
unable to continue interbreeding as a result.
Separated in this way, the two populations will take their
separate courses in evolution. It is now highly unlikely
that, without interbreeding to normalize the distribution
of genetic traits across the entire population, these two
populations will continue as a single species. The
vicissitudes of their territories and the separate
ecosystems means that no matter how similar, some
mutations' advantages will increase fitness in one area,
and not in the other. Over time, natural selection will
effect changes in the population's genetics such that
they become separate species, despite their common
genetic heritage.
Cases ofAllopatric Speciation
- The variation between populations on
different islands in a chain, such as on the
Galapagos, shows how evolution proceeds
in its own direction within a particular
habitat. The species called "Darwin's
finches" is a good example ofthis, though
Darwin himselfonly connected them to the
process ofevolution later, after he
returned to England.
- The African elephant, once thought ofas
a single species, is now considered as
three subspecies by some researchers.
Geographic isolation is theorized as
creating these differences. The Asian
elephant also has four distinct sub-species.
- Fruit flies can show mating preference
based on food source, after being isolated
to a particular food source for only eight
generations.
But the face of the earth is always changing. Depending
on the species and its territory, a toplogical shift such as
a river swinging its course, the rise of a mountain range,
climate shift such that a species depended on for food or
other resources splits its own territory, or any other
spontaneous reallignment of biome and geography could
potentially rend a population into two halves, which are
unable to continue interbreeding as a result.
Separated in this way, the two populations will take their
separate courses in evolution. It is now highly unlikely
that, without interbreeding to normalize the distribution
of genetic traits across the entire population, these two
populations will continue as a single species. The
vicissitudes of their territories and the separate
ecosystems means that no matter how similar, some
mutations' advantages will increase fitness in one area,
and not in the other. Over time, natural selection will
effect changes in the population's genetics such that
they become separate species, despite their common
genetic heritage.
After speciation has occurred, the species will live
independently even if their territory is rejoined.
Sexual selection or genetic and physiological
incompatibilities will ensure that the gene pools of the
two species are separate from now on. The two
populations are now species sharing territory, or if
evolved far enough apart, they might occupy different
niches as if they were separate territories.
After speciation has occurred, the species will live
independently even if their territory is rejoined.
Peripatric Speciation
3
Theories ofSpeciation....
Peripatric speciation is a subform of allopartic speciation. The
main principle is the same, but it occurs with a much smaller
sub-population.
Peripatric speciation begins when a small portion of the
species separates from the main population. This
separation typically occurs over a distance, as this sort of
geographic separation is more likely to happen to a small
number, whereas a territorial split would take a sizeable
amount of the population with it.
d
d+1
d+2
d+3
d+x
Peripatric Speciation
Peripatric speciation is a subform of allopartic speciation. The
main principle is the same, but it occurs with a much smaller
sub-population.
Once the population has a chance to establish itself, it can
become its own population, growing to fill this new territory.
Because of the small initial size of the population, this is a
characteristic situation for genetic drift. "Founder's Effect"
is a loss of genetic variation occurring when a small number
of individuals increases into a large population. This loss of
variation can cause the propagation of rarer traits.
Once the population has a chance to establish itself, it can
become its own population, growing to fill this new territory.
Examples ofFounder's Effect
- Island Populations, such as the
human populations ofIceland, the
Faroe Islands, Easter Islands, and
Pitcairn Islands all have relatively
low genetic variation.
- There is a statistically high
population ofdeafpeople born
on Martha's Vinyard. Additionally,
this resulted in the development
ofMartha's Vinyard Sign
Language.
- Polydactyly (extra fingers and
toes) are more common in
endogamous Amish populations
than the general population.
Because of the small initial size of the population, this is a
characteristic situation for genetic drift. "Founder's Effect"
is a loss of genetic variation occurring when a small number
of individuals increases into a large population. This loss of
variation can cause the propagation of rarer traits.
- After a typhoon killed all but
twenty inhabitants on the island
ofPingelap, total color-blindness
in the since-regained population
is at 5%.
Examples ofFounder's Effect
- Island Populations, such as the
human populations ofIceland, the
Faroe Islands, Easter Islands, and
Pitcairn Islands all have relatively
low genetic variation.
- There is a statistically high
population ofdeafpeople born
on Martha's Vinyard. Additionally,
this resulted in the development
ofMartha's Vinyard Sign
Language.
- Polydactyly (extra fingers and
toes) are more common in
endogamous Amish populations
than the general population.
In such a bottleneck as when a population's genetic
diversity is shifted by Founder's Effect, peripatric
speciation can occur. It is essentially the same as the
Founders' atypically large genetic drift affect on the gene
pool of the population, but with adaptive mutation to a
point at which the smaller population cannot interbreed
with the main population any longer.
- After a typhoon killed all but
twenty inhabitants on the island
ofPingelap, total color-blindness
in the since-regained population
is at 5%.
At this point, if members of the departing population
were to return to the territory of the original population,
they would find themselves to be two separate species,
inhabiting the same territory. Or, two overlapping
territories. The dynamics of competition and cooperative
survival of the gene pool are the territory, in that they
define niches within the system of resources, and thusly,
the entirety of the individuals' lives of breeding and
survival.
In such a bottleneck as when a population's genetic
diversity is shifted by Founder's Effect, peripatric
speciation can occur. It is essentially the same as the
Founders' atypically large genetic drift affect on the gene
pool of the population, but with adaptive mutation to a
point at which the smaller population cannot interbreed
with the main population any longer.
d
d+1
d+2
d+3
d+x
Examples ofPeripatric Speciation
- The Australian Pacific Robin
- Fruit flies have been induced to form
separate reproductive populations as as
result ofbottlenecking
- Polar Bears are believed to have diverged
from the Brown Bear species, after straying
out from the margin ofthe parent species'
range.
At this point, if members of the departing population
were to return to the territory of the original population,
they would find themselves to be two separate species,
inhabiting the same territory. Or, two overlapping
territories. The dynamics of competition and cooperative
survival of the gene pool are the territory, in that they
define niches within the system of resources, and thusly,
the entirety of the individuals' lives of breeding and
survival.
Theories ofSpeciation....
Parapatric
Speciation
4
Follow the territory, species!
Find your niche!
Theories ofSpeciation....
Parapatric
Speciation
4
Parapatric speciation, or the formation of a ring species, is
a unique and more complicated pattern. Variations in
mating habits among members of a species in a
continuous, but gradiated habitat prevent gene flow
across the entire species, and create a continuum of
speciation in small steps, wherein neighbors can
interbreed or hybridize with neighbors, but the entirety
cannot.
This sort of speciation
happens in unique terrain,
where the territory of the
species stretches over a thin
span of space, and slight
variations make the species'
niche different along its
length, and yet still conducive
to that species' survival.
Parapatric speciation, or the formation of a ring species, is
a unique and more complicated pattern. Variations in
mating habits among members of a species in a
continuous, but gradiated habitat prevent gene flow
across the entire species, and create a continuum of
speciation in small steps, wherein neighbors can
interbreed or hybridize with neighbors, but the entirety
cannot.
This sort of speciation
happens in unique terrain,
where the territory of the
species stretches over a thin
span of space, and slight
variations make the species'
niche different along its
length, and yet still conducive
to that species' survival.
There is no geographic
boundary line in parapatric
speciation, but a geographic
gradient. Because of
convenience, as well as
shared specialization to deal
with their local conditions,
members of a population are
more likely to breed with
those near each other, and
not those further away.
Accordingly, genetic
variations will build up in
zones along this gradient,
reinforced by these breeding
choices.
There is no geographic
boundary line in parapatric
speciation, but a geographic
gradient. Because of
convenience, as well as
shared specialization to deal
with their local conditions,
members of a population are
more likely to breed with
those near each other, and
not those further away.
Accordingly, genetic
variations will build up in
zones along this gradient,
reinforced by these breeding
choices.
When this gradient rejoins
itself, a ring species results.
This can happen around a ring
of islands, around a pole, or
even around elevations of
valleys.
When this gradient rejoins
itself, a ring species results.
This can happen around a ring
of islands, around a pole, or
even around elevations of
valleys.
Larus gulls are a prime example of
a ring species. Seven different subspecies extend in a ring around the
Artic circle, each able to interbreed
or hybridize with its neighbors in a
circular continuum except for one
pair, the "gap" in the ring, so to
speak. A separate species has
resulted from the overlapping ends
of a gradient genepool.
Other ring species include the
Ensatina salamanders, which
encircle the Central Valley in
California, and the Greenish
Warbler, which ring the
Himalayas.
Larus gulls are a prime example of
a ring species. Seven different subspecies extend in a ring around the
Artic circle, each able to interbreed
or hybridize with its neighbors in a
circular continuum except for one
pair, the "gap" in the ring, so to
speak. A separate species has
resulted from the overlapping ends
of a gradient genepool.
Theories ofSpeciation....
5
Sympatric Speciation
Allopatric and peripatric speciation have rigid geographic
boundaries that encourage population separations that
result in speciation. Parapatric speciation does not have a
barrier so much as a gradient, that spreads the obstacles to
complete interbreeding between members of a population
over a varied terrain, thereby creating a varied speciation.
With sympatric speciation there is a firm population division.
However, there is no geographic boundary. This type of
speciation occurs within a single population in a single
territory, but is no less of a genetic split resulting from a
bifurcating gene pool. One might wonder, if this sort of
speciation can occur, on what basis can we say that a
population is a single population, or that it inhabits a single
territory? What sorts of topological segmentation is there
that is not geographic, and yet no less affects the breeding
behavior of a species?
Sympatric Speciation
Allopatric and peripatric speciation have rigid geographic
boundaries that encourage population separations that
result in speciation. Parapatric speciation does not have a
barrier so much as a gradient, that spreads the obstacles to
complete interbreeding between members of a population
over a varied terrain, thereby creating a varied speciation.
With sympatric speciation there is a firm population division.
However, there is no geographic boundary. This type of
speciation occurs within a single population in a single
territory, but is no less of a genetic split resulting from a
bifurcating gene pool. One might wonder, if this sort of
speciation can occur, on what basis can we say that a
population is a single population, or that it inhabits a single
territory? What sorts of topological segmentation is there
that is not geographic, and yet no less affects the breeding
behavior of a species?
Within a population group, slight variations
begin to occur, which exhibit traits with
behavioral or physiological differences that are
perceivable, at least to the extent that it affects
breeding behavior. For example, certain
members of a population might be taller or
shorter, or have markings that are slightly
different.
Within a population group, slight variations
begin to occur, which exhibit traits with
behavioral or physiological differences that are
perceivable, at least to the extent that it affects
breeding behavior. For example, certain
members of a population might be taller or
shorter, or have markings that are slightly
different.
If the trait encourages sexual selection in such a
manner that it isolates particular individuals from
the wider population, it becomes its own limiting
effect on the continuity of the overall gene pool.
If, to continue the example, tall individuals only
wish to breed with tall individuals, and this choice
is widespread enough, eventually, the genotype
expressing that trait will become withdrawn from
the general population and form its own subpopulation.
The border in this case does not physically exist, but
is imposed topologically on the breeding environment
by the population's behavior. And yet, these behaviors,
when determining sexual selection, are just as real to
the gene pool as the geographic obstacle of a
mountain or a river.
If the trait encourages sexual selection in such a
manner that it isolates particular individuals from
the wider population, it becomes its own limiting
effect on the continuity of the overall gene pool.
If, to continue the example, tall individuals only
wish to breed with tall individuals, and this choice
is widespread enough, eventually, the genotype
expressing that trait will become withdrawn from
the general population and form its own subpopulation.
The border in this case does not physically exist, but
is imposed topologically on the breeding environment
by the population's behavior. And yet, these behaviors,
when determining sexual selection, are just as real to
the gene pool as the geographic obstacle of a
mountain or a river.
Sooner or later, a separate species results, living
among the original species. What was begun as a
matter of sexual choice is reinforced by genetics,
that has had a chance to mutate within the subpopulation, and via natural selection and genetic
drift permanently branch from the main population.
Examples ofSpecies That Have Branched Due to Sympatric
Speciation
- Cichlids ofLake Nabugabo in East Africa
- Three-spined sticklebacks in British Columbia
- The Hawthorn fly in North America
Sooner or later, a separate species results, living
among the original species. What was begun as a
matter of sexual choice is reinforced by genetics,
that has had a chance to mutate within the subpopulation, and via natural selection and genetic
drift permanently branch from the main population.
Examples ofSpecies That Have Branched Due to Sympatric
Speciation
- Cichlids ofLake Nabugabo in East Africa
- Three-spined sticklebacks in British Columbia
- The Hawthorn fly in North America
Speciation: A Diagram Book
designed and printed by Adam Rothstein
for
Bordertown
Information in the text is sourced through Wikipedia.
Please visit the article on "Speciation" as well as
relevant sub-articles for the latest word on speciation
theories, as well as the scientific research status of
particular species as regards these theories.
Speciation: A Diagram Book by Adam Rothstein is
licensed under a Creative Commons AttributionNonCommercial-ShareAlike 3.0 Unported License.
http://www.poszu.com/projects/speciation
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