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Author Topic:   Speciation + Evolution = More Diversity
RAZD
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Message 31 of 47 (493775)
01-10-2009 5:57 PM
Reply to: Message 22 by Huntard
01-09-2009 9:16 AM


moving on ...
hey Huntard,

There are people that are interested in discussing this.

Most definitely ... on the appropriate threads:

  • Definition of Evolution

  • Definition of Species

    And then, once the definitions have been resolved, perhaps we can continue with the question of continued evolution after speciation.

    We can discuss different rates of evolution, and the effect of ecology on those rates.

    From evidence such as the foraminifera we do see different rates of evolution at different times and for different reasons:

    http://web.archive.org/web/19990203140657/gly.fsu.edu/tour/article_7.html


    Click to enlarge

    We can see that speciation is not a "one-shot wonder" but a repeated process that allows species to take fuller advantage of the available ecosystems. This shows in the response to the K-T extinction event:

    quote:
    One of the last great extinctions occurred roughly 66 million years ago and, according to one popular theory, it resulted from Earth's receiving a direct hit from a large asteroid. Whatever the cause, the event proved to be the dinosaurs' coup de grace, and so wiped out a good portion of the marine life--including almost all species of planktonic forams.

    This period of massive death, which ended the Cretaceous Period, ushered in the modern chapter of biological development. Earth entered the new era, the Cenozoic, with a wide range of ecosystems virtually deviod of life (and thus competition between species), yet quite fertile and primed for repopulation.

    The ancient record of foram evolution reveals that the story of recovery after extinction is indeed busy and colorful. "What we've found suggests that the rate of speciation increases dramatically in a biological vacuum," says Parker. "After the Cretaceous extinction, the few surviving foram species rapidly evolved into new species, and for the first time we're able to see just how this happens, and how fast."

    As the available niches fill up with these new creatures, the speciation rates slow down, and the pressure from competition between species appears to bear down in earnest. The extinction rate then rises accordingly. This scenario, says Arnold, suggests that the speciation process is sensitive to how fully packed the biosphere is with other species, not the number of individuals. Ecologists, in referring to a given environment's ability to sustain life as its carrying capacity, generally mean the natural limit, in shear numbers, of individual organisms that any environment can support, as opposed to the number of different kinds of organisms or species. "This is an intriguing concept--a species carrying capacity, so to speak," says Arnold. "This implies that the speciation process is sensitive to how many spesies are already out there."


    Actually, I think this is the same response, each species reaches their carrying capacity for the particular ecology, branching into neighboring ecologies and speciating as necessary to fill that ecology. It's an opportunistic response: the more opportunity there is the more evolution will likely take advantage of it as individual organisms try to survive and reproduce.

    We can also see different rates of evolution in the aftermath of speciation for Pelycodus, as they evolve to reduce competition between the two daughter populations:

    quote:

    Click to enlarge

    The dashed lines show the overall trend. The species at the bottom is Pelycodus ralstoni, but at the top we find two species, Notharctus nunienus and Notharctus venticolus.

    When two similar species compete, it is not uncommon that one fairly quickly becomes different - in this case, smaller. This presumably reduces the competition between the species.


    The rate of evolution from Pelycodus jarrovii to Notharctus nunienus is faster than the overall rate of evolution from Pelycodus ralstoni to Notharctus venticolus (although one could argue that it varies around this overall trend with fast and slow periods).

    The difference in size would also result in the smaller Notharctus nunienus being able to take better advantage of feeding higher in the trees, while the larger Notharctus venticolus was able to take better advantage of feeding on the ground, thus resulting in different ecologies even if they inhabited the same geological area.

    Certainly this simple graph shows that they indeed diverged further after speciation. What would be interesting would be to follow each branch further.

    Enjoy.

    Edited by RAZD, : switched to copied pictures


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  • RAZD
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    Message 32 of 47 (493878)
    01-11-2009 11:03 AM
    Reply to: Message 3 by Coyote
    01-07-2009 9:06 PM


    Barriers to Evolution?
    Hi Coyote, sorry about the snafu on the great debate thread.

    In other words, what mechanism prevents evolution from going beyond "kinds" (which is not a scientific term, or even a defined term, but may serve here to represent the idea). What mechanism prohibits speciation, followed by speciation and still more speciation?

    I would answer this with the evidence that invalidates the possibility of any such barrier, as I did on the great debate thread when seekingfirstthekingdom raised the issue of "genetic boundaries"

    From Message 33

    quote:
    ... the fossil record points to kinds staying within genetic boundaries instituted by our creator in genesis.

    The problem I have with this claim is convergent evolution. Consider these fellas:

    Berkeley - evolution 101:

    quote:

    However, these animals also have some key differences:

  • Sugar gliders live in Australia, and flying squirrels live in North America.

  • Sugar gliders have a pouch (like a kangaroo does), which provides shelter and safety for their tiny babies - at birth, a baby sugar glider is smaller than a peanut! Flying squirrels, on the other hand, have much larger babies and no pouch.

    By studying their genes and other traits, biologists have figured out that sugar gliders and flying squirrels are probably not very closely related. Sugar gliders are marsupial mammals and flying squirrels are placental mammals.


  • From this (and many other examples) I would conclude that there is no barrier that prevents a marsupial from evolving to be virtually identical in behavior, size, appearance, etc, to a placental mammal.

    When you look at the fossil record the ancestors of these animals are less similar than these two, so they have been evolving separately to be similar towards a common end.

    The alternative is that all mammals back to the first mammal are one "kind" - thus including not only duckbilled platypus, kangaroos, koala bears and echidna, but elephants, whales, giraffes, and mole rats ... to say nothing of humans.


    Another example of convergent evolution that extends even further into the dark ages of life on earth is the killer whale and the white shark:

    quote:
    KILLER WHALE
    Kingdom: Animalia
    Phylum: Chordata
    Class: Mammalia

    The Orca or Killer Whale (Orcinus orca), less commonly, Blackfish or Seawolf, is the largest species of the dolphin family. It is found in all the world's oceans, from the frigid Arctic and Antarctic regions to warm, tropical seas.

    Orca are versatile and opportunistic predators. Some populations feed mostly on fish, and other populations hunt marine mammals, including sea lions, seals, walruses and even large whales. They are considered the apex predator of the marine world.


    http://en.wikipedia.org/wiki/White_shark

    quote:
    WHITE SHARK
    Kingdom: Animalia
    Phylum: Chordata
    Class: Chondrichthyes


    The great white shark, also known as white pointer, white shark, or white death, is an exceptionally large lamniform shark found in coastal surface waters in all major oceans. Reaching lengths of more than 6 m (20 ft) and weighing up to 2,250 kg (5,000 lb), the great white shark is arguably the world's largest known predatory fish. It is the only surviving species of its genus, Carcharodon.

    (except that a shark is not a "true" fish ...)

    It appears there is no "genetic barrier" that prevents mammal evolution from becoming similar to sharks, which are from an ancient order:

    Cartilaginous fish diverged from the branch that mammals are on over 450 million years ago, and pre-date "true fish" ... that's a lot for one "kind" eh? This puts true fish, amphibians, birds and mammals together with Cartilaginous Fish into one "Kind" ...

    Enjoy.

    Edited by RAZD, : one kind word

    Edited by RAZD, : ...

    Edited by RAZD, : — to -


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    This message is a reply to:
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    Coyote
    Member (Idle past 179 days)
    Posts: 6117
    Joined: 01-12-2008


    Message 33 of 47 (493882)
    01-11-2009 11:26 AM
    Reply to: Message 32 by RAZD
    01-11-2009 11:03 AM


    Re: Barriers to Evolution?
    I agree that there is no mechanism known to science to prevent lots of micro-evolutionary events from becoming macro-evolution.

    Yet we keep hearing from creationists that nothing can evolve beyond its own kind (which is variously defined as anything from a species to a class or phylum, whichever is most convenient at the time).

    Given this, it is a fair question to ask of creationists--what mechanism prevents those micros from adding up to a macro?

    I have asked this numerous times on different websites, and have never received a satisfactory answer.

    In truth, they have no idea. They just believe that kinds are immutable and that's it. When challenged they come up with some "what if" explanation, and when that is disproved they move on to another. Eventually they come back to the first "what if" and start again. But, no matter now many "what ifs" are disproved it will not shake their belief that kinds are immutable.

    And that's why it is called creation "science" instead of real science.

    /rant


    Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
    This message is a reply to:
     Message 32 by RAZD, posted 01-11-2009 11:03 AM RAZD has responded

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    RAZD
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    Message 34 of 47 (493887)
    01-11-2009 1:22 PM
    Reply to: Message 33 by Coyote
    01-11-2009 11:26 AM


    What comes after Pelycodus?
    Hey Coyote,

    I have asked this numerous times on different websites, and have never received a satisfactory answer.

    And I don't think you will get one.

    In truth, they have no idea. They just believe that kinds are immutable and that's it. When challenged they come up with some "what if" explanation, and when that is disproved they move on to another. Eventually they come back to the first "what if" and start again. But, no matter now many "what ifs" are disproved it will not shake their belief that kinds are immutable.

    Or try to divert the discussion to another topic, like what the definitions of the words are.

    Given this, it is a fair question to ask of creationists--what mechanism prevents those micros from adding up to a macro?

    Given that they (rarely) understand genetics and (rarely) have any knowledge of the fossil record, it is not possible for them to provide evidence that they do not know. They go on the assumption that there were an original set of organisms, and then assume that this is supported by evidence.

    That is one of the reasons I want to focus this thread of the evidence of step by step evolution after speciation. Pelycodus is good for showing how evolution results in speciation, but the data seems to stop there.

    I found an on-line copy of a paper by Gingrich with a review of the fossil data for pelycodus and another version of his chart:

    SYSTEMATICS, PHYLOGENY, AND EVOLUTION OF EARLY EOCENE ADAPIDAE (MAMMALIA, PRIMATES) IN NORTH AMERICA
    Vol. 24, No. 22, p. 245-279 (13 text-figs.) August 15,1977

    I want to quote one particular section as it mirrors what I've said:

    quote:
    Given the pattern of phylogeny in text-fig. 10, and the details of morphological change discussed in the section of this paper on systematics, it is possible to subdivide each lineage into a sequence of valid species. Pelycodus ralstoni evolved into P. mckennai, which evolved into P. trigonodus, and SO forth. While the distinction between lineages is nonarbitrary, it must be emphasized that the exact boundary between successive species within a lineage is arbitrary (although each species as a whole can be distinguished morphologically). No natural breaks are obvious, and it is necessary for ease of discussion and for use in biostratigraphy to make essentially artificial boundaries between species. It turns out, largely for historical reasons, that these correspond fairly well with established subdivisions of the Wasatchian (Sand Coulee, lower Gray Bull, etc. - which themselves are poorly defined at present). Since the boundaries between time successive species must be time-parallel to make taxonomic diversity reflect biological diversity, the successive species of Pelycodus can potentially serve as a useful substitute in zonation of the Wasatchian, pending a full scale faunal study of this interval of evolutionary history. In this connection it is important to emphasize that the distinctions between species are based on comparisons of whole samples from each locality, and the transitions between species appear in every case to be continuous and gradual. Thus any zonation based on Pelycodus could be used, at best, to subdivide the Wasatchian into five subunits.
    (p273)

    Here's the graphic:


    Click to enlarge

    quote:
    Our primary interest in studying Pelycodus and Copelemur has not been biostratigraphic zonation of the Wasatchian, but rather the patterns of phylogeny and evolution exhibited by these genera. The genealogical relationships of the species of Copelemur are still somewhat obscure, owing to the inadequate stratigraphic record of these species. The only reasonably certain relationship is the ancestor-descendant relationship of C. feretutus and C. consortutus. Within Pelycodus, on the other hand, we can be much more certain about genealogical relationships. The four species from P. ralstoni to P. abditus appear to be a single ancestor-descendant sequence, with P. abditus giving rise to both P. frugivoms and P. jarrovii.

    It looks like biostratigraphy is the direction to go, in order to find this kind of data organization.

    I found some information on Notharctus here
    http://www.nycep.org/ed/download/pdf/1979e-4.pdf

    It does seem to discuss later evolution, but I could not tie it into the biostratigraphy above.

    Enjoy.

    Edited by RAZD, : notharctus


    we are limited in our ability to understand
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    This message is a reply to:
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    onifre
    Member (Idle past 1023 days)
    Posts: 4854
    From: Dark Side of the Moon
    Joined: 02-20-2008


    Message 35 of 47 (493893)
    01-11-2009 1:54 PM
    Reply to: Message 1 by RAZD
    01-07-2009 8:26 PM


    Re: Evolution after Speciation
    Hi RAZD,

    I have a couple of questions. Hope they are not too stupid- lol

    After speciation has occurred, the daughter populations no longer share genes through reproduction, and they are free to evolve completely different traits.

    What actually drives speciation...?

    You wrote,

    quote:
    the species forms a band made up of several varieties around some barrier to their survival ability,

    Could you give a more laymen explanation, please?

    Does this mean the species know which members within their group are better suited for survival and they hangout together insuring a better success rate? Like some elitist group of birds weeding out lesser members, eventually leading to a parent/daughter population split?

    If that is right, my next question would be, wouldn't that almost guarantee the parent populations extinction, since it's a split of better suited species from their lesser suited kin?

    Also, you wrote,

    quote:
    when they meet on the other side of the barrier, the two ends do not mate.

    Cannot mate or choose not to mate due to selective reproduction?

    That should be enough for starters. There is more to discuss about where change occurs, but this is long enough for now.

    I hope when you're done weeding out the creationist babel you can continue with a more detailed explanations, thanks for another great thread.

    - Oni


    "I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

    "I never knew there was another option other than to question everything"--Noam Chomsky


    This message is a reply to:
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    NosyNed
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    Message 36 of 47 (493899)
    01-11-2009 2:45 PM
    Reply to: Message 35 by onifre
    01-11-2009 1:54 PM


    speciation drivers
    What actually drives speciation...?

    I'm sure RAZD will do a better job than I will but I'll have a go at it:

    It used to be thought that only if a population was separated geographically could a speciation event occur. This is called "allopatric" speciation. In this case it might be "driven" by lots of things. Great distance might do it if the genes can not flow easily throughout the range. Note the ring-species case: if part of the ring is killed off (by whatever) then there are two (or more) separated populations. Once that is true the the accumulating changes to the now separate gene pools will eventually (and this appears to take perhaps, millions of years for mammals) will be completely incompatible. (E.g., lions and tigers have been separated for that kind of time and are nearly completely separate).

    We now know that many things can drive speciation. E.g., there is a parasite of (I think) fruit flies (don't remember too well) that changes them so only infected animals can breed with each other. It is an immediate separation of populations. There have been cases (many in plants, fewer in animals) where a chromosome number change separates the populations. This can produce nearly "instantaneous" speciation.

    A mutation changing something like a birds song can cause a separation of a population into those without is and those with it.

    And so on...

    Does this mean the species know which members within their group are better suited for survival and they hangout together insuring a better success rate? Like some elitist group of birds weeding out lesser members, eventually leading to a parent/daughter population split?

    No. They don't "know". Some survive some don't.

    In the specific case of ring species both daughter species may be well suited to the environment. Let's take a case where there are only 3 sub-species in the "ring".

    A in the middle and X on the east and Y on the west. We'll take it that A is the parent. The range of the populations is long and narrow (like around a mountain range). The differences in X and Y from A and from each other maybe small. But if the individuals don't travel far relative to the range then there may be enough separation to stop the population from being exactly like one well-mixed gene pool. So there is a possibility of drift occurring.

    If the environment where X and Y live is very different then there will be a high selection pressure on them and they may diverge more rapidly.

    Now if the remaining gene flow is disrupted from A to X and A to Y and if X and Y are already different enough on the far side of the ring so they don't interbreed (much or at all) we now have room for new species to arise.

    It may be that the disruption is by a environmental change (a big city appearing?) in the home range of the parent sub-species and it goes extinct or it maybe that the range is disrupted enough to reduce the gene flow to very, very low levels.

    If that is right, my next question would be, wouldn't that almost guarantee the parent populations extinction, since it's a split of better suited species from their lesser suited kin?

    In general, no. There are too many variables for a general answer most times :). It is possible to have a speciation event and have both parent and daughter populations do just fine in the same area. There are a lot of niches available.

    Cannot mate or choose not to mate due to selective reproduction?

    Both. It doesn't matter. Some animals select a mate on song, color or behavior. If any change enough they may "choose" not to mate but it amounts to being unable to mate really. It is entirely possible that we may be interfertile with chimpanzees but we choose not to mate with them (though I have heard rumours ). If we can't get interested then we can't mate.


    This message is a reply to:
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    Coyote
    Member (Idle past 179 days)
    Posts: 6117
    Joined: 01-12-2008


    Message 37 of 47 (493902)
    01-11-2009 3:28 PM
    Reply to: Message 34 by RAZD
    01-11-2009 1:22 PM


    Re: What comes after Pelycodus?
    RAZD--

    That text figure 10 is an excellent way to display and interpret the data. It is far superior to the standard charts we see.

    And, for creationists, the thing to note is there is no "missing link" in that sequence, nor are there any gaps to be filled. There is a gradual transition, most likely made up of a series of micro-evolutionary events which over time added up to macro-evolution (speciation), just like we've been saying for years. And all members of the population can truly be said to be transitional between their ancestors and their descendants.

    This also illustrates the fallacy that creationists often challenge us with--"If that chicken suddenly gives birth to a lizard what's that poor lone lizard going to mate with?"

    While your figure shows evolution through time, the example of ring species gives the same example contemporaneously--with geography rather than time being the separating factor. The advantage of that form of speciation is that all transitional populations are still alive, from end to end, so that they can be studied while still living.

    [quote]

    Ring species provide unusual and valuable situations in which we can observe two species and the intermediate forms connecting them. In a ring species:

    • A ring of populations encircles an area of unsuitable habitat.
    • At one location in the ring of populations, two distinct forms coexist without interbreeding, and hence are different species.
    • Around the rest of the ring, the traits of one of these species change gradually, through intermediate populations, into the traits of the second species.

    A ring species, therefore, is a ring of populations in which there is only one place where two distinct species meet. Ernst Mayr called ring species "the perfect demonstration of speciation" because they show a range of intermediate forms between two species. They allow us to use variation in space to infer how changes occurred over time. This approach is especially powerful when we can reconstruct the biogeographical history of a ring species, as has been done in two cases. [b]Source [/quote]


    Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
    This message is a reply to:
     Message 34 by RAZD, posted 01-11-2009 1:22 PM RAZD has responded

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    RAZD
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    Message 38 of 47 (493903)
    01-11-2009 3:30 PM
    Reply to: Message 35 by onifre
    01-11-2009 1:54 PM


    Re: Evolution after Speciation - review
    Thanks onifre

    What actually drives speciation...?

    Quick answer - evolution: adapting to more than one ecosystem. A species population inhabiting two or more ecosystems will undergo different selection pressure in each one. If interruption of gene flow, or "reproductive isolation," occurs, then divergence can reach the point that daughter species do not interbreed when they have the opportunity.

    See

  • Definition of Species for more.

    Could you give a more laymen explanation, please?

    See asian greenish warblers, California Ensatina salamanders, discussion of ring species and article on Ring species as bridges between microevolution and speciation for more information.

    Rather than speciation branching in time these can be thought of as speciation branching in space.

    Does this mean the species know which members within their group are better suited for survival and they hangout together insuring a better success rate? Like some elitist group of birds weeding out lesser members, eventually leading to a parent/daughter population split?

    It is not unusual for a species to inhabit several ecologies, making partial adaptations to each. If there is sufficient separation between ecologies, they can form hybrid zones in between pockets of relatively stable ecologies. The populations in those pockets will tend to adapt specifically to that pocket ecology, even though they can still share gene flow through the hybrid zones, eventually around to the other varieties.

    There is also an effect called the "Wallace Effect" (Alfred Russel Wallace was the "other" Darwin ... and is sometimes called the "father of biogeography": the "Wallace Line" is also named after him):

    quote:
    The Wallace Effect is the hypothesis that natural selection can contribute to the reproductive isolation of incipient species by encouraging varieties to develop barriers to hybridization.

    Note that this means that a species in a stable environment will tend to select for the most average phenotype, and thus stay relatively the same from generation to generation (stasis in the punk-eek terminology).

    quote:
    When two varieties of a species had diverged beyond a certain point, each adapted to particular conditions, hybrid offspring would be less well adapted than either parent form. At that point natural selection will tend to eliminate the hybrids. Under such conditions natural selection would also favor the development of barriers to hybridization, since individuals that avoided hybrid matings would tend to have more fit offspring. This would contribute to the reproductive isolation of the two incipient species. [1]

    Note how this ties in to the ring species issue discussed above, with varieties separated by small hybrid zones: incipient speciation.

    If that is right, my next question would be, wouldn't that almost guarantee the parent populations extinction, since it's a split of better suited species from their lesser suited kin?

    Depends on how you view extinction: they continue in each daughter population. Now it may be possible for an intermediate daughter population to go extinct, could even be due to competition from the end varieties if they overlap far enough, and that would de facto leave the remaining varieties - the ones that don't interbreed - as new species.

    Cannot mate or choose not to mate due to selective reproduction?

    Yes. It doesn't matter as the result is the same: the daughter populations no longer share mutations by gene flow, and thus diverge from generation to generation.

    I hope when you're done weeding out the creationist babel you can continue with a more detailed explanations, thanks for another great thread.

    I don't have too much trouble with creationist babel comments that discuss the topic, only when they try to move the topic to something else or dodge the issues. They can assert silly things, such as genetic barriers, just as anyone without a full understanding of biology (and that includes me) can, and it provides a "teaching\learning opportunity" which can benefit others.

    For instance, it seems I am going to have to "bone-up" on Biostratigraphy to be able to go further with the available information on evolution after speciation, and be able to show how step by step, generation to generation, greater diversification of descendant lineages is achieved after speciation.

    quote:
    Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at some other section. The fossils are useful because sediments of the same age can look completely different because of local variations in the sedimentary environment.

    Biostratigraphy takes the relative age relationships of layers, by the principle of superposition, and then finds the fossils that show the succession of life from generation to generation, from layer to layer, and looks for fossils that are specific to a single layer to then use as an "index fossil" to compare ages of layers in other locations.

    Except that I want to turn it around and look at the original stratigraphic data points that establish the lineage of the fossils in time. I want to find the succession of forms of life in the different layers, as was done for Pelycodus above, extending further than a single speciation event. Strato-biology anyone?

    We know from Pelycodus that as species evolve over time that they become different from their ancestors, and at some point reach sufficient difference that we poor humans need to arbitrarily divide them into different species to discuss those differences.

    This would also occur after speciation, and because there is no sharing of genes\mutations\hereditary traits between the two new species that each will go through this process in different ways.

    The questions are: how far does this divergence go, and how fast does it get there?

    Enjoy.

    Edited by RAZD, : deleted dupes


    we are limited in our ability to understand
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  • RAZD
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    Message 39 of 47 (493904)
    01-11-2009 3:55 PM
    Reply to: Message 37 by Coyote
    01-11-2009 3:28 PM


    Stratigraphic Biology
    Hey Coyote,

    That text figure 10 is an excellent way to display and interpret the data. It is far superior to the standard charts we see.

    Yes, it correlates age, location and fossil diversity in one simple graphic.

    Of course paleontologists do this with individual finds: the document the dates, the sedimentary layers, the locations, and the ecology with each fossil found.

    Another presentation that is similar, but the geographic information is presented more as a schematic than the actual layer by layer used by Gingrich is the horse evolution:


    Click to enlarge

    And it only shows Genus stages with actual fossils. Imagine this with the same detail as in Pelycodus. We know there is a lot of information available, it is more a matter of making the correlation than finding the data.

    Stratigraphic framework of early Pliocene fossil localities along the north bank of the Cimarron River, Meade County, Kansas

    quote:
    Abstract

    The stratigraphy of early Pliocene (early Blancan) fossiliferous sediments exposed in canyons along the north bank of the Cimarron River in Meade County, Kansas is described as part of a larger, ongoing project to create a refined biostratigraphic model for late Neogene and Pleistocene mammalian fossil localities from the Meade Basin. Because the utility of previously named formation and member names is questionable, we introduce a set of informal names for stratigraphic units in our study area. Sediments in the region are up to 34 m thick, and include a basal sand and gravel (?Bishop gravel?) at least 9 m thick, overlain by up to 17 m of lightto pinkish-gray, fine-grained sand and silt, with interbedded calcium carbonate layers. These fine-grained sediments are overlain in turn by a second, 8.5 m-thick sand and gravel (?Wolf gravel?) that is itself overlain by about 5 m of calcareous silts culminating in a thick caliche. The stratigraphic positions of fifteen fossil localities, some with rich vertebrate assemblages, were determined in this study. The sites are found in a variety of sediments representing fluvial, pond, spring, and sinkhole depositional environments. Rodent fossils are especially common, and certain taxa, such as the geomyids, sigmodontines, and arvicolids, support the stratigraphic hypothesis based on field mapping. This combined stratigraphic and faunal information provides an essential part of the early Pliocene component of the Meade Basin Neogene and Pleistocene faunal database, to be used to examine the history of biological diversity in southwestern Kansas.

    Introduction

    The purpose of this paper is to present the stratigraphic framework of rocks previously referred to the Pliocene Rexroad Formation in canyons immediately north of the Cimarron River in southern Meade County, Kansas (figure 1). This project is part of a larger effort to develop a refined biostratigraphic model for the entire Meade Basin, leading eventually to a detailed examination of small mammal community evolution over at least the past five million years. In a series of studies from 1936 until his death in 1973, the late C.W. Hibbard and his students provided a faunal and stratigraphic succession for the basin (see bibliography of C.W. Hibbard in Smith and Friedland, 1975). The lowest part of this succession includes mammalian assemblages from the Rexroad Formation and rocks referred to the Rexroad Formation. Most of these older assemblages were recovered from localities in upland areas away from the Cimarron River where stratigraphic correlation is very difficult because the sites are located in small outcrops isolated by ranchand farmlands. Early in this project we recognized that the longest sections and more extensive exposure in relatively deep canyons along the Cimarron River might provide a superposed series of mammalian localities from which a more refined biostratigraphy could be determined.


    Sounds like the stuff we want, but no graphic presentation.

    Enjoy.

    Edited by RAZD, : sp

    Edited by RAZD, : added info after horse chart


    we are limited in our ability to understand
    by our ability to understand
    Rebel American Zen Deist
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    This message is a reply to:
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    onifre
    Member (Idle past 1023 days)
    Posts: 4854
    From: Dark Side of the Moon
    Joined: 02-20-2008


    Message 40 of 47 (493940)
    01-11-2009 8:22 PM
    Reply to: Message 36 by NosyNed
    01-11-2009 2:45 PM


    Re: speciation drivers
    Hi Ned,

    It used to be thought that only if a population was separated geographically could a speciation event occur. This is called "allopatric" speciation. In this case it might be "driven" by lots of things. Great distance might do it if the genes can not flow easily throughout the range. Note the ring-species case: if part of the ring is killed off (by whatever) then there are two (or more) separated populations. Once that is true the the accumulating changes to the now separate gene pools will eventually (and this appears to take perhaps, millions of years for mammals) will be completely incompatible. (E.g., lions and tigers have been separated for that kind of time and are nearly completely separate).

    We now know that many things can drive speciation. E.g., there is a parasite of (I think) fruit flies (don't remember too well) that changes them so only infected animals can breed with each other. It is an immediate separation of populations. There have been cases (many in plants, fewer in animals) where a chromosome number change separates the populations. This can produce nearly "instantaneous" speciation.

    A mutation changing something like a birds song can cause a separation of a population into those without is and those with it.

    So basically what you're saying is not only can the environment cause speciation, but, the species itself can create conditions that drive them to speciation. Ok. I thought only environmental adaptation was the 'driving' force.

    No. They don't "know". Some survive some don't.

    Didn't phrase it properly. The lesser adapted species are weeded out by ONLY natural selection or by sexual selection as well?

    It may be that the disruption is by a environmental change (a big city appearing?) in the home range of the parent sub-species and it goes extinct or it maybe that the range is disrupted enough to reduce the gene flow to very, very low levels.

    Say then that the disruption causes A and X or A and Y to co-exist now in the same environment, would that force the 2 to eventually mate again, perhaps spawning off a new species. Or will one of them have to go?

    Take your lion/tiger example. Say some sort of environmental change causes these two daughter species to co-exist. There will definitely be competition for food. So, would one have to take out the other?

    It is possible to have a speciation event and have both parent and daughter populations do just fine in the same area.

    Well, an environmental change that causes speciation could not give both equal survival rates, right?

    If we can't get interested then we can't mate.

    Cool. Makes sense.

    Thanks Ned.


    "I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

    "I never knew there was another option other than to question everything"--Noam Chomsky


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    onifre
    Member (Idle past 1023 days)
    Posts: 4854
    From: Dark Side of the Moon
    Joined: 02-20-2008


    Message 41 of 47 (493942)
    01-11-2009 9:08 PM
    Reply to: Message 38 by RAZD
    01-11-2009 3:30 PM


    Re: Evolution after Speciation - review
    Hi RAZD,

    Quick answer - evolution:

    But as Ned noted, speciation can occur by a mutation to the species, or some other cause, like his parasite in the fruit fly example. I figured that the species would evolve, but I meant more along the lines of, is this solely driven by environmental changes or can the species itself cause conditions to seperate?

    As Ned noted, both, but, a non-environmental speciation isn't covered in the links you gave me...

    quote:
    Speciation often begins when a single species becomes geographically separated into two populations. Individuals cannot travel between the populations, preventing the two populations from interbreeding.

    ...so is it both or not?

    It is not unusual for a species to inhabit several ecologies, making partial adaptations to each. If there is sufficient separation between ecologies, they can form hybrid zones in between pockets of relatively stable ecologies. The populations in those pockets will tend to adapt specifically to that pocket ecology, even though they can still share gene flow through the hybrid zones, eventually around to the other varieties.

    There is also an effect called the "Wallace Effect" (Alfred Russel Wallace was the "other" Darwin ... and is sometimes called the "father of biogeography": the "Wallace Line" is also named after him):

    quote:
    He suggested the following scenario. When two varieties of a species had diverged beyond a certain point, each adapted to particular conditions, hybrid offspring would be less well adapted than either parent form. At that point natural selection will tend to eliminate the hybrids.

    According to this hybrid species will be eliminated. But as with the question I asked Ned, if 2 daughter species find themselves having to co-exist, would that cause one of the two to be eliminated?

    Note that this means that a species in a stable environment will tend to select for the most average phenotype, and thus stay relatively the same from generation to generation

    Sexual selection...?

    Depends on how you view extinction: they continue in each daughter population. Now it may be possible for an intermediate daughter population to go extinct, could even be due to competition from the end varieties if they overlap far enough, and that would de facto leave the remaining varieties - the ones that don't interbreed - as new species.

    When you say intermediate, would this be a the hybrid type, that will be selected against?

    Yes. It doesn't matter as the result is the same: the daughter populations no longer share mutations by gene flow, and thus diverge from generation to generation.

    Ok.

    I don't have too much trouble with creationist babel comments that discuss the topic, only when they try to move the topic to something else or dodge the issues.

    It seems like that's all they do. I've been waiting for this thread to take off since I had so much interest in it. It kept getting held up with deviating "comments".

    Biostratigraphy takes the relative age relationships of layers, by the principle of superposition, and then finds the fossils that show the succession of life from generation to generation, from layer to layer, and looks for fossils that are specific to a single layer to then use as an "index fossil" to compare ages of layers in other locations.

    Except that I want to turn it around and look at the original stratigraphic data points that establish the lineage of the fossils in time. I want to find the succession of forms of life in the different layers, as was done for Pelycodus above, extending further than a single speciation event. Strato-biology anyone?

    We know from Pelycodus that as species evolve over time that they become different from their ancestors, and at some point reach sufficient difference that we poor humans need to arbitrarily divide them into different species to discuss those differences.

    This would also occur after speciation, and because there is no sharing of genes\mutations\hereditary traits between the two new species that each will go through this process in different ways.

    The questions are: how far does this divergence go, and how fast does it get there?

    I wish you success in this, sorry, don't know shit about it. But, I will ask you questions when you figure it out. :D

    Just a question that maybe along the lines of what you're looking for, wouldn't you say that there is no end to the divergence until something occurs to the species?


    "I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

    "I never knew there was another option other than to question everything"--Noam Chomsky


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     Message 42 by NosyNed, posted 01-11-2009 11:44 PM onifre has responded

        
    NosyNed
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    Posts: 8837
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    Message 42 of 47 (493953)
    01-11-2009 11:44 PM
    Reply to: Message 41 by onifre
    01-11-2009 9:08 PM


    Re: Evolution after Speciation - review
    But as Ned noted, speciation can occur by a mutation to the species, or some other cause, like his parasite in the fruit fly example. I figured that the species would evolve, but I meant more along the lines of, is this solely driven by environmental changes or can the species itself cause conditions to seperate?

    I think you are still a bit mixed up (perhaps my fault). There are lots of ways that a single gene pool (an interbreeding population) can be separated so the gene flow is reduced. It seems as we learn more we find that there are a big bunch of ways that a gene pool can be split. It is as simple as that.

    Once it is split then mutations will happen differently to the two pools. Moreover, even if the same mutation occurs in both pools it may be selected for in one pool and against in the other.

    All of this depends on the exact circumstances: How different are the environments; what is causing the split (geography, mutation, niches) and so on. On what I think are rare occasions a common mutation to a few individuals can split them off instantly. For plants this can be one individual. The parent can be one species and the many seeds can be a different one, never to meet again in a common gene pool.

    According to this hybrid species will be eliminated. But as with the question I asked Ned, if 2 daughter species find themselves having to co-exist, would that cause one of the two to be eliminated?

    Again: It depends. Over and over this will be the answer. If they compete for exactly the same resources then yes one will probably be eliminated. (or there will be some quasi-stable state reached). But if the split happens because they occupy slightly different niches then no both may survive in close proximity. Sticklebacks in lakes in this province have speciated in not very big lakes with one living mid lake and one near shore (IIRC).


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     Message 41 by onifre, posted 01-11-2009 9:08 PM onifre has responded

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    onifre
    Member (Idle past 1023 days)
    Posts: 4854
    From: Dark Side of the Moon
    Joined: 02-20-2008


    Message 43 of 47 (493969)
    01-12-2009 7:30 AM
    Reply to: Message 42 by NosyNed
    01-11-2009 11:44 PM


    Re: Evolution after Speciation - review
    Once it is split then mutations will happen differently to the two pools. Moreover, even if the same mutation occurs in both pools it may be selected for in one pool and against in the other.

    Ok, now im getting it.

    On what I think are rare occasions a common mutation to a few individuals can split them off instantly.

    Wouldn't it require that the mutation be in a large portion of the population before a split into parent/daughter can occur?

    You did say rare, im just wondering how rare?

    Again: It depends. Over and over this will be the answer.

    Noted. I think im understand why, too many variables, right?

    But if the split happens because they occupy slightly different niches then no both may survive in close proximity.

    Cool.

    Thanks again Ned,

    - Oni


    "I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

    "I never knew there was another option other than to question everything"--Noam Chomsky


    This message is a reply to:
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    RAZD
    Member
    Posts: 19754
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    Message 44 of 47 (493975)
    01-12-2009 8:21 AM
    Reply to: Message 43 by onifre
    01-12-2009 7:30 AM


    topic drift - please discuss speciation elsewhere
    Onifre

    ...so is it both or not?

    Either. Reproductive isolation has occurred and the two populations now reproduce and evolve independently.

    According to this hybrid species will be eliminated. But as with the question I asked Ned, if 2 daughter species find themselves having to co-exist, would that cause one of the two to be eliminated?

    Not hybrid species, hybrid zones. It is still one species until isolation occurs. The zones will be eliminated as hybrids become less viable than either of the two daughter populations. As the numbers decrease the zones will cease to exist, completing the reproductive isolation of the two daughter populations.

    You did say rare, im just wondering how rare?

    Irrelevant to this thread.

    The point here is that speciation has occurred. How does this effect the evolution of the two (or more) daughter species to evolve further.

    If you want to discuss speciation, I suggest a new thread.

    Enjoy.


    we are limited in our ability to understand
    by our ability to understand
    Rebel American Zen Deist
    ... to learn ... to think ... to live ... to laugh ...
    to share.


    • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

    This message is a reply to:
     Message 43 by onifre, posted 01-12-2009 7:30 AM onifre has responded

    Replies to this message:
     Message 45 by onifre, posted 01-12-2009 7:06 PM RAZD has responded

      
    onifre
    Member (Idle past 1023 days)
    Posts: 4854
    From: Dark Side of the Moon
    Joined: 02-20-2008


    Message 45 of 47 (494029)
    01-12-2009 7:06 PM
    Reply to: Message 44 by RAZD
    01-12-2009 8:21 AM


    Re: topic drift - please discuss speciation elsewhere
    Either. Reproductive isolation has occurred and the two populations now reproduce and evolve independently.

    Ok.

    Not hybrid species, hybrid zones. It is still one species until isolation occurs. The zones will be eliminated as hybrids become less viable than either of the two daughter populations. As the numbers decrease the zones will cease to exist, completing the reproductive isolation of the two daughter populations.

    Ok.

    If you want to discuss speciation, I suggest a new thread.

    I think I understand all of the variables now thanks to you and Ned so that won't be needed.

    Thanks again,

    - Oni


    "I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

    "I never knew there was another option other than to question everything"--Noam Chomsky


    This message is a reply to:
     Message 44 by RAZD, posted 01-12-2009 8:21 AM RAZD has responded

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