Triassic-Jurassic: paving the way for giant beasts?
Background and Mass Extinctions: The
Alternation of Macroevolutionary Regimes
By: David Jablonski
This paper starts off by
discussing background extinctions. He explains that for the marine bottom
dwelling organisms, which make up much of the fossil record, there are three
factors that affect survivorship during background extinction. They include:
larval development, geographic range, and the number of species within the
taxonomic group. He discusses that speciation and extinction rates are higher in
nonplanktotrophic species than in planktotrophic ones. He then goes into
geographic range and discusses how significant differences were found among
restricted, intermediate, and broad ranged species. Species richness also plays
a role. Clades with lower number of species are more likely to die due to
random extinction than clades with higher numbers of species. Bivalves and
gastropods in the late Cretaceous have higher geologic durations when species
richness was high. He states that endemic genera’s evolutionary patterns are a
good index of pure background processes. Larval development and species
richness had no effect of survival of mollusks during the end cretaceous mass
extinction. It was more directed at geographic range at the clade level.
Planktotrophs and non-planktotrophs showed the same amount of extinction. 55
percent of the widespread bivalves survived while 9 percent of the endemic ones
did not. There were similar results for the gastropods. Reversal of the
background pattern where only 29 percent species rich survived and 47 percent
species poor survived. After the extinction event normal background levels
returned and a different constellation of traits that favor survival arose.
Endemic bivalves diversified during background times but suffered greatly
during all four mass extinctions. Taxonomic structure had little effect on the
survival of a clade in the end Cretaceous extinction. He discusses that the
micro and macro evolutionary processes are disrupted and replaced by mass
extinction events. Mass extinction is not random and is not an intensification
of background patterns. Results imply that mass extinctions play a larger role
in faunal change than given credit for. Traits that increase survival during
mass extinctions are poorly correlated with traits that increase survival
during background events. This means that important or often useful traits of
adaptations can be lost due to mass extinction events regardless of their role
in survival and reproductive success.Questions:
Why are mass extinctions considered non-random and not an intensification of background patterns?
What is it about mass extinction events that allow them to disrupt the current evolutionary patterns in such a drastic way?
It is believed that we are currently in the 6th mass extinction. What is the likelihood that current species will be able to evolve new traits in time to “save” them from extinction? (Not including species being hunted to extinction) Do you think that certain background traits could be helpful when dealing with a mass extinction event?
An Explanation for Conflicting Records of
Triassic-Jurassic Plant Diversity
Mander et. Al.
The study in Greenland was aimed to provide quantitative estimates of Tr-J terrestrial plant diversity. Along with an assessment of the nature and timing of changes in vegetation during the TR-J. Results showed sporomorph records do not preserve complete estimates of biodiversity because of their lack in preserving specialized reproducing plants. For example plants such as; cycads, bennettites, and seed-fern were underrepresented in the records. This may explain some of the discrepancy between macrofossils and sporomorph records. It was concluded that in Greenland there was not supporting evidence, in the sporomorph records, of diversity loss in the Tr-J. While, macrofossils showed evidence of abrupt biodiversity loss and changes in forest structure. The Greenland experiment concluded this discrepancy was due to the poor representation of certain plant lineages. The article concludes by stating sporomorph records show greater diversity loss during the PETM (Paleocene-Eocene Thermal Maximum) which was not a faunal mass extinction than during TR-J mass extinction.
Questions:
1) After reading the article, do you believe sporomorph is an accurate way of examining biodiversity loss? Why or Why not?
2) Do you believe macrofossils are the best way to examine biodiversity loss or is there a better type of fossil record to examine?
3) Based on evidence from this article and prior knowledge, do you believe there was a great loss of plant biodiversity after the TR-J extinction?
Background extinction represents the effects of competition and natural selection on a taxon, whereas mass extinction is the effects of an extreme alteration of the environment in which a taxon lives. During background extinctions, clades are protected from extinction, if their life cycle facilitates gene flow (planktotrophic larval stages), prevents genetic drift (endemic to a broad biogeographic range), and is diverse with species. In this scenario, the success of a clade is based on how well it has adapted to an environment. Mass extinctions, however, impact the entire biosphere (“impact” being the operative word for the End-Cretaceous extinction). A substantive adjustment to normal conditions occurs. Clades that are unable to quickly adapt to a drastic change in their environment will go extinct. There is some protection for those taxa that are dispersed throughout a wide geographic area, as some parts of the globe will be more susceptible to environmental disturbances than others.
ReplyDeleteUsing sporomorph fossils or macrofossils alone will produce an inaccurate representation of plant abundance and diversity in the fossil record. Ferns, for example, have a delicate, leafy structure which would only fossilize under ideal conditions. Their spores, however, are tough, chemically inert structures that fossilize much more readily. Gymnosperms, with their ligneous mature phase and seed phase, are expected to fossilize at comparable rates. The extremely small, lightweight pollen of monosulcates would be disseminated over a large area and, in any given location, would be of a lower concentration than the mature plant. I think the statistical model that Mander, Kürscherner, and McElwain developed is a valuable tool for assaying extinction of plants.
Jablonski 1986
ReplyDeleteJablonski states that evolutionary patterns indicate that mass extinction are not entirely random. He does note that though these extinction patterns are different than those observed during background extinctions, there are still prevailing traits which significantly influence an organism’s likelihood of survival during mass extinctions. Traits which may have given advantage to an organism may curry them no favor in times of mass extinction, and the same applied to traits which previously were not beneficial that may grant benefit during times of rapid change. Considering the current rate of global warming, it seems unlikely that the majority of life will be able to evolve traits that will save them. Organisms in the end-Permian mass extinction were unable to evolve quickly enough to adapt to the warming climate at that time, so it seems unlikely that modern organisms will be able to.
Mander et al. 2010
The authors acknowledge that local and regional evolutionary patterns were strongly influences by the fossil assemblages selected to perform analysis. They also note that changes in community structure are not reflected accurately by sporomorph records. Therefore, I would not trust sporomorph records to give an accurate picture of a region’s overall biodiversity patterns, including extinction events. Adding macrofossils would fill in more of the story, but I believe an extensive survey incorporating multiple fossil records would be required to get the most accurate biodiversity record possible. It seems that relying too heavily on one specific genera or species is beneficial while looking specifically at that group, but can lead to biased conclusions when a pattern is expanded to an entire region or group of organisms. When the authors complied their fossil data, they concluded that there was an overall loss of plant biodiversity during the TR-J extinction, though the various species and genera level extinction rates varied based on which fossil record was examined.
Jablonski 1986
ReplyDeleteMass and background extinctions do not follow the same patterns in terms of extinctions. Background extinctions are survived by certain developmental traits, large distribution the landscape of constituent species, and great species richness. Mass extinctions, on the other hand, of lineages was enhanced by having a large distribution over a large range of geographic areas. Mass extinction events do not depend on survival strategies developed during background extinctions, but seem to wipe out whole lineages indiscriminately. It seems that developing new traits to better survive the 6th mass extinction is not likely to occur, if looking at past mass extinctions provides any clues. Developing traits to enable species to widely colonize the globe would be helpful, otherwise, traits that are developed during periods of background extinctions will not be helpful in surviving future mass extinctions.
Mander et al. 2010
Using sporomorphs to determine biodiversity loss does not represent reproductively specialized plants, nor does it take into account emigrations and extirpation of plants in an area. When examining biodiversity loss, it is best to include different approaches, such as sporomorphs and macrofossils, to gain a more comprehensive look at what was happening during this time as each of these tend to exclude different populations of the plant world. Given the information that I have, I do not believe that there was a large loss of plant biodiversity at the Tr-J extinction. Due to ecological changes in specific areas (those closest to the bolide impact and those further away) factors such as the atmospheric make-up, amount of sunlight, and changes in temperature lead to changes in forest structure and the development of vast grasslands which supported different animal species. The emigration extirpation of plant species also helped to keep plant biodiversity high.
1. Mass extinctions are considered non-random because they don't follow the same patterns as background extinctions. Background extinctions are considered normal in the grand scheme of things; sometimes species die out, and another species will fill the empty niche. Rather than an intensification, mass extinctions tend to be triggered by something large scale happening- even if the large scale trigger is happening over time, it is all a kill mechanism.
ReplyDelete2. The events that cause mass extinctions disrupt current evolutionary patterns by being on such a large scale- half of the species on the planet going extinct quickly is not an insignificant event. Not only do a lot of evolutionary trees abruptly end, but the ones that remain have a lot of empty niches to fill. This can cause adaptive radiation- so while mass extinctions do cause disruptions, they can also cause rapid evolution.
3. The likelihood that current species will be able to evolve new traits to save them from extinction seems pretty low. Especially since the climate has changed so drastically in only a few hundred years due to human causes- a few hundred years isn't enough time to evolve drastic new traits at all.
4. Certain background traits could be helpful, but it is impossible to say which ones. Some mass extinctions affected more life in oceans than others, for example, but one cannot say what traits would give a species more of an edge when it comes to survival.
1. Using sporomorphs is not an accurate way of examining biodiversity - it limits the biodiversity to sporomorphs and does not portray the way the plant life actually looked during a certain time.
2. Macrofossils are a good way to examine biodiversity loss, but with the sporomorph question, it isn't best to only look at one type of fossil. The best way to get an accurate idea of biodiversity is to look at everything that can be looked at, really.
3. Based on the data, it looks like there was a lot of loss of plant biodiversity after the TR-J extinction, and the degree of which species were affected varied. Not all species were affected equally.
Background extinction is seen as somewhat of a norm that occurs regularly because of competition natural selection whereas mass extinctions are caused by some large scale change in the environment like a bolide impact or volcanism. These events are the beginning of a downward spiral that leads to the proximate cause for the mass extinction. These events cause such a drastic change in a relatively short amount of time that species living can't evolve in time to survive these changes. I don't think that many organisms will evolve in time to survive a sixth mass extinction, just like the ones proceeding it there will likely be a sudden proximate cause that will lead to the mass extinction where only organisms already evolved to survive will survive. I also don't believe background traits would help organisms to survive because mass extinctions and background extinctions are caused from such different things that these traits won't help during a mass extinction.
ReplyDeleteI don't believe sporomorph is an accurate way of examining biodiversity loss because it is not an accurate way of portraying the plant life that was actually alive at this time period. I believe that when examining biodiversity loss the best thing to do is to include different approaches to looking at the biodiversity to be able to see a more complete view of what was happening during this time as all approaches tend to leave out certain aspects that others do not. Based on the evidence it looks as though there was a lot of plant biodiversity that was lost after the TR-J extinction even though not all species were affected in quite the same way.
Mass extinctions disrupt evolutionary patterns significantly. Even though mass extinctions wipe out over 50% of species, by definition, they allow for adaptive radiation to happen, that is, they allow for the species that do survive to have a major increase in species diversification. We have learned from lectures that these mass extinctions have really paved the way for mammal diversification, in giving one example. There are always background extinctions happening, this is the "circle of life" according to the Lion King. However, mass extinctions are coined non-random because there is always an ultimate cause that greatly changed the composition of the earth, whether or not that is in the atmosphere, hydrosphere, biosphere, lithosphere, or (more likely) a combination of the above.
ReplyDeleteI do think that we lost a significant amount of terrestrial life in all of the more recent mass extinctions, possibly even some during the Devonian mass extinction. I think that our fossil record of terrestrial life is better the more recent the fossil, and because of that we have more proof behind our hypothesis of mass terrestrial loss. Many of the plants that we have today will make poor fossils at best, so we can hypothesize in saying that there is much unaccounted terrestrial loss dating back to before the Permian period.
Jablonski Paper Response:
ReplyDelete1) Mass extinctions are considered as non-random processes due to natural selection pressures on species. This sounds simple enough, however, it is really the ability of a clade to survive and outcompete other clades. It also involves the ability of a clade or species to adapt to changes in the environment, for instance, changes that come with climate during occurrences of extinction. The clades that can survive background extinctions can ultimately "survive" mass extinctions, and most likely have better chances of coming back in during recovery periods.
2) Mass extinctions disrupt current evolutionary patterns because although extinction happens regardless, large extinctions wipe out most existing species. Such a large change in numbers surely can disrupt pre-existing patterns. If such a large change occurs so abruptly, patterns are interrupted and need to be re-established.
3) The likelihood that current species will be able to evolve new traits in time to save themselves from extinction is probably near impossible. It would take millions of years to evolve these traits, and even if it were possible, there have been 5 mass extinctions already. There hasn't been much proof to say that our existing species evolved in time to be "saved", at least not definitively. There is enough information to say there was more diversification, however.
Mander Paper Response:
1) Because sporomorphs do not include plants that are reproductively specialized, they cannot determine biodiversity. Sexual reproduction is a huge basis for biodiversity so using something that does not use specialized reproduction to account for diversification does not really make sense. We can use sporomorphs along with other fossils to come up with more of an understanding, but using sporomorphs alone wouldn't do anything for biodiversity as a whole.
2) Macrofossils include a better range of material to examine, but as with any research, I think that the more fossils you can use, the better.
3) According to the data it does appear that there was a large loss of plant biodiversity after the TR-J extinction.
I think that the mass extinctions aren't considered an intensification of background extinctions and are considered non-random because all of the mass extinction events that we know of have clear events that we can link together. Mass extinctions usually occur due to a specific event. For example, a huge LIP event usually leads to significant changes in the atmosphere and environment of the earth, which causes more species to go extinct than they would normally. Significant changes in the environment will lead to more extinctions. I think it is possible that while background extinctions are due to things such as competition between species and not enough niche space, mass extinctions are caused by upheaval in the environment that animals can't readily acclimate or adapt to given the short amount of time that they have to do so.
ReplyDeleteFor the Tr-J Plant Diversity paper, I agree with the paper's conclusion that the sporomorph fossils found aren't representative of certain plant lineages and are therefore biased in terms of the effects that the mass extinction event had on plant flora. I believe that macrofossils are the best thing we have currently to examine biodiversity and biodiversity loss in the past. In the future we may develop technology that will allow us to more thoroughly and creatively examine past biodiversity, but for now macrofossils, in combination with trace fossils and bio/chemical markers, are our best way of studying past biodiversity.
Jablonski Paper
ReplyDeleteMass extinctions are considered non-random, because they follow the pattern of a larger biological cycle that goes from background extinctions to mass extinction environments as far back as we can tell at least on Earth. Mass extinctions are also not considered to be intensification of background extinction rates, because there is no connection between what helps an organism to survive during regular background extinction and what helps an organism survive during a mass extinction period; if it was really just an intensification of background extinction pressures, then we would expect to see the same organisms that do well during background levels be just as good at surviving during mass extinction periods, but we do not see this. Similar to why mass extinctions are not just intensification of background pressures, is why they are so able to disrupt the current evolutionary patterns that can be observed in the background time periods. This is can answered in the same way, because the mass extinction event will almost always favor organisms with a trait or habitat that do not match those who were reigning during the background times, the whole reason it’s called a mass extinction, is because they tend to throw a curve into the evolutionary process up until that point creating environments that greatly favored obscure traits that were not needed until these newly very specific conditions.
Mander et. All Paper
After reading the paper I believe that sporomorphs are not an accurate way of examining biodiversity, because they as with all other limited samples can only tell you so much about a process; in this case they tend to be highly likely to survive this mass extinction event while the rest of the macrofossil record showed a huge spike in extinctions occurring during this time period. I also do not believe that macrofossils are the best way to examine biodiversity, because they too are just a limited sample of all of the life that lived on/in the world at that time period and thus will also only tell us about what impacted them and only them as compared to the “truth”. Based on the fossil evidence from both the macrofossils and the sporomorph fossils, I believe that there was a great loss of plant biodiversity during the Tr-J extinction, but it just did not affect the sporomorphs are much as the event affected the macro fossil species.
Jablonski:
ReplyDelete1) extinctions aren't considered random because not every species has the same chance of going extinct just by chance or bad luck. Its not as if pulled the short straw or didn't pick the right lottery numbers but instead they did not have the traits to allow them adapt quickly enough to survive the massive changes that were occurring. Those clades did not go extinct because they were not valuable but because they weren't able to tolerate or evolve to tolerate the new habitat. These massive events causes not just an increase in extinction in a couple of clades, but wholly affected an environment (i.e. sea, land, etc) therefore it is more than just an intense background extinction, but an extinction which wipes clean the slate in which the changes are occurring.
3) Many species cannot keep up with the rate at which the Earth is changing. There has been a massive change to the composition of land from the 1900s until now, particular with warming and habitat loss. Animals are not given much time to adapt to these changes, as evolution typically takes at least 10,000 years (which is rapid). It is very unlikely that the animals we see here on earth will all survive if we continue the way we are. For example, the Panda is endangered because their habitat is being decreased as populations in China grow. They require a large amount of food each day, which means they need a lot of space to graze and eat from. They also do not reproduce as quickly or as often as other animals (only fertile 2-3 days a year), and take a long time to reach sexual maturity, which gives them less hope and less ability to be able to evolve because they live longer lives with smaller population sizes.
Mander:
1) sporomorphs do not encompass all ways in which plants may reproduce, so like anything I do not think one fossilization type can represent a whole or show diversity of all plants.
2)it is better to include macrofossils alongside sporomorphs to determine biodiversity. These may be more rare or harder to find, but they could possibly bridge the gap between diversity of sporomorphs and other plants present at the time.
Jablonski:
ReplyDeleteMass extinctions are considered non-random and not an intensification of background extinctions because they both target different traits. Background extinctions happen all the time. As far as mass extinctions go, there have only been five. During background extinctions, species are able to adapt and gain traits that are better for survival in that environment. But during mass extinctions, those traits are useless and extinctions occur all over the globe. During times of mass extinctions, the environment changes drastically and in a short amount of time. This causes vulnerable species to go extinct along with other species that just happened to live in the wrong environment, such as the ocean. Background extinctions are different in that the environment does not have a drastic change. Instead, natural selection is occurring where some species are hunted by others or they have poor traits that do not allow them to succeed and they die out. So, a high amount of background extinctions does not equal a mass extinction because they target different traits, such as great geographical ranges, species richness, and living in a certain environment that had the greatest impact for that mass extinction.
Mander:
After reading the paper, I do not believe that sporomorphs are a good way at looking at biodiversity loss. In order to become a fossil, you have to have the right characteristics. There are just some plants and animals that do not meet those standards and therefore do not become a fossil. There are some sporomorphs that were not fossilized during this time period, which may explain why there is a difference in the biodiversity between sporomorphs and macrofossils. I believe using macrofossils to examine the biodiversity is better than using sporomorphs, but fossilization is a tricky thing. I believe we will never fully know the extent of biodiversity on Earths surface because a good amount of species didn't and will never fossilize. The best thing we can do is use multiple fossil records and try to piece them together, but as this paper showes, it is not always that simple.
Jablonski et. al.
ReplyDeleteA. Mass extinctions are not considered random and are not intensifications of background patterns because mass extinctions tend to occur (we think, anyway) when living conditions drastically change, either through ocean anoxia/acidification, changing atmospheric conditions, or a mixture of other factors that all somewhat affect each other.
B. Mass extinctions disrupt evolutionary patterns because they do not give organisms enough generation time to truly adjust to drastic changes in living conditions, and organisms that lack the qualities to persevere, even though they may have reached great success in ideal living conditions, will suffer.
C. If we are currently experiencing a 6th mass extinction (only time will tell), many species will likely not be able to survive. On the other hand, numerous efforts are being made on behalf of some species, whether endangered through human actions or through natural causes such as disease, to preserve a species and help it overcome pressures that are leading toward extinction. Human kind tends to disrupt evolutionary processes in its own way, so it's hard to predict what will happen in the future using only concepts of the past.
Mander et. Al.
I believe that sporomorphs, like many other aspects of the fossil record, do not necessarily provide a complete picture; however, scientists have established an incredible view of the past through what we do have in the fossil record and, therefore, I think sporomorphs should not necessarily be discounted as inaccurate as much as they should be analyzed with the full realization of both their limits and their strengths. I think the same should apply to macrofossils.
I am also interested in an elaboration on why mass extinctions are not random (the Jablonski summary). I got the impression that mass extinctions were random because it impacted species regardless of the development of traits that made them resistant to background extinction. The impression I got from that paper is that mass extinctions present a unique event that is more geographically oriented rather than selection-oriented, which subverts traditional evolutionary patterns.
ReplyDeleteGiven the pressures by the current mass extinction, habitat loss combined with climate change, as well as how quickly it has onset, I suspect most species will struggle to survive or develop traits to aid in their survival, particularly if they are specialized to their niche, have few offspring, and/or long gestation times. Smaller, faster breeding, generalized animals with a large geographic range seem best positioned to survive the difficulties ahead.
I think this article underscores one of the potential problems or complexities in determining extinction events, namely the fossil record's biases toward certain species, families, or clades. It's hard to envision using sporomorph or macrofossil biodiversity will reveal anything compelling, or even reliable. They would require the proper context, particularly herbivorous fauna before and after the extinction event, to contribute to a useful measure of biodiversity loss. Though the results among taxa are inconsistent, overall it certainly seems like there was a significant loss of plant diversity after the Triassic-Jurassic mass extinction.
Based on what we have seen with mass extinctions versus background extinctions, there is not enough time for a species to evolve new traits to save them from the 6th mass extinction. There are environmental changes that are affecting them at a much larger rate than would be seen for a background extinction. With background extinctions, there would be enough time for a species to evolve based on the fact of the slower rate of environmental changes in and around their habitat. Mass extinctions can happen over very large ranges and will cause a snowball effect that will affect land, water, plants, and organisms all in one go. These drastic changes are the cause for mass extinctions and organisms not being able to keep up with their environments. If species can have a very large range compared to the mass extinction ranges, they might be able to survive, but I don’t think one specific background trait could be helpful with mass extinctions. Past mass extinctions have shown to affect large groups of species on a global scale. There were times where some species were hardly effected and then the next mass extinction completely eradicated them all.
ReplyDeleteI do not believe that macrofossils are the best way to examine biodiversity loss. Macrofossils would be missing out on so much more of the environment and species that this would not make up for a good fossil record. There are other fossil records that would need to be included to give a clearer picture of previous life. Plants are a good example of diversity that are not all found in macrofossils either from their soft parts or small sizes.
Mass extinctions are considered non-random because they do not have the same causations and effects on their environments. Background extinctions are the result of normal competition and natural selection acting on species and perhaps other small-scale environmental changes. Mass extinctions however are the result of intense and abrupt environmental changes that leads to effects on multiple clades of life as opposed to the more focused driven background extinctions. The factors that exert pressure on biodiversity are different.
ReplyDeleteMass extinctions cause such drastic patterns in evolution due to the scale of the event. Typically, mass extinctions are triggered by global events that cause environmental changes that greatly impact existing life- examples are global warming or global cooling due to existing taxa or bollids or weather patterns. After mass extinctions, many taxon disappear completely and global ecosystems can be transformed in biodiversity and abiotic conditions. This allows for a completely different collection of life to take over after.
I may be biased but I think that the causes of this 6th extinction is unique compared to ones in the past. The time-frame and environmental impacts are those that haven’t completely been witnessed before. I think it’s extremely unknown that our current species will be able to evolve new traits to survive. Perhaps species may change their niches or adapt in ways that aren’t going to come from new trait adaptations. Certain background traits could perhaps help but I’m not sure which those would be and how large their effect could be.
If one was to solely base examinations of biodiversity loss off of sporomorph fossil record representation, then no, it isn’t an accurate way. It can obviously cause a wide discrepancy and misunderstanding of mass extinction impacts due to the wide gap of the record. For example the contrast between the marcofossil to the sporomorph record at the end of the cretaceous; which is 70-90% to 25-30%, respectfully. However, the sporomorph record isn’t invaluable because it shows even some of the effects on reproductively-specialized plants.
I think that this question has both a yes and no answer to it. Macrofossils seem to provide very generous evidence of plant biodiversity loss after mass extinctions. Due to the fact that the record shows such abrupt changes, I believe it can be valuable to rebuilding much of our knowledge about not only plant life, but how these species impacted environmental factors along with terrestrial life. The macrofossil records could accompany perhaps records of faunal species to rebuild ecosystem interactions.
I think that if there is a loss seen in macrofossils, then that record is probably a stronger indicator of biodiversity loss over sporomorphs. I think that the loss in macrofossils needs to still be accounted for and that can be lead to the conclusion of there had being a decrease in biodiversity. I think this is where it is valuable to compare numerous beds before and after the extinction event. There is a difference in comparing the abundancy of a fossil and the consistency of its appearances throughout time.
Jablonski
ReplyDelete1.Mass extinction are not considered random because if they where random there would be a better survivorship of clades that are geologically widespread and rich in species however this is not what is seen suggestion some sort or selection is taken place. Even though some sort of selection is taking place this selection is not similar to background selection, as Mass extinction seems to see a shift in high survivorship in widespread clades to disproportionately large survivorship in restricted clades and species poor. In addition Mass extinction seems to affect each regardless of supposed higher chances od survival or how well adapted the clade is.
2.Mass extinctions wipe can wipe out clades regardless of how well adapted they are to the environment prior the extinction event. This can destroy all the evolution that has been taking place to “carefully craft” a well-suited species. It is like someone taking the time fiddle with a design to withstand the reoccurring problems only to have an new never before seen problem that simply destroys what ever you fiddled with only to leave the other object that just randomly seems to have resistance to the event through almost sheer luck. It makes the clade that wasn’t all that successful before more successful because some new space opens up as well.
3.I don’t think there is enough time for current species to evolve new traits if we are truly in a mass extinction event, as these events seem to be random wonton event. I don’t think past adaptation will help too much as mass extinction tend to be caused by pressure that is sudden and not constant to slowly develop resistance too.
Mander et. Al.
1)I don’t think there are an accurate way of measuring biodiversity loss as they do excluded specialized reproduction plants but even though they do exclude these plants there are a bit similar to how fossils in general favored hard bodied organisms and how we can get a general idea of what is happening but simply to remember the biased that comes along with using this method as no fossil method is going to be perfect.
2)I don’t think macrofossils are better in general as once again different sampling methods will favor different things, but macrofossils do make identifying the clade a lot easier opposed to using pollen or spores.
3)I would imagine there would be a great loss in biodiversity during the extinction event as the environment is changing rapidly. In addition the interaction animals and plants have could cause negative impacts on the plants or negative ones. The environmental changes may have been less harsh for plants though as more CO2 is general beneficial towards plants along with decreased herbivory.
Mass extinctions are considered non-random because of the mechanistic way they occur, in that an ultimate cause leads to proximal causes of extinction. An example of how mass extinctions can alter evolutionary patterns drastically is how they wipe out existing species/families, creating new niches and therefore new evolutionary patterns to be followed. Since mass extinctions occur over a short period of time, I do not think victims of the 6th mass extinction will be able to have the opportunity to evolve thier way out of extinction.
ReplyDeleteI do not believe using sporomorph to examine biodiversity loss is effective. It is too narrow of a group to be able to accurately tell about the full loss of biodiversity. However, while we may never know the full story, using macrofossils and sporomorphs do help to provide a slice of the full picture, which is still valuable. Though individual results varied, the article seemed to come to the conclusion that there was an overall loss of plant biodiversity after the Tr-J extinction.
Mass extinctions are considered non-random because, unlike background extinctions, they are not the result of ordinary, ongoing biogeological interactions. Instead, they are the result of catastrophic events that vastly modify Earth’s environment in a widespread manner. Whereas background extinctions are generally characterized by gradual factors, such as poor adaptation to ongoing environmental changes, mass extinctions are studied in order to determine a specific event that caused sudden detrimental change and resulting massive loss of diversity.
ReplyDeleteMass extinction events disrupt evolutionary patterns because they do not allow for the gradual change in a species. The sudden exposure to extremely harsh conditions makes it difficult for species to adapt and evolve according to their environment over time. Furthermore, only those organisms who are capable of thriving in this new environment will show substantial levels of diversification directly following a catastrophic event.
If we are in the 6th mass extinction, I don’t see it being very likely that many current species will be able to evolve new traits in time to avoid extinction. Evolution is not a quick process, and organisms must accumulate changes at a rate that is more rapid than human industrialization if they are to be capable of persisting in this continually fluctuating environment.
After reading this article, it does not appear that analyzing sporomorphs will provide us with an accurate representation of biodiversity patterns from that time. If they do not provide us with records of entire groups of specialized plants, it would be hard to truly quantify a loss of diversity by only taking these fossils into account.
Mass extinctions are considered non-random and are not an intensification of background patterns because a mass extinction represents a massive event that takes out many niches and organisms. Organisms are not able to adapt to the changes that are happening so quickly and therefore are more than just an intensification of background extinctions. Background extinctions allows organisms to adapt to changes much more easily than when a mass extinction occurs because these extinctions occur due to a smaller or less abrupt kill mechanism. A mass extinction happens from something much larger and much quicker resulting in the difference of intensifications of each. There is a drastic change due the larger impacts or events occurring, which changes the depth of how much a mass extinction kills off organisms and diversity.
ReplyDeleteI do not think sporomorphs are an accurate way of determining or examining the biodiversity loss. A sporomorph is a preserved pollen or spore from plants, which I think can determine some biodiversity but I do not think it is relative for examining all of biodiversity loss. I think there needs to be more evidence to observe and determine characteristics and diversity in a particular time. I do not think they preserve enough material or evidence to show any diversity loss or they are not being fossilized correctly and in the right conditions to show a lot of biodiversity loss.
Jablonski
ReplyDeletea) Mass extinctions are not considered random and are separate from intensifications of background extinctions because they're caused by dramatic changes in the environment and characterized by lag periods of diversity afterwards and then a radiation in diversity.
b) The extinction events have to be characterized with elements that are beyond species' abilities to adjust. This allows for large-scale destruction of environments and species.
c) I don't think it's very likely that species will be able to evolve new traits in time to save them from the 6th extinction, because then it would not be a mass extinction, right? Certain background traits that allow certain individuals to survive should be able to contribute to an eventual diversifying radition, however!
Mander
1) I don't think so because sporomorph records lack in preserving specialized reproducing plants.
2) Macrofossils also display some discrepancy in the fossil records, but seem to be more consistent than sporomorphs.
3) I believe there was a large loss of plant diversity after the TR-J extinction based on the fossil records indicating the slight lag period.
Mass extinctions are considered non-random due to catastrophic events that leave species unable to evolve to a new environment. They way I understand mass extinction events are, they are affects from abiotic factors that impact more than one species causing them to go extinct in a short amount of time, where as background patterns happen quiet often due to biotic factors due to competition of species in a geological location. It’s interesting to hear about what species the 6th mass extinction will effect because humans are the driving factors in this extinction, this creates a higher number of background extinctions to occur, which open up niches for new species to fill. Although, we are unable to see the evolutionary process happening right now I do believe that it is happening.
ReplyDeleteAccording to the Mander article Macrofossils, and Sporomorph’s should be the only evidence used to examine biodiversity, I think both would aide in the research being analyzed during this time frame providing credibility to other types of data collected in examining biodiversity. I do think that there was a great loss of plant biodiversity after the Triassic-Jurassic extinction due to temperature, soil, and humidity change, we maybe able to understand this information if we studied core samples in dry lakes to determine what types of erosions have occurred over time, and understand the change in organic matter that have decomposed during a specific time frame.
Jablonski paper:
ReplyDeleteMass extinctions are not considered an intensification of background extinctions because of the mechanisms that mass and background extinctions are controlled by. In a background extinction, there are specific traits that assist an organism to adapt to its environment for survival. However, in a mass extinction you may have a particular catastrophic event that alters a large scale of the environment. For example, if the earth were struck by a certain bolide, the ability for an organism to quickly adapt and have some traits that allow them to quickly adapt to the change in atmosphere will determine its survival. If the 6th mass extinction were approaching in the near future I think it will have sudden and catastrophic effects and many organisms would not be ready to adapt when this happens. I believe the ultimate cause for the 6th mass will be human caused and could be as serious as other mass extinctions such as the Permian or Devonian extinctions.
Manner et al paper
I do not believe that measuring the sporomorph is an accurate way of measuring biodiversity. This type of measuring of biodiversity only takes sporomorphs into account and is leaving out other plants that have specialized reproductive qualities. Therefore if I was conducting this study I would find alternative studies to include in measuring biodiversity for plants. However in my option, macrofossils is a better approach to take when looking at plant biodiversity, with macrofossils you have a larger range of plants to study as opposed to the limitations of sporomorphs. If I were conducting this study, I would include sporomorph, macrofossils and alternative studies to gain broader knowledge of the biodiversity. Based on the evidence claimed by the paper, It is my opinion that it lacks a significant amount of data to support the claim of great loss in plant biodiversity in the TR-J extinction
Background and Mass Extinctions: The Alternation of Macroevolutionary Regimes
ReplyDeleteBy: David Jablonski
Mass extinctions are considered non-random and not an intensification of background patterns because the mechanisms in which cause mass extinctions greatly affect/alter the environment in a catastrophic manner and a majority of the species over a relatively short period of time while background patterns are always occurring but don't have the same affect (may be due to organisms not being able to adapt the the ongoing changes in the environment, species competition, etc). Mass extinction events disrupt the current evolutionary patterns in such a drastic way because they are usually events in which occur suddenly and impact resources/natural environment (ocean anoxia, compounds in the atmosphere/toxic chemicals, etc). I think the likelihood that current species will be able to evolve new traits in time to "save" them from the 6th mass extinction is not likely. It takes organisms time to develop and perfect new traits and even more time for the trait to be present in all the organisms by reproduction. I think certain background traits could be helpful when dealing with a mass extinction event such as being able to camouflage, burrow, fly, etc.
An Explanation for Conflicting Records of Triassic-Jurassic Plant Diversity
Mander et. Al.
After reading the article, I do not believe sporomorph is an accurate way of examining biodiversity loss because this technique doesn't take into account other plants that may have very different mechanisms/traits. I do believe macrofossils are the best way to examine biodiversity loss because you are able to look at multiple species of plants and have more diversity to consider. I think using both techniques is the best option because you will get more information and can compare all the findings from both techniques. Based on evidence from this article and prior knowledge, I do believe that there was a great loss of plant biodiversity after the TR-J extinction because there was evidence of a lag period in which it took a long time for things to diversify (which is usually expected to occur after a mass extinction event) and the article seemed to come to the conclusion that there was a great loss of plant diversity after this mass extinction.
Jablonski et al. 1986
ReplyDelete1.) Background extinctions are considered normal. Species evolve and species die out due to poor/ obsolete survival strategies. Mass extinction are not a continuous pattern and they involve a massive die off of a majority of species in a relatively short period of time. It is not an intensification of background extinctions because there seems to be a single cause of the event.
2.) They are a die off of a massive amount of species whom, we would assume, would eventually continue evolving. Initially, mass extinctions eliminate evolution in progress. However, mass extinctions also create vacant niches which allow for massive adaptive radiation. Therefore, one could propose that they are major drivers of evolution.
3.) The likelihood that current species will evolve new traits to "save" them from extinction depends on their adaptive abilities to change. For example, generalists would be more likely to survive, over specialists, because they are not as limited in their resources.
Mander et al. 2010
1.) I do not believe sporomorph is an accurate way of examining biodiversity loss because it limits the discussion of biodiversity. Sporomorph do not account for reproductively specialized plants. This is an important concept when determining biodiversity. We must examine more than sporomorphs if we want to accurately state which plants and animals were alive during this time period.
2.) Macrofossils are great indications of biodiversity. However, it would also be beneficial to examine other aspects of the fossil record as well (including sporophorms).
3.) The data does suggest a large loss of plant biodiversity. So yes, I am inclined to believe the research.
Jablonski 198?
ReplyDeleteIn my opinion, mass extinctions are considered non- random because of the drastic effect that they have on the environment and the species that are existing at the current time. They do not follow the same criteria as a background extinction. Background extinctions are more of the norm, with speciation, completion for natural selection, whereas mass extinctions are a grand event and force species to survive. If we are really heading towards the 6th mass extinction I don’t think that species in my opinion have any time in order to evolve this magical trait in order to save them from extinction. I think that when it happens and if it happens animals of all shapes and sizes will be in trouble because of the drastic harm we as humans have done to this world.
Mander et al. 2010
I don’t really think that using sporomorphs/macrofossils alone is an accurate way to examine biodiversity loss, I think that it will only produce an inaccurate representation of plant loss and abundance. No, I do not think that macrofossils are the best way to examine biodiversity loss because not everything lands in the proper place in order to become a fossil. In my opinion I think that there was a great loss in plant life throughout the Mesozoic.
They are considered non-random because they don’t have to do with evolutionary fitness but rather external events that are normally sudden, rapid, and intense and cannot be entirely prepared for; for example, an asteroid impact or volcanic eruption. Background extinctions occur more slowly over time and are related to evolutionary success.
ReplyDeleteMass extinction events happen on vast geographical scales and affect most, if not every, layer of trophic hierarchies. By disrupting catastrophically many parts of a system, the system becomes broken in many ways and will require huge amounts of time to recover.
Certain species can adapt to our quickly changing environment, like some bacteria and insects that reproduce and evolve rapidly; however, most species will not be able to adapt as fast as change is occurring. In our situation, it would help to be very small, aridity and high temperature resistant, and to live in varying habitats.
In many cases, the parent of a spore is unknown and sporomorphs can be morphologically similar among species of the same genera, meaning they cannot always provide detailed evidence on the state of biodiversity in a fossil record. Having said that, they can be used as a strong estimate for biodiversity and biodiversity loss, but on higher taxonomic scales than the species level.
Macrofossils provide diverse “batches” of biodiversity that provide significant information of species loss as well as species pairing patterns or relationships between plant species. I think, though, that they should not be examined on their own, but cross-referenced with other fossils (such as sporomorphs) to fill information gaps and to balance the weaknesses and advantages of each method of examining biodiversity.
Yes there was loss at least somewhat, because the fossil record, despite biases and incompleteness, reveals obvious biodiversity loss of plants during this time, meaning other types of vegetation could likely have gone extinct despite that they are not represented as well.