Extinction and Evolution(1/20 and 1/22)
Extinction and Evolution(1/20 and 1/22) GEOL105
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Popular in Earth History
Popular in Geology
This 11 page Class Notes was uploaded by Maddibrooks on Friday January 22, 2016. The Class Notes belongs to GEOL105 at College of Charleston taught by Egerton in Spring 2016. Since its upload, it has received 53 views. For similar materials see Earth History in Geology at College of Charleston.
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Date Created: 01/22/16
Notes 1/20 I. Extinction a. The ultimate death of a species b. Over the past 500 million years, there have been 5 mass extinction events c. Many scientists think we are in the 6 mass extinction event and humans are the cause of it i. Because more species are going extinct faster than any other time in Earth’s history d. Extinction is an inevitable consequence of evolution e. A species is extinct when all interbreeding populations have been eliminated f. Average lifespan of a species is about 2-‐11 million years g. 99.9% of all species that have ever lived are now extinct II. Background Extinctions a. Background extinction rate averages 2.0-‐4.6 families per million years b. Species with wider geographic distributions better resist extinctions i. They adapt better to changes in environment c. Causes of background extinctions i. Disease ii. Habitat disruption 1. Volcano iii. Climate change iv. Introduction of new predators 1. Humans made the Dodo bird go extinct v. Introduction of new parasites 1. Can kill the host vi. Niche competition 1. New, sharper beak can allow another bird to get more grubs from the ground than a bird with a more blunt beak—causing competition for food vii. Ocean current changes III. Mass Extinctions a. Identified by the pattern, duration, breadth, and magnitude i. Short geological time (a few million years) 1. <10 million years; most <5 million years ii. Wide spectrum of habitats 1. Talking about marine and land species IV. Extinction a. Prevent biases in patterns and magnitude of extinction: high sampling worldwide b. Lazarus Taxa i. Appear to be extinct, but may occur later in time (pseudo-‐ extinction) ii. During an extinction event, a species finds a very small habitat to survive through the extinction and then reappear later in time iii. Ex: Coelacanths: no fossil record after 66 million years, but found living today 1. Occupy a very rare environment that typically doesn’t get preserved c. Mass extinction = global change of the physical environment i. Affects widespread species ii. Environmental stress must generally be abnormally severe 1. Stretch across ecological lines 2. Too rapid for species to adapt or migrate from changing environment a. Ex: deforestation, global temperature change (some species are migrating to higher latitudes, because it’s getting too hot for them where they are) d. The Big Five Extinctions i. Ordovician-‐Silurian Extinction 1. 450-‐440 million years ago 2. 60-‐70% of species became extinct ii. Late Devonian Extinction 1. 375-‐359 million years ago 2. 70-‐80% of species became extinction iii. Permian-‐Triassic (Biggest!) 1. 251 million years ago 2. Marine=90-‐97% of species extinct 3. Terrestrial (land)=75% extinct 4. The biggest mass extinction iv. Triassic-‐Jurassic Extinction 1. 200 million years ago 2. 70-‐75% species became extinct v. Cretaceous-‐Paleocene (Most famous) 1. Extinction of the dinosaurs 2. 66 million years ago 3. 75-‐80% species extinct 4. Only one attributed to an asteroid hitting Earth e. Common Proposed Causes i. Sea-‐level change 1. Associated in one way or another with all of the major mass extinctions 2. Changes can affect most environments 3. Issue: sea level changes may pre-‐ or post-‐date the extinction event; no evidence that this causes mass extinction 4. Raising sea level can cause reef environments to become submerged too deep in the sea, so then they won’t be getting enough sunlight, thus becoming extinct ii. Climatic Change 1. Associated with all of the major mass extinctions 2. Temperature is the main force a. Caused by all factors mentioned in Climate Change lecture (1/15) 3. Issue: climatic changes may pre-‐ or post-‐date the extinction event iii. Bolide Impact 1. Proposed for all major mass extinctions 2. Giant asteroid hits Earth 3. First proposed for the Cretaceous-‐Paleocene extinction 4. Evidence: Iridium, microtektites, shock quartz, impact crater a. Spike in Iridium in fossil samples b. Microtektites= tiny molten pieces of glass, thrown up into the atmosphere from impact, and rains back down 5. Issue: may pre-‐ or post-‐date the extinction event iv. Volcanic Activity 1. Proposed for most major mass extinctions 2. Alternative to bolide impact 3. Flood basalts a. Sulfuric-‐acid aerosols into atmosphere i. Thick blanket around the Earth, that prevents sunlight from coming in ii. Causes a freezing cold climate that animals can’t adapt to b. Increased Iridium c. Shock Quartz 4. Both, volcanic activity and Bolide impact have similar evidence, that’s why people go back and forth between which one is the more accurate one V. Recovery a. Survival interval after extinction i. Initial period: only rare appearances of taxa, low diversity ii. Dominant taxa appear to be those that can flourish in stressful conditions (disaster species) iii. Rebound phase: new species start to appear and other reappear as Lazarus taxa iv. Recovery interval: sustained rapid diversification VI. Diversification a. Origins of diversity i. Diversification can occur when evolutionary innovations allow biota to invade empty ecospace 1. Cambrian explosion 2. Ordovician= proliferation and expansion of suspension feeding communities Notes 1/22 I. Evolution a. Decent with modification from a common ancestor i. Passed on via genes 1. Genes that allow a species to survive favorably over another type ii. Populations evolve, not individuals b. Constrained by the history of the evolving organisms i. Had a beak to start with, so the beak is what changed (didn’t grow a whole new beak) II. Fitness a. The ability to survive and pass on genes to the next generation i. Not necessarily the strongest, fastest, or biggest, but the organisms that survive better than others ii. Must reproduce and the offspring with the new characteristic also must reproduce III. Adaptation a. Goodness of fit of an organism to its environment, modified by natural selection i. How well does that organism fit in with that environment? ii. Ex: dolphins vs. sharks iii. The organism that has the characteristic to survive better=adaptation 1. It’s a random mutation 2. A bird can’t decide to grow a bigger beak iv. Must be heritable, functional to the current organism, and increase the fitness of the organisms that have it IV. Adaptations and Exaptations a. Exaptations: functionally useful structures that were not shaped by natural selection for current use i. Biological structures that may have multiple functions ii. Example: Feathers didn’t evolve for flying, initially evolved to keep an animal warm (downy), but over time, they developed other useful functions (flight) V. Natural Selection a. Ability of organisms of one generation to obtain representation in the next generation b. Offspring survive preferentially over other varieties c. NOT survival of the fittest, it’s what survives better! d. Examples i. Variation in traits…some beetles are green and some are brown ii. Differential reproduction…green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do 1. More brown beetles iii. There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis 1. Random! The beetles didn’t decide brown is better, birds just happened to like the green beetles better iv. End result: brown coloration=more offspring=more common in population e. Pesticide Resistance i. Non-‐random survival=what survives is not random, the characteristic that allows a species to survive is random VI. Natural Selection (again) a. Ability of organisms of one generation to obtain representation in the next generation b. Mutations that allow the organism to favorably survive, such as characteristics that allow organisms to: i. Obtaining food 1. Different beaks for different types of food (picture of finches) ii. Avoiding being food (camouflage) 1. Good example of not being the strongest or the biggest, the ability to hide well is what allows it to survive iii. Successful reproduction: helps explain unusual structures and behaviors 1. Acts on behaviors as well as physical structures 2. Male birds with flashy, bright feathers to attract the attention of a female 3. The best features that allow males to attract females 4. Ex: Peacocks a. Male peacocks have an average of 150 eyes i. Usually the ones that mate b. Males with fewer than 130 eyes rarely mate c. Illustrates female choice d. The big feathers of peacocks have no use other than to attract female c. Descent with modification: descendants from a common parent i. Explains the grouping of all organic beings ii. Evolution is the descent with modification from a common ancestor, but exactly what has been modified? iii. Evolution only occurs when there is a change in gene frequency within a population over time. iv. These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change. • “The difference in weight in example 1 came about because of environmental influences — the low food supply — not because of a change in the frequency of genes. Therefore, example 1 is not evolution. The changing color in example 2 is definitely evolution: these two generations of the same population are genetically different” d. Descent with modification: Alteration of Pre-‐existing structures i. Evolution is constrained by the history of the evolving organism 1. Builds upon what is already present genetically 2. Pre-‐existing structures modified to perform functions different from the original function 3. Ex: arms a. Variety of organisms that have the same structure, but it’s slightly modified (can be seen below) VII. Homologous a. Reveals ancestry b. Traits inherited by two different organisms from a common ancestor c. Evolutionary relationship but may have different function. Feature evolved once. d. Example: The arm of a human, the wing of a bird or a bat, the leg of a dog and the flipper of a dolphin or whale are homologous structures i. They have different purposes, but share common traits. ii. They are considered homologous structures because they have a similar underlying anatomy. VIII. Analogous a. Evolutionary convergence in function between unrelated groups. Feature appears multiple times in unrelated lineages b. Similarity due to convergent evolution, not common ancestry i. Convergent evolution: “Process in which two distinct lineages evolve a similar characteristic independently of one another.” ii. Often occurs because both lineages face similar environmental challenges and selective pressures. c. Examples: There are many kinds of flying animals—bats, birds, insects, etc. All of these organisms have wings. Comparing the wing of these animals reveals more differences than similarities. i. Insects have two pairs of wings, while bats and birds have one pair ii. Insect wings lack bones, but bird and bat wings have them. iii. Butterfly wings are covered in scales, bird wings in feathers, and bat wings with bare skin. d. All of these organisms have adapted to life in the air by evolving wings i. These wings evolved independently in each of these groups and don’t indicate that they are closely related, so the possession of wings is an analogous trait IX. Panda’s Thumb a. A modified wrist bone that acts like a thumb (but is not a thumb) b. Allows it to hold bamboo better and eat more bamboo successfully c. Was passed down to offspring and now all pandas have it d. The panda thumb and the human thumb don't grow from the same bones. i. This is more evidence that they are analogous structures. ii. However, the panda thumb is homologous to a wrist bone in humans, and the human thumb is homologous to the first finger in pandas!
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