lectures4,5,6-collegeofforestry,guangxiuniversity

1、Lecture 4Evolution and Life Histories,Principles of EcologyEben GoodaleCollege of Forestry, Guangxi University,Readings,Up until now I have made reading notes for each lecture.I will make one more of these for Tuesda

2、y lecture (my wife presenting).It will be available Sunday night.After that, we will have 2 chapters of textbook (ocassionally 1) per lecture.,Readings,The textbook chapters will be available as .xps files (10 pages pe

3、r file).I will give out today pendrives with Chapters 9-12 (Apr 4, Apr 7 lectures).Please DO NOT give copies of these files to anyone outside of class (technically illegal).I do not like distributing like this, but do

4、 so because textbook not distributed in China, and very expensive to buy privately.,Readings,Please do readings before class, because it will serve as a preparation for class.The exam material will, however, be directly

5、 take from lectures, not the textbook.Before the exam, I will make a summary for you on the concepts in the lectures that I will test you on.Lecture PPTs will continue to be available before class on Thursdays and Sund

6、ays.,Schedule,Lecture times:,Review I,We have been talking about how organisms interact with their environment, obtaining water, maintaining their temperature, and obtaining energy.We have described features of organism

7、s which are “adapted（適應(yīng)）” to their environment (fit their environment due to evolution).We have described some examples of “convergent evolution（趨同進(jìn)化）”, where different organisms in similar environments look alike.,Toda

8、y we talk more in depth about evolution,Today’s class,EvolutionEvolution as changeNatural selection as mechanism of evolutionOther mechanisms of evolutionSpeciation and evolutionary patternsLife histories,Evolution（

9、進(jìn)化） is change,At the large time scale evolution is modification (change) in living things over time.Contrasted with creationism, which says that:species were developed independently of each otherspecies are fixed enti

10、ties, they do not changecreation was recent,Evolution is change,Things that led Darwin to believe in evolution:FossilsVestigial（退化的） featuresRelations between species,Vestigial features have lost their function, li

11、ke eyes on blind salamanders, or the human tail bone.,Evolution is change,Things that led Darwin to believe in evolution:FossilsVestigial featuresRelations between species,Galapagos “Darwin” finches…The birds on di

12、fferent islands resembleeach other but also have differences.,Evolution is change,Contrasted with creationism, which says that:species were developed independently of each other. Clear relationships among species.spec

13、ies are fixed entities, they do not change. Fossil animals, vestigial features.creation was recent. Evidence of ancient earth.,Question: was Charles Darwin the first to postulate evolution?,Evolution is change,At a smal

14、l time scale, evolution is the change in alleles（等位基因） (or change in gene frequencies) in a population over generations.Example of allele controlling coat color, or beak size.,An allele is an alternative version of a ge

15、ne.,Natural selection is a mechanism of evolution,So how to explain evolution as the small time scale in a population?Darwin postulated natural selection（自然選擇） as a mechanism of evolution (this was his novel contributi

16、on).Let’s review the basic steps in the process.,Natural selection,What are the basic steps in this process:Variation between individuals in traitsThis variation is the trait is heritable（可繼承的）In every generation, th

17、ere are more offspring produced than can survive. Individuals with traits that fit the environment well survive and reproduce.More individuals in the next generation will have the favored trait.,An important distinctio

18、n:phenotype vs. genotype,We see that the first ingredient for natural selection is variation, and we note that if variation is hereditary, natural selection will occur.BUT not all variation is genetic. Some of how an o

19、rganism appears (its phenotype（表現(xiàn)型）) is environmental. Think of a large, spreading tree in a good sunny place, compared to one in the middle of a forest.We should keep in mind that phenotypic plasticity（表現(xiàn)型可塑性） can expl

20、ain variation among individuals.What human examples can you think of?,Natural selection in action,Images from: Freeman and Herron (2001),Darwin’s Finches,Natural selection in action,Daphne Major,Peter and Rosemary Grant

21、,Beak of the Finch1995By J. Weiner,Natural selection in action,1. Variation between individuals in traits,Images from: Freeman and Herron (2001),Natural selection in action,2. This variation is heritable,Images from: F

22、reeman and Herron (2001),Natural selection in action,3. In every generation, there are more offspring produced than can survive.,Images from: Freeman and Herron (2001),# Birds,1975,1979,# Seeds,4. Individuals with traits

23、 that fit the environment well survive and reproduce.5. More individuals in the next generation will have the favored trait.,Images from: Freeman and Herron (2001),,,Natural selection in action,Characteristicof seeds,S

24、mall seeds,Large seeds,4. Individuals with traits（特質(zhì)） that fit the environment well survive and reproduce.5. More individuals in the next generation will have the favored trait.,,,Natural selection in action,,,Images fr

25、om: Freeman and Herron (2001),1976,1978,Review: using another example, explain how evolution occurred,Year,1975,2005,Weight of sheep,Horn length,What Darwin didn’t know: genetics and mutations.,We now know that genetic

26、information is encoded in DNA. Mistakes in DNA copying make mutations（突變）, which create variation.,James Watson and Francis Crick, 1953,What Darwin didn’t know: genetics and mutations.,Mutations can also be larger: like

27、 the deletion of entire parts of a chromosome.In addition to mutation, recombination（重組）, which occurs during sexual reproduction, also produces variation,Mutation as an evolutionary force,Mutation and recombination pro

28、duce variation among individuals, the first ingredients for natural selection.Mutation can also be thought of as a mechanism of evolution because it creates new alleles.,Another evolutionary force: genetic drift,,,,,Gen

29、etic drift（基因漂變） is the change in the frequency of alleles in a population over time through random events,Before,After,Genetic drift,Genetic drift is more important factor in smallpopulations than large ones.,Cheetahs

30、are an exampleof a small population,One example of genetic drift is when a species gets very rare,“Bottleneck”,Demonstration of Genetic drift in simulation:http://sites.sinauer.com/ecology3e/problem06.html,Or when a s

31、mall group of individuals starts a new colony,Another evolutionary force: gene flow,Gene flow（基因流） is when alleles move between populations.Because it tend to make populations more similar to each other, it acts to slow

32、 evolution.,Summary of evolutionary forces,Natural selection: increases frequency of advantageous alleles.Mutation: creates new alleles.Genetic drift: change in frequency of alleles, can lose to loss of alleles in smal

33、l populations.Gene flow: movement of alleles between populations. Tends to decrease changes in alleles.,Only one of these mechanisms of evolution leads to adaptation.Which is it?,Only natural selection creates adaptati

34、ons,Adaptation is the match of an organism to its environment.A great example is the story of the Soapberry Bugs.,The length of beak of soapberrybugs in different populations,There are limit to adaptations,There needs

35、to be the variation for natural selection to work with.The history of animals limits their possibilities. For example, mammals that return to the sea (dolphins) can’t just evolve the ability to breathe under water.Gene

36、 flow often acts against adaptation.The environment is itself changing… so there’s a “moving target”.,Nor can a panda immediately evolve an opposable thumb.,What does natural selection lead to?,What kind of selection

37、was our bird example? Our sheep example?,Stabilizing（穩(wěn)定性） selection,Idea of trade-offs,Size of babies,Low birth weightoften higher riskof infection,High birth weightcomplications at birth,www.kellymannophotography.com

38、/,Disruptive selection,Back to Darwin’s finches …what would happen if twotypes of seeds were available…very large and very small?,www.blackwellpublishing.com,This kind of natural selection is rare and maylead to spec

39、iation…,T. B. Smith, Nature, 1987,Speciation,Speciation（物種形成） can occur when:Two populations become isolatedEach population undergoes evolution, usually through natural selection.When they meet again they do not repro

40、duce.,Speciation,Often occurs because these two populations are in different places (allopatric speciation（區(qū)域種化）), but can occur in same place (sympatric speciation（同域物種形成）) in some circumstances.,Famous example ofsympa

41、tric evolution, whereone population of applefly adapted to new invasivetree species,Speciation,How does Benkman (2003) hypothesize that speciation is occuring?,Assortative mating,Each type of cross-bill has itsown ca

42、ll type (so they canRecognize each other),A phylogenetic (= evolutionary) treeshows history of speciation and extinction,This recent example of whale evolution similar to ideas Darwin proposed in his notebooks in the 1

43、850’s,Story of life includes periods of mass extinction, followed by adaptive radiations,In history of earth, 5 mass extinction（大量消亡） events may have removed many species.Adaptive radiations（適應(yīng)輻射） are when a group of or

44、ganisms give rise to many species in a short time,Evolution and ecology and linked together,Take for example, the case of predator and prey, an ecological relationship.Over time predators become more efficient at catchi

45、ng prey through natural selection.But at the same time, prey become more efficient at escaping predators!Ecology at one instance a product of ever-changing “coevolutionary（共同進(jìn)化） armsrace”.,Evolution and ecology and lin

46、ked together,Ecology also influences evolution:Take care for instance the soapberry bugs.New environments (different trees) make different kinds of beaks adaptive.Leads to two different kinds of populations and eventu

47、ally speciation.Ecological change has lead to evolution.,Today’s class,EvolutionEvolution as changeNatural selection as mechanism of evolutionOther mechanisms of evolutionSpeciation and evolutionary patternsLife hi

48、stories（生活史）,The case study of Nemo,We all know that movie’s are not realistic… but did you know that in real life Nemo’s father probably would have changed sex and turned into a female?Sequential （連續(xù)地）hermaphroditism（

49、雌雄同體）,The diversity and complexity of lifecycles,,Polyp reproducesasexually,Small larva floating at sea,Metamorphosis into attached polyp,Colony of identical polyps,Release egg and sperm,Note :Sexual / Asexual life p

50、hasesMetamorphosis（變形） Estimated 80% of animal species undergo,The diversity and complexity of lifecycles,,,Even more strange (to humans) becauseHaploid（單一的） life stages aremulticellular.,Basic question: to be sexu

51、al or not?,Advantages asexual,,Basic question: to be sexual or not?,Advantages sexualSexual reproduction increases genetic variability (new combinations of genes, recombination)Evidence from C. elegans worms,Life histo

52、ry,The study of life history looks at the timing of how organisms grow, develop, reproduce and survive until death.Stress on trade-offs（物質(zhì)交換）. For example, early reproduction often means low survival.,When firstreprodu

53、ce?,How manyoffspring?,Size of offspring?,How long survive?,Trade-off I: size of offspring,,Trade-off: the bigger your offspring, the less you can have of them.,For plants:,For animals:,Advantages of being BIG,Bigger

54、organisms have fewer predators bigger than they are.Big seeds, eggs have more resources to sustain when very young,Bigger seed, better chance of surviving, growing,Seed size,Seedlingheight,Advantages of being small,Sm

55、all things can disperse fartherThink small wind-blown seeds of weedy plant.Or young fish that is so small it has little resistance to waterflow and disperses widelySmall things can also undergo dormancy（休眠）, and wait

56、until conditions are good to grow.,Trade-off II: age when first reproduce,Trade-off: the more investment in reproduction early,the less survival.,It takes a lot of energy just to find mates (fly example)In addition, an

57、y that puts a lot of energy into reproduction has lessresources for its own growth and survival (tree example),Trade-off II: age when first reproduce,Trade-off: the more investment in reproduction early,the less survi

58、val.,In birds, individuals with increased clutches Survive the winter less well.,From Santos and Nakagawa 2012,Extreme lifecycle called semelparous（只生一胎的） (reproduce only once): annual plants, insects…also bamboo, salmo

59、n (“big-bang”).Only once but big numbers.In contrast humans, perrenial plants are iteroparous（多繁殖的）.Reproduce repeatedly but not large numbers at any one time.,Trade-off II: age when first reproduce,Advantages of shor

60、t, long life,Advantages short life,Advantages long life,Get in, get out of new area,Stick around, but faceThe growing competition,Think weedy plants,r vs. K selection,Putting together these trade-offs, we see two differ

61、ent strategies as extremes on a continuum:“r species（R-選擇物種）”: short-lived species that make many, highly dispersible young. Think of a weed.These species go to a disturbed environment (plowed ground), grow quickly, r

62、eproduce, and leave (are out-competed).,r vs. K selection,“K species（K-選擇物種）”: long-lived species that have only a few, large offspring at a time, invest in each of them.These species live in mature (undisturbed) enviro

63、nments which are competitive (like a high canopy forest).Hence, life histories are influenced by ecological stability,Note: we will understand why these species are called ‘r’ and ‘K’ whenwe talk about population growt

64、h.,Explaining the clownfish strange system,Clownfish live in anemones, stinging stationary animals, and are immune to the sting.Tiny young are planktonic and disperse widelyLarger fish find anemones, which can support

65、several fish; the group of fish at one anemone are not related.There’s a strong hierarchy among these fish: the biggest fish is the breeding female, second biggest breeding male, others are sexually immature.If breedin

66、g female dies, male changes sex and becomes female.,Explaining the clownfish strange system,What could explain this strange system?Predation on reef very high, so small fish leave.Large fish able to invest more in eggs

67、 (the larger gamete), so the largest fish are female.Why do smaller fish wait their turn?,Homework,Go over lecture notes again (Lecture 4).By Sunday night, lecture 5 with notes available on internet; read over.http://

68、sites.sinauer.com/ecology3e/problem06.html This is the problem we looked at in class today.Reading for lecture 5: Petrie 4 on sexual selection in peacocks.,Key concepts,Evolution is the modification of living things o

69、ver time, and change in gene frequencies in a population.Natural selection is the only mechanism of evolution that produces adaptation, a fit between organism and environment. But there are other mechanisms of evolutio