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Unformatted text preview: Scientific method, Evolution & Ecological Genetics Overview ES 100: Lecture 2 Logistics Add codes will be emailed to students being admitted to the class. Should be done with this later today or tomorrow. You must have signed up on the waiting list to get in.
– https://waitlist.ucsb.edu/ 46 People on waiting list. 22 Slots in class. 24 Seniors on waiting list. ALL SENIORS WILL BE ADMITTED. ALTERNATIVES: – EEMB 168 (see email@example.com) – EEMB 120 (firstname.lastname@example.org) Sections: Added students may not have gotten into section of their choice. Email TAs and let them sort it out. We want you to have section that is best for you. But rooms are tiny. We have requested bigger section rooms but may not receive them. Go to assigned rooms. Class web site Will be created on gauchospace. Space just freed up for that today. Site should be up by Thursday. I will post some ppts from lecture. They contain no notes only slides. Reserve right to deviate from ppts and from syllabus. Notices will be posted when relevant. Recap: lecture 1-key points. Define ‘ecology’ Distinguish it from ‘environmentalism’ Describe some reasons why ecology should be useful to all ES majors. Today:
I. II. III. How we do ecology? Examples. Evolution. Definition. Fundamental elements of theory of evolution by natural selection. Ecotypes: Between population variation. I. How to do ecology….. the scientific method
• • • *• • • • • Observation Question Hypothesis formation Hypothesis testing Data collection Data analysis Conclusions Theory formation ow to test hypotheses:
A. Do an experiment or series of experiments. B. Take advantage of a natural experiment. C. Take detailed observations. Look for best explanatory variable or do before/after observations. A. An experiment Observation: Young oak trees are largely absent Observation: from the California landscape. from Question: What factors limit oak recruitment in California savannas and grasslands ? UCSB’s Sedgwick Reserve, Santa Ynez Approximately 85% of CA oak woodlands are grazed by livestock Hypotheses: Oak establishment limited by livestock grazing grazing Oak recruitment limited by deer browsing Oak recruitment limited by small mammal browsing Hypotheses: Oak establishment limited by….. •Livestock grazing •Deer browsing •Small mammals (gophers, ground squirrels) •Non-native annual grasses •Low rainfall – low water availability AN EXPERIMENT •Establish grazing exclosures •Plant acorns inside versus outside livestock grazing exclosures Add treatments with - deer exclusion - small mammal exclusion •Replicate exclosures •Plant in multiple years It isn’t always possible to have a It perfect experimental design perfect Small mammal exclosure tubes are nested within deer exclosure Analyze Acorn Survival to Sapling: Importance of cows (open plantings with vs without cows) Small mammals +deer (with/without cows) Deer (with/without cows) By planting in different years, you can look at the effect of rainfall year Dr. Claudia Tyler, CCS email@example.com B. Natural experiment:
Brown trout introduced to NZ Spread all over, maybe eliminating native species How do trout affect native fish and food web? Hypothesis: Trout have no affect on native fish or on food web structure or productivity Trout reduce native fish and invertebrates and alter productivity. Compare food webs in streams Compare with Trout Native fish and no trout No fish at all Problem with these comparisons? Trout may be absent from some streams because those streams have different chemistry or are physically different Thus troutless versus trout filled streams may differ for reasons other than the presence of the trout. Stream physical and chemical factors must be compared and controlled for when possible Sample within same stream above and below waterfalls:
TROUT ABSENT (native=Galaxias present,or no fish) TROUT PRESENT (Galaxias gone) Data: analysis and presentation Fig. 1.8, text Findings: Native fish mostly lacking where trout are present (probably from predation) Behavior of invertebrate herbivores is affected by trout Invertebrate biomass reduced in trout areas Algal production is higher in trout areas Study used a ‘natural experiment’ Study approach approach Assumes differences between stream food webs = due to trout and not physical and chemical differences between streams Use of this sort of approach = common. E.g. Comparison of polluted versus unpolluted lakes. OR comparing different aged lava flows to understand plant succession. C. Before/after control impact
CANNOT DO REPLICATED CANNOT EXPERIMENT Observation: Power plants produce warm water effluent. Hypothesis: Effluent from power plants alters marine communities. Establish nearby ‘control’ area out of effluent pathway Monitor impact and control areas for 2+ years BEFORE power plant comes on line and then for many years after. I. Scientific methodsummary Describe basic steps in scientific method Describe three different ways of testing hypotheses. What are some of assumptions with latter two methods? II. Evolution. Nothing in biology makes sense except in the light of evolution. (Dobzhansky) But equally, very little in evolution makes sense except in the light of ecology: ecology provides the stage directions through which the ‘evolutionary play’ is performed. Your text book Evolution Change in the heritable characteristics of a species over time. Darwin & Wallace Theory of Evolution by natural selection…. Fundamental Elements
1. 2. 3. Individuals within populations are not identical Some of the variation between individuals is genetically based (heritable) Most individuals in wild populations die before they reproduce. Adult populations are a subset of what ‘could’ be there if there were no environmental filters. 1. Individuals do not contribute equally to subsequent generations. Some leave more offspring than others. These contribute differentially to the future. (THEY HAVE GREATER FITNESS) Fitness Evolutionary term for your genetic contribution to future generations Comes from yourself + your relatives Depends on environment Ecology Study of environmental filters, including species interactions, that act on the fitness of individuals and genetics of populations Evolution Key Element: Genetic Evolution variation variation Within individual level: Among individuals within population: – heterozygosity Landscape level (between populations over space): – Ecotypic variation/differentiation Disease…if no genetic variation within Disease…if population , everyone susceptible…. population America chestnut blight, changed New England forests, Early 1900s Sudden oak death pathogen in California
Live oak: genetic variation in resistance exists, not all infected trees die (Pathogen = selective agent) Tan oak: no genetic variation for resistance. All infected trees die. (Pathogen = agent of extinction) Ecologically Ecologically Genetic variation influences extent of community change with selective force Will community dominance change with changing selective forces? III. Ecotypes: Between population III. variation variation Genetically distinct populations of a single species that appear to be adapted to slightly different environments. How do we determine whether observed phenotypic variation between populations is genetic? between California poppy (Escholtzia Californica)
Foggy coastal areas, ‘ecotype’ Interior, hotter climate ‘ecotype’ Coast Interior Shorter stature Perennial Thicker leaves Mildew resistant Taller, faster growing Annual Lvs thin, more vibrant green Mildew susceptible Does environment make them look Does different or are they genetically distinct ? distinct Get seeds from each Grow in common garden Do they retain their distinctions when grown in common conditions? Ultimate goal=identify if differences Ultimate between populations are ‘adaptive’ between DEFINE ADAPTATION….. •Trait that increases your fitness in a given environment. •If you did not have that trait, you would have lower fitness in that environment. Coast Interior Shorter stature Perennial Thicker leaves Mildew resistant Taller, faster growing Annual Lvs thin, more vibrant green Mildew susceptible Poppies: thorough studies not yet done but anecdotal evidence suggests the ecotypes are genetically distinct Interior form grown at coast = highly susceptible to mildew Coastal form in interior = inferior competitor Effects on individual reproduction ? population dynamics ? persistence in restoration sites? When is a trait ‘adaptive’? When Can you just assume trait differences are adaptive? adaptive? Mainland bush poppy Santa Cruz Island bush poppy Narrow leaves Smaller leaves Shorter stature shrubs Large, wide leaves Plants almost treelike in stature Why ?? Hypotheses:
Differences are environmentally induced, not genetic Biotic selective pressures different on island (fewer herbivores, pathogens etc) Physical environment more harsh on mainland (smaller leaves adapted to harsher environment) Accident of history (original island colonist had bigger leaves?) Possible experiments: Establish common gardens (mainland and on island). Grow both forms. Subject forms to environmental stress, herbivores, pathogens… Establish measures of performance Compare between populations grown at ‘home’ vs away and between ecotypes. Many plant studies with reciprocal Many transplanting or common gardens transplanting
ANIMALS FORM ECOTYPES TOO BUT ecological importance harder to test Text example of sea anemones…
•Transplanted three colonies from each site to all other sites •Measured proportion of adults brooding young after time •Green island forms do best everywhere! •Strickland Bay forms do worst Why do we care about ecotypic Why differences in natural populations? differences Restoration: use best adapted genotypes Conservation rare spp: ensure appropriate genetic structure of population you are protecting. Ethnobotany: preserveindigenous genetic diversity Insure survival of species if disease wipes out some populations Ecological genetics questions:
What role does lack of genetic variation play in population extinction? How do population size and genetic variation relate ? How does genetic variation influence role that a species plays in a community? How will populations/species change with climate change? How does human harvesting of wild populations influence genetics? Can you…. Define evolution by natural selection Define fitness, adaptation, ecotypic Describe essential elements for evolution? variation Figure out if two populations are different ecotypes? When are genetic differences When strong enough to result in speciation? speciation? Selective force = pollution NOT SPECIATION Members of a species can breed in Members nature and produce fertile offspring For speciation to occur there must be a barrier between populations to prevent interbreeding OR selection must be very strong Interbreeding = gene flow Speciation only possible without gene flow unless selection is extremely strong Barriers….. Finch speciation Galapogos Islands Ecotypes become different species Ecotypes when they can no longer interbreed and produce successful offspring and Barrier could be – Physical/space – Temporal differences in breeding – Physiological (chemical, morphological) – Behavioral or mate recognition Evolution with gene flow
Plants on and off serpentine soils California state rock =Serpentinite Serpentine soil = high in heavy metals (nickel, lead, arsenic, etc) + abnormally high in magnesium Mimulus guttatus widespread Mimulus nudatus Serpentine endemic M. guttatus is the “parent” of M. nudatus. M. nudatus tolerates higher Ni and Mg and lower Ca than M. guttatus. It also flowers earlier than M. guttatus, and attracts sweat bees rather than bumblebees. Species are NOT interfertile. Speciation Model: First step in the origin of M. nudatus is Mg and Ni tolerance. Pollen still likely being interchanged. Further strong selection on serpentine favored adaptations to drought and low nutrients, including early flowering time and flowers that attracted different pollinators. This led to the fixation of genes for intersterility with M. guttatus. How do we know they are different How species ? species Look different Cannot produce fertile offspring ! Species = unit of operation for Species much of ecology much
Yet we do not always know if two populations can interbreed or not or how genetically distinct they are. BUT we need to group individuals into units and species = reasonable classifications. So we mostly use morphology/phenotype to classify species. (rarely do breeding experiments) Ecology: Ecology: study of distribution and abundance abundance of species Must include history….current distributions might reflect past environments, or speciation events ...
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- Fall '08