Ecology, Week 4
Ecology, Week 4 LIFE 320
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This 6 page Class Notes was uploaded by Rheanna Gimple on Wednesday September 21, 2016. The Class Notes belongs to LIFE 320 at Colorado State University taught by Dale R Lockwood in Fall 2016. Since its upload, it has received 10 views. For similar materials see Ecology in Biology at Colorado State University.
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Date Created: 09/21/16
Evolution and Life History Evolution Part 2 • Genetic drift: random evolutionary force o Stronger in smaller populations o Results in fixation of alleles -‐ tends towards homozygosity o Never maintains allele diversity • Always decreases diversity • Base pair mutation typ es: o Point mutation: single base pair change • Due to errors in DNA replication or repair o Insertion/Deletion: add/lose base pair(s) • AKA shift mutations o Synonymous: silent mutations • Change in base pair but amino acid remains the same • Creates redundancy in genetic code o Non-‐synonymous: base pair change causes amino acid change • Mis-‐sense: amino acid change • Non-‐sense: stop/start codon change • Frame-‐shift: insertion/deletion • Chromosomal mutations: o Changes to area of a chromosome • Deletion • Duplication • Inversion • Translocation o Duplicate entire chromosome • Trisomies o Duplicate entire genome • Polyploidy • Migration o Gene flow: transfer alleles from one population to another o Allele frequencies change in a given gene pool (population) • Doesn't change frequency in entire species o Implies individuals reproduce with individuals from different populations • Not just physical migration • Adaptation: trait naturally selected for because it increases fitness o Adaptations come from: • Mutations that create new phenotypes § If creates more fitness, that trait will become more common • Can be deleted by random chance § Mutations allow for populations to change in new ways over time § Less fit genotypes controlled by differences in fitness o Constraint: • Environment influences adaptations § Beneficial adaptation in one environment can be disadvantage in another • Some differences are not adaptive • Population genetics: study of how genetic composition of populations change o Mathematically predictable rates of genetic change • Phenotypic plasticity: ability to have different phenotypes for a genotype under different environmental conditions o Phenotype, not genotype, responds to natural selection • Phenotype is combination of genes and environment o Natural selection favors organisms with phenotypic plasticity • Able to adapt better o Spatial variability due to microhabitats and/or temporal variation • Areas of environment with different distinct conditions § Temperature, food, humidity, water • Organism may have to move from one microhabitat to other to satisfy constraints o acclimations • Phenotype changes due to change in environment § Winter coat, enzyme with certain temperature optima, red blood cell count • Capacity usually reflects an organisms' range of environmental conditions • Species in constant environments lose ability to acclimate § Uses a lot of energy to acclimatize • Acclimations usually can be reversed • Can occur during development § Persistent structural environmental conditions give rise to structural changes § Longer response times • i.e. developmental stage or life long • Polyphenic traits: multiple different phenotypes due to environmental conditions o i.e. snow hares -‐ brown in summer, white in winter • Why populations differ: o Environment o Genes o Combination of both • Lots of genes respond to a certain environment • Adaptions can be advantageous an d disadvantageous o Environment dictates success • Ex: if a species has recently dealt with a bacterial pandemic, population will have a high proportion of individuals with resistance to that bacteria § Population without the pandemic will have low proportion of individuals with resistance -‐ no selective pressure Life Histories • Resource allocation • Trade-‐offs • Strategies for reproducing and when to die • Life History: o The schedule of life of an individual in a species • Age of maturity • Number of offspring • Life span o These include behavioral and physiological adaptations • Important points o Evolution should act to maximize optimal life histories • Pushes towards optima but things push against that o Not all life histories are perfectly optimized: • Constraints: § Not enough time and/or genetic variation to evolve to new optimum • Tradeoffs: § Size v. number of offspring § Number of offspring v. parental survivorship § What is best for mother, father and offspring can be different • Life history tradeoffs o Individuals need to maximize reproduction with limited time and energy • Tradeoffs are required § Investments in one part of reproduction means less investment in another • Example of tradeoffs § Invest in growth v. early reproduction § Invest in current offspring v. future offspring § Invest in a lot of small v. few, big offspring • Classic Study o David Lack, Oxford University -‐ placed life histories in evolutionary context: • Tropical songbirds lay less eggs per clutch than temperate counterparts • Lack thought this difference was because of different abilities to find food for babies: § Birds nesting in temperate regions have longer days to find food during breeding season • Lack's proposal § 3 key points: suggesting life histories shaped by natural selection: • Because life history traits (i.e. nu mber of eggs per clutch) contribute to reproductive success -‐ also influence evolutionary fitness • Life histories vary in consistent way due to factors in the environment • Hypotheses about life histories are subject to experimental tests • An experimental test § Someone could artificially increase the number of eggs per clutch to show that number of offspring is limited by food supply § This proposal has been tested a lot • Goren Hogstedt used European magpies • About 50% survive up to a clutch of 7 • Over that all tend to start starving • Living in the oceans o Lecithotrophy • Egg yolk provides nutrients § Larvae don't have to find food right away • Few big larvae o Planktotrophy • Feed on plankton • Lots of smaller larvae o Right whales-‐ produce single calf every 3 -‐5 years • Reproductive tradeoff in sand crickets o Female's have two forms: • Long-‐winged forms § Resources allocated to flight § Delayed ovary development (produce fewer offspring) • Short-‐winged forms § Poorly developed wings and limited ability to fly § Quick ovary development • Reproduce early • You can grow or reproduce, not both o Reproductive effort: time and energy allocated to reproduction o Trade-‐off between growth, maintenance and reproduction • negative relationship between annual growth and allocation of reproduction § If you grow more you reproduce less • Fecundity: ability to reproduce sexually o Largely depends on size o Maturity and fecundity are size dependent • Age and size go together o Range of fecundity is vast • Rats reach maturity in 20 days • Rockfish take 15 years • Saguaro cacti at 50 years o Ectothermic animals • Production of offspring in fish increases with size/age • Gizzard shad: at 2-‐yr produces 59,000 eggs, at 3 -‐yr produces 379,000 eggs o Percentage of annual production (energy) devoted to reproduction: • Perennials: 15-‐20% • Wild annuals: 15 -‐30% • Crops: 25-‐30% • Maize/barley: 35 -‐40% • Lizard: 7-‐9% • Salamander: 48% • Larger organisms tend to devote more energy o Annual fecundity and annual mortality rate correlate • Species differ in timing of reproduction o Semelparity • Use all resources for one reproductive effort, then death • Most insects, other invertebrates, some fish (salmon) and a lot of plants (bamboo, ragweed) • organisms are often small, short lived, grown in disturbed habitats • Environmental effect can be disastrous • Example: Talipot palm § Leaves up to 5 m in diameter § Flowers once at 30 to 80 years § Dies after fruiting • Example: octopus § Produce thousands of eggs before starving to death while protecting eggs o Iteroparity • Produce less young at one time but repeat reproduct ion throughout lifetime • Multiple reproduction cycles § balance growth, maintenance, escaping predation, defending territory, etc. against reproduction • Most vertebrates, perennial herbaceous plants, shrubs and trees o Oncorhynchus mykiss: rainbow trout/ steelhe ad salmon • Can do both o Anadromous: migrating up freshwater rivers from ocean to reproduce o Catadromous: migrating down rivers to ocean to reproduce o Why semelparity (or iteroparity) • Three proposed explanations § Bet hedging model • Iteroparity preferred in varied/unpredictable environments • Risky to limit reproduction to one year if there is a bad year • Some semelparous plants can be in habitats that are more variable • Annuals and biennials are typically found in habitats that are transient and unpredictable • Successionally (disturbed sites) • Cities • Edaphically (deserts and dunes) • Related to soil content • In annual plants • Strong seed dormancy gives a lot of variation in generation time within each cohort • In non-‐annual • Varied post-‐germination maturation times • possibly genetically based • likely due to micro-‐environmental changes § Reproductive effort model • Want offspring produced to be at max compared to offspring forgone • When reproductive success per unit of reproductive effort has positive correlation, semelparity favored • If no/negative relationship, iteroparity favored § Demographic models • Mathematically analyze when semelparity makes sense • Semelparity favored when • High population growth rate • Low adult survivorship (after first reproduction event) • Long time periods between reproductive events • High % juvenile survivorship • Early senescence • Senescence: traits that contribute to death at old age • Increased mortality and decreased fecundity over time • senescence is life-‐history trait • Most organisms show drop off in fecundity and increased risk of mortality with age • senescence seem to be under natural selection • Selection against early senescence rises as survivorship rises • Lots of early deaths mean senescence isn't selected against • Environment works with genetics for senescence
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