Ecology- Week Five
Ecology- Week Five Bio317
Virginia Commonwealth University
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This 12 page Class Notes was uploaded by Jayda Abrams on Saturday October 1, 2016. The Class Notes belongs to Bio317 at Virginia Commonwealth University taught by Dr. Bissett in Fall 2016. Since its upload, it has received 8 views. For similar materials see Ecology in Biology at Virginia Commonwealth University.
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Date Created: 10/01/16
Ecology- Week Five 9/26/2016 9/28/2016 9/30/2016 Chapter 7 Continued CAM Photosynthesis (Crassulacean Acid Metabolism): Typically associated with desert plants, cacti and succulents Carbon fixation takes place at night this reduces water loss Low rates of photosynthesis and high rates of water use Slow growth Very high WUE CAM Temporal Separation: Limited to succulent plants in arid environments. Forms four carbon acids at night (still in the mesophyll), and breaks down during the day and creates CO2. Stomata are open at night and in this environment the nights are cool and the days are hot. Loss of Water for Each Type of Photosynthesis C4 380-390 C5 250-255 CAM 50 Review All 3 types of photosynthesis eventually use PGA and enzymes from the C3 pathway. (Ex: Ribose and RuBG) Rate of Photosynthetic Response Curves Different plants adapt This is done by looking at carbon fixations (amount of CO2 in vs the amount of CO2 out) at many levels. Starts linearly then starts to level off. Most level off but some decline. Photosynthetic levels are different for different types of plants and how adaptive it is. Photosynthetic rate increases linearly with photon flux density at low light intensities. It rises slowly with intermediate light intensities and tend to level off. ISAT stands for saturated. It cannot use anymore and it must be deflected or dispersed as heat. Chemosynthesis Occurs with bacteria and hypothermal vents. These vents are places deep in the sea that are well oxygenated, cold/low energy and high pressure. This can also occur on land in soils. Within the soil ammonium can be oxidized making energy for the tree. Chapter 4 Population Ecology Darwin 1835- Darwin studied the Galapagos Islands and observed animals and made predictions of evolution 1838- He theorized natural selection after reading an essay by Thomas Malthus Darwin’s Theory of Natural Selection Organisms reproduce and there may be a chance of variation between individuals (Some heritable) More offspring will be produced than can survive Some genetic drift Some will have advantages and those with better advantages will survive and reproduce. Mendel Monk Studied pea plants Discovered that characteristics are passed from parent to offspring in forms of genes Defined alleles as alternate forms of genes Stated that dominant and recessive genes control and prevent expression Life History- Characteristics or adaptations of an organism that influences reproduction. Strategy- An adaptation (usually behavioral) that increased the success of organism’s population or species (ex: avoiding predators). Fitness- Genetic contribution of an individual descendent to future generations (how many offspring one produces/ how many genes an individual passes on). The main goal is to pass on genes! Life history represents different evolutionary strategies for maximizing fitness. The amount of success life history has is strongly dependent on the environment. This is because the environment controls what works (Ex: Does an organism conserve water? Does an organism have nocturnal habits?). There is always trade off (Ex: photosynthetic preferences) Evolution- Change in population gene frequency through time due to change in selection pressure. Selection Pressure- Differential reproduction and survival of individuals with a population due to the environment or biotic influences. Selection pressure can be natural like climate change or can be artificial like breeding. What about sexual selection? What is a species? A species in a group of animals that interbreed with each other or potentially interbreeding individuals. They share a common gene pool and are reproductively isolated from all other organisms. Distribution is limited by environmental factors (no species can live everywhere) and individual factors (soil nutrients, light, and humidity). Example: Encelia Distribution Multiple species Live near each other but are genetically isolated Reproductively isolated They have adapted to different environments because water availability Different microclimates What is a population? A population is a small subset of species that is a group of inbreeding individuals. This is the unit of evolution because gene frequencies change in the population gene pool. Population distribution is based on resource availability and biotic interactions (of the same or different species). Example: a small bunch of migrating animals. Subdivisions Metapopulation- subdivision population living in separate locations. Minor environmental differences with active exchange of individuals among subpopulations. Plant populations- Many species differ dramatically in forms of one elevation to another. Common garden experiment- Common Garden Experiment- How can one determine if a phenotypic difference comes from the environment or a genotype? Experiment: Grow plants of the same species that vary in phenotype in the same environmental conditions. Then if you observe differences you can conclude that they come from the genotype. This experiment can be done with plants and animals. Common Garden says: If E varies the effect of G on P can vary. Distinctive ecotypes Ecotypes-Population living in separate locations with significant environmental differences and with almost no exchange of individuals (can lead to specialization). Ecotypes are generally distinct. And genetic differences may be expressed in appearance, behavior and physiology. Ecotypes are more common with plants than animals because they cannot move and they are dictated by the environment (ex: potentilla glandulosa). Ecotypes are more common in species with broad geographical range. A broad range leads to variance selection pressure among the population (opportunity for a different trait to be successful). Variations in selection pressure through time will result in changes in gene frequencies within the gene pool. Changes in gene frequencies represent local adaptation resulting in deviation of ecotypes. When does an ecotype become a new species? When the organisms can no longer interbreed. Hardy Weinberg Hard Weinberg principle states that in a population mating at random in the absence of evolutionary forces, allele frequencies will remain constant. Equilibrium occurs within one generation of random mating and return back to equilibrium. Calculating Gene Frequencies - SS (81%) SA (18%) AA(1%) - Frequency of S allele? o SS + 1/2SA = .81 + ½(.18) = .90 (.90) +2(.9x.1 Conditions Necessary for Hardy Weinberg Random mating No mutations Large population size. o Kind of have a dilution effect in large populations, whereas in small populations a mutation can largely affect the population. No immigration or emigration Equitable fitness between all genotypes o Likely, at least one of these will not be met and allele frequencies will change. Potential for evolutionary change in natural populations is very great. The Process of Natural Selection Differential fitness of phenotypes Fitness is the measure of an individual’s contribution of offspring, or genes, to future generations. Natural selection can favor, disfavor, or conserve the genetic makeup of a population. He doesn’t consider it successful until there is an F2 generation. Stabilizing Selection Impedes changes in population. The environmental factors acting on the phenotype are acting against extremes in phenotype in the population. Average state of the phenotype is favored. Directional Selection- Leads to changes in phenotypes by favoring an extreme phenotype; and overtime selection shifts towards a more extreme phenotype. Disruptive Selection Creates bimodal distributions by favoring two or more extreme phenotypes over the average phenotype in a population. Two peaks – bimodal. Two extremes are favored, average phenotype is not favored. Evolution by Natural Selection Natural selection, which changes genotype and phenotypic frequencies in populations, can result in adaptation to the environment. o Depends on heritability of trait h = V /G P o V G Genetic variance o V P Phenotypic variance The genotype determines the phenotype, but the environment doesn’t act on the genotype directly, it acts on the phenotype, which is determined by the genotype. Stabilizing Selection: Egg Size among Ural Owls - Kontiainen et al. o Ural owl (Strix uralensis) egg size differs among females and influenced by the environment. Found egg size was highly heritable Lowered fitness in individuals producing small and very large eggs. o Lowered hating success o Fewer fledglings Directional Selection: Rapid Adaptation by Soapberry Bugs - Carroll and Boyd o Soapberry bug (Jadera haemotaoloma) feeds on seeds from family Sapindaceae. Slender beaks to pierce fruit walls. Distance from outside fruit wall to seeds varies widely – beak length should be under selection. o Found close relationship between fruit radius and beak length. In Florida introduced species had larger fruit, which made them evolve with longer beak length because there would be less competition. Disruptive Selection: Darwin’s Finches - Henry, Hube, de Leon, Herrel, and Podos o Darwin observed “perfect gradation” of beak sizes and in a closely- related group. o 2009 study showed two distinctive groups on Santa Cruz Change Due to Chance: Random processes such as genetic drift can change gene frequencies in populations, especially in small populations. Major concern of habitat fragmentation is reducing habitat availability to the point where genetic drift will reduce genetic diversity within natural populations. Evidence of Genetic Drift: Chihahua Spruce - Picea chichuahahna now restricted to peaks of Sierra Madre Occidental in N. Mexico. o Ledig et al. tested for loss of diversity as a consequence of reduced population size. Found significant positive correlation between population size and genetic diversity of study populations. Genetic Variation in Island Populations In general, genetic variation is lower in isolated and generally smaller, island populations. o Reduced genetic variation indicates a lower potential for a population to evolve. Genetic Diversity and Butterfly Extinctions - Frankham and Ralls point out inbreeding may be a contributor to higher extinction rates in small populations. o Reduced fecundity, depressed juvenile survival, shortened life- span. - Saccheri et al. conducted genetic studies on populations of Glanville fritillary butterflies (Melitacea cinxia.) o Populations with highest levels of inbreeding had highest probabilities of extinction. Less likely to hatch eggs. Smaller offspring. Spend more time as a pupa. More likely to be eaten. Fixation of alleles of a small population reduces genetic diversity, leading to a fixation of a 1 allele. In larger populations genetic drift is happening but it bounces back and forth. Evolution and Agriculture - “Artificial Selection” - Vs “Genetic Engineering” Corn Unintended Evolutionary Consequences - The use of chemicals in agriculture can have evolutionary consequences o Plant and animal pests may evolve resistance to the chemicals used to control them. Resistance among pests have been shown to be quick and widespread Vila-Aiub et al. showed how Johnsongrass quickly evolved resistance to herbicides in Argentina. Chapter 8 Social Behaviors Behavioral Ecology- Study of social relations. Interactions between organisms with in the environment. Occurs on the population and community level. Sociobiology- Branch of biology concerned with study of social relations. Fitness- Number of offspring (genes) contributed by an individual of future generations. Sociobiology vs. Behavioral Ecology Sociobiology looks at the biological reasoning behind something. Behavioral Ecology looks at the actual behavior. Male/ Female- Dependent on gamete size Hermaphrodite- Both functions/ both gametes. Example: slugs, worms, some plants, and the blue headed damsel fish. Sexual Selection- Difference reproductive rates resulting from different mating success. Intrasexual- male to male competition, reproduction occurs with the winner (Ex: head-butting rams). Intersexual- female has the choice Attention- Potential negative trade-off with sexual selection Mate Choice and Sexual Selection in Guppies Females had a preference for brightly colored males however, brightly colored males attract predators. o Advantageous traits: Brightness Number of spots Total pigmented area Endler’s Natural Selection Study Lab setup: Field Study: Guppies from a low predation area was moved to a high predation area, and guppies from a high predation area were moved to a low predation area. It was observed that guppies that were upstream had few large offspring whereas guppies downstream had many small offspring. Downstream guppies were often prey to fish who primarily sought out guppies however upstream guppies did not have this problem because the general predators were not good at catching them. Fish with a higher number of offspring were moved to the higher pool and the hypothesis was that over generations the fish would produce fewer offspring that are larger in size. It was also found that the number of spots increased after fifteen generations. Male Choice and Resource Provisioning A male finds a dead individual and guards it and excretes pheromones to attract females. Larger pray are more impressive and; larger males are more successful. Non Random Mating in Plant Populations Both field and lab experiments shows evidence of non-random mating in both conditions. Success dependent of seed size, position in the ovule and the seed set (of fruit). Possible causes? o Maternal control o Pollen competition The study did not look at genetic compatibility. Sociality Evolution generally accompanied by: o Cooperative feeding o Defense of the social group o Restricted reproductive opportunities Different/multiple types of cooperation. Esociality o More complex level of sociality, defined by: o Multiple generations of co-habitating. Queens, grandparents, generation, etc. Cooperative care of young, and division of individuals into reproductive and non-reproductive castes. Cooperative breeding Benefits to helpers: Inclusive fitness- Improve survival and reproduction of family (Your family’s genes will be passed on). Inherited territory- Increase future reproductive success (Hang out until your parents leave, take over their nesting spot). Kin selection-Evolutionary force favoring helping behaviors (Selection for your own genes and your inclusive family and kin). Inclusive fitness and kin selection are the only rational explanations for altruistic behavior in nature.
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