Diversity and Selection What’s wrong! Why is it wrong? Could this ever happen? Ecological niche The total requirements of a species for all resources and physical conditions determine where it can live and how abundant it can be at any point. These requirements determine the species ecological niche. The ecological niche of a plant might be determined by: the range of temperatures the species can tolerate, the intensity of light it requires for photosynthesis, humidity regimes, minimum quantities of soil nutrients. The ecological niche can be thought of as a plants address and it’s profession (these are not always the same but often are) Ecological niches in old-growth forest Long-lived pioneer Douglas-fir Shade-tolerant secondary succession species, e.g., western hemlock, Pacific yew Forest floor species, e.g., bryophytes What about introduced species? Sitka spruce Alaska & PNW Sitka spruce works at its profession in both regions of the world the niche is realized in both places Scotland Humans move plants around – but the plants only thrive if the new environment is a suitable ecological niche. How do plants become suited to an ecological niche? Natural Selection Darwin’s view: Natural selection is the outcome of variations in shared traits that influence which individuals of a population survive and reproduce in each generation Natural selection can lead to increased fitness – that is to an increase in adaptation to the environment Page 285 Darwin’s argument summarized: Populations have reproductive capacity to increase But no population can increase indefinitely So there will be competition between individuals in a population All individuals in a population have the same genes But genes occur in different forms resulting in different phenotypes. Some phenotypes are better than than others at helping the individual compete. The alleles producing those phenotypes increase over time. Page 285 Natural selection can lead to increased fitness – increased adaptation What actually happens is more complicated than simply an “increase in fitness” Three types of Natural Selection Directional selection An environmental pressure causes a change in frequency of alleles Stabilizing selection Multiple environmental pressures constrain evolution and may reduce variation in alleles Disruptive (diversifying) selection Environmental variation favors opposite ends of a range of natural variation. Pages 286-289 Directional Selection Number of individuals in the population The effects of pollution on the selection of Peppered moths. Number of individuals in the population Range of values for the trait at time 1 Number of individuals in the population Range of values for the trait at time 2 Range of values for the trait at time 3 Page 286 Artificial Selection Examples of directional selection Stabilizing selection – insect induction of galls Number of individuals in the population Larvae of Eurosta solidaginis induce gall formation Range of values for the trait at time 1 Wood peckers eat larvae in big galls. Range of values for the trait at time 2 The parasitic wasp penetrates the walls of thin galls Range of values for the trait at time 3 Stabilizing selection is responsible for the long term existence of some types of organisms that have origins hundreds Page 288 of millions of years ago in the population Number of individuals Disruptive (diversifying) selection in the population Number of individuals Range of values for the trait at time 1 in the population Number of individuals Range of values for the trait at time 2 Range of values for the trait at time 3 Page 289 Escherichia coli You’ve got millions of these bacteria inside of you! Occasional mutations, combined with inadequate cooking of meat products, can cause outbreaks of food poisoning. Kingdom: Eubacterium Scientific Name: Escherichia coli Image Courtesy of: Shirley Owens, Center for Electron Optics, MSU Image Width: 9.5 microns Image Technology: SEM (Scanning Electron Microscope) An experiment: place E. coli in a solution in a chemostat – a vessel that has a constant input of glucose … … then introduce the T4 bacteriophage! Bacteriophage T4 injects DNA into the E. coli cell DNA replicates, new phage is produced and released when the cell dies Log10 density, numbers/ml Diversifying selection E coli Why did the E. coli increase? T4 phage How did the virus survive after emergence of a resistant mutant? Emergence of an E. coli resistant mutant It so happened that the phage resistant mutant was less efficient at glucose metabolism than the non-mutant – so some non-mutants continued to survive Convergent evolution Species from different evolutionary branches may come to resemble one another if they live in similar environments Astrophytum asterias Cactaceae Mexico and Texas Euphorbia valida Euphorbiaceae South Africa Ecological Niche 1. Plants accumulate matter and make growth The amount of growth depends upon ecological conditions 2. Plant growth is an organized process following rules of anatomy and morphology Plant form determines plant function and varies with ecological niche 3. Plants maintain their heat and water balance Physical conditions of water supply, temperature and radiation vary between ecological conditions and pose different problems for plants 4. Plants have a life cycle with reproduction and dispersal 5. Evolution is a constant process Life cycles are adapted to suit ecological conditions Selection occurs that suits plants for a particular niche Yucca glauca Yucca brevifolia Naming organisms and its scientific basis Binomial classification for all organisms Taxonomy – how organisms are known Hierarchical naming system Classification systems that organize species according to their relationships Cladistic analysis The method of classifying according to similarities and differences The hierarchical naming system KINGDOM Plantae Plantae PHYLUM Anthophyta (flowering plants) Anthophyta CLASS Monocotyledonae (monocots) Monocotyledonae ORDER Commelinales Orchidales FAMILY Poaceae Orchidaceae GENUS Zea Vanilla SPECIES Z. mays V. planifolia COMMON NAME: corn vanilla orchid Page 320 Constructing a cladogram Lamprey Taxon Jaws Limbs Hair Lungs Tail Shell Turtle Cat Traits (Characters) Lamprey - - - - + - Turtle + + - + + + Cat Gorilla Lungfish Trout Human + + + + + + + + + + + + + + + + + + - - Gorilla Taxon Human Using the lamprey as the outgroup Jaws Limbs Hair Lungs Tail Shell Lungfish Trout Traits (Characters) Presence/Absence of characters Lamprey 0 0 0 0 0 0 Turtle 1 1 0 1 0 1 Cat Gorilla Lungfish Trout Human 1 1 1 1 1 1 1 0 0 1 1 1 0 0 1 1 1 1 0 1 0 1 0 0 1 0 0 0 0 0 Organise by shared derived traits Fig. 20.14, p. 324 Cladistic Analysis turtle, gorilla, trout, cat, lugfish, human lamprey lamprey trout turtle, gorilla, cat, lugfish, human lungs jaws jaws Relative relatedness lamprey trout gorilla human lungfish turtle cat In-group and out-group Primitive characters Derived characters node 1 Parsimony node 2 Use of molecular methods Fig. 20.15, p. 324-25 Any Questions ?