Biology 1010 Lecture Notes

Unit 4. Introduction to Ecology


This page was last updated April 7, 2003

Key terms and phrases
  1. Introduction
    1. observation--members of a species are not uniformly distributed over the world; groups of species sometimes seem to occur together
      1. leads to the concepts of populations, communities, ecosystems, biomes
      2. raises the questions of what are the major influences on the distribution of species and do communities form integrated units (Gaia hypothesis in its broadest form)
      3. in this unit we are concerned with what are the factors that give rise to the structure of ecosystems
    2. role of abiotic factors
      1. physical/chemical factors
        1. types
        2. for each physical chemical factor there is a certain limit range of values that can be tolerated by individuals and by members of a species; within this range there is a certain optimum where the individual or species does the best; each individual or species has a particular set of abiotic factors it can tolerate, these define the boundaries of its theoretical habitat; niche refers to the way organisms uses the habitat and the resources therein
      2. island biogeography
        1. geographic barrier blocks movement of organisms
        2. size of island affects the number of habitats
        3. dynamic between colonization and extinction
      3. environmental catastrophes (meteorites, volcanic eruptions, free O2) can severly limit the numbers of individuals
    3. role of biotic factors
      1. competition within or between species for a limiting resource
        1. scramble (exploitative) vs interference competition
        2. competitive exclusion principle, resource partitioning and character displacement; realized niches; Darwinian evolution
      2. predation and parasitism
        1. food chains and food webs
        2. prey defenses
          1. chemical defenses--secondary metabolites in plants, poisons and toxins
          2. camouflage
          3. mimicry and warning coloration
      3. commensalism and mutualism
      4. keystone species--predator that promotes diverisity
    4. which is more important?
  2. Global systems
    1. Aquatic systems
      1. pelagic systems
        1. geologic/geographic profile
          1. continental shelf--less than 200 meters
          2. continental slope
          3. abyssal plain--average around 3000 meters
        2. physical/chemical profile
          1. light and temperature profiles; thermocline
          2. nutrient levels; upwelling
        3. biological profile
          1. euphotic zone
            1. phytoplankton (ultraplankton)
            2. zooplankton
            3. fish
            4. numbers of organisms
          2. deeper waters
          3. benthos
            1. abyssal plain
            2. hydrothermal vents
      2. neritic and littoral systems
        1. physical/chemical conditions
          1. light and temperature
          2. tides
          3. wave action
          4. nutrient status
        2. biological conditions
    2. Terrestrial systems
      1. controlled primarily by moisture
        1. latitudinal variation
        2. topographic factors
      2. biological interactions/trends in biodiversity
  3. Ecosystem dynamics--population growth
    1. general ideas
      1. birth, death, immigration, emigration
      2. techniques
        1. census
        2. mark and recapture
        3. proportional areas
    2. models
      1. exponential models; rate of increase
        1. doubling time in bacterial cultures
        2. human population growth, r = 1.4%, P = 6 billion
      2. logistic models and the carrying capacity
        1. basic features
        2. components of the carrying capacity
        3. r-selection and K-selection
        4. what is the carrying capacity of the Earth for humans?
      3. demographic models
        1. mortality; age-dependent mortality
        2. fertility; age-dependent fertility; total fertility; replacement fertility
        3. survivor curves
          1. type I--almost all live until reach old age then die rapidly
          2. type II--equal chance of dying at any age
          3. type III--most mortality in newborns; after certain age there is a good chance of surviving
        4. examples
          1. humans with high infant mortality
          2. previous example with 0 infant mortality
          3. previous example with replacement rate fertility
        5. population momentum
  4. Ecosystem dynamics--ecosystem function
    1. introduction--life support systems
    2. application to spaceship Earth
    3. Basic rules governing everything
      1. matter is neither created nor destroyed
      2. First Law of Thermodynamics--the amount of energy does not change, only the form
      3. Second Law of Thermodynamics--the quality (usefulness) of the energy decreases with every change
        1. version two--entropy increases in closed systems
        2. implications
    4. Energy flow in ecosystems
      1. light driven systems
        1. initial input = sunlight
          1. solar constant = 1360 Watts/m2 (0.325 kcals/m2/sec); equivalent to about 5 million kcals/m2/year (because of day-night cycles)
          2. about 30% of the energy is reflected back into space and another 20% absorbed by the air, bringing the total to 2.5 million kcals/m2/year; value less at the poles because of the spherical shape of the Earth
        2. plants and algae absorb a small fraction of the light (roughly 30% in forests and lakes, much less in deserts); an even smaller fraction of the light absorbed (usually about 2%) is converted to chemical energy through photosynthesis--this is referred to as gross primary productivity (maximum less than 15,000 kcals/m2/year)
        3. plants and algae first use the converted energy to battle entropy (referred to as respiratory losses); anything left over can be used for growth and reproduction--the left over is referred to as net primary production
        4. grazers (herbivores) eat a fraction of the plant material (clearly they can't eat it all) and assimilate some of the ingested energy; the assimilated energy is used first to battle entropy; anything left over is available for growth and reproduction (net secondary productivity)
          1. assimilation efficiency depends on the type of food (seed, stem, flower, etc)
          2. net production efficiency depends on the metabolism of the herbivore
          3. ecological efficiency is defined as consumer productivity/prey productivity; in terrestrial systems usually estimated as about 10%, somewhat higher in aquatic systems
        5. predators eat a fraction of the herbivores and assimilate some of the ingested energy (usually a higher percentage than herbivores get from their food); energy is used to first battle entropy, then for growth and reproduction (net tertiary productivity)
        6. some questions
          1. how long can food chains be?
            1. short in terrestrial systems, longer in aquatic systems
          2. what about all of the unassimilated material?
            1. detritus food chains and the role of bacteria
          3. what happens to all of the heat and and all of the light absorbed by the Earth?
            1. must eventually be lost to space or the Earth would melt
            2. basic mechanisms of heat transfer:  conduction, convection, radiation; only radiation applicable
          4. what does this imply about life-support systems for space-flight?
            1. what kinds of yields would be necessary to sustain human life?  how much volume would that take?
            2. how do space ships solve the heat problem?
      2. chemically-driven systems
        1. relatively rare accept near vents
        2. basic on the production of ATP and organic molecules by chemoautotrophs; otherwise similar to what happens in light
        3. where does the energy come from? i.e., why is the center of the Earth hot? recall famous debate between Lord Kelvin and Darwin
    5. Element cycling in ecosystems and globally
      1. most important elements: CHNOPS
      2. carbon
        1. functions in organisms
        2. major pools of carbon
        3. connections between the pools
          1. biological cycle
          2. mineralogical/geological  cycle
        4. problems
          1. increasing CO2 in the atmosphere could lead to climate change
          2. shortage of fossil fuels
      3. oxygen
        1. functions in organisms
        2. major pools: water, O2 in the air, oxygen in inorganic molecules and minerals (carbon dioxide, silicates, oxides, etc.), oxygen in organic molecules
        3. connections: photosynthesis, respiration (electron chains)
        4. problems
      4. nitrogen
        1. functions in organisms
        2. major pools:  N2 in the air, ammonium ions, nitrate ions, and nitrite ions in water and soil, nitrogenous compounds in organisms
        3. connections
          1. nitrogen fixation by bacteria and cyanobacteria
            1. N2 converted to ammonium by nitrogenase; energy expensive
            2. nitrogenase usually can only work in the absence of oxygen
          2. nitrogen in organic wastes usually converted first to ammonia (ammonification) then to nitrite then to nitrate (nitrification) which can be used by plants
          3. some nitrate is converted to N2 again in the process of denitrification
        4. problems
          1. aquatic pollution--eutrophication
            1. lake dynamics and phytoplankton blooms
            2. eutrophication
            3. other water pollution problems
          2. NOx compounds and smog
      5. phosphate
        1. functions in organisms
        2. major pools: PO4 ions in soil and water, organisms, detritus, phosphate rocks
        3. connections: uptake, ingestion, decomposition, binding at low and high pH
      6. pesticide cycling
        1. definitions
        2. biological amplification
        3. genetic pesticides
    6. Prospects
      1. summary of current problems
        1. population growth
        2. energy requirements
        3. carbon dioxide increases and global warming
        4. air and water pollution

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