Organism and its Environment 1

• The physical environment


  • Temperature, light, moisture differ with latitude, region, and locality
  • Variables vary daily and seasonally
• Homeostasis


  Organisms have to maintain fairly constant internal environment
• When environmental pressures become intense and unbearable


  • A population will ultimately adapt to those changes
  • Adaptation involves genetic changes (evolution) in the population
• Adaptation


  A change in an organism's structure or habits that better enables the organism to adjust to the environment
• Adaptation


  Process by which the present match between organisms and their environment, and the constraints on this match, have been determined by evolutionary forces acting on ancestors
• Limiting Factors or Conditions


  • Physico-chemical limiting factors (Temperature, Moisture, Nutrients)
  • Biotic limiting factors (Competition, Predation pressure, Food availability)
• Varying environment


  • Cyclic changes (Rhythmically repetitive - seasons, tides, day and night patterns)
  • Directional changes (Direction of change maintained over period that may be long in relation to the life span of the organism)
  • Erratic changes (No rhythm and constant direction)
• Regulatory Factors


  • Physical factors used as cue to regulate the activities of organisms and program their life histories
  • Maximal benefits from local favorable conditions
• Biological clocks


  • Physiological mechanisms for measuring time
  • Timing is accomplished by cellular oscillators operating as feedback loop involving "clock" genes
• Biological rhythms


  • Circadian rhythms
  • Tidal rhythms
  • Photoperiods
• Photoperiodism in "short-day" plant Poinsettia


  • Phytochrome: blue-green pigment
  • Artificially accelerated light regimen (day length or photoperiod) to bring brook trout into breeding condition

  
• The two-way interaction between biotic and abiotic component is subject to the two Great Ecological Laws
• Liebig's Law of the Minimum


  The growth and survival of an organism is dependent primarily on the nutrient that is LEAST available
• Limitations of Liebig's Law of the Minimum:
• Shelford's Law of Tolerance


  Each environmental factor has both minimum and maximum levels called tolerance limits beyond which a particular species cannot survive
• Tolerance types


  • Stenothermal
  • Eurythermal

  Stenohydric

  • Euryhydric

  Stenohaline

  • Euryhaline

  Stenophagic

  • Euryphagic

  Stenoecious

  • Euryecious
• Frequently, organisms in nature are NOT actually living at the optimum range of a particular physical factor
• Reproduction is usually a critical period when environmental factors are most likely to be limiting
• Factor Compensation


  Prolonged exposure to conditions slightly to one side of the optimum results in shift of the tolerance curve to produce a NEW optimum at the ambient value and upper and lower limits
• Acclimation


  Compensatory mechanism (or reversible changes) that may be induced under experimental conditions
• Acclimatization


  Compensatory change that is induced (usually a longer time scale) under natural conditions
• Ways organisms reduce the limiting effects of the abiotic factors


  • Avoidance
  • Tolerance (by adapting to environment, modifying the physical environment)
• Avoidance mechanisms


  • Stomatal and cuticular resistance
  • Changes in leaf morphology, and/or changes in leaf orientation
• Tolerance mechanisms


  • Changes in tissue elasticity

  Osmotic adjustment involving inorganic ions, carbohydrates, and organic acids (including compatible solutes)
• Ecotype


  Genetically differentiated subspecies

  Genetic varieties within a single species
• Ecotypic differentiation (genetic fixation) in yarrow, Achillea millefolium


  • Height of plants varies with elevation from which seed was collected
• Ecotypic differentiation (genetic fixation) in Achillea borealis


  • Height of plants varies with elevation from which seed was collected
• Ecosystem engineers


  Allogenic engineers (modify the environment by mechanically changing materials from one form to another, e.g. earthworms)

  Autogenic engineers (modify the environment by modifying themselves, e.g. forest trees, lianas)
• Charles Darwin: '"It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change."'