MOD2: BIO150 LEC Abiotic and Biotic Factors

• Biotic components in an ecosystem can be classified according to their functional role, reflecting feeding relationships
• Producers:

  • Produce their own food; autotroph ("self-feeding")
  • Supply the needed vitamins, minerals, and energy for consumers
  • Photoautotrophs obtain energy for making food from radiant energy through photosynthesis
  • Chemoautotrophs obtain energy for making food from oxidation of inorganic chemicals through chemosynthesis
• Consumers:

  • Includes animals that feed directly or indirectly on producers for food
  • Heterotrophs
  • Part of the grazing food chain
  • Herbivores (1° consumers) feed only on producers and regulate plant growth
  • Frugivores eat fruits
  • Folivores graze or browse on leaves and/or twigs
  • Nectarivores feed on nectar
  • Granivores eat seeds
  • Palynivores feed on pollen
  • Mucivores sip plant fluids
  • Xylophages eat wood
  • Omnivores feed on both plants and animals
  • Carnivores feed directly on other animals and act as natural enemies
  • 2° consumers feed only on herbivores
• • 3° and higher level consumers feed only on other carnivores
• Decomposers, Detritivores, Scavengers:

  • Special type of consumers that thrive on decomposing matter or cast-off fragments of living organisms
  • Participate in the detrital food chain
  • Recycle matter into nutrients that are available for re-entry into the grazing food chain
  • Important for nutrient cycling to prevent life from ceasing
• Feeding Relationships:

  • Food produced by autotrophs is passed on to consumers
  • Each level in the successive food/energy transfer is called a trophic level
  • Represented through food chain, food web, or food pyramid
• Law of Tolerance:

  • The ability of an organism to maintain its ecological niche is determined by its ability to tolerate a range of physical and chemical factors present in the environment
• Response Curve 1:

  • Generalized response
  • Extreme conditions are lethal; less extreme conditions prevent growth; only optimal conditions allow reproduction
  • Appropriate for conditions like temperature and pH
• Response Curve 2:

  • Lethal only at high intensities
  • Low-level intensity or concentration of the factor has no detectable effect but an increase begins to cause damage and a further increase may be lethal
  • Response curve for toxins, radioactive emissions, chemical pollutants
• Response Curve 3:

  • Response to conditions that are toxic at high levels but essential, as a resource for growth, at low levels
  • This is the case for NaCl and for many elements that are essential micronutrients (e.g. Cu, Zn, Mn, etc.)
• Important notes:

  • Tolerance to adverse environmental conditions is highly desirable for agricultural crops
  • Tolerance can break down under the influence of confounding factors
  • Actual responses are modified under field conditions
  • There are trade-offs in tolerance
  • High tolerance to one condition may cause high susceptibility to another condition
• • Heliophytes (Sun Plants): need full sun for growth, efficient use of high light intensity, never reach photosynthetic saturation
  • Sciophytes (Shade Plants): more efficient photosynthesis at low light intensities, often reach saturation levels at 20% full sunlight
• • Fate of incoming solar radiation: transmitted, reflected, refracted, absorbed, scattered
  • Light as an environmental factor:
  • Involved in circadian rhythms, photoperiodism, phototropism, phototaxis
  • Involved in phototrophy, photosynthesis (utilizing Photosynthetically Active Radiation, PAR wavelengths)
  • Shade is a resource depletion zone (RDZ) because shading reduces light intensity and changes transmitted wavelengths
  • Types of plants based on light utilization:
• Light:

  • Visible electromagnetic radiation (400-700 nm); primary energy source for the biosphere
  • Intensity: strength of light; measured in lux or footcandles; depends on distance from source, season, weather, cloud cover, time of day, plant cover, air particles, angle of incoming light, variations in Earth’s orbit, and variations in solar energy output
  • Quality: refers to what wavelengths of light are present
  • Periodicity: duration of day length; function of latitude and season
  • Directionality: from what angle light is coming
• • Interaction of temperature with other factors: disease, competition, humidity
• • Ectotherm (heat from environment) vs. Endotherm (heat from metabolism)
  • Effects of extreme temperatures on organisms:
  • Low temperature: chilling injury, freezing
  • High temperature: denaturation of proteins, dehydration
  • Adaptations to extreme temperatures:
  • Insulation, evaporative cooling, adjustment of supercooling points, countercurrent heat exchangers, freeze-avoidance, freeze-tolerance
  • Resting stages under extreme temperatures: torpor, hibernation, estivation
  • Temperature as a stimulus for development, growth, flowering, germination, ripening of fruits
• Temperature & Heat:

  • Temperature: measure of average kinetic energy of atoms or molecules in the system
  • Heat: thermal energy transferred from hotter to cooler system; 0 heat flow if in thermal equilibrium
  • Affected by altitude, latitude, continental/maritime location, surface features
  • Organisms respond to temperature based on Response Curve 1 of Shelford’s Law of Tolerance
  • Types of organisms based on stability of body temperature and source of energy for regulating body temperature:
  • Poikilotherm (varying body temperature) vs. Homeotherm (constant body temperature)
• Water is a critical resource for organisms, composing approximately 80% of their body
• Hydration is necessary for metabolic reactions in organisms
• Water content in organisms needs continual replenishment
• Water incorporated in the plant body is less than the volume of water that flows through the transpiration stream, highlighting the importance of root systems
• Most terrestrial animals drink free water and generate some from the metabolism of food
• Animals in arid zones may obtain all their water from their food
• Humidity refers to the moisture content of air relative to an equal volume of saturated air at a given temperature
• Humidity is an important source of water and is affected by temperature, land use, and vegetation
• Plants transpire and affect humidity in the area
• Rainfall or precipitation is water condensed from atmospheric vapor and falling in drops
• Rainfall allows the redistribution of water, bringing water from the oceans to areas over land
• Water scarcity and abundance determine vegetation types
• Rainfall replenishes groundwater and is a medium of life in aquatic habitats
• In streams and rivers, there is a constant hazard of being washed away
• Repeated pounding and suction of wave action on sea shores pose challenges, addressed by holdfasts, flexible bodies, and behavioral strategies of avoidance
• The pH of water and soil has direct effects like toxicity, upsetting osmoregulation, enzyme activities, and gas exchange
• The pH of water and soil also has indirect effects, influencing the availability of nutrients and/or concentration of toxins
• Environments with neutral to slightly alkaline pH are more hospitable than acidic ones
• Some prokaryotes can thrive under very acidic conditions (acidophiles) or very alkaline conditions (alkaliphiles)
• Organisms respond to the salinity of water similarly to the Response Curve, creating osmoregulatory problems and osmotic resistance to water uptake
• Halophytes have metabolites for osmoregulation, while others pump out excess salt from their tissues to avoid damage
• Organisms respond to mineral nutrients similarly to the Response Curve
• There are interactions between foraging for water and nutrients, especially for plants