Abiotic Factors and Limits

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Abiotic Factors and Limits

• Part I

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Physical Resources and Limiting Factors

• Physical Resources abiotic factors an organism
  must assimilate to survive and thrive (e. g.)
• Physical Factors abiotic parameters whose
  effects define where life is possible (e. g.)
• Limiting Factors when factors determine if a
  species is present or absent (also biotic)

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Physical Resources and Limiting Factors
(continued)

• Distinction between physical resources and
  factors often blurs
• Physical factors are a selective force
• Physical factors usually not independent
• Law of the Minimum one abiotic factor is usually
  the limiting one
• Law of Tolerance upper and lower bounds to
  physical factors an organism can tolerate (no
  organism can live everywhere)
• Organisms can adapt or acclimatize

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Effects of Abiotic Factors on Species
Distribution and Abundance

• The two laws define an organisms niche
• Niche a place and role for an organism in the
  environment
• Temperature, Water Abundance, Salinity, Nutrient
  Availability

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Temperature

• Low temp. yields cold temp., short growing
  season, desiccation
• Latitudinal and altitudinal limits of treelines
  determined by temperature
• Butterflies from Alaska and Georgia
• Coral bleaching
• Cacti in Arizona
• Huddling behavior of flying squirrels

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Water Abundance

• Water channels can greatly affect vegetation in
  desert habitats, or on slopes in prairie grasses
• Few meters can make a great difference
• Animals too (amphibians)

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Salinity

• Many plants and animals are limited by salinity
  gradients
• Salt marsh
• Zebra mussels
• Desert valleys (dried-up lakes)

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Nutrient Availability

• Plants frequently limited by Nitrogen and
  Phosphorus, or CO2 (Rubisco)
• Ungulates seek out nutrient licks (areas of soil
  with high Sodium or Calcium)
• Lemmings

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Adaptive Responses

• Homeostatic Mechanisms,
• Avoidance strategies

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Homeostatic Mechanisms

• Evolving physiological mechanisms to counteract
  the effects of physical factors
• Constant body temperature in mammals
• Shivering, sweating or panting
• Internal solute concentration (birds)
• Exudates

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Avoidance Strategies

• Hibernation
• Resistant life-cycles (plants, spores)
• Migration

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Thermal Stress and its adaptations

• Life can inhabit temperatures from -50 oC to near
  boiling (100oC)
• Increasing temperature increases reaction rate,
  thus energy expenditure, oxygen consumption
• High temperature affects DNA, protein, membranes
• Low temperature can cause cell damage or
  dehydration (plants)

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Methods of heat transfer

• Conduction heat transfer between two objects in
  contact
• Convection heat transfer by the mass movement of
  fluids (liquids or gases)
• Radiation heat transfer by electromagnetic
  radiation (emissivity and absorptivity)

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Emissivity and Absorptivity

• Emissivity virtually the same regardless of color
  in the visible spectrum
• Absorptivity differs widely
• Evaporation

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Adaptations to thermal stress

• Homeotherms regulate internal temperature
• Poikilotherms body temperature fluctuates with
  the environment
• Endotherms produce sufficient metabolic heat to
  maintain internal temperature
• Ectotherms obtain much of their heat from the
  environment

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Adaptations (continued)

• Sweating, panting
• Storage (antelope ground squirrel)
• Shivering
• Brown fat
• Fur, fat, blubber, feathers, reduced surface
  area, increased body size

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Avoidance

• Reptiles
• Hibernation
• Huddling
• Estivation (torpor during summer to avoid
  excessive heat)

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Plant adaptations

• Leaf size
• Leaf shape
• Leaf thickness
• Dropping leaves
• Parabolic flower shape
• Flower orientation
• Water loss because of temperature (CAM)
• Switching life-history habits