Lesson 3: Species in the environmental complex

Shelford s Law of Tolerance
• Shelford in 1913 noted a weakness in Liebig s general law
which came to be known as the Law of Tolerance. And this
in turn was modified by Ronald Good, a plant geographer:
• “Each and every plant species is able to exist and
reproduce successfully only within a definite range of
environmental conditions.
• Good rated climatic factors above edaphic factors.
• Some Examples:
– Salinity tolerance in plants (intertidal zonation)
– Thermal constraints on activity (sparrow microclimates,
shown in the diagram from Smith s Ecology and Field
Ecology.)