Abundance and Distribution of Species

Liebig's law of the minimum:

The single factor closest to these survival limits is the critical limiting factor that determines where a particular organism can live. The major factor is one in the minimum.

or:single environmental factor in shortest supply relative to demand is the critical determinant in species distribution

Shelford added to Liebig's work:

Single environmental factor closest to tolerance limits determines where a particular organism can live

Shelford's principle of tolerance limits:

Each environmental factor has both minimum and maximum levels called Tolerance limits, beyond, which a particular species cannot survive or is unable to reproduce.

For terrestrial organisms: temperature, moisture, and nutrient availability.

For aquatic organisms: salinity, gradient (water current).

Sometimes the requirements and tolerances of species are useful indicators of specific environmental characteristics - environmental indicators (trout, lichens etc.).

Limiting factors include ABIOTIC (physical) factors and BIOTIC factors

Abiotic Factors:Light availability/day length, seasonality; moisture/water availability; temperature, diurnal temperature range; height or depth, pressure; salinity; wind; pH, CO₂, O₂, availability of N, P, K, Ca, etc.

Biotic Factors:Competition; predation; parasitism; disease; pollinators, dispersal agents; food availability; species density /distance to nearest neighbour).