Glossary of Ecology (6th ed.) by Krebs (2009)
- a factor is defined as limiting if a change in the factor produces a change in average or equilibrium density.
Glossary of "Environmental Science: Earth as a Living Planet (2nd ed.)" by Botkin & Keller (1998)
- The single requirement for growth available in the least supply in comparison to the need of an organism. Originally applied to crops but now often applied to any species.
- Botkin, D. B. & Keller, E. A. 1998. Environmental Science: Earth as a Living Planet, 2nd ed. -xxxxii + 649 pp. John Wiley & Sons, Inc., New York.
- Krebs, C. J. 2009. Ecology, 6th ed. -xvi + 655 pp. Pearson Benjamin Cummings, San Francisco.