Many different environmental factors have the potential to control the growth of a population. These factors include the abundance of prey or nutrients that the population consumes and also the activities of predators. A given population will usually interact with a multitude of different prey and predator species, and ecologists have described these many interactions by drawing food webs. Yet, although a given population may interact with many different species in a food web, and also interact with many different abiotic factors outside the food web, not all of these interactions are of equal importance in controlling that population's growth. Experience shows that "only one or two other species dominate the feedback structure of a population at any one time and place (Berryman, 1993)". The identity of these dominating species may change with time and location, but the number of species that limits a given population (i.e. actively controls its dynamics) is usually only one or two.
Liebig's Law (Liebig, 1840), in its modern form, expresses this idea. It says that of all the biotic or abiotic factors that control a given population, one has to be limiting (i.e. active, controlling the dynamics) (Berryman, 1993, 2003). Time delays produced by this limiting factor are usually one or two generations long (Berryman, 1999). Moreover, Liebig's Law stresses the importance of limiting factors in ecology. "A factor is defined as limiting if a change in the factor produces a change in average or equilibrium density" (Krebs, 2001).
To summarize, "the functioning of an organism is controlled or limited by that essential environmental factor or combination of factors present in the least favorable amount. The factors may not be continuously effective but only at some critical period during the year or only during some critical year in a climatic cycle".
Was this article helpful?