A<unk>  or<unk>  resource is one that controls a process, such as organism growth or species population size or distribution. The availability of food, predation pressure, or availability of shelter are examples of<unk> s that could be<unk>  for a species population in a specific area. The<unk>  changes the amount or organisms a population can hold. The concept is based upon Liebig's Law of the Minimum put forth by German geochemist, Justus von Liebig, in 1840.  It can be easy to conceive how a<unk> " resource (say, food) controls a process (say, growth) by running low or running out.  However, some biological and ecological processes are controlled by too much of a<unk>  (such as heat) rather than too little.  Or, processes may be controlled by complex interactions of<unk> s (Shelford, 1952). Walter Taylor (1934) proposed the following broad, restatement of the law of the minimum:
The functioning of an organism is controlled, or limited, by that essential environmental<unk>  or combination of<unk> s present in the least favorable amount. The<unk> s may not be continuously effective but only at some critical period during the year or perhaps only during some critical year in a climatic cycle.
Limiting factor
Impact factor
Confounder
System dynamics
Scientific consensus
Incidence 
Prevalence
Association 