Environmental factors whose abundance, concentration, or properties do not change in response to the density of the population are called passive or nonreactive factors. Nonreactive factors act as one-way inputs into the population system. Non-reactive factors are often physical factors like climate, solar energy, mineral nutrients, but biotic factors can also be classified as non-reactive if they do not change in response to population density. Space is a major passive factor in that organisms need space in which to gather sunlight, chemicals, food and water, or in which to avoid or escape enemies (enemy-free-space), but the total space available does not change in response to population density.

Passive factors do not create circular causal pathways and do not evoke the 4^th principle so that the endogenous dynamics of populations interacting with non-reactive environmental factors are determined by the first three principles alone. Hence, any stabilizing - feedback resulting from interactions with passive environmental factors can only be caused by the action of the 3^rd principle (intraspecific competition). Feedback of this kind is sometimes termed self-regulation (or self-loops) and, as we mentioned previously, it gives rise to first order dynamics.

Although the total quantity of a non-reactive factor present in the environment does not change in response to population density, its physical location can change. For example, phosphorus can be extracted from the soil by plants and stored in plant tissues for decades but this same phosphorus is released back into the soil upon the death and decay of the plant. The total quantity present in the environment, including soil, plants and animals, remains roughly the same. Similarly predators may aggregate in certain locations, say where prey are more abundant, yet the density of the predator population remains unchanged over larger areas. Such predator populations are also considered to be non-reactive.

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