A density-dependent factor
would retard population growth, as the density increases beyond a hypothetical equilibrium point (K) by decreasing births and increasing deaths.
Recent publications have indicated that, despite high fecundity, invertebrates that are subject to high levels of exploitation such as tridacnid clams (Munro 1989) and some scallops (Caddy 1989) may be limited by density-dependent factors
that are positive.
Ecologists have debated the generality and importance of density-dependent factors
The effect of so-called density-dependent factors
such as predation, disease and dispersal -- that have a proportionally greater effect on mouse numbers when population densities are high -- is included in the model.
Notably, Sinclair (1989:210) dismissed Murray's (1982) contention that population equilibrium in territorial species could occur without the action of density-dependent factors
Populations can be affected by simple density-dependent factors
(Nicholson 1933, Lack 1954; see references in Dennis and Taper 1994), density-independent factors (Andrewartha and Birch 1954, see references in Martinat 1987), and time-delayed or nonlinear density-dependent forces (sometimes leading to chaotic fluctuations; May 1976, Hastings et al.
Thus, the average Malthusian fitness is almost equivalent to the intrinsic rate under uncrowded conditions, but is modified by extrinsic density-dependent factors
under crowded conditions.
When the information on fluctuations in resource availability, dynamics of natural enemies and other density-dependent factors
is unavailable, models with time-varying parameters and high-order lags can be used to describe the influence from these unknown density-dependent factors
on population dynamics (Zeng 1996).
For gypsy moth, high-density populations are constrained by virus diseases (Doane 1970, 1976) and other density-dependent factors
, including competition for food, but for low-density populations, the existence of density-dependent regulation is debatable.
All of these significant differences were in the direction expected if density-dependent factors