If the birth rate increases, the mortality increases. Density dependent mechanisms affecting natality and mortality act largely through environmental shortages and competitive interactions among members of the population to obtain those resources. This eliminates or greatly reduces the wastage of resources, permits the maintenance of a relatively high population density and maintains some numerical constancy Growth and Fecundity As population density increases to a point where resources are insufficient to meet their needs, individuals reduce their their food intake - like scramble competition. These relationships among density and fecundity extend to other vertebrate groups. Recruitmment of young into grizzly bear population declines as the number of adult bears increases.
Many plants respond to density in a scramble-like fashion through reduction in individual growth.
Individuals adjust their growth form, size, shape, number of leaves, flowers, and the production of seeds in a scramble fashion to the limited resources available, a response known as phenotypic plasticity . The trees of an artificially thinned stand are fewer, larger in diameter, and taller. Those in an unthinned stand are thicker on the ground, smaller in diameter, and shorter in height. If you cut and weighed uniform samples of stands, you would find that the total biomass on both plots was similiar, but mean weight of the plant would be greatest on thinned plots with the lower density. Density Independent Influences Density independent influences are those whose action does not come about because of the population's density, but because of some independent factor.