在种群生态学中，密度制约是描述种群密度对种群增长的影响的一种假说。一般认为密度制约效应主要发生在物种的种子和幼苗阶段。

In population ecology, density-dependent processes occur when population growth rates are regulated by the density of a population. This article will focus on density-dependence in the context of macroparasite life cycles.