下面这段话最后一句中的act是个什么意思?

题目

下面这段话最后一句中的act是个什么意思?
in order to understand the nature of the ecologist "s investigation ,we may think of the density-dependent effects on growth parameters as the "signal " ecologists are trying to isolate and interpret ,one that tends to make the population increase from relatively low values or decrease from relatively high ones ,while the desity -independent effects act to produce "noise" in the population dynamics.

答案

act to是一个词组,不知道你百度了没有?连起来意思是（会采取措施）做某事