下面这段话最后一句中的act是个什么意思?

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.

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
再问： 恩，是的，我百度了！是有act to do 采取行动做某事。 我想的是不是还i有其他的用法。谢谢你！