This paper focuses on those parts of 20th century applied mathematics that have entered into the toolkit of ecology. Historically, the recent trend of applying mathematics to ecology is discussed. It is proposed that this new development can be seen in the extension of its application as the natural development of applied mathematics. There is no assumption that the mathematical concepts and methods employed would be significantly different from those used in mainstream applied mathematics. In terms of estimates for reference to empirical data, conventional concepts and methods of statistical physics can be successfully applied. A case study on the history of statistics and operational research discusses several ways to integrate the development of applied mathematics of the twentieth century into an ecological context.