Mechanism of Male Choice: Sex Ratios

Abstract

In this short chapter I want to discuss the role of sex ratios in choosiness. So far, we have mostly reviewed intrinsic reasons for male choosiness to be expressed such as male investment and female quality; however, sex ratios may also be important drivers of choosiness. Sex ratios are important in population biology and influence the evolution and structure of mating systems. Most important for the purpose of this book is that they can change quickly in time and space. Male and female choice are sensitive to such changes and can lead to situations where females are choosy when they are rare in a population but change to courtship and competition when males are rare. There are not many examples of this process, but there are likely some that have been overlooked. Interestingly, the majority of data on preferences are collected using binary choice tests, which almost always represent a 2:1 sex ratio. Furthermore, sex ratios do not take into account differences in mate quality, as all adult individuals are classified as either male or female without making any further distinction.