Sexual size dimorphism and female ornaments

Abstract

Abstract In many animal species males differ in size from females. For example, females are considerably larger than males in many invertebrates, fish, amphibians, and reptiles, whereas males are larger than females in most birds and mammals (Darwin 1871 ). Why is this the case? Size differences between the two sexes are most readily explained by selection processes affecting individuals differently (section 12.2). Sexual size dimorphism may result from natural or sexual selection, as already emphasized by Charles Darwin (1871). Natural selection will affect the morphology of males and females both during reproduction and the non-reproductive period. For example, males and females may have slightly different foraging behaviour and habitat choice, and the different natural selection pressures under two kinds of environmental conditions may result in sexual differences in morphology. Intersexual competition for food resources may thus lead to sexual size dimorphism due to natural selection acting on heritable variation in morphology.