Sexual size dimorphism

Sexual size dimorphism is a difference in average body size between males and females of the same species. Its direction and magnitude vary across species.

Sexual selection: Differences in reproductive success caused by competition for mates or by mate choice. Mate competition and preference can favor larger bodies in one sex.
Anglerfish: A group of deep-sea fishes that includes species with tiny males attached to much larger females. Some species show extreme female-biased size dimorphism and permanent male attachment.
Body size: The physical scale of an organism, commonly measured using mass, length, or volume. Dimorphism depends on which aspect of body size is compared.
Sexual size dimorphism in raptors: The common pattern in birds of prey where females are larger than males. A marked size difference can let the sexes exploit different prey or hunting roles.
Intrasexual selection: Competition among members of one sex for access to mates. Male-male contests often favor greater size and strength in males.
Elephant seal: A large marine mammal whose males are substantially larger than females. Male size supports competition for territories and access to females.
Allometry: The study of how biological traits scale with body size or with other traits. It helps distinguish size differences from differences in body proportions.
Sexual size dimorphism in pinnipeds: The often pronounced size differences between male and female seals and sea lions. Large males can gain advantages in breeding contests and territory defense.
Intersexual selection: Mate choice by one sex based on traits of potential partners. Preferences can favor size differences through unequal reproductive benefits.
Peafowl: Pheasants in which males bear elaborate trains and are larger than females. Their size difference accompanies conspicuous male ornaments and mate choice.

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