Reptiles, Biodiversity of

Abstract

Most of the more than 11,000 extant species of nonavian reptiles are squamates (lizards and snakes); there are about 360 extant species of turtles, 26 crocodylians, and one rhynchocephalian. Although the diversity of reptiles is greatest in the tropics, many species occur in temperate regions and a few have geographic ranges that extend north of the Arctic Circle. Antarctica is the only continent with no extant reptiles. Oviparity is the ancestral mode of reproduction, but viviparity has evolved repeatedly among squamates. Both genetic sex determination (XX/XY and ZW/ZZ) and environmental sex determination are represented, and genetic, environmental, and non-genetic maternal factors interact in some species. Environmental sex-determination is universal in crocodylians, widespread among turtles, and present in some clades of squamates. Parental care is universal among crocodylians and is present in some species of squamates and turtles. Ectothermy, an ancestral character, is central to the biology of reptiles, and is responsible for their low metabolic rates and their high efficiency of secondary production. Lizards typically eat daily and consume many small prey items, whereas snakes eat less frequently and consume larger prey items relative to their body size. Low metabolic rates make small body sizes energetically feasible for ectotherms, and more than half of the extant species of lizards are smaller than nearly all mammals and birds. Among squamates, the mode of predation – from sit-and-wait to widely foraging – has a strong phylogenetic component and correlates with many elements of ecology, morphology, physiology, and behavior. Many species of snakes and a few lizards are venomous, and some snakes are poisonous because they sequester toxins from their prey. Although most species of reptiles have little economic value, they are important components of energy and nutrient flow in terrestrial ecosystems. Habitat loss, pollution, invasive species, disease, and global climate change affect many species. The life histories of most large species of turtles, lizards, snakes, and crocodylians depend on prolonged adult survival and reproduction, and these species are vulnerable to commercial exploitation.