定义：motion characterized by wave-like movement patterns that act to propel an animal forward. eg: crawling in snakes, or swimming in the lamprey. Typically utilized by limbless animals
定义：The duration of the development from fertilized, deposited or implanted egg to hatching/birth. Corresponds to egg incubation duration in oviparous animals and to gestation period duration in viviparous animals.
定义：A group of species that exploit the same food resources, and/or use the same feeding or foraging methods. http://en.wikipedia.org/wiki/Guild_(ecology)
