![]() Clearly, some strong endogenous control is present in many species. The question of whether circadian cycles are endogenous (internally controlled) or exogenous(ultimately regulated by external stimuli) has occupied the attention of many biologists. the circadian rhythm of an animal is part of its total adaptation to its particular mode of life and environment and has evolved just as have the form and structure of its body parts. Two species of fishing bats, both of which feed over water, avoid interfering with one another partly by foraging at different times of the night and also by eating different prey. In some cases, competition between species is reduced or eliminated because their activity cycles are out of phase. The activity cycles of carnivores seem to be geared to the circadian cycles of their prey or to the period when hunting is most rewarding.Ĭircadian rhythms are also influenced by interactions between species with similar environmental needs. In general, small mammals that are especially vulnerable to predation, such as rodents, tend to be nocturnal, whereas less vulnerable species, such as many ungulates(mammals with hooves), may be active during the day. Most mammals are nocturnal, but even in two nocturnal species there are contrasts between the patterns of activity. Daily activity rhythms, those based on a 24-hour cycle, are termed circadian rhythms and are better understood than other types of rhythms.Ĭircadian rhythms differ markedly from one species to another. The timing of reproduction is cyclic, and in some mammals, such as some rodents and bats, daily or seasonal shifts occur between highly active and torpid states. Animals also exhibit other kinds of cyclic behavior. The time of emergence of a particular species of bat may differ by no more than two or three minutes night after night. The activity periods tend to be at regular intervals. Some species are active at night(nocturnal) and some during the day(diurnal) others are active primarily at dawn and dusk. One striking aspect of animal behavior is the rhythmic, or cyclic, pattern of activity. ![]() Certain mammalian behaviors serve to promote the survival of the individual. ![]()
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