3-24 sensory systems - SENSORY SYSTE MS L IFE 53.3.6 53.4...

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SENSORY SYSTEMS LIFE 53.3.6 - 53.4 & 45 - 45.3 53.3.6 Animals must find their way around their environment -Most animals find their way by knowing and remembering the structure of their environment in a process called piloting . (i.e. Gray whales migrate seasonally between the Bering Sea and the coastal lagoons of Mexico. They find their way in part by following the west coast of North America. Coastlines, mountain chains, rivers, water currents, and wind patterns can all serve as piloting cues.) -The ability to return over long distances to a nest site, burrow, or other specific location is called homing . -Because many homing and migrating species are able to take direct routes to their destinations through environments they have never experienced, they must have mechanisms of navigation other than piloting. There are two systems of navigation: Distance-and-direction navigation requires knowing in what direction and how far away the destination is. With a compass to determine direction and a means of measuring distance, humans can navigate. Bicoordinate navigation , also known as true navigation , requires knowing the latitude and longitude (the map coordinates) of both the current position and the destination. -The behavior of many animals suggests that they are capable of bicoordinate navigation. -During the day, the sun can serve as a compass, as long as the time of day is known. Animals can use their circadian clocks to determine direction using the position of the sun. -Many animals are normally active at night; in addition, many diurnal bird species migrate at night and thus cannot use the sun to determine direction. The stars offer two sources of information about direction: moving constellations and a fixed point. 53.4.1 Visual signals are rapid and versatile -Visual signals are easy to produce, come in an endless variety, can be changed rapidly, and clearly indicate the position of the signaler. Most animals are sensitive to light and can therefore receive visual signals . -Visual communication is not useful at night or in environments that lack light, such as caves and the ocean depths. Some species have surmounted this constraint by evolving their own light-emitting mechanisms (i.e. fireflies) 53.4.2 Chemical signals are durable - Molecules used for chemical communication between individuals of the same species are called pheromones . Because of the diversity of their molecular structures, pheromones can communicate very specific, information-rich messages.
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- Pheromones remain in the environment for some time after they are released. The durability of pheromones makes them useful for marking trails (as ants do), marking territories (as many mammals do), or indicating location (as with the moth sex attractant). Their durability, however, makes pheromones unsuitable for a rapid exchange of information.
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