Predators vs. Prey
All animals must eat to survive. With predators always on the lookout for a meal, prey must constantly avoid being eaten. Any adaptation the prey uses adds to the chances of survival for the species. Some adaptations are defense mechanisms which can give the prey an advantage against enemies.
Prey Defense Mechanisms
There are many ways animals avoid falling prey to a predator.
Tools of the Trade
One of the most striking physical traits of many predators is the forward location of the eyes. This arrangement provides the predator with binocular vision. Since the field of view of the two eyes overlaps, the brain receives two images of the same object at one time. This allows the brain to make precise judgements of depth and distance.
The sense of smell is of vital importance to many predators. They use it not only to locate prey, but also to communicate with others of their species. While mammals smell with their nose, other creatures have different arrangements - snakes smell with their flickering tongues, and insects smell with their antennae. Most birds have no sense of smell at all.
Among mammals, an elongated snout often indicates an increased reliance on the sense of smell. The longer snout provides more room for complex nasal passages housing chemically sensitive cells that do the actual smelling. Compare the skull of the bobcat with the skull of the coyote. The bobcat, like other felines, hunts primarily by sight and so has a fairly short snout. The coyote, on the other hand, relies heavily on his long nose to help him find his prey.
Most mammalian predators possess a keen sense of hearing. Their external ear flaps, or pinnae, can be swiveled forward or back to focus on a particular source of sound. The ears of bats are often highly specialized, with strange shapes that help catch the echoes of their sonar-like calls as they fly.
Birds also hear extremely well. Among the most remarkable avian ears are those of the barn owl. Its ears are not symmetrically placed - one is higher than the other. With its ears offset in this way, the barn owl can pinpoint the direction from which a sound is coming. Scientists have shown that barn owls can locate and catch mice, even when blindfolded!
Some predators do quite nicely without any sense of hearing at all. Snakes, for example, have no external ears. They can pick up vibrations through the bones of their lower jaws, but rely on their other senses - sight, smell, and even heat detection - to find prey.
Beaks and Feet
Mammals aren't the only animals with adaptations for catching prey. Birds display a wide variety of physical adaptations that help them obtain food. These adaptations are most easily observable in birds' beaks and feet.
Long beaks for probing, hooked beaks for tearing, thick ones for crunching seeds, thin ones for picking insects - each beak tells a story about its owner. Beaks provide birds with a lightweight alternative to a mouthful of teeth - like hollow bones, they are an adaptation for flying.
The legs and feet of birds also provide clues to their way of life. Long legs generally signify a wader, while large claws are found on birds of prey. Swimming birds have either webbed feet, like ducks, or lobed toes, as in coots and grebes. Many other species also have specializations in the form or arrangement of their toes.
Many predatory mammals use their jaws to seize and subdue their prey. Their jaw muscles must maximize the leverage and gripping power at the front part of the jaws. This increased power is provided by a muscle called the temporalis. The temporalis muscle pulls the lower jaw toward the top of the skull. To strengthen this connection, predator skulls often bear a central bony ridge called the sagittal crest. The sagittal crest provides a strong, secure anchor point for the temporalis muscle.
The power needed to crush bones is provided by a different muscle, the masseter. The masseter muscle pulls the lower jaw toward the cheekbone, or zygomatic arch. In predators, the masseter muscle is usually smaller than the temporalis, suggesting that it is more important to seize prey than to crush it.
Among plant eaters, the reverse is often true. The temporalis muscle is generally smaller than the masseter. Rather than a sagittal crest, there may be an enlargement of the lower jaw to provide a better anchor for the masseter. This arrangement suggests that, for the plant-eater, crushing and grinding vegetation is more important than biting it off the plant.
The method used by a predator to pursue its prey is determined by many factors, including the adaptations of the predator, the adaptations of the prey, and the nature of the habitat in which they live. A technique that works well in one situation may prove quite ineffective in another. Each strategy has its own inherent risks and rewards. Consider three commonly employed techniques: the chase, the stalk, and the ambush.
Hawks are among the many predators that catch their prey by chasing it. Chasing may involve a significant expenditure of both time and effort to make a successful capture. To be efficient, predators that chase their prey must concentrate on species that will provide enough nutrition to offset the energy burned up in capture. Thus the hawk tends to eat more rodents and birds than grasshoppers, because grasshoppers just don't provide enough food value to justify the effort it takes to catch them.
Herons employ a different technique. Standing motionless inshallow water or wading slowly along the shore, the heron patiently searches for prey, which it captures with a quick lunge of its long, sharp beak. This method doesn't require much energy; the search time may be great, but the time to catch prey once it's found is minimal. A stalking predator can afford to choose smaller prey and still meet its energy requirements.
The alligator prefers to lie in wait until something edible happens by. This method of hunting requires little effort at all; however, chances for success are fairly low. The alligator, a reptile and therefore cold-blooded, has minimal energy requirements; its metabolism is so slow that it can get by with infrequent meals. Because a successful ambush depends on the predator avoiding detection until it strikes, most ambush hunters are fairly small.
Camouflage (matching colors or patterns)
Many animals have fur, feather or scale coverings that match the plants, soil or rocks where they live. The tawny fur of lions helps them to hide in the dry, yellow-brown grasslands of the African savannah. Many desert animals have sandy brown coats that help them to blend into their background. Animals that live in rainforests may be green or brown to match the colors of foliage and tree trunks.
Predators Use Lots of Energy Hunting Prey
For a predator, hunting down active prey can be an energy-expensive proposition. There's the energy involved in searching for prey; the energy involved in chasing the prey; and the energy involved in capturing and killing the prey. That's assuming the prey is caught - for many predators, the majority of their attempts end in failure. For the predator to be successful, these energy losses must be repaid by the energy it gains from its food.
There is another way. Rather than going through all the trouble of killing something to eat, a meat eater could simply feed on the carcass of an animal that was already dead. Such behavior, called scavenging, can provide the benefits of eating meat (high nutrition, easy digestibility) without many of the associated costs. Indeed, many predators do not hesitate to take advantage of such opportunities when they occur.
So why don't predators become full-time scavengers? Probably because there simply aren't enough dead animals to go around. The odds of an animal finding a carcass every time it's hungry are fairly small. So, even though predation takes more effort than scavenging, in the long run, it may provide a more dependable source of energy.
Importance of the Predator-Prey Relationship
To sum it all up, the predator-prey relationship is important in maintaining balance among different animal species. Adaptations that are beneficial to prey, such as chemical and physical defenses, ensure that the species will survive. At the same time, predators must undergo certain adaptive changes to make finding and capturing prey less difficult. Without predators, certain species of prey would drive other species to extinction through competition. Without prey, there would be no predators. Thus, this relationship is vital to the existence of life as we know it.