Predator and prey is one of the most common type of relationships in the animal kingdom. Animals need to survive and feed themselves, and for predators that occurs through them hunting smaller animals or prey. Ecosystems are complex and diverse, with many levels and intricate relationships between organisms. Removing any level from an ecosystem disrupts a delicate balance that may have evolved over millions of years.
Populations rarely, if ever, live in isolation from populations of other species and in most cases, numerous species share a habitat. The interactions between these populations play a major role in regulating population growth and abundance. All populations occupying the same habitat form a community. The number of species occupying the same habitat and their relative abundance is known as species diversity.
There is usually a natural balance in the populations and relationships between predators and prey. More prey means more food for the predators, more energy and therefore more offspring. More offspring mean more consumption of the prey, hence reduction in the number of prey populations. Fewer prey populations mean less food for the predator, and hence predator populations suffer or reduce. The most obvious result of the removal of the top predators in an ecosystem is a population explosion in the prey species. Predators keep herbivore populations in check. The reverse is also true, of course — predator populations are limited by the availability of prey. When prey is abundant, predator populations increase because more young are able to survive. More predators kill more prey, which, along with food scarcity, decreases the population. When prey becomes scarcer, the predator population declines until prey is again more abundant. Therefore, the two balance each other. When the predators are removed, prey populations explode. Without any predators to limit population growth, herbivorous prey species reproduce without check, and all of them are hungry. More herbivores eat more plants, and without anything to control them, they can quickly degrade their habitat. This puts pressure on the plants that they depend on for food, sometimes to the point of impeding plant reproduction and defoliating the habitat. This is known as a trophic cascade, and in extreme cases, can lead to the complete destruction of the ecosystem.
Perhaps the classical example of species interaction is predation: the symbiotic relationship in which one species survives on consuming the other species. The species that consume or win is the predator and the species that is eaten is the prey. Populations of predators and prey in a community are not constant over time and in many cases vary in cycles that appear to be related. The most often cited example of predator-prey dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), using nearly two-hundred-year trapping data from North American forests. This cycle of predator and prey lasts approximately 10 years, with the predator population lagging 1–2 years behind that of the prey population. As the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare population begins to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due in part, to low predation pressure, starting the cycle anew.
It is therefore obvious that the predator-prey relationship remains to be one of the most delicate symbiotic relationship for the survival of species that share a common habitat, and should be carefully studied and documented before humans attempt to put their hands into the situation.