The above graph fits the following criteria:
• A population in which mortality as a proportion of survivors is constant-- curve II
• A population in which there is little early death and most individuals live to old age-curve I
• A population that experiences heavy mortality of the very young but with the survivors living to old age-curve III
Examples from real world of each survivorship pattern are:
• Curve I - Age structure of humans.
• Curve II - Birds and animals that care for their young ones.
• Curve III - Offspring of vertebrate fishes
A keystone species keeps the other species in check by not allowing any particular species to overgrow others. So, when a keystone species is removed, overgrowth of one species occurs and the extinction of the other species in the same habitat.
Predation describes a biological interaction where a predator (a hunter) feeds on its prey (the hunted).
Predator-prey relationships are those in which a predator kills its prey. In a parasite-host relationship, the parasite uses the host as a home and also for nutrition. The parasite usually does not kill the host but prefers to stay and multiply in the host.
In the evolutionary race between predator and prey the predator cannot afford to win as if it wins and kills all the prey, the next generation of the predator will have nothing to eat and will soon go extinct.