Respuesta :
For characteristic features of key stone species, option 1, 2 and 4 are correct.
What are keystone species ?
The presence of the species whether plant or animal in an ecosystem largely influence on a given environment called as keystone species.
It affect the habitat of all living organisms, so that the ecosystem would become functionless in absence of keystone species.
On of the best example is prey-predator relationship.
Some important environmental influence of keystone species are, it affect organism's physical appearance.
There is an impact of parasites, diseases on prey and host population, act as a mutualist, absence of key stone species leads to domino effect.
For example in absence of carnivore, number of herbivores increased, hence the environment cannot support the infinite number of herbivore population.
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