Explain how the intensity of disturbances can affect equilibrium and species diversity.?

Every pattern is seen across the globe, but in the most general case, disturbances can lead to a hump-shaped pattern in species diversity.  Systems that are undisturbed for a long time can approach a monoculture, with few species.  Disturbances clear-out patches of vegetation and increase the different kinds of habitats that may be occupied.  This allows colonizing species to occupy areas, such as North American species fireweed, dandilion, and other weeds, as well as species like coyotes.

At some point, disturbances become so common that the number of species that can endure decreases.  Instead of increasing diversity of habitats, disturbances begin to simplify things.  Species diversity then decreases.  

A contrived example might be a closed forest in Hawaii, which would have a given number of bird species.  Some disturbance would open up gaps and allow edge bird species to move in.  If disturbances become extremely common, like lava flows moving through regularly, few species could live there.  So a humped shape response.

If you are rolling along in a species, you don't go through much change unless a major environmental disturbance comes your way.  Those individuals who survive the disturbance,  win the right to reproduce will pass those genes on to the next generation, leading to more diversity.

You need to add to this example:

I would google "how fast does evolution occur?" - that could help also.