The diversity index takes in account both the species richness and the species abundance into account.
D = (N(N-1))/(£ n(n-1))
N is the total number of organisms of all species
n is the total numbers of organisms of each individual species
£ is the sun of all values that follow
Usually when an environment has extreme environmental conditions (e.g a desert) the biodiversity is low. Any change in this extreme environment has a big impact on population numbers as thus type of ecosystem tends to be unstable and very susceptible to change. This type of environment has some unfilled niches. This means that an incoming organism can be established very rapidly and overpower an existing species if they are competing for food or territories
In less hostile areas, biodiversity can be very high. This results in a stable ecosystem, because a new species moving in or out will have almost no effect
Biodiversity can be lost due to natural events such as volcanic eruption or flooding, but also as a result of human activities
Small or isolated ecosystems are particularly vulnerable to damage and destruction. When these easily damaged areas are also biodiversity hotspots, there is a higher risk of losing that biodiversity
Biodiversity is not constant. For example, the animal species in an area can vary with the time of day, e.g nocturnal species