More insect species will provide food for more bird species, etc. Crop rotation and agroforestry are management practices that increase biodiversity. Genetic diversity, that is having many different organisms of the same species, is also important to keep the gene pool large so that inbreeding doen't occur and the species is better able to survive. Competition among several species or several individuals of the same species will assure that the strongest, most suited individuals survive in any given area and reproduce, passing their genes on to the next generation. Thereby, the strongest and fittest survive and reproduce again.
Succession is the process of the species populations in an area changing over time.
For example, a grassland will become a brushland which will become a forest eventually if succession continues. A disturbance might set back the process of succession to an earlier stage. For example, a fire in a prairie will burn back the encroaching brush and set the process back to the grassland stage. Different species of plants and animals will inhabit the same area at different successional stages, once again increasing diversity, over time.