Which of the following is true of ecological succession?
select one:
a. pioneer organisms move into to new communities first
b. primary productivity decreases as succession proceeds
c. secondary succession takes place within new communities with no previous soil
d. all of the above are true

a. Pioneer organisms move into to new communities first.

Explanation:

An ecological succession can be define as the series of gradual changes that occur in the biotic community of the ecosystem with respect to changes that occur on non-living factors until the ecosystem attains the stability.

Among the options given, a. Pioneer organisms move into to new communities first. is the correct option this is because of the fact that pioneer species are the first species which colonize in a region which is not previously occupied by any living species. Such species experience no competition from other living species and they actually make the environment suitable for survival of other species.