Succession occurs because

a.

organisms gradually change the environment

b.

climax communities are not possible

c.

dominant organisms drive out pioneer species

d.

ecosystems never reach a sustainable point

Correct A) Organisms gradually change the environment

Succession occurs when a disturbance takes place in the environment, it can occur either by the disturbance of minor or major order disturbance.

The major disturbance can be caused due to the natural cause like the volcanic eruption and minor disturbance caused due to a natural or human cause like the forest fire.

Based on the type of disturbance succession is classified into two types of primary and secondary succession.

Primary succession is said to occur when a community or a group of the species evolve from a barren land. The land is fresh and new and no life is found on it.

Example: Succession after the volcanic eruption is said to be primary succession.

Secondary succession is said to occur when the disturbance destroys the whole ecosystem, but still, there is an availability of soil, nutrient, and seed in the ecosystem.

Example: Forest fire

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.