Final answer:
The process by which an organism fills a void in nature and diversifies into many new species is known as adaptive radiation, which involves speciation and results in increased biodiversity.
Step-by-step explanation:
The macroevolutionary process by which an organism fills a void in nature, through niche diversification and the emergence of many new species, is called adaptive radiation. This process involves a single species evolving into a multitude of new species to fill available ecological niches. Speciation is key to understanding this process, as it explains how one species can diverge and form many distinct species over time. Darwin's theory of evolution and natural selection are pivotal in explaining this phenomenon, as adaptive radiation results in increased biodiversity due to organisms adapting to fill different ecological roles.
Examples of adaptive radiation can be seen in the various finch species that Darwin studied on the Galapagos Islands. These birds evolved from a common ancestor but diversified to exploit different food sources and habitats. The radiation led to the formation of multiple new species, each adapted to a specific way of life.