Question

with the extinction of the dinosaurs 65 million years ago, multiple niches that the dinosaurs once filled opened up and allowed mammals the opportunity to evolve and exploit those niches. this is an example of ____. sympatric speciation adaptive radiation phylogeny reproductive isolation phylogenetic isolation

Explanation:

• Sympatric speciation is when new species evolve from a single ancestral species while inhabiting the same geographic region. This is not the case here as the focus is on filling niches after dinosaurs' extinction.
• Adaptive radiation is the process by which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches. After the dinosaurs (a major group) went extinct, mammals had new niches (resources, habitats etc.) available and they diversified (evolved to exploit those niches), which fits the concept of adaptive radiation.
• Phylogeny is the evolutionary history and relationships among a species or group of species. The question is not about evolutionary history relationships in the sense of phylogeny but about a process of diversification into niches.
• Reproductive isolation is the mechanism that stops species from interbreeding. This is not relevant to the scenario of mammals evolving to fill niches after dinosaur extinction.
• Phylogenetic isolation is not a standard term in the context of this biological process described. The key here is the diversification into niches which is adaptive radiation.

Answer:

adaptive radiation