Large-scale, worldwide adaptive radiations have occurred in which of the following situations?


a. when there are no available ecological niches
b. after each of the big five mass extinctions
c. after colonization of an isolated island that contains suitable habitat and few competitor species
d. whenever an evolutionary innovation was needed for organisms to thrive

Verified step by step guidance

1. Identify the concept of adaptive radiation, which refers to the rapid evolution of diversely adapted species from a common ancestor when they invade new, varied environments.
2. Analyze each answer choice in the context of adaptive radiation: a) Adaptive radiation typically requires available ecological niches to provide opportunities for diversification, not when there are none available.
3. Consider the historical context of mass extinctions and the opportunities they create: b) Mass extinctions often lead to vacant ecological niches, which can spur adaptive radiations as new species evolve to fill these niches.
4. Evaluate the scenario of an isolated island: c) Isolated islands with suitable habitats and few competitors are classic sites for adaptive radiation, as seen in Darwin's finches on the Galápagos Islands.
5. Reflect on the role of evolutionary innovations: d) While evolutionary innovations can lead to the success of certain species, adaptive radiation specifically involves the diversification into multiple new forms, which is not solely dependent on innovation but also on the availability of diverse ecological roles.

Key Concepts

Adaptive Radiation

Adaptive radiation is an evolutionary process where organisms diversify rapidly into a wide variety of forms to adapt to different environments. This typically occurs when a species colonizes a new habitat with available ecological niches, leading to the emergence of new species that exploit these niches. Understanding this concept is crucial for analyzing scenarios where large-scale radiations might occur.

Mass Extinctions

Mass extinctions are significant and rapid decreases in biodiversity on Earth, often resulting in the loss of a large number of species. The five major mass extinctions in Earth's history have been followed by periods of adaptive radiation, as surviving species exploit the vacant ecological niches left behind. This concept is essential for understanding the relationship between extinction events and subsequent evolutionary opportunities.

Ecological Niches

An ecological niche refers to the role and position a species has in its environment, including its habitat, resource use, and interactions with other organisms. The availability of ecological niches is a key factor that drives adaptive radiation, as it allows new species to evolve and thrive in diverse environments. Recognizing the importance of niches helps in evaluating the conditions under which adaptive radiations can occur.