Adaptive Radiation as a Source of Biodiversity
- From the Galápagos finches to African cichlids, adaptive radiation has repeatedly shaped ecosystems.
- It creates biodiversity hotspots and drives the emergence of new species.
Definition
Adaptive radiation
Adaptive radiation is the evolutionary process by which a single ancestral species rapidly diversifies into many species, each specialized to exploit a different ecological niche.
Adaptive Radiation Has 4 Key Tenets
- Common Ancestry: All species arise from a shared ancestor.
- Rapid Speciation: Multiple species evolve in a relatively short evolutionary timeframe.
- Ecological Specialization: Each species adapts to a specific niche, reducing competition.
- Morphological Divergence: Species evolve distinct traits suited to their roles in the ecosystem.
Darwin’s Finches
- The 14 species of finches on the Galápagos Islands are a classic example of adaptive radiation.
- Descended from a single ancestral species that likely arrived from South America.
- These finches evolved over millions of years to exploit different food sources.
- For example:
- The large ground finchuses its robust beak to crack hard seeds.
- The cactus finchhas a long, pointed beak for feeding on cactus flowers.
- The warbler finch employs its slender beak to catch insects.
- These specialized adaptations reduced competition among the finches, enabling them to coexist on the same islands.
Adaptive Radiation Increases Biodiversity
1. Filling Vacant Niches
- Adaptive radiation often occurs when species encounter unoccupied niches which are ecological opportunities not yet exploited by others.
After the extinction of dinosaurs, mammals diversified to fill roles once dominated by reptiles, leading to the rise of herbivores, predators, and aquatic species.
Analogy- Imagine a group of students entering a large, empty library.
- Each student chooses a different area to study, some head to the quiet study rooms, others to the computer stations, and a few to the group discussion tables.
- By spreading out, they avoid crowding and can concentrate on their tasks.
- Similarly, species undergoing adaptive radiation "spread out" into different ecological roles, reducing competition.
2. Minimizing Competition
- Adaptive radiation enables closely related species to coexist by occupying distinct niches, a phenomenon known as niche differentiation.
Closely related species can coexist by specializing in different niches, a process called niche differentiation.
TipWhen studying adaptive radiation, focus on the ecological niches that species occupy. This helps explain how closely related species can coexist without intense competition.
3. Promoting Speciation
- As populations adapt to different niches, they accumulate genetic differences.
- Over time, this divergence can lead to reproductive isolation and the formation of new species.
Examples of Adaptive Radiation in Nature
1. Cichlid Fish in African Lakes
- Lakes such as Victoria and Malawi are home to hundreds of cichlid species that evolved through adaptive radiation.
- These species exhibit diverse feeding strategies, such as algae scraping, snail crushing, and even scale eating.
