Environmental change and adaptation in Galápagos finches | Middle school biology | Khan Academy

Summary

The transcript describes how a drought on the Galapagos Islands influenced the evolution of ground finches between 1976 and 1978. As smaller seeds became scarce, only finches with larger beaks, capable of cracking larger seeds, survived and reproduced. Over two years, the average beak depth shifted from 8.8 mm to 9.8 mm, demonstrating rapid adaptation to environmental change. This example highlights how natural selection drives evolutionary changes within a species, as finches with favorable traits survived and passed them to their offspring, altering the species' overall traits.

Takeaways

• 🦜 The ground finch of the Galapagos Islands primarily feeds on seeds it finds on the ground.
• 📏 In 1976, the distribution of beak depths among finches showed many with a depth of 8.8 millimeters, though there was variation.
• 🌱 A drought occurred after the 1976 data was collected, resulting in fewer seeds, especially the smaller ones which were easier to eat.
• 🥜 The remaining seeds after the drought were larger, requiring finches with bigger beaks to crack and access the food.
• 🐦 Finches with larger beaks were more likely to survive because they could eat the larger seeds, and they passed on this trait to their offspring.
• 📊 By 1978, scientists observed a shift in the beak depth distribution, with the most common depth increasing to 9.8 millimeters.
• ⏳ This is an example of environmental changes, like a drought, leading to a rapid evolutionary shift in just two years.
• ⚠️ Environmental changes don’t always lead to adaptation—if too severe, they can cause extinction instead.
• 🧬 Evolution occurs through natural selection—birds with favorable traits (larger beaks) survived and reproduced more successfully.
• 🌍 The species as a whole adapted to the changing environment, even though no individual bird could consciously change its beak size.

Q & A

What is the primary source of food for the ground finch of the Galapagos Islands?

The primary source of food for the ground finch is seeds found on the ground.

What measurement unit is used for the beak depths of finches?

The beak depths are measured in millimeters.

What was the most common beak depth for the ground finches in 1976?

In 1976, the most common beak depth was 8.8 millimeters.

What environmental event occurred after the 1976 data collection?

A drought occurred, which resulted in fewer seeds being available.

How did the drought affect the availability of seeds for the finches?

The smaller seeds, which were easier to eat, were quickly consumed, leaving mostly larger seeds that required bigger beaks to crack.

How did the finches' beak size affect their survival during the drought?

Finches with larger beak depths were more likely to survive because they could crack the larger seeds, which were the only ones left during the drought.

What change was observed in the beak depth distribution between 1976 and 1978?

The beak depth distribution shifted to the right, with the most common beak depth increasing to 9.8 millimeters by 1978.

How did the drought drive evolutionary adaptation in the ground finches?

The drought created an environmental pressure where finches with larger beaks had a survival advantage. These finches were more likely to reproduce and pass on their traits, leading to a shift in the population's beak depth distribution.

Why didn't individual finches grow larger beaks in response to the drought?

No individual finch could change its beak size, but finches with naturally larger beaks had a higher chance of surviving and reproducing. Over time, this led to a population-level adaptation.

What could have happened if the drought had been even more severe?

If the drought had been more severe and no seeds were available, the finches could have faced extinction instead of adaptation.