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.

Outlines

00:00

🦜 Ground Finch and Beak Depth Distribution (1976)

This paragraph introduces the ground finch from the Galapagos Islands, highlighting its primary food source—seeds found on the ground. It describes the beak depth distribution observed in 1976, with most finches having a beak depth of 8.8 millimeters. The data sets the stage for an environmental change, a drought, that will affect the finch population.

🌵 Drought Impact on Seed Availability

This paragraph explains how a drought reduced the availability of smaller seeds, leaving only larger seeds. Finches with larger beaks had a survival advantage because they could crack these bigger seeds. This sets up the conditions for a change in the finch population’s beak sizes over time due to natural selection.

🦢 Natural Selection in Action (1976–1978)

This section describes the observable shift in beak depth distribution over two years, from 1976 to 1978, as larger-beaked finches were more likely to survive and reproduce. Scientists noted that the most common beak depth shifted from 8.8 mm to 9.8 mm, demonstrating an evolutionary adaptation to the changing food supply caused by the drought.

🌍 Environmental Change and Species Adaptation

This paragraph emphasizes that environmental changes like droughts can drive adaptation in species. It notes that while some changes can lead to extinction, the finches were able to adapt by favoring individuals with traits that helped them survive. The example shows how natural selection leads to a gradual shift in a species’ traits in response to environmental pressures.

🔄 Adaptation Without Individual Awareness

Here, the text clarifies that individual finches did not consciously grow larger beaks. Instead, the population had natural variations in beak size, and those with bigger beaks were more likely to survive and pass on their genes. Over generations, the species as a whole adapted to the new environmental conditions, showcasing the process of evolution by natural selection.

Keywords

💡Ground Finch

The ground finch is a species native to the Galapagos Islands, central to the video’s example. It primarily feeds on seeds found on the ground. The finch is used to illustrate how environmental changes can lead to adaptations in species. In this case, the variation in beak depths of the finch population plays a crucial role in their survival during drought conditions.

💡Beak Depth

Beak depth refers to the measurement, likely in millimeters, of the thickness or size of a finch's beak. This trait is essential in determining which finches survive during periods of environmental stress. In the video, finches with larger beak depths were better able to crack larger seeds, a key factor in their survival during a drought.

💡Distribution

In the context of the video, distribution refers to how the beak depths of finches vary within a population. The video discusses how, in 1976, most finches had a beak depth of around 8.8 millimeters, but there was a range. After environmental changes, such as the drought, this distribution shifted, with larger beaks becoming more common.

💡Drought

The drought, mentioned as occurring after 1976, significantly impacted the food supply available to the finches. It led to fewer seeds, especially small seeds, pushing the finch population to adapt. Only finches with larger beaks could crack the larger remaining seeds, which caused a shift in the population’s beak size distribution over two years.

💡Seeds

Seeds are the primary food source for ground finches, and the availability of seeds influences their survival. In the video, the depletion of small seeds due to the drought meant that only finches with larger beaks could access the larger seeds that were left, driving a shift in beak size among the finch population.

💡Environmental Change

Environmental change refers to any alteration in the ecosystem that impacts the survival of species. In this case, the drought caused a significant environmental change that led to a shift in food availability. As a result, the finch population had to adapt, and over two years, the distribution of beak depths shifted toward larger beaks.

💡Adaptation

Adaptation is the process through which species adjust to changes in their environment. In the video, the finch population adapted to the new conditions caused by the drought. Finches with larger beaks, who could access the remaining large seeds, were more likely to survive and pass on their traits, leading to a shift in beak size in the population.

💡Survival

Survival in the video refers to the ability of finches to endure the harsh conditions created by the drought. The finches with larger beaks were more likely to survive because they could crack the remaining large seeds, while those with smaller beaks struggled and were less likely to reproduce.

💡Reproduction

Reproduction is the process by which organisms pass their genetic traits to their offspring. In the video, finches with larger beaks were more likely to survive and reproduce, passing on their larger beak size to the next generation, which over time led to a shift in the population’s average beak size.

💡Extinction

Extinction is the complete disappearance of a species. The video highlights that if environmental changes are too severe, like if the drought had eliminated all seeds, the finch species could have faced extinction. However, in this case, the species adapted instead of disappearing.

Highlights

The ground finch of the Galapagos Islands primarily feeds on seeds found on the ground.

In 1976, scientists observed the distribution of beak depths in finches, with a peak around 8.8 millimeters.

After the data was collected, a drought occurred, leading to fewer seeds available.

Smaller seeds, which were easier to eat, were consumed quickly during the drought.

The larger seeds, which required a larger beak to crack, were the only ones left after the drought.

Finches with larger beak depths were more likely to survive and reproduce due to the availability of larger seeds.

From 1976 to 1978, the distribution of finch beak depths shifted to the right, with 9.8 millimeters becoming the most common.

This shift in beak depth distribution was a direct response to environmental changes caused by the drought.

Environmental changes, such as drought, can lead to adaptation in species if the conditions are not too severe.

If environmental changes are too extreme, such as the complete lack of seeds, species could face extinction instead of adaptation.

The finches adapted over two years by natural selection, where birds with larger beaks were more likely to pass on their traits.

No individual finch knew to grow a larger beak, but there was natural variation in beak depths within the population.

Year after year, finches with larger beak depths had a higher survival and reproduction rate.

This example demonstrates how a species can adapt to new environmental conditions over a short period.

The study of finch beak adaptation shows how natural selection acts on existing variations to drive evolutionary change.

Transcripts

- This here is a picture of the ground finch

of the Galapagos Islands.

And one of its primary sources of food

is seeds that it finds on the ground.

And if we go back to 1976,

we can look at the distribution of beak depths.

And these beak depths,

I would assume these are given in millimeters.

Finches are quite small birds.

And you can see in 1976,

you have a large number of finches

that had a beak depth of 8.8 millimeters,

but it was a distribution around that.

Now, after this data was collected,

it turns out there was a drought and there were fewer seeds.

So the smaller seeds,

which were easy to eat for all of these finches,

would have been consumed quickly.

And all that would have been left were the larger seeds,

the ones that you need a larger beak

in order to crack and get at the good stuff.

So what do you think would have happened

to the distribution of beak depths

over the course of the next two years?

Well, you might guess that the birds,

the finches that have larger beak depths,

are more likely to survive because they're more likely

to be able to crack the larger seeds.

And the finches that are more likely to survive

are also more likely to reproduce,

and pass their large beak trait to their offspring.

And that is indeed what scientists observed.

As we go from 1976 to 1978,

the distribution has shifted a pretty good bit to the right.

Now the most common beak depth is 9.8.

So this is an example of an environmental change, a drought,

changing the food supply,

because now there's fewer small seeds available,

that changed a distribution in beak depths

over just two years.

Now, environmental changes don't always cause adaptation.

If it's too severe,

if the drought was so strong that there were no seeds,

you could have extinction.

So the species disappears altogether.

But here we have an example that in just two years,

a species was actually able to adapt a pretty good bit.

Now, no individual member of the species

knew to somehow grew their beak.

But as we saw, you always have a variation of beak depths.

And year after year,

the birds with the bigger beak depth,

were more likely to survive and reproduce.

So the species as a whole

adapted to the new environmental conditions.