Environmental change and adaptation in Galápagos finches | Middle school biology | Khan Academy
Summary
TLDRThe 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
🦜 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.
Mindmap
Keywords
💡Ground Finch
💡Beak Depth
💡Distribution
💡Drought
💡Seeds
💡Environmental Change
💡Adaptation
💡Survival
💡Reproduction
💡Extinction
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.
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