ACTIVITY 2
Effects of Global Warming on Populations Answer Key
Name_______________________________
Date_____________________
Below are graphs showing rate of development for various insects at different
temperatures.
Temperature C
Temperature C
Temperature C
1. What can you generally conclude from the above graphs about insect development?
The rate of development for insects is increased at higher temperatures until it reaches an optimal
temperature where development then starts to decrease.
The Great Tit is a song bird native to the Netherlands that
primarily feed on caterpillars. With springtime coming earlier
due to climate change, the first generation of caterpillars for the
season has been hatching earlier. Butterflies usually reproduce
several times a season.
*NOTE: Great Tit is the actual name of the song bird, but if
you feel your students would make inappropriate comments/remarks, feel free to simply
say ‘a species of song bird’ instead. Be sure to change in the questions below too.
2. Based on your answer to Question 1, why does it make sense that the caterpillars would be
hatching earlier?
Since spring is coming sooner, the temperature is getting warmer earlier in the year. Since
insects tend to develop faster at higher temperatures, the eggs are being laid sooner and they
hatch earlier.
3. Even though spring is coming earlier, it has been observed that Great Tits are not hatching
earlier. What do you think happens to the Great Tits’ food supply by the time they hatch?
There are less caterpillars for the Great Tits to feed on since they are developing into butterflies
sooner. Therefore, their food supply will be reduced.
4. What do you predict will happen to the caterpillar population as a result?
The caterpillar population will likely increase since it is not being preyed upon by the Great Tit
song birds until later in the season when they’ve likely already developed into butterflies.
5. What do you predict will happen to the Great Tit population as a
result?
The Great Tit population will likely decrease if there are fewer
caterpillars to eat. There would be more competition for a limited
food source.
6. The Eurasion Sparrowhawk is a predator of the Great Tit. Draw
a food web for the plant, caterpillar, Great Tit, and Eurasion
Sparrowhawk. Label the autotroph (producer), the primary
consumer, secondary consumer, and tertiary consumer. How much energy is passed from one
trophic level to the next?
Plant (autotroph) →Caterpillar (primary consumer) → Great Tit (secondary consumer) →
Eurasion Sparrowhawk (tertiary consumer)
Only about 10% of energy is passed from one trophic level to the next.
7. What do you predict will happen to the Eurasion Sparrowhawk population as a result?
The Eurasion Sparrowhawk population will likely decline as well if the Great Tit bird population
is declining. They will also have less food available and more competition.
8. What is a carrying capacity? What will happen to the caterpillar population once it reaches its
carrying capacity?
The carrying capacity is the maximum amount of individuals in a population that an environment
can sustain. When the caterpillars reach the carrying capacity they will likely temporarily
overshoot the capacity and then begin to decline as resources become limited and reduced. The
population will then likely level off.
9. Imagine that the butterflies resulting from the above mentioned caterpillars spread over acres
of land into more regions. In 200 years’ time you try mating a female butterfly from one region
with a male butterfly from a much further region and realize that they do not produce viable
offspring. What has happened? Explain.
The separation of time and space from the original population has resulted in genetic drift so that
one of the butterflies evolved into a different species through speciation. This means that they
cannot mate and produce viable offspring with a different species.
10. It has been observed that by the next breeding season there is NOT a drop in numbers of the
Great Tit population. Why do you think that is? (HINT: Think about competition for resources
throughout the season)
Since the Great Tits are not hatching earlier like the caterpillars, their food supply is initially
limited. This produces competition between the song birds. The ones that are most adept at
competing for food are the ones that survive and have a successful reproduction rate. Since
butterflies reproduce several times a season, the song birds that do survive the shortage of the
first generation of caterpillars then have plenty of food when the following generations of
caterpillars hatch.
11. Based on this new information, what do you predict happens to the Eurasion Sparrowhawk
population?
Answers will vary. The Eurasion Sparrowhawk may also have an initial decline in population
due to a shortage in song birds and then bounce back as more song birds reproduce. Students
could also suggest there could be no change in population if the Sparrowhawk preys on other
birds/organisms for food instead.