Question

Scientists performed an experiment on a genus of small aquatic crustaceans called Daphnia. These animals are filter feeders that trap and eat protists and bacteria. Scientists placed different numbers of young Daphnia in similarly-sized tanks. This meant that in some tanks, individuals had a large amount of space, and in other tanks, individuals had less space and were crowded. Scientists gave each group plenty of food to ensure there was enough for every individual.

picture of adult daphnia and young daphnia under microscope

The results showed that during the early juvenile stages, Daphnia in the different tanks grew at similar rates. However, in tanks with fewer Daphnia, adults grew larger than in tanks with more Daphnia. Based on this information, what is the impact of a lack of space on Daphnia?
A.
Lack of space has no impact on how Daphnia grow.
B.
Lack of space causes Daphnia to grow to smaller sizes as adults.
C.
Lack of space causes Daphnia to grow faster when they are young.
D.
Lack of space keeps Daphnia from reaching adulthood.

Answer 1

B. Lack of space causes Daphnia to grow to smaller sizes as adults.

Reason: Juvenile growth was similar in all tanks, but adults in crowded tanks (less space) were smaller than adults in tanks with more space, so crowding reduces adult size.