[问答题]
[Maximum mark: 3]
Two different mesocosms were used for a study to understand the population dynamics of two ecosystems, one without fish (C ) and one with fish (F). Each mesocosm had the following added to it: two different species of snails and the same (one) species of phytoplankton. The snails feed on the phytoplankton and are, in turn, preyed upon by the fish.
The following diagrams show the mesocosms used for the study. C is the control without fish, and F is the experimental mesocosm with one fish added. Both mesocosms were maintained at the same temperature and light conditions.
[© Revision Village 2023]
After a period of time, as shown in the graph below, the density of phytoplankton was seen to vary in the two mesocosms used in the study.
[Source: adapted from Cheng, H., Feng, M., Zhang, P., Zhang, H., Wang, H., Xu, J., & Zhang, M. (2022, December 30). Effects of warming on aquatic snails and periphyton in freshwater ecosystems with and without predation by common carp. MDPI. Retrieved January 10, 2023, from https
://www.mdpi.com/2073-4441/15/1/153, Copyright under CC-BY 4.0]
1.Outline a reason for the variation seen in the density of the phytoplankton in the two mesocosms, as shown above.
2.Explain whether this is indicative of a top-down or bottom–up control of the simulated ecosystem.
