[问答题]
Two different mesocosms were used
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zo8kcyqp*g 8wh+s9 8 sstudy 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
s8swz+*qc9p8 kyg 8ho 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.
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.
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.
