This is an activity that I created to use with my students to help show them limits to an ecosystem. I tied this in with carrying capacity but also use this to show how human can impact an ecosystem.
In this activity students are in groups. Groups of 4 worked very well. Students are given cheese fish shaped crackers and a straw to use as their fishing pole. When the round starts all students in a group fish from their ocean (plate). Each round is 30 seconds long but can be shortened if needed. Usually the first round students will overfish their ecosystem causing a complete failure to their ecosystem. I usually use the first round as a practice round but still make my students record the data. After the 1st round any remaining fish multiply. I also include an environmental change scenarios after the fish multiply. This is to show students how other factors might affect the ecosystem. The students then fish again and record their data. We then repeat these step for several more rounds. This was a great activity for allowing my students to explore changes to an ecosystem. Students then discuss the activity in their groups and then we come back whole groups to discuss a bit more an to reflect.