This activity in the published book, Argument-Driven Inquiry in Life Science: Lab Investigations for Grades 6-8, is a 4-5 day lesson sequence that requires students to analyze data about the various species found in an ecosystem. The resource gives thorough teacher background, as well as access (via the NSTA website) to slides that students will use to gather data on each species. The resource gives some great ideas for discussion with the students in order to reflect on the concepts and investigation-design that the students participate in. The student pages include some background information as well as a scenario that the guiding question is based on. Since the students use the slides (provided) to acquire data, there is not much to set up prior to having the students complete the task. The questions that the students are given allow them to develop an argument and require them to use evidence and justification to support the argument that they make. This is allows them to learn a format to follow when developing a scientific argument.
For student materials, see three documents for lab 11 that can be accessed on-line at http://www.nsta.org/publications/press/extras/adi-lifescience.aspx. Teacher materials are in the purchased book.