As you saw in the examples from Phase I, experiments start with a question. As a team, you will need to identify at least 3 questions that you could potentially answer with an experiment. You'll then develop those experiments, and ultimately conduct them.
Herbivory is an enormous topic. There are myriad directions that you could take this project. Here are a few thoughts to help get you started.
Did you notice any plants with consistently high levels of herbivory? If so, which? Do you think this is consistent across that species' range, or is it unique to that place?
Did you notice any plants with consistently low levels of herbivory? If so, which? Does that species produce secondary metabolites that differ from other plants?
Were there any habitats where herbivory, overall, seemed especially high? Is that due to the herbivores living there, or to the plants themselves? How could you test this?
Which of the plants you identified were native, and which were invasive? Do invasive plants have more herbivory, or less? Invasion biologists theorize that invasive species become invasive partly because the native herbivores don't recognize them as food, allowing them to outcompete native plants. Evidence for this theory is mixed. Does it seem to be true in your habitats? Could you test this?
Do plants close to the ground experience more herbivory than plants higher up?
Were there any species that seemed to be heavily grazed in one habitat, but not in another? Do you think that's due to the herbivores living in those habitats? Or could it be because the plants are producing different secondary metabolites in the different habitats?
What types of herbivores do you think are responsible for the damage you observed? Do you think they are large or small? Occupying the leaf for long periods, or visiting it briefly?
The pilot experiment you conducted was an observational study, in the sense that you did not experimentally manipulate anything. As you've seen, observational data can be very powerful, and can be used to address interesting questions. Your main "experiments" do not have to be experiments at all -- you could opt to conduct an entire study with observational data alone! (In that case, we'd be better off calling it a "main study", don't you think?)
That said, you certainly could do manipulative experiments. Experiments can be a powerful way to understand the mechanism driving patterns that you observe in nature. Many of the questions above deal with plasticity --i.e., the possibility that plant phenotypes can be different in different environments. How can we know if plasticity is driven by plant-herbivore interactions or by plant-environment interactions? We would need to do an experiment!
By the same token, if we want to know how a particular plant species would perform in a different habitat, there's only one way to find out -- move it to the other habitat!
Two common types of experiments that plant biologists use are common garden experiments and reciprocal transfer experiments. You can read more abut these designs here. You won't have time to grow plants in different habitats in this course, but you could do these experiments by making 'bouquets' of cut leaves which you stake out in different habitats for a short time.
You could also think about the herbivore's point of view -- what herbivores are we talking about? Do they have preferences for particular plants? Do they avoid other plants? Do these patterns correlate with your observational data? You could trap herbivorous invertebrates to bring indoors for controlled experiments.
We cannot trap vertebrate herbivores for this course, as we do not have IACUC approval. However, vertebrates are generally much larger than invertebrates in this system, so one way to examine vertrebrate herbivory would be through exclusion experiments in which you build a protective cage around plants to keep out large herbivores, while still letting insects in. Chicken wire makes a cheap and effective caging material.