Today we spent some much needed time developing our experiment and making decisions on our plants and lighting apparatus. We began our class by discussing the options that the light team came up with.
John gave us an update on the best type of lights for us to use in the field: a long line of LED lights that can be cut into different lengths and hooked up to a battery. We decided that we need wire to hook up our light segments to a battery in series. However, we have yet to decide whether we need another 12V battery or whether Marshall’s will be enough. We also did not decide if we want to get a waterproof or non-weather-proof LED line. For this option, it came out to be below $200, which stays on track with our budget and leaves us more wiggle room for building our actual structures and for anything else that may come up in the future. There is still a huge decision to be made about the lights, however.
The plant team presented four potential plants to use for our study: alfalfa, Brassica, tomato, and strawberry. Cameron was able to get approximately 1000 alfalfa seeds from an on campus lab, however, we decided not to use this plant because it seems like it would take too long to reach a large enough size to be useful to our study. We also decided against strawberry because the only option to order these plants is in bare root form, which are difficult to cultivate. Collectively, we decided that Brassica nigra and tomato would be great options because they are easy and cheap to get, grow quickly, and lend themselves well to our study. Both plants have many known herbivores, the two plants represent different plant groups that are common in this area, and they will hopefully complement each other. Ivana Li from the BIS 2B lab offered us 40 fast plant (Brassica) seeds that will be fully grown within 3 weeks and she sent the link for us to order more. The 40 seeds will be picked up tomorrow and 200 more have been ordered and should arrive in 2 days. Marshall has been corresponding with the student farms to start growing tomatoes, which should be ready for us to use by the start of April- just in time! We also decided to add snap peas to our plant group because they represent a third group of plants and are easy and fast to grow. Those have been ordered as well.
We also need to make sure we have soil, fertilizer, and pots to grow our plants in. Louie contacted the campus greenhouse to see if we will be able to use any of their equipment and soil.
After our debrief and decision-making session, we had a brief discussion on the large scope of our experiment. We addressed big picture questions such as: what is our design intending and what are our assumptions? The latter question presented a good point; we are assuming that spiders and other insects are attracted to light. This seems like a safe assumption considering the literature pointing to it though, so it seems like our question is fairly legitimate.
Insect Finding Challenge
After our brief discussion, Asia had us do a challenge she created for us to determine the best way to measure herbivory and categorize insects, and determine how quickly we can complete our measurements. We split into groups to streamline the measurement process. In our group, John explained a visual counting method for determining diversity and richness in a quick way. It has three timed counts starting with the first one, where you count your assigned object (eg. one person counts ladybugs while the other counts aphids, etc.). For the second count, everyone counts everything. For the third count, you determine the number of different things you see. This seemed like a good method for this challenge, but it is important to note that we will be mainly collecting insects in sticky traps and pitfall traps and doing our measurements in lab. We did determine, however, that it should take approximately 5 minutes per set up for us to do our measurements. We also determined that we should complete more readings on quantifying herbivory.
After our challenge, we delved back into a discussion about what type of light to use and how to best set up our experiment. We discussed multiple papers on the attractiveness of light to insects. Our set up should potentially have the goal to attract insects, since we are looking at the trophic cascade and herbivory and are relying on insect presence. The papers we discussed seemed to point us towards 4000K LED bulbs in the warmer spectrum of wavelength, though for LED it doesn’t seem to be detrimental if we use a cooler bulb. This ended up working really well for us since the average street light falls within the spectrum of light that seems to attract insects the best.
Along the lines of making our lights attractive to insects, we also presented the idea of using white mesh to act as a reflector (just like a white wall near a street light). Louie found a paper that mentioned that light intensity does not matter as much as the ration of foreground to background contrast. This could be beneficial because not only would the mesh help attract insects, but it would also act as a wind shield and substrate for spiders to build webs on.
As far as experimental design, it seemed like most people were on the same page about having three treatments: “light”, “dark”, and “light with spiders removed”. Our original plan of having “light with spiders removed” and “light with spiders added” seemed a little bit redundant and difficult to do in reality. We also toyed with the idea of having a “dark with spiders removed” treatment, but that may add confounding variables or may just be a duplicate of our “dark” treatment. Having three treatments could potentially allow us to have 40 replicates per treatment, for a total of 120 apparatus set ups. This would give us more power than if we separated the 120 set ups between four treatments.
We also discussed potentially having a continuous study (light intensity gradient) versus a categorical study (binary presence/absence), but we ended up sticking with categorical because of simplicity and because other studies seem to have already ruled out light intensity as a cue for insects.
Some limitations we discussed were the fact that we have to wire all our lights together, thus making it difficult to distance them enough and squeeze our dark treatments randomly in with our light without compromising them. Should we use two field sites then? Or multiple batteries? These are questions we still need to address.
For next class, we need to fully discuss our question and further develop our methods. We should also aim to discuss our in-lab experiment and determine if it would be feasible to do or not. We also need to make groups to come in on Friday or the weekend to plant our brassica and snap pea seeds.
1:40-2:10 Discuss lighting and make decision on what to get
2:10-2:50 Discussion on lab experiment (Marshall)
2:50-4:00 Large group discussion on experimental design for field experiment
4:00-4:10 Make groups for planting over the weekend
4:10-4:30 Discuss next steps