The Shape of Things to Come

This week has been all about data analysis and response curves; yes-more response curves. If you don't remember from a few months ago, a response curve broadly describes how an organism responds to its environment. If the environmental cues (temperature, salinity, etc.) fall within an organism's optimal levels for the cues, the organism will not be negatively affected by the environmental factors. However, there may be instances where the salinity, temperature, etc. level drops below what the organism can tolerate, and therefore it will die in that environment. This week, I learned that if an organism's response curve falls outside of the environmental cue data the organism or model group will immediately crash in the model.

I spent most of my time this week working on two new environmental parameters for the model: TSS and dissolved oxygen. These two parameters are really interesting because the response curve shapes do not resemble the shapes for salinity and temperature, and these variables actually show opposing or mirrored shapes. Consider that TSS, or total suspended solids, make life more difficult for organisms when more solids are in the water column. Therefore, organisms will more likely tolerate low levels of TSS and show stress responses when TSS levels are high. The shape of this response curve, therefore, is what's called a left shoulder-a trapezoid that lacks a lower left bounding point, shown here in the first panel.

While organisms likely respond poorly to high levels of TSS, aerobic respirating organisms respond well to high levels of oxygen in their environment. In fact, it's unlikely that many organisms that need oxygen would be stressed by an overabundance of it in the water column. Therefore, for many organisms, lack of oxygen will cause stress and creates response curves that are right shoulder or sigmoid shaped, shown here in the second panel. We expect that at high levels of oxygen, organisms will survive quite well, which is why the horizontal portion of the response curves may extend quite far for these dissolved oxygen response curves.

​The addition of TSS and dissolved oxygen response curves to our model will help us address questions related to how increased sedimentation from sediment plumes in the Mississippi River affect the health of organisms in our model and how low oxygen or hypoxic events in the Mississippi Sound affect this ecosystem. While we still have some work to complete to make sure the model runs without crashing, I think we are quite close to full model runs and I'm excited to see the outcomes of the work we've done over the past six+ months. I do want to mention that unfortunately I won't be able to show results from this work for a while, as our deliverables for this project are different from when I was completing my Ph.D. Once we finish our work and we have published the report, however, I will be sure to link it for you to see and I will write a post explaining and reiterating our key findings. Until then, stay tuned for more updates on my adventures in quantitative ecology.

---