I’m extremely honored that the Ecological Society of America (ESA) Early Career Section chose my paper, Nonlinear Effects of Intraspecific Competition Alter Landscape-Wide Scaling-Up of Ecosystem Function, for their Outstanding Paper Award this year. The paper was published earlier this year in The American Naturalist and it’s work that I’m especially proud of. I realized I never did a Twitter thread or blog post about this paper even though it’s the one I love the most out of everything I’ve published, so here I’ll talk about it a little bit!
The idea that eventually became this paper arose out of a discussion I had with Emanuel Fronhofer when we were planning out my part of the Dispersal Network experiment. I wanted to look at whether dispersing and resident (non-dispersing) amphipods consumed detritus at different rates, because if they did, then dispersers might have different impacts on ecosystem function (spoiler: we found that this is sometimes the case!). At some point in this conversation, I realized that there was a confounding factor here: density. Dispersers are typically at lower infraspecific densities because they are by definition the first arrivals in a new patch. So if density had any effect on their feeding behavior, it would be hard to tell whether the differences between dispersers and residents were due to traits or to density. To address this, as we ran our experiment comparing residents and dispersers, we *at the same time* (yes this made a lot of work…) ran an experiment looking at detritus consumption across a density gradient.
What we found was exciting: indeed, in both amphipod species, per-capita consumption was much higher when individuals were alone or with only a few neighbors, and was quite low when they were in crowded mesocosms. Importantly, this relationship was highly nonlinear. We attributed the results to interference competition, since food resources were not limiting in our experiments.
This already might have made this work my favorite project, because the density aspect was a question that I felt I really came up with independently and pushed to test as part of our other experiment. It is kind of the inverse of how we typically think of a “functional response”: instead of feeding rate being a function of prey/resource density, it is also a function of consumer density. But we went even further! Out in nature, there is immense variation in population size between different ecosystems. So, I used geostatistical modeling to map the density-dependent per-capita consumption rates onto stream networks where we had done extensive surveys of population sizes. This generated maps that showed hotspots of amphipod density but fairly homogenous patterns in detrital consumption due to the nonlinear relationship between the two. I could then integrate over the entire networks of each of the ten small catchments (watersheds) I had surveyed, to get estimates of the total amount of detritus being processed in each one. This mode of scaling up estimates of ecosystem function is novel and was really fun to work out.
I find this work so exciting, and it drew from nearly every aspect of my PhD: lab experiments, field experiments, spatial modeling, and meta-ecosystem theory. Please go have a read!