My first year of grad school has been a roller coaster. Developing my questions, taking classes, doing fieldwork, and so much reading. It has been a whirlwind learning about and discussing countless ecological theories, so I was really excited this week to read about one that admittedly has always confused me. Neutral theory is one of those “classic” theories that is taught in modern ecology classes and has always rubbed me the wrong way. The idea that there are no ecological differences between organisms or species seems like a non-starter, why would different species exist if all species were equal and the survival of a species was simply the result of stochastic processes?
To try to understand it, I went back and read some of Hubbell’s early papers on the topic including his work in Costa Rica and Tree Dispersal1 to try to understand why the concept of neutral theory seemed so at odds with my understanding of species interactions. Of all of Hubbell’s papers, why was this one included on the penultimate list by Courchamp and Bradshaw? It was there in the very last paragraph that things started to make sense again. Hubbell spends most of the paper discussing tree abundance and seed dispersal and how the tree community can be explained in simple terms by a stochastic model, but what caught my attention was the statement right at the end, so small I nearly missed it.
“Obviously this model is an oversimplified representation of the dynamics of natural communities, but it does provide a number of important lessons….”
There it was. Proof that even the author of the paper thinks neutral theory isn’t the full story. I turned next to a 2012 paper by Rosindell et al. that I hoped would hold all the answers. In The case for Ecological Neutral Theory2 the authors discuss some of the contentious debates surrounding neutral theory. They make a case that the concept of ‘neutral theory’ is not to treat all organisms as equal but to be used as a null model for comparison when species are not. They point out that at some scales neutral theory may be the simplest explanation for the data, and it’s the job of the scientist to prove otherwise. Finally, a clear explanation for why Neutral theory is still relevant to modern ecology.
Perhaps, I missed the boat in my other ecology courses, but I can’t imagine presenting neutral theory in any other way but as a tool to be used. I’m left with more questions than answers about other “classic” theories and how they are taught in ecology courses, but at least on this topic I feel relatively satisfied.
The concluding thoughts of the Rosindell paper are a reminder to us all, that theories change and evolve, and we must recognize the limitations of our understanding.
References:
- Hubbell, S. P. Tree Dispersion, Abundance, and Diversity in a Tropical Dry Forest. Science (80-. ). 203, 1299–1309 (1979).
- Rosindell, J., Hubbell, S. P., He, F., Harmon, L. J. & Etienne, R. S. The case for ecological neutral theory. Trends Ecol. Evol. 27, 203–208 (2012).