INTEGRATING TOOLS OF ECOLOGICAL STOICHIOMETRY AND NUTRITIONAL GEOMETRY

Submitted by editor on 6 September 2016.Get the paper!

Background: ES/NG working group at Woodstoich III

Upon meeting at the Woodstoich III workshop in Sydney, Australia in the summer of 2014, we and four other working groups sought to explore connections between ecological stoichiometry (ES), nutritional geometry (NG), and diverse other topics. Our diverse group (from Australia, Germany, Canada, and USA) was tasked with bridging concepts of ES and NG using our broad expertise in animal nutritional ecology. We quickly saw wide potential to combine ES and NG, but any synthesis would need to reconcile inherent differences between the two frameworks owing to (1) historically distinct model organisms and study systems, (2) emphases on different fields of inquiry and scales of biological organization, and (3) dichotomous nutritional currencies (elements in ES and macro- and micronutrients in NG). After the five day workshop and many emails and conference calls, we integrated complementary methodologies and concepts of each framework using the strengths of both ES and NG without compromising either framework’s currency. We applied our combined approach to data from existing case studies through two exercises, described below.

Exercise 1: Response surface plots of organism elemental budgets

In the first exercise, we combine the relative ease of organism elemental budgeting, a conceptual strength of ES, with state-space and response surface plots, a methodological strength of NG. We demonstrate the approach by constructing spatial plots of elemental budget components and growth of the detritivorous caddisfly larvae Pycnopsyche lepida across a gradient of carbon and phosphorus intake. The results show how both intake quantity and quality can affect organism elemental budgets, including excretion and egestion, body and waste stoichiometry, and growth rates. Elemental response surfaces better address inter-individual variation and accommodate nonlinear (allometric) relationships between animal nutritional regulation and intake. Notably, this tool provides enhanced organismal resolution to ES studies and can be applied to diverse taxa beyond the focal organisms of either ES or NG.

Exercise 2: Biochemical resolution of consumer-driven nutrient recycling

The second exercise combines consumer-driven nutrient recycling (CNR) theory, offered by ES, with response surface plots and enhanced biochemical resolution of animal nutrient wastes provided by NG. We use the biochemical form of nitrogen wastes (uric acid, amino acids, and protein) from the locust Locusta migratoria fed varying protein:carbohydrate diets to predict microbial breakdown and mineralization of nitrogen specific to each form of waste. Because L. migratoria released nitrogen predominantly as slow-breakdown protein and shifted to greater relative release of fast-breakdown uric and amino acids with increasing protein intake, nitrogen mineralization was proportionally faster and greater on high-protein diets. We demonstrate the biochemically-explicit model improves estimation of microbial nitrogen mineralization compared to a null model ignoring waste biochemistry and based on total waste nitrogen content. By considering the biochemistry of heterogeneous animal wastes, the ES/NG approach permits more holistic approaches to CNR, including broader phylogenetic comparisons and application of CNR to a greater diversity of systems outside the historical foci of either framework.

Experiences and what we learnt

Besides having a lot of fun during the intense workshop period at the beautiful Chowder Bay in Sydney, we also learned and gained a lot. Our group, with members of very different, but complementary backgrounds, has established a lasting collaboration and our paper points to potential future collaborations. The workshop also gave opportunities to build up an international network of collaborators both within and between group members as an important step in the career of young researchers. The native English speakers among us also learned to use vocabulary and writing styles that are easier for readers without English as their first language. For instance, avoiding jargon or profuse terminology that is not required to make a point can improve scientific communication with international audiences. Despite being sometimes challenging to have diverse perspectives within our group, we were able to come to consensus when necessary, thereby learning about the writing and scientific styles of other scientists beyond own advisors and labmates. Finally, it was wonderful to have mentorship from expert senior colleagues who gave valuable hints and insight into our topic and also have more experience in guiding the publication process.

Erik Sperfeld, Halvor Halvorson, Matthew Malishev, Fiona Clissold, and Nicole Wagner

Figure: (left) ES/NG group members in discussion with mentor David Raubenheimer, (middle) view of downtown Sydney during the workshop outing to nearby Taronga Zoo, (right) ES/NG group members with mentor Robert Sterner upon completion of a manuscript draft.

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