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Ecological Stoichiometry

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  1. Ecological Stoichiometry Hao Wang MATH 570 University of Alberta

  2. What is STOICHIOMETRY? Stoichiometry in chemistry: Focuses on the balance of elements within chemical equations. Stoichiometry in biology: Focuses on the balance of elements and energy within biological systems. This includes metabolism, growth, etc. Stoichiometry in ecology: Focuses on the balance of elements and energy within ecological systems. This includes competition, commensalisms, etc.

  3. Why need STOICHIOMETRY? Carbon (C), nitrogen (N), and phosphorus (P) are vital constitutes in biomass: C supplies energy to cells, N is essential to build proteins, and P is an essential component of nucleic acids. The scarcity of any of these elements can Severely restrict organism and population growth.

  4. What would happen to cows if there wasn't so much sunlight? Expectations from a 9-year old ecologist James J. Elser’s son

  5. What would happen to secondary production if solar radiation were reduced? Expectations from single-currency ecological theory Primary Production, Autotroph Biomass Solar Radiation High Low Secondary Production, Herbivore Biomass High Low Solar Radiation

  6. Stoichiometric Imbalance Impairs Herbivores In Freshwater and Terrestrial Ecosystems Freshwater herbivore (Daphnia) Terrestrial herbivore (Pieris) From: Elser, J.J., W.F. Fagan, R.F. Denno, D.R. Dobberfuhl, A. Folarin, A. Huberty, S. Interlandi, S.S. Kilham, E. McCauley, K.L. Schulz, E.H. Siemann, and R.W. Sterner. 2000. Nutritional constraints in terrestrial and freshwater food webs. Nature 408: 578-580.

  7. Secondary Production, Herbivore Biomass High Very High Low Solar Radiation Junk food Starvation

  8. (CXNYPZ)inorganic+(CXNYPZ)autotroph+ light->Q (CXNYPZ)'autotroph+(CXNYPZ)’ inorganic (CXNYPZ)prey+(CXNYPZ)predator->Q (CXNYPZ)predator+(CXNYPZ)’waste From: Elser, J.J., and J. Urabe. 1999. The stoichiometry of consumer-driven nutrient recycling: theory, observations, and consequences. Ecology 80: 735-751.

  9. C, N, and P are three of the main constitutes in biological structural molecules. HOWEVER, C, N, and P are not particularly abundant on Earth or in the universe as a whole and thus it seems that living things made a very discriminating selection of elements from the environment.

  10. O 50.02 Si 25.80 Composition of Earth’s Crust Al 7.30 Fe 4.18 S 0.11 C 0.18 Ca 3.22 Na 2.36 K 2.28 H 0.25 P 0.11 N 0.03 Fe 0.01 P 1.14 S 0.14 Ca 2.5 Na 0.10 K 0.11 N 2.5 H 9.9 C 20.2 Composition of Human Body O 63.0

  11. Laws and Hypotheses • Conservation Law of Matter • Homeostasis • Liebig’s Minimum Law • Growth Rate Hypothesis • Light:Nutrient Hypothesis

  12. Conservation Law of Matter In an ordinary chemical reaction, matter and component elements are neither created nor destroyed.

  13. Homeostasis Consumers have fixed elemental composition in biomass. This is often called “strict homeostasis”. However, plants have highly variable nutrient contents because of physiological plasticity in relation to environmental conditions such as light, nutrient supply, CO2, etc. (examined via bifurcations in Hao Wang, Robert W. Sterner, and James J. Elser. On the "strict homeostasis" assumption in ecological stoichiometry, Ecological Modelling, Vol. 243: 81-88, 2012).

  14. [Strict] Homeostasis (animals, heterotrophic bacteria, etc.) Herbivore C:nutrient 0 Producer C:nutrient Nonhomeostasis (plants, etc.) Producer C:nutrient 0 Substrate C:nutrient

  15. Droop Equation Plant growth rate as a function of cell quota (P:C or N:C ratio) is modeled and experimentally verified by Michael Droop in 1973-1974.

  16. Liebig’s Minimum Law The growth of an organism is controlled by the most limiting element. From: C.A. Klausmeier et al. 2004. Optimal nitrogen-to-phosphorus stoichiometry of phytoplankton. Nature.

  17. Growth Rate Hypothesis Rapid growth requires increased allocation to P-rich ribosomal RNA to meet the protein synthesis demands of rapid growth. Based on: Elser, J.J., D.R. Dobberfuhl, N.A. MacKay, and J.H. Schampel. Organism size, life history, and N:P stoichiometry: toward a unified view of cellular and ecosystem processes. BioScience 46: 674-684.

  18. Autotroph C : Nutrient Ratio Increases (Nutrient Content Declines) With Increasing Light Intensity Nutrient-limited Cyanobacterium (Synechococcus linearis) From Healey (1985) Nutrient-limited Red pine (Pinus resinosa) From Elliot and White (1994) From: Sterner, R.W. and J.J. Elser . 2002. Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere. Princeton University Press, Princeton, NJ.

  19. Light:Nutrient Hypothesis Aquatic ecosystems with low light:nutrient ratios should have several trophic levels simultaneously carbon (or energy) limited, while ecosystems with high light:nutrient ratios should have several trophic levels simultaneously limited by nutrients.

  20. Evaluating The Light:Nutrient Hypothesis: A Mix of Strategies Simple Controlled Replicated Short Small Artificial Complex Uncontrolled Unreplicated Long Large Natural Analytical model Simulation model Lab flask Small indoor microcosms Big indoor microcosms Field microcosms Whole-ecosystem manipulation Field sampling

  21. Theoretical Test of Light:Nutrient Effects x' (t) = bx(1 - ) - f (x)y x min[K, (P - qy)/ q] (P - qy) / x q Model of Loladze, Kuang and Elser (modified from model of T. Andersen) y' (t) = emin (1, ) f (x)y - dy Grazer (carbon biomass) Producer From: Loladze, I, Y. Kuang, and J.J. Elser. 2000. Stoichiometry in producer-grazer systems: linking energy flow and element cycling. Bull. Math. Biol. 62: 1137-1162.

  22. Assumption 1 Fixed total mass of phosphorus, P, in the entire system. Assumption 2 Plant P:C varies with a minimum q; herbivore P:C is a constant, θ. Assumption 3 All phosphorus of the system is either in plants or in herbivores. Logistic growth (light-dependent) Droop equation (nutrient-dependent) Liebig’s Law Plant P:C ratio Herbivore P:C ratio

  23. Theoretical Test of Light:Nutrient Effects light light Model of Loladze, Kuang and Elser (modified from model of T. Andersen) light From: Loladze, I, Y. Kuang, and J.J. Elser. 2000. Stoichiometry in producer-grazer systems: linking energy flow and element cycling. Bull. Math. Biol. 62: 1137-1162.

  24. Theoretical Test of Light:Nutrient Effects light Model of Loladze, Kuang and Elser (modified from model of T. Andersen) Grazer From: Loladze, I, Y. Kuang, and J.J. Elser. 2000. Stoichiometry in producer-grazer systems: linking energy flow and element cycling. Bull. Math. Biol. 62: 1137-1162.

  25. Experimental Test of the Light:Nutrient Hypothesis "Aquatron" Experiment (summer 2000) by Urabe and Elser

  26. Aquatron Dynamics (Extra) High Light (380 µE / sq m / s) Low Light (40 µE / sq m / s) High Light (310 µE / sq m / s) Daphnia Daphnia Algal P:C Algal C Algal C Algal C Daphnia Extinction? C transfer efficiency: ~30% C transfer efficiency: ~7% Urabe, J., J.J. Elser, M. Kyle, T. Sekino and Z. Kawabata. 2002. Herbivorous animals can mitigate unfavorable ratios of energy and material supplies by enhancing nutrient recycling. Ecology Letters: in press.

  27. Field Test of the Light:Nutrient Hypothesis 100 % treatment 25 % treatment The Light : Nutrient Project

  28. The Light:Nutrient Hypothesis: Consequences Based on: Sterner, R.W., J.J. Elser, E.J. Fee, S.J. Guildford, and T.H. Chrzanowski. 1997. The light:nutrient balance in lakes: the balance of energy and materials affects ecosystem structure and process. Am. Nat. 150: 663-684.

  29. Light:Nutrient Balance and Global Change Under future climate scenarios in the continental boreal regions (Schindler 1998), runoff to lakes will likely decrease. Effects of such shifts on lakes remain unclear.  However, such climate changes will likely lower external nutrient supply while simultaneously raising light intensity (due to lower DOC inputs). Light:nutrient supply may become increasingly unbalanced. These effects are analogous to effects of elevated pCO2 in terrestrial systems and appear to be driven by similar mechanisms.

  30. Daphnia-Algae Experiment Study organisms Daphnia pulex: a widespread and important planktonic herbivore in N. America Daphnia lumholtzi: a daphnia native to Africa but now invasive in N. America. Scenedesmus obliquus: a Chlorophyte (green algae) found in many lakes and easily grown in the laboratory. Pictures courtesy of: Paul Hebert; aslo.org; and www.biol.tsukuba.ac.jp/

  31. Methods Experimental Design High Light Low Light 21.8uE/m2/s 3-L Jars 218uE/m2/s n = 3 n = 3 No Daphnia Daphnia pulex alone n = 3 n = 3 n = 3 n = 3 Daphnia lumholtzi alone n = 3 n = 3 D. pulex and D. lumholtzi together Population sizes and species composition were measured twice weekly, while algal carbon and phosphorus data and Daphnia body sizes and egg numbers were measured once weekly.

  32. Main Experimental Results Competitive Exclusion in both high light or low light!

  33. Competition Model Algal C Pulex C Lumholtzi C Algal P

  34. Hypothesis D. lumholtzi has higher requirements for C (energy) while D. pulex has higher requirements for P (nutrient). measured in carbon biomass High Light Low Light

  35. Rich Dynamics Low light intensity in the experiment High light intensity in the experiment

  36. A chaotic attractor

  37. The Light:Nutrient Hypothesis: Consequences Based on: Sterner, R.W., J.J. Elser, E.J. Fee, S.J. Guildford, and T.H. Chrzanowski. 1997. The light:nutrient balance in lakes: the balance of energy and materials affects ecosystem structure and process. Am. Nat. 150: 663-684.

  38. Dynamics of Stoichiometric Bacteria-Algae Interactions in the Epilimnion

  39. Question 1 What is the relationship between cyanobacteria and algae? How do light and nutrient availability regulate relative abundances of bacteria and algae in the Epilimnion?

  40. A Lake System river brook input Epilimnion quickly well mixed water exchange input input Hypolimnion quiescent

  41. Scenario The Epilimnion is quickly well mixed in the sense that it is well mixed over night. AssumptionThe Epilimnion is well mixed all the time.

  42. Algae Competitive System Algae Cell Quota DIP Flexible stoichiometry of algae using Droop’s form as a nutrient limitng factor Average sunlight uptake efficiency of algae in the mixing layer Respiration loss Algal sinking and water exchange This system is modeled for Epilimnion following ‘quickly well mixed’. The cell quota depletion rate is proportional to algal growth rate The replenishment rate of cell quota is the per unit consumption rate Phosphorus consumption by algae Phosphorus input and water exchange Hao Wang, Hal L. Smith, Yang Kuang, and James J. Elser. 2007. Dynamics of Stoichiometric Bacteria-Algae Interactions in the Epilimnion. SIAM J. Appl. Math, Vol. 68, pp. 503-522.