Keynote Speakers

Erik Muller (USA)

DYNAMIC ENERGY BUDGET THEORY AS INTEGRATIVE HUB FOR EVALUATING ORGANISMAL PERFORMANCE IN MULTIVARIATE ENVIRONMENTS

 Title: Dynamic Energy Budget Theory as integrative hub for evaluating organismal performance in multivariate environments.

 Abstract: The statement that organisms in their natural environments are subject to a multitude of environmental factors – some beneficial, some adverse and some either favorable or neutral or detrimental depending on their intensity or that of other factors – is a truism that nonetheless stresses a major challenge for ecologists. Societal needs press us to find answers to questions such as “What will be the implications of rising sea surface temperatures, acidifying oceans, increasing run-off and intensifying storms expected due to climate change on reef-building corals?” and “How will materials emerging through technological innovation, such as the rapid development of nanotechnology, compound with existing stress factors to affect organisms in their natural environment and food crops?”.

Perhaps somewhat less of a commonplace statement, a single environmental factor can have multiple physiological effects on a single organism. For instance, ocean acidification, i.e. the changes in the ocean carbonate system due to an increasing atmospheric pCO2, may have physiological impacts that are both positive, e.g. stimulating photosynthesis through CO2 enrichment, and negative, e.g. inducing pH stress and increasing the costs for calcification. As another example, toxic compounds often interfere with several organismal processes; e.g. cadmium may enhance the production of reactive oxygen species, inhibit enzymes via binding to sulfhydryl groups and cause zinc deficiencies, among other potential interferences.

Complex problems such as those outlined abovecall for an integrative metabolic theory, such as Dynamic Energy Budget (DEB) theory,that considers a multivariate environment with stressors that are potentially interfering with several physiological processes simultaneously. I will illustrate how those kinds of complex problems can be addressed inDEB theorywith various examples, including the impact of global change induced stress on marine calciferous organisms, the impact of engineered nanoparticles on the stability of symbioses of plants and nitrogen-fixing bacteria with generalized, process-based DEBtox theory.

Starrlight Augustine (Denmark)

Title:  What is maturity? Discussing links between the concept and the underlying physiology of organisms.

Abstract: Energy investment into maturation encompasses any expenses linked to tissue differentiation, i.e. reorganization of body structure during development. This is different from growth which can be conceptualized as synthesis of more of the same. Energy invested into growth is fixed into the biomass of the organism (with some overheads), but energy invested in maturation is oxidized as metabolic work making it more difficult to quantify in practice. Nonetheless it can be quantified and it can even represent a substantial part of the energy budget of living organisms. In this talk I will give an overview of different studies where investment in maturity was quantified. The focus will be on 5 different types of organisms: cnidarians, ctenophores, teleost fishes, frogs and dinoflagellates. I will further discuss what type of eco‐physiological effects might be expected when an organism modifies its investment into these processes. Some intriguing literature studies will be presented which can be re‐interpreted in perhaps unexpected ways when investment into maturation is taken into account. This raises the question of just how important and how flexible such costs might actually be. Maturity can be used as a quantifier for internal time. Seven criteria were proposed which should be respected by any such metric: (1) independent of morphology, (2) independent of body size, (3) depend on one a priori homologous event, (4) unaffected by changes in temperature, (5) similar between closely related species, (6) increase with clock time, and (7) physically quantifiable (Reiss 1989). We showed that the maturity concept of Dynamic Energy Budget theory complies with all those criteria and on the basis of this information and the studies presented above I will finish by discussing the potential role of maturity in shaping metabolic flexibility.

Ulrike Feudel (Germany)

Title: Competition of species using a synthesizing unit approach

Abstract: In many studies of competition models Liebig’s law of the minimum is used to account for the fact that the least available nutrient will determine the growth rate of the plankton species. However, this would require that the organisms can instantaneously switch their physiological regulation system, which is problematic. It is more natural to assume that there is a co-limitation for all ressources, so that all ressources contribute to the growth rate. Therefore, we study models which use the concept of a synthezising unit developed in the framework of energy budget theory [1]. This concept is based on the mechanisms of enzyme kinetics and considers all ressources as complementary. Using this model we study the dynamics of the competing species which can exhibit competitive exclusion, heteroclinic cycles, stable coexistence in a fixed point and periodic solutions. Moreover, we find the coexistence of more species than ressources in parameter regions where periodic and chaotic solutions are possible. Hence, we can show that supersaturation is possible in a model with a more realistic approach to the uptake of ressources. It is important to note that this model exhibits supersaturation in parameter ranges which are realistic. Our study reveals the dynamical mechanism how supersaturation can occur: it is due to a transcritical bifurcation of limit cycles. Furthermore, we show, how general competition theory can be explained in terms of bifurcation theory to account for a much larger class of systems then originally studied by Tilman [2]. This mathematical approach complements and extends the graphical methods developed by Tilman [2] to include models with co-limitation and with a larger number of species.

REFERENCES

[1]      Kooijman, S.A.L.M.: Dynamic Energy Budget theoryformetabolicorganisation. Cambridge University Press, Cambridge, 2010.

[2] Tilman, D.: Resource competition and community structure. Princeton University Press, Princeton, 1982

Andre de Roos (The Netherlands)

Title: On the relevance and irrelevance of dynamic energy budget models for population and community dynamics

 Abstract: Dynamic Energy Budget (DEB) models describe how individual organisms acquire and use energy from food and have therefore been argued to consistently link different levels of biological organisation. Various types of DEB models, differing in the organisation and precedence of metabolic processes such as growth, maintenance and reproduction, have been proposed and investigated, although recently the term DEB theory has become more and more identified with the framework developed by Kooijman. 
In this lecture I will address the question to what extent differences between DEB models affect the dynamics at the population and community level. I will show that maintenance costs, which are accounted for in all DEB models, have a crucial influence, but that metabolic organisation is of lesser importance. I will furthermore show that population and community dynamics are mostly determined by differences in the capacity of individuals with different body sizes or in different stages of their life history to transform food into new biomass. Such differences, which I refer to as ontogenetic asymmetry in energetics, are however influenced more by the types of food that individuals forage on in different stages of their life history than by their internal energetics. Ontogenetic shifts in resource use during life history are therefore likely to have a larger influence on population and community dynamics than the details of the individual energy budget.

 

Wilco Verberk (The Netherlands)

Title: Size matters for balancing energy supply and demand in aquatic ectotherms.

Abstract: Oxygen is essential for burning food and generate energy, but may become limiting for aquatic organisms that rely on gas exchange under water. This is because breathing under water is challenging: the diffusion of oxygen is orders of magnitude lower in water than in air, while the higher density and viscosity of water greatly enhance the cost of breathing. Given that oxygen may be also be a limiting resource, respiration physiology may be relevant to understand energy budgets in aquatic ectotherms.
Traditionally, respiration physiology has focused on the benefits of extracting sufficient amounts of oxygen and thus prevent asphyxiation. However, breathing oxygen is intrinsically dangerous: while a shortage of oxygen quickly leads to asphyxiation, too much oxygen is toxic. Therefore, the ability to regulate oxygen consumption rates (i.e. respiratory control) is at a premium; good respiratory control will enable ectotherms to balance oxygen toxicity against the risk of asphyxiation across a wide range of temperatures.
In this presentation I will focus on the effects of body size and temperature on this balancing act with regard to oxygen uptake and consumption. Body size is intimately tied to oxygen budgets and hence energy budgets through size related changes in oxygen requirements and respiratory surfaces. Furthermore, a larger body size may represent a respiratory advantage that helps to overcome viscosity. Given that viscous forces are larger in cold water, this respiratory advantage represents a novel explanation for the pattern of larger body sizes in cold water, with polar gigantism as the extreme manifestation.
Temperature is also intimately tied to oxygen budgets and hence energy budgets through thermal controls on metabolism and temperature related changes in the availability of dissolved oxygen (notably diffusivity, viscosity and solubility). Thus, differences in temperatures may act more strongly on ectotherms that rely on aquatic rather than on aerial gas exchange. Comparing four different insect orders, I demonstrate that thermal tolerance is indeed affected more by the prevalent oxygen conditions in species with poor respiration control. In conclusion, the ability to regulate gas exchange (i.e. respiratory control) is thus a key attribute of species that helps to explain thermal responses from an oxygen perspective.