Theoretical Ecology course 2012 DEB theory Bas Kooijman Dept theoretical biology Vrije Universiteit Amsterdam Bas@bio.vu.nl http://www.bio.vu.nl/thb

Contents of 4 lectures on DEB theory Preliminary concepts required to link predictions to data Outline of basic theory for a 1-reserve, 1-structure isomorph Implications of theory for mass fluxes, body size scaling relationships Population consequences interactions between individuals

Dynamic Energy Budget theory for metabolic organization links levels of organization molecules, cells, individuals, populations, ecosystems scales in space and time: scale separation interplay between biology, mathematics, physics, chemistry, earth system sciences framework of general systems theory quantitative; first principles only equivalent of theoretical physics fundamental to biology; many practical applications (bio)production, medicine, (eco)toxicity, climate change

Space-time scales Each process has its characteristic domain of space-time scales molecule cell individual population ecosystem system earth time space When changing the space-time scale, new processes will become important other will become less important Individuals are special because of unit of evolutionary selection straightforward energy/mass balances

Some DEB principles life as coupled chemical transformations life cycle perspective of individual as primary target energy & mass balances stoichiometric constraints via Synthesizing Units surface area/ volume relationships spatial structure & transport synthrophy (basis for symbioses) homeostasis intensive/extensive parameters: scaling evolutionary perspective

Empirical patterns Feeding During starvation, organisms are able to reproduce, grow and survive for some time At abundant food, the feeding rate is at some maximum, independent of food density Growth Many species continue to grow after reproduction has started Growth of isomorphic organisms at abundant food is well described by the von Bertalanffy For different constant food levels the inverse von Bertalanffy growth rate increases linearly with ultimate length The von Bertalanffy growth rate of different species decreases almost linearly with the maximum body length Fetuses increase in weight approximately proportional to cubed time Reproduction Reproduction increases with size intra-specifically, but decreases with size inter-specifically Respiration Animal eggs and plant seeds initially hardly use O2 The use of O2 increases with decreasing mass in embryos and increases with mass in juveniles and adults The use of O2 scales approximately with body weight raised to a power close to 0.75 Animals show a transient increase in metabolic rate after ingesting food (heat increment of feeding) Stoichiometry The chemical composition of organisms depends on the nutritional status (starved vs well-fed) The chemical composition of organisms growing at constant food density becomes constant Energy Dissipating heat is a weighted sum of 3 mass flows: CO2, O2 and N-waste

Supply-demand spectrum 1.2.5 Species can be ranked in the gradient from supply to demand systems as stages in the evolution toward a high level of homeostasis. Extreme supply or demand systems don’t exist, all species represent a mixture of these extremes. Plants come close to the supply-end of the spectrum and can adapt their metabolism to the local environment relatively well. Demand systems adapt their metabolism much less and compensate that by a high level of behavioural flexibility. The characterizing property of demand systems is that the use of resources (growth, reproduction) is `pre-programmed’, which causes a particular need for food and growth curves that are given functions of age.

Energy Budgets Basic processes All have ecological implications Feeding Digestion Storing Growth Maturation Maintenance Reproduction Product formation Aging All have ecological implications All interact during the life cycle

Not age, but size: : These gouramis are from the same nest, they have the same age and lived in the same tank Social interaction during feeding caused the huge size difference Age-based models for growth are bound to fail; growth depends on food intake Trichopsis vittatus

Surface area/volume interactions biosphere: thin skin wrapping the earth light from outside, nutrient exchange from inside is across surfaces production (nutrient concentration)  volume of environment food availability for cows: amount of grass per surface area environment food availability for daphnids: amount of algae per volume environment feeding rate  surface area; maintenance rate  volume (Wallace, 1865) many enzymes are only active if linked to membranes (surfaces) substrate and product concentrations linked to volumes change in their concentrations gives local info about cell size ratio of volume and surface area gives a length

Change in body shape Isomorph: surface area  volume2/3 volumetric length = volume1/3 Mucor Ceratium Merismopedia V0-morph: surface area  volume0 V1-morph: surface area  volume1

Shape correction function at volume V actual surface area at volume V isomorphic surface area at volume V = for V1-morphs are special because surfaces do not play an explicit role their population dynamics reduce to an unstructured dynamics; reserve densities of all individuals converge to the same value in homogeneous environments V0-morph V1-morph isomorph Static mixtures between V0- and V1-morphs for aspect ratio

Biofilms solid substrate biomass Isomorph: V1 = 0 mixture between iso- & V0-morph V0-morph: V1 =  biomass grows, but surface area that is involved in nutrient exchange does not

Mixtures of changes in shape 2 Dynamic mixtures between morphs V1- V0-morph outer annulus behaves as a V1-morph, inner part as a V0-morph. Result: diameter increases  time Lichen Rhizocarpon V1- iso- V0-morph

Biomass: reserve(s) + structure(s) Reserve(s), structure(s): generalized compounds, mixtures of proteins, lipids, carbohydrates: fixed composition Reasons to delineate reserve, distinct from structure metabolic memory biomass composition depends on growth rate explanation of respiration patterns (freshly laid eggs don’t respire) method of indirect calorimetry fluxes are linear sums of assimilation, dissipation and growth fate of metabolites (e.g. conversion into energy vs buiding blocks) inter-species body size scaling relationships

Reserve vs structure 2.3 Reserve does not mean: “set apart for later use” compounds in reserve can have active functions Life span of compounds in reserve: limited due to turnover of reserve all reserve compounds have the same mean life span structure: controlled by somatic maintenance structure compounds can differ in mean life span Important difference between reserve and structure: no maintenance costs for reserve Empirical evidence: freshly laid eggs consist of reserve and do not respire

Homeostasis strong constant composition of pools (reserves/structures) generalized compounds, stoichiometric contraints on synthesis weak constant composition of biomass during growth in constant environments determines reserve dynamics (in combination with strong homeostasis) structural constant relative proportions during growth in constant environments isomorphy .work load allocation thermal ectothermy  homeothermy  endothermy acquisition supply  demand systems; development of sensors, behavioural adaptations

Body size length: depends on shape and choice (shape coefficient) volumetric length: cubic root of volume; does not depend on shape contribution of reserve in lengths is usually small use of lengths unavoidable because of role of surfaces and volumes weight: wet, dry, ash-free dry contribution of reserve in weights can be substantial easy to measure, but difficult to interpret C-moles (number of C-atoms as multiple of number of Avogadro) 1 mol glucose = 6 Cmol glucose useful for mass balances, but destructive measurement Problem: with reserve and structure, body size becomes bivariate We have only indirect access to these quantities

Storage Plants store water and carbohydrates, Animals frequently store lipids Many reserve materials are less visible specialized Myrmecocystus serves as adipose tissue for the ant colony

Flux vs Concentration concept “concentration” implies spatial homogeneity (at least locally) biomass of constant composition for intracellular compounds concept “flux” allows spatial heterogeneity classic enzyme kinetics relate production flux to substrate concentration Synthesizing Unit kinetics relate production flux to substrate flux in homogeneous systems: flux  conc. (diffusion, convection) concept “density” resembles “concentration” but no homogeneous mixing at the molecular level density = ratio between two amounts

Macrochemical reaction eq 3.5

Synthesizing units Are enzymes that follow classic enzyme kinetics E + S  ES  EP  E + P With two modifications: back flux is negligibly small E + S  ES  EP  E + P specification of transformation is on the basis of arrival fluxes of substrates rather than concentrations The concept concentration is problematic in spatially heterogeneous environments, such as inside cells In spatially homogeneous environments, arrival fluxes are proportional to concentrations

Evolution of DEB systems variable structure composition strong homeostasis for structure delay of use of internal substrates increase of maintenance costs inernalization of maintenance installation of maturation program 1 2 3 4 5 6 prokaryotes 7 9 plants 8 animals Kooijman & Troost 2007 Biol Rev, 82, 1-30 reproduction juvenile  embryo + adult strong homeostasis for reserve specialization of structure

Symbiogenesis 2.7 Ga 2.1 Ga 1.27 Ga phagocytosis

Life stages embryo juvenile adult fertilization birth death puberty baby infant weaning fertilization birth death puberty Essential: switch points, not periods birth: start of feeding puberty: start of allocation to reproduction Switch points sometimes in reversed order (aphids)

Arrhenius relationship ln rate reproduction young/d ingestion 106 cells/h Daphnia magna growth, d-1 aging, d-1 104 T-1, K-1

Arrhenius relationship ln pop growth rate, h-1 r1 = 1.94 h-1 T1 = 310 K TH = 318 K TL = 293 K TA = 4370 K TAL = 20110 K TAH = 69490 K 103/T, K-1 103/TH 103/TL

Concept overview supply-demand spectrum not age, but size surface area/volume iso-, V0-, V1-morphs shape correction function reserve & structure 5 types of homeostasis body size: weight, Cmol, .. body composition flux vs concentration macrochemical reactions Synthesizing Units evolutionary aspects life stages effects of temperature