1 Appendix S1: Additional information on model parameterization and goodness-of-fit criteria 2 Initialization. Initial biomasses (Table 1) for the 24 guilds were the same in all models and given values 3 derived from a 10-year average of spring values. For fish inital biomasses, we used sonar and catch data 4 (Appenzeller 1998). For APP, we used lower initial values (20 μgC/m3, see Table 1) than observed to give 5 eukaryotic algae a head start in spring, mimicking slower onset of APP’s spring growth (Weisse 6 1988;Padisak et al. 1997) which is not appropriately reflected in allometric relationships. 7 Allometric parameterization. To achieve generality, we mostly applied allometric algorithms to estimate 8 parameter values (Tables 1 and S1) following Williams (Williams 2008) from the average body sizes of the 9 organisms of the 24 guilds (Lang 1997). These estimates involved normalization; the growth rate ri of 10 producer i is normalized to the growth rate of a chosen reference producer species k (Eq.1) by the 11 relationship 12 producer k, and the allometric constant 13 (Brose et al. 2006). Following (de Castro & Gaedke 2008), we set the allometric scaling exponent A to 0.15 14 for all species except fishes for which A=0.11 (Killen et al. 2010;Killen et al. 2007;Killen et al. 2007). 15 Consumers' 16 2006), we set 17 The allometrically estimated ri of APP and xi of Bac were reduced by a factor of 4 and 25, respectively, to 18 mimic the relatively slow metabolic rates of their populations (Makarieva et al. 2005;Chen & Liu 2010;Cole 19 et al. 1988;Joint 1990;Nielsen 2006) (Gaedke&Straile 1994, Simon 1998). Although individual bacterial cells 20 may achieve maximal growth rates based on allometric scaling under favorable conditions, the majority is 21 strongly resource-limited and partly in a state of metabolic inertia under natural conditions, resulting in an 22 overall low metabolic rate of the population. The ri of Alg3 which comprises several thermophilic species 23 was reduced by 75% in the LC-specific models M2-M4 to mimic its relative rarity before summer. 24 Diet-specific parameters. Following (Brose et al. 2006;Yodzis & Innes 1992), we set yij = 10. Placing 25 planktivore assimilation efficiency intermediate between herbivores and carnivores, we set eij to the 26 empirically supported value of 0.66 (Bierman & McIlroy 1986;Nielsen & Olsen 1989). Bacteria were assigned 27 eij =1 because they are osmotrophs. 1 , where is the body mass of species i, (massA/time) and the body mass of the reference (massA/time) which is 1 for all producers is also normalized by reference producer k. Following Brose et al. (Brose et al. = 0.314 (massA/time) for all plankton species i and = 0.88 (massA/time) for all fishes i. 1 Functional response. We set the functional response F to a weak Holling type III response with q= 1.2 2 (Williams & Martinez 2004) to account for minimal refuges in pelagic freshwater systems q > 1 (Sarnelle 3 2003). We set 4 ( 5 abundances (Williams 2008). We varied dkj of the functional response (Eq. 5) to mimic observed increases in 6 grazing resistance due to increased grazer density in 55 (37 for zooplankton, 1 for bacteria, and 17 for fish 7 predation) of the 107 feeding links in LC (see below and Table S3). Given the uncertainties involved in 8 extrapolating half saturation constants from lab measures to field conditions, and to avoid too many free 9 parameters, we set the same, low half saturation constant B0ij (cf. Eq. 5) for all zooplankton guilds (Table 10 S1). For the fishes, the half saturation constants differed among links (Table S2) to balance allometry- 11 independent effects of varying predation pressure on the competing crustacean guilds Dap and Cyc (also see 12 “prey resistance” below). 13 Fish mortality. A mortality term M(B) was used for fishes to maintain their total biomass at levels observed 14 in LC (Appenzeller 1998). For the generalizable models M0-M1, we set M ( B) mBi 2 , with the mortality 15 coefficient m = 1.2 * 10-5. For the LC-specific models M2-M4, we replaced the quadratic term by a fisheries 16 model which simulates human exploitation of the two adult fish guilds that are commercially intensively 17 exploited in LC to a considerable extent. The fishery effort’s time derivative dF/dt is based on an equation by 18 Conrad (Conrad 1999): 19 dF n( pqBj c ) F dt 20 , with the economic openness n = 0.0055, the price per unit biomass p = 0.5, the catchability q = 0.00005, and 21 the exploitation cost per unit of fishery c = 0.03. The mortality of the exploited fish guild with biomass Bi then 22 becomes M ( B) qBiF . We set F=500μgC/m3 as an initial value for the fisheries’ effort and the dynamics 23 of F were nearly constant during the simulation. 24 We excluded the fish from the evaluation of model fit because a.) there is no seasonal data on the four fish 25 guilds for validation comparable to the plankton community, and b.) we calibrated the mortality coefficient 2 making the relative inverse attack rates on prey range add up to one ) and causing generalists to consume at lower feeding rates than specialists at similar prey 1 m and the economic coefficients n, p, q, and c in the way that the top predators would not surpass the coarse 2 biomass estimates available from LC catch and sonar data. 3 Activity and maintenance respiration. The approach to separate activity from maintenance costs (when 4 the animal is resting) is in agreement e.g. with Humphreys (Humphreys 1979), showing a rather constant 5 relationship between production (P) and respiration (R) of P/(P+R) ≤ 0.5. That is, in long-term sustainable 6 communities, production maximally equals respiration, but is often lower especially for highly active 7 animals (e.g. flying insects) or endotherms with higher maintenance costs (Begon et al. 2006). The idea to 8 separate activity and maintenance metabolic costs in plankton communities into a production-dependent 9 and a biomass-dependent part was elaborated in (Anderson 1992). Following previous studies (Humphreys 10 1979), we set fa = 0.4 describing the fraction of assimilated carbon gained for production and fm = 0.1 (Eq. 2) 11 describing the fraction lost by maintenance respiration. The fractions fa and fm (Eq.2) which determine the 12 relative balance of maintenance vs. activity costs depend on metabolic type because maintenance costs are 13 much higher (and transfer efficiencies lower) e.g. for endotherm vertebrate consumers. 14 Model time scale. All ordinary differential equations in the model describe the biomass change of species i 15 as 16 primary producer k (Alg1). Since Alg1 doubles every day (rk=1), one model time step equals one real-time 17 day. 18 Detritivores’ consumption. The detrital loop was closed for carbon in all models so that bacteria were 19 treated as consumers according to Eq. 2 with detritus as resource. The dead (particular and dissolved) 20 organic carbon pool (detritus) was made available to Bac with a time lag as a very coarse simulation of 21 photolysis. Following Davidson (Davidson 1996), we used an exponential decay function of the form dBi in model time t’=t/rk which is normalized by the mass-specific growth rate (rk) of the reference dt ' N, 22 with . = newly available detritus in each time step, = 23 amount of detritus produced by the ATN model (Eq. 3), k=fragmentation rate, N=time lag constant. We set 24 k=0.45 and N=3500 for a time lag of approximately 1 week in the model. 25 Producer competition. There is strong evidence that competition for shared resources is generally lower 26 between than within LC phytoplankton guilds due to e.g. different nutrient requirements, resource uptake 3 1 capacities and other niche differentiation. We set cij = 1 for i ≠ j (neutral effect) and cii = 1.8 otherwise 2 (inhibitory effect) in the producer growth equation (Eq.4) for the LC-specific models M2-M4 to account for 3 moderately increased intra-guild competition within phytoplankton guilds. Using intra-guild producer 4 competition coefficients improved the biomass fit among the 6 phytoplankton groups which compete for a 5 common system capacity Ks in the model. The reason for the improved fit was that intra-guild producer 6 competition prevented the guild with the highest growth rate (Alg1) from dominating the others after the 7 CWP when predation pressure was temporarily lower than before and during the CWP. 8 Abiotic forcing. Abiotic forcing of autotrophs was modelled by continuously reducing KS from 100% to a 9 minimum of 50% until summer by multiplying KS with a coefficient k 1/ (1 e z (t t max) ) , with decay exponent 10 z = 0.1, t as the current simulation time and tmax = 110 time steps (beginning of summer). Increasing nutrient 11 limitation was further reflected by multiplying autotrophs' ri by a light coefficient (cl) equal to 12 cl 13 extinction with epilimnion depth h, while λ2 is the degree of self-shading in presence of phytoplankton at 14 concentration CPhyt, h = depth, and I0 = the half-saturation irradiance for phytoplankton growth (Wallace et 15 al. 1996). Abiotic forcing of consumers was modelled by multiplying xi by a temperature coefficient (ct) equal 16 to ct=Q10(T-T0)/10 where T = temperature, T0= the standard temperature and Q10 = temperature-dependency 17 coefficient. Daily T and I values for the calculation of ct and cl were interpolated from weekly LC observations 18 in 1990 (Fig. S1). 19 Prey resistance to grazing pressure. Prey defense is very widespread in nature, embraces several 20 phenomena occurring in natural communities, and may change due to e.g. inducible defense, behavioural or 21 morphological changes, shifts in clonal or species composition , and microevolution. However, it comes at a 22 cost since defense structures and mechanisms require energy which could otherwise be invested in growth 23 and reproduction. Hence, undefended individuals or species generally dominate under low predation 24 pressure and are replaced by more resistant ones at high predator abundance. The outcome of such a 25 variable degree of prey resistance is that predators consume per capita less when they are at high density 26 which influences the shape of predator-prey cycles (Jones et al. 2009). An explicit modeling of the multiple 4 1 log 10 I 0I h where I = irradiance, λ = light extinction = λ1λ2 CPhyt. The factor λ1 accounts for light I 0 Ie , h 1 causal mechanisms underlying alterations in prey resistance was not appropriate in the present context to 2 maintain generality of the modeling approach. 3 Numerous studies confirmed the importance of changes in prey resistance in response to 4 altered predation pressure, e.g. for algal-ciliate or –rotifer systems (Tollrian & Harvell 1999;Yoshida 5 et al. 2003;Fussmann et al. 2003;Abrams & Matsuda 1997;Lass & Spaak 2003), bacterial strains 6 (Matz & Kjelleberg 2005;Corno 2006), crustacean zooplankton resisting and/or avoiding fish 7 predation (Geller 1989;Stich & Lampert 1981;Straile & Halbich 2000) and beyond (Abrams & 8 Matsuda 1997;Jones et al. 2009). Despite a rather constant overall algal biomass, the biomass of 9 different algal species exhibited fast and pronounced changes in LC during spring, indicating that 10 edible and less edible species or morphotypes alternated in response to changes in grazing pressure 11 (Tirok & Gaedke 2007;Tirok & Gaedke 2007;Tirok & Gaedke 2010). Such changes in trait values 12 within predator and prey communities may strongly dampen their overall dynamics (Tirok & Gaedke 13 2010; Tirok et al. 2011). 14 Based on this argumentation in our ATN model, the prey resistance coefficient dkj (cf. Eq. 5 15 and see (Beddington 1975;DeAngelis et al. 1975)) was fitted to links between predator k and prey 16 species j when the occurrence of variable prey resistance was supported by empirical evidence. We 17 applied dkj to all links involving fast growing, diverse prey groups with a high potential to adjust fast 18 to changing grazing pressure: 1. small grazers (ciliates and rotifers) and Cyc consuming eukaryotic 19 algae, 2. all bacterivorous links, 3. Dap's and Cyc's consumption of rotifers, 4. Asp's consumption of 20 ciliates and rotifers, and 5. Fish predation on crustaceans. The parameter dkj was further fitted to 21 Bac’s consumption of detritus to mimic interference competition of bacterial strains at high densities 22 (Hibbing et al. 2010). 23 We first fitted dkj manually to strong interactions that cause the CWP, e.g. the links from 24 daphnids and ciliates to phytoplankton groups. In addition, we fitted dkj to balance fish predation 25 pressure on the competing crustacean guilds Dap and Cyc. Adult Dap (mostly daphnids) are larger 26 than Cyc (cyclopoid copepods), but they are known to metabolize and reproduce faster (also by 27 parthenogenesis) than copepods. In addition, the dominant cyclopoid copepod species (Cyclops 28 vicinus included in Cyc) enters a diapause from the CWP onwards until autumn. We modeled its 5 1 absence in this time by higher predation pressure of fish larvae (Fish1) and juveniles (Fish2) on Cyc. In 2 summer and autumn, in line with empirical evidence, the adult fish (Fish3 and Fish4) prey more strongly on 3 daphnids (Dap) through lower B0ij and dkj than set on links to Cyc. As a result, Cyc are able to increase again, 4 mimicking their return from the diapause. 5 All link-specific values of dkj in the models M2-M4 are given in Table S3. 6 We used the same parameter values in M2-M4 to maintain comparability and assess how close the 7 ATN model fitted to the biomass patterns. Our conclusion is that the broad biomass patterns (A/H ratios or 8 the intermediate 8-groups resolution) could be reproduced without the manually calibrated parameter 9 values (cf. M1), whereas the full range of LC-specific seasonal biomass patterns for each guild could only be 10 reproduced using the LC-specific parameter set. 11 Size-abundance distribution. We calculated the slope of the size-abundance distribution equivalent to the 12 normalized biomass size spectrum (Sheldon et al. 1972) by binning biomass densities into 33 size classes of 13 log body mass of the 20 plankton guilds. Pelagic food webs are characterized by a continuum of organisms 14 along the size gradient and an often rather even biomass distribution (Sheldon et al. 1972) which also holds 15 for the LC food web (Gaedke 1992b;Gaedke 1992a). Pelagic food webs are highly size-structured 16 communities because body size and trophic level are positively correlated. From the relation B = NM = 17 constant, with biomass B, abundance N, and body mass M, follows that the size-abundance distribution has a 18 slope of approximately -1 when log(abundance per size class) is plotted against log(body mass). This slope 19 estimates the efficiency of the energy flow from smaller to larger organisms (Gaedke 1993). A steeper 20 (=more negative) slope indicates that small organisms are relatively more abundant and a lower transfer 21 efficiency, yielding lower biomass in larger size classes. 22 Impact of temporal resolution on the goodness-of-fit. The interannual variability in the empirical data is 23 largely caused by site-specific abiotic forcing and weather events that we deliberately intended to average 24 out in our construction of an average year. Hence, we calculated averages across years and within phases to 25 compare modeled and LC data (see Methods and Fig S2). This, however, may imply that we overlooked 26 misfits at a finer time scale, i.e. within phases. Hence, we tested whether the biomass similarity was sensitive 27 to the model’s and LC’s within-phase variability, . In each year, LC biomass data was sampled with maximal 28 weekly resolution which determines the maximal temporal resolution for calculating the biomass similarity. 6 1 . Since the longest phase (87 days) in summer provided the most empirical data points, we used this phase to 2 calculate the 20-guilds biomass similarity using a bi-weekly and weekly resolution. We found that using this 3 higher resolution to calculate the biomass similarity did not change the general results, but provided insights 4 into the dynamics of each model on a finer time scale (Table S5a). 5 When using a biweekly or weekly average instead of the phase mean, M0’s low 20-guilds biomass similarity 6 in summer (20-guilds avg. sim. = 0.25) decreased very slightly (avg. decrease -0.04). M1’s intermediate 20- 7 guilds biomass similarity in summer (20-guilds avg. sim. = 0.41) decreased more than in M0 (avg. decrease - 8 0.14), largely due to oscillations between bacteria and HNF (cf. Fig. S4b). M2’s intermediate 20-guilds 9 biomass similarity in summer (20-guilds avg. sim. = 0.71) only decreased very slightly (avg. decrease -0.05). 10 M3’s high biomass similarity in summer (20-guilds avg. sim. = 0.85) was also relatively insensitive to using 11 biweekly or weekly averages instead of the phase means (avg. decrease = -0.09, Table S5a). M4’s 12 intermediate 20-guilds biomass similarity in summer (20-guilds avg. sim. = 0.77) decreased the most (avg. 13 decrease -0.19), presumably because of the absence of weak, but stabilizing links (cf. Fig. S4e). 14 Statistical significance of the goodness-of-fit. Moreover, we tested to what extent the modeled phase 15 means XATNi fell into the range of values observed over 10 years in the corresponding phase (Fig. S2). For 16 each guild i and phase p, we calculated the distance of the modeled phase-mean XATNi from the observed 17 phase-means XLCi 1/ k k xy , with x y as the phase-means observed over k=10 years. We used the y years 18 normalized distance 1/ m m p phase p , with p 1/ n n i guilds di / 2 LCi , m = number of phases, n = number of 19 guilds, and the distance di | XATNi XLCi | between XATNi and XLCi in reference to the standard deviation 20 LC around XLC calculated from the individual phase means x y observed over 10 years. If 1, the 21 modeled phase-averages stay within the natural variability of the LC data set. 22 Generally, M2 and M3 performed best because their phase means fell on average within 2 LCi around XLCi 23 (Table S5b-c). 24 In M0, only 17% of all XATNi fall within 2 LCi around XLCi ( = 4.93). The corresponding value for M1 is29% 25 ( = 5.01,). In M2 and M3, 74% of the modeled XATNi fall within 2 LCi around XLCi ( = 0.86 and = 0.71, i 7 i 1 respectively). 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The dashed lines connect observations of three 5 example years (1987, 1992, and 1996). Annual and within-phase variability ranges between 1-2 orders of 6 magnitude for some guilds in highly dynamic phases, e.g. the second daphnid peak during summer (phase 5) in 7 1987 and 1992 was not observed in 1996. We used the interval within two standard deviations LC around the 8 10-year LC phase-means XLCi (whiskers above and below the blue dots) to test whether the phase-means of the 9 model simulation XATNi (red line, red squares) fell within LC’s natural variability. 10 11 Figure S3 title: Comparison of relative biomass and production of models M0-M4 12 Caption: 13 Figure S3. Upper panel: Relative biomasses for LC data and models M0-M4. Lower panels: Relative production for 14 models M0-M4. 15 16 Figure S4 title: Relative biomass of 20-guilds in M0-M4 compared to LC data 17 Caption: 18 Figure S4. (a-c) Relative biomass for each guild in models M0-M4 compared to LC data. Arrows connect phases 2- 19 6. Dashed line at x=y indicates perfect fit. Each reference line above (below) the x=y line indicates a 10% 20 increase (decrease) of the model in reference to total biomass. 21 22 Figure S5 title: Relative production in M0-M4 compared to LC data 23 Caption: 24 Figure S5. (a-c) Relative production for each major planktonic group in models M0-M4 compared to LC data. 25 Arrows connect phases 2-6. Dashed line at x=y indicates perfect fit. Each reference line above (below) the x=y 26 line indicates a 10% increase (decrease) of the model in reference to total production. 27 11 1 2 12