Gabriel Yvon-Durocher
email: g.yvon-durocher@qmul.ac.uk

José M Montoya
email: montoya@icm.csic.es

Mark Trimmer
email: m.trimmer@qmul.ac.uk

Gabriel Yvon

Warming Alters the Size Spectrum and Shifts the Distribution of Biomass in Aquatic Ecosystems

Keywords: Global Warming, Body Size, Size Spectra, Mass-abundance relationships, Biomass Global Warming, Body Size, Size Spectra, Mass-abundance relationships, 16 Biomass, Food Webs, Phytoplankton, Zooplankton

Body size is one of the key determinants of community structure. The relationship between abundance and body size can explain how community biomass is partitioned among the biota of an ecosystem. We used an aquatic mesocosm experiment to determine how warming of ~4˚C would affect the body size, biomass and taxonomic structure of planktonic communities. We found that warming increased the steepness of the slope of the community size spectrum, primarily by altering the phytoplankton size spectrum. Warming also reduced the mean and maximum body size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in large shifts in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton body size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganisation of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure of aquatic communities.

Body size is one of the key determinants of community structure. The relationship 30 between abundance and body size can explain how community biomass is partitioned 31 among the biota of an ecosystem. We used an aquatic mesocosm experiment to determine 32 how warming of ~4˚C would affect the body size, biomass and taxonomic structure of 33 planktonic communities. We found that warming increased the steepness of the slope of 34 the community size spectrum, primarily by altering the phytoplankton size spectrum. 35

Warming also reduced the mean and maximum body size of phytoplankton by 36 approximately one order of magnitude. The observed shifts in phytoplankton size 37 structure were reflected in large shifts in phytoplankton community composition, though 38 zooplankton taxonomic composition was unaffected by warming. Furthermore, warming 39 reduced community biomass and total phytoplankton biomass, although zooplankton 40 biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton 41 biomass ratio in the warmed mesocosms, which could be explained by faster turnover 42 within the phytoplankton assemblages. Overall, warming shifted the distribution of 43 phytoplankton body size towards smaller individuals with rapid turnover and low 44 standing biomass, resulting in a reorganisation of the biomass structure of the food webs. 45

These results indicate future environmental warming may have profound effects on the 46 structure of aquatic communities. 47 Body size can play a key role in determining community structure [START_REF] Elton | Animal Ecology[END_REF], Lindeman 49 1942[START_REF] Damuth | Population density and body size in mammals[END_REF][START_REF] Peters | The ecological implications of body size[END_REF][START_REF] Brown | Toward a metabolic 562 theory of ecology[END_REF][START_REF] Petchey | Size, foraging, and food web 641 structure[END_REF] because it 50 influences ecological processes across multiple levels of organisation; from individuals 51 [START_REF] Peters | The ecological implications of body size[END_REF][START_REF] Brown | Toward a metabolic 562 theory of ecology[END_REF], and their interactions [START_REF] Emmerson | Predator-prey body size, interaction strength and the 574 stability of a real food web[END_REF], 52 Berlow et al. 2009), to populations [START_REF] Damuth | Population density and body size in mammals[END_REF][START_REF] Jennings | Abundance-body mass relationships in size-structured 610 food webs[END_REF], Reuman 53 et al. 2008), communities and ecosystems [START_REF] Petchey | Size, foraging, and food web 641 structure[END_REF]). Understanding how this 54 "size-structure" might then be altered by human impacts is an important contemporary 55 challenge for ecology given recent concerns over accelerating rates of biodiversity loss 56 and climate change [START_REF] Pimm | Climate Disruption and Biodiversity[END_REF][START_REF] Montoya | Climate change, biotic interactions and ecosystem 632 services[END_REF]. 57

The relationship between abundance and body size (equal to body mass; terms are 58 interchangeable hereafter) is potentially a very powerful descriptor of how energy and 59 nutrients are partitioned within the biomass of an ecosystem (White et al. 2007). It is also 60 an emergent property of size structure at lower levels of organisation: for example, body 61 size can be important for determining the presence and strength of trophic interactions 62 between individuals because it constrains their metabolic requirements (Berlow et al. 63 2009). The trophic architecture of the community determines the amount of energy 64 available to an organism of a given size, and therefore its population abundance (Damuth 65 1981). The relationship between abundance and body mass therefore integrates size-66 structure over many levels of organisation. 67

Since the pioneering work of Sheldon et al. (1972) the relationship between 68 abundance and body size in pelagic food webs has typically been conceptualised as a 69 frequency distribution of individual body sizes (Sheldon et al. 1972). This relationship 70 [START_REF] Kerr | The Biomass Spectrum: A predator Prey Theory of Aquatic 617 Production[END_REF]. The negative slopes of size 71 spectra describe how quickly abundance decreases with size, and have often been used to 72 assess the ecological status of ecosystems impacted by fisheries (Rice & Gislason 1995) 73 and, more recently, agricultural practices in terrestrial ecosystems [START_REF] Mulder | Soil acidity, ecological stoichiometry and allometric scaling in 637 grassland food webs[END_REF]. 74

For example, steep size spectra with negative slopes in marine ecosystems are indicative 75 of over-fishing because the relative abundance of large organisms is suppressed by size-76 selective harvesting [START_REF] Pauly | Fishing down marine 639 food webs[END_REF]. 77

Understanding how the distribution of biomass in aquatic ecosystems might 78 respond to warming is crucial for predicting the robustness and functioning of these 79 ecosystems in the future warmer climate. New evidence suggests that "reduced body size 80 is the third universal response to global warming, besides range, and phenological 81 shifts" [START_REF] Daufresne | Global warming benefits the small in 568 aquatic ecosystems[END_REF]. Changes in the size-structure of communities in response 82 to warming are now being documented across a range of ecosystem types and spatial 83 scales. For instance, experiments on aquatic micro-organisms have found that warmed 84 communities tend to be dominated by smaller bacteria [START_REF] Daufresne | Global warming benefits the small in 568 aquatic ecosystems[END_REF]. 85

Macroecological studies across latitudinal temperature gradients [START_REF] Moran | Increasing importance of 635 small phytoplankton in a warmer ocean[END_REF], and 86 paleoecological studies [START_REF] Finkel | Climatically 583 driven macroevolutionary patterns in the size of marine diatoms over the 584 cenozoic[END_REF] in the open ocean have revealed an increased 87 prevalence of small phytoplankton in warmer oceanic regions. These studies suggest that 88 the underlying size structure of aquatic ecosystems might not be robust to global warming 89 [START_REF] Finkel | Climatically 583 driven macroevolutionary patterns in the size of marine diatoms over the 584 cenozoic[END_REF][START_REF] Falkowski | Mix and match: how climate selects phytoplankton[END_REF][START_REF] Daufresne | Global warming benefits the small in 568 aquatic ecosystems[END_REF], Winder et al. 2009, 90 Finkel et al. 2010[START_REF] Moran | Increasing importance of 635 small phytoplankton in a warmer ocean[END_REF]. 91

However, these studies have tended to focus on the effects of warming on 92 restricted subsets of species (e.g. diatoms or phytoplankton) within an ecosystem ( [START_REF] Moran | Increasing importance of 635 small phytoplankton in a warmer ocean[END_REF]. At present, we still lack sufficient data documenting the 96 effects of warming per se on the size-structure of entire local communities comprising 97 multiple trophic levels to be able to isolate its effects at this level of biological 98 organisation. 99

Here we attempt to address this current knowledge gap by measuring for the first 100 time the consequences of experimental warming on the community size structure and 101 distribution of biomass of entire planktonic food webs from 20 replicated freshwater 102 mesocosms. These experimental systems were maintained at either ambient temperature 103 (n = 10), or ~ 4ºC above ambient (n = 10), in line with warming scenarios predicted for 104 temperate latitudes by the end of the 21 st century (IPCC 2007). Mesocosm scale 105 experiments such as these afford the opportunity to isolate the effects of temperature from 106 other potentially confounding variables (e.g. spatial gradients in available nutrients) on 107 the structure of entire replicated communities. They also permit direct comparisons to be 108 made between the structure of communities under ambient conditions with that of their 109 "future" warmed counterparts. We used this experiment to test the following hypotheses: 110 (i) Warming will shift the distribution of body size by increasing the prevalence 111 of small sized species, resulting in an overall steepening of the slope of the community 112 size spectrum. We expect this effect to be most pronounced in the phytoplankton 113 assemblages because phytoplankton size structure tends to be strongly related to the 114 prevailing physical and chemical environment (Reynolds 1984) and recent observations 115 in aquatic ecosystems suggest that warming tends to favour smaller phytoplankton 116 [START_REF] Finkel | Climatically 583 driven macroevolutionary patterns in the size of marine diatoms over the 584 cenozoic[END_REF][START_REF] Falkowski | Mix and match: how climate selects phytoplankton[END_REF][START_REF] Daufresne | Global warming benefits the small in 568 aquatic ecosystems[END_REF], Winder et al. 2009, 117 Moran et al. 2010). 118 (ii) Warming will reduce total standing community biomass. Again, we expect 119 this effect to be most pronounced for phytoplankton for two reasons. First, a shift in the 120 community size spectrum towards smaller species should result in an overall reduction in 121 the standing biomass. Second, theoretical expectations from the metabolic theory of 122 ecology (MTE) suggest total standing biomass should decline with increasing 123 temperature [START_REF] Allen | Global biodiversity, biochemical kinetics, and 551 the energetic-equivalence rule[END_REF], such that the total standing biomass in a community (B tot ) 124 is predicted to vary as B tot = r 0 e -E/kT M 1/4 where r 0 is the resource supply rate, e -E/kT is 125 the Boltzmann factor where E is the activation energy of metabolism, k is Boltzmann's 126 constant and T is absolute temperature. Therefore, holding r 0 constant (i.e. if the supply 127 rate of limiting resources does not vary with T), B tot should decline with increases in 128 environmental temperature according to e -E/kT . 129 (iii) Warming will alter the relative distribution of biomass between 130 phytoplankton and zooplankton assemblages. We expect that a shift in phytoplankton size 131 structure and a concomitant reduction in standing biomass will result in elevated 132 zooplankton-to-phytoplankton biomass ratios in the warmed mesocosms. We also predict 133 that relatively high zooplankton biomass will be retained in the warmed mesocosms, 134 because phytoplankton turnover rates should increase in response to metabolic 135 stimulation by warming and by a shift towards smaller species with faster generation 136 times. Comparable shifts in the organisation of plankton communities have been 137

F o r R e v i e w O n l y 6 (
observed in the open ocean [START_REF] Gasol | Biomass distribution in marine planktonic 591 communities[END_REF] individuals (age 1+) per mesocosm (~12 g C m -3 )] in all mesocosoms and monitored via 159 regular eletro-fishing surveys. Because the fish were maintained at predetermined 160 biomass-densities they merely served to "complete" the food webs to mimic natural 161 shallow lakes and were not considered further in the analyses. 162

Measuring the Size Spectrum 164

The plankton communities from each of the 20 mescosms were sampled at the beginning 165 and end of the growing season in April and October 2007 respectively (Yvon-Durocher et 166 al. 2010). The entire water column (depth 0.5m) from the sediment surface to the water 167 surface was sampled using a 0.8m -long tube sampler (Volume: 2L), which was 168 positioned at random in each mesocosm on each date. Each sample was divided into two 169 size categories for preservation and subsequent analyses, via filtration through a 80µm 170 sieve: organisms that were retained were preserved in 4% Formalin, and of the remaining 171 sample (i.e. organisms <80 µm), a 100ml sub-sample was preserved in 1% Lugol's iodine 172 for microscopy analyses. 173 Plankton >80 µm were counted, measured and identified by microscopy (using a 174 Nikon SMZ1500 dissection microscope). Zooplankton > 80 µm were typically assigned 175 to taxonomic orders, though in a number of cases rotifers were identified to species level. 176 Planktonic organisms <80µm were counted, measured and identified by inverted 177 microscopy. Phytoplankton <80µm were typically identified to genus level, which is 178 generally considered to be of sufficient taxonomic resolution to detect the effects of a 179 perturbation [START_REF] Cottingham | Population, community, and ecosystem variates as 564 ecological indicators: Phytoplankton responses to whole-lake enrichment[END_REF]. Organisms were settled for 24 h in a 10ml 180 Utermöhl sedimentation chamber before viewing under an inverted light microscope 181 (Leica DMIRE2). An initial scan of the sample, viewed under low magnification (150×), 182 of a fixed area (50 mm 2 ) was used to count and measure large, rare organisms. At higher 183 magnification (630×), n fields of view were chosen at random and all organisms were 184 counted, sized and identified until a minimum of 400 individuals were measured from 185 Linear body dimensions were determined with an interactive image analysis 190 system (Hamamatsu C4742-95 camera and Openlab software). Body size of all 191 organisms was expressed in units of carbon (µg C). For organisms >80µm (typically 192 zooplankton), biovolumes were determined by assigning organisms to geometric shapes 193 that closely represented the real shape of the organism [START_REF] Ruttner-Kolisko | Suggestions for biomass calculations of plankton rotifers. 661[END_REF], Reiss & 194 Schmid-Araya 2008). Body mass was determined by converting biovolume to 195 freshweight using a factor of 1.1, and carbon content was then estimated from a dry/wet 196 weight ratio of 0.25 and a dry carbon content of 40% [START_REF] Reiss | Existing in plenty: abundance, biomass and diversity 651 of ciliates and meiofauna in small streams[END_REF]. For 197 organisms <80µm (typically phytoplankton) biovolumes, were similarly estimated from 198 geometric shapes that were most similar to the shape of the organism (Hillebrand et al. 199 1999). Biovolume was then converted into carbon units assuming a multiplication factor 200 of 0.109 [START_REF] Montagnes | Estimating carbon, nitrogen, 629 protein and chlorophyll-a from volume in marine phytoplankton[END_REF]. In total 47,699 individual organisms of both 201 phytoplankton and zooplankton were measured. 202

203

Phytoplankton turnover 204

Turnover rates of the phytoplankton assemblages (µg C m -3 d -1 /µg C m -3 ) were estimated 205 for each mesocosm on each sampling occasion (n = 40). Phytoplankton turnover was 206 calculated as the quotient of primary production and standing phytoplankton biomass 207 after [START_REF] Gasol | Biomass distribution in marine planktonic 591 communities[END_REF]. This gives an estimate of the biomass specific production, or the 208 are presented in detail in [START_REF] Yvon-Durocher | Warming 103 alters the metabolic balance of ecosystems[END_REF]. Benthic metabolism measured 211 using in-situ benthic chambers contributed, on average, 35 % of whole system respiration 212 (see S7 in supplementary material for further details). From this we infer that our 213 measures of primary production predominantly reflect planktonic metabolism and 214 provide reliable estimates of carbon turnover within the phytoplankton assemblages. population abundance of all organisms with log 10 (M) in each bin was regressed against 226 the bin centres [START_REF] Reuman | Three allometric relations of 653 population density to body mass: theoretical integration and empirical tests in 149 654 food webs[END_REF], White et al. 2008). The slope of the linear model 227 describes how quickly the abundance of individuals declines with increasing size in the 228 size spectrum (see Tables S5 andS6 in supplementary material). We also measured two 229 normalisation constants of the linear model. The intercept at x = 0: its variation between 230 warmed and ambient treatments gives information on the relative abundance of large 231

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organisms, and the intercept at x = -8: its variation provides information on the 232 differences among treatments in the relative abundance of the smallest organisms. For 233 both the community and the phytoplankton size spectrum, non-significant coefficients of 234 the linear models (i.e. at P>0.05) were excluded from further analyses (n = 5 out of 40 for 235 the phytoplankton size spectrum). 236 237

Statistical Analyses 238

We analysed differences between treatments in the following community properties: size 239 spectrum slopes and intercepts; total community biomass; total phytoplankton biomass; 240 total zooplankton biomass; and mean individual body mass, using ANOVA, with 241 treatment (either warmed or ambient) and sampling occasion (April or October) as fixed 242 factors. The relationships between phytoplankton and zooplankton biomass and the 243 biomass ratio of zooplankton to phytoplankton were determined using ANCOVA, again 244 using treatment and sampling occasion as factors. In all statistical modelling procedures 245 the most parsimonious model was identified using the Akaike Information Criterion 246 (AIC). Statistical analyses were performed using R statistical software (R. Development. 247 Core. 2006). 248 Multivariate analysis of phytoplankton taxonomic composition was conducted 249 using the vegan package in R. Redundancy analysis (RDA) was used to test for a 250 significant linear trend in community composition. RDA is a constrained form of 251 principal components analysis and assesses the variation in taxonomic composition that 252 can be explained by specific environmental variables defined as the constraints. Here, the 253 first RDA axis quantified the linear component of the between treatment variation in 254 prior to the construction of the RDA by taking the proportional contribution of a given 261 taxa as a fraction of the total biomass in a given mesocosm. Furthermore, rare genera 262 defined as those occurring in less than two mesocosms per sampling date were excluded 263 from the RDA analysis to reduce noise in the data. 264

265

RESULTS

266

Effects of Warming on the Size Spectrum 267

Warming significantly increased the steepness of the slope of the community size 268 spectrum from -0.86 (95% CI -0.83 to -0.89) in the systems at ambient temperature to -269 0.95 (95% CI -0.92 to -0.98) in the warmed mesocosms (Fig. 1 a, b &c; Table 1), i.e., 270 smaller organisms were relatively more abundant than large organisms in the warmed 271 communities. Furthermore, the intercept of the community size spectrum at x = 0 (i.e. at 272 large body masses) was significantly reduced, whilst the intercept at x = -8 (i.e. at small 273 body masses) was significantly elevated in the warmed mesocosms (Table 1). Thus, the 274 abundance of larger organisms declined on average, while the abundance of small 275 organisms increased in response to warming. 276

F o r R e v i e w O n l y 13
Comparable patterns were observed for the phytoplankton size spectrum (Fig. 1d, 277 e & f). Warming significantly increased the steepness of the slope of the phytoplankton 278 size spectrum from -0.36 (95% CI -0.32 to -0.40) in the systems at ambient temperature 279 to -0.49 (95% CI -0.43 to -0.55) in the warmed mesocosms (Table 1; Fig. 1d, e &f). 280

Warming also significantly reduced the intercept of the phytoplankton size spectrum 281 (Table 1). Therefore, small organisms were relatively more abundant than large 282 organisms in the warmed mesocosms. Additionally, warming truncated the upper size 283 classes of the phytoplankton size spectrum (Fig. 1 d). The maximum phytoplankton body 284 mass in the ambient mesocosms was 1.36×10 -2 µg C, while in the heated the maximum 285 body mass was only 3.88×10 -3 µg C. Furthermore, the average body mass of an individual 286 phytoplankter was almost an order of magnitude smaller in the warmed mesocosms 287 relative to the ambient systems (Fig. 2; Table 1), while the average size of an individual 288 zooplankter was unaffected by warming (Fig. 2; Table 1). 289 290

Effects of Warming on Community Composition 291

Redundancy analysis of the phytoplankton taxa revealed that the composition of the 292 phytoplankton assemblages were significantly different between warmed and ambient 293 treatments in both April (Fig. 3a; F-ratio = 5.72; P = 0.011; permutation number = 999) 294 and October (Fig. 3b; F-ratio = 5.87; P = 0.001; permutation number = 999). RDA1 295 which was constrained by treatment, explained 24.1% and 24.6% of the variation in the 296 taxonomic composition of the phytoplankton assemblages in April and October 297 respectively, which in both cases was greater than the variation explained by PCA1, 298 indicating that treatment effects were the dominant predictor of phytoplankton taxonomic 299 , total 301 inorganic N:P) using permutation tests, though none of these variables significantly 302 predicted taxonomic composition. Certain taxa were strongly associated with either 303 warmed or ambient treatments. For example, in both April and October, the large 304 chlorophyte, Botryococcus clustered towards the ambient treatment centroid, while the 305 small cyanophyte Synechocystis, and the small chlorophyte Monoraphidium, typically 306 clustered towards the heated centroid. The phytoplankton assemblages consisted of many 307 rare, generalist taxa that were present in both treatments; however, in most of the 308 mesocosms the biomass was dominated by a few indicator taxa (named above) that were 309 associated with either the heated or the ambient treatments. Furthermore, figures 3a and 310 3b show that a large core contingent of the phytoplankton assemblages were present in 311 both April and October and that only a few taxa were present in only one month, 312 suggesting that temporal succession was less important than treatment effects in 313 determining phytoplankton community composition. 314

In contrast to the phytoplankton assemblages the taxonomic composition of the 315 zooplankton assemblages differed very little between treatments in both April and 316 October (Fig. 4a &b). In heated and ambient treatments calanoid and cyclopoid copepods 317 dominated zooplankton biomass with cladocerans and rotifers forming a smaller 318 secondary contingent of the assemblages. These patterns were consistent between April 319 and October, though ostracods, oligochates and the rotifer Asplanchna were absent from 320 the zooplankton assemblage in October. 321 322

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Effects of Warming on the Distribution of Biomass 323

Total planktonic community biomass differed between April and October in the ambient 324 but not in the warmed mesocosms (Fig. 5). Overall, warming significantly reduced total 325 community biomass (Fig. 5; Table 1). This was principally driven by a considerable 326 reduction in total phytoplankton biomass in the warmed mescocosms (Fig. 5; Table 1). 327

Overall, warming shifted the distribution of biomass and body size of phytoplankton from 328 assemblages comprised of large individuals with high standing biomass to assemblages 329 with low standing biomass and many small individuals. In contrast, warming appeared to 330 have no effect on the distribution of size and biomass within the zooplankton 331 assemblages (Fig. 5; Table 1). 332

Zooplankton and phytoplankton biomass were not correlated within the 333 mesocosms (Fig. 6a; Table 2). The former varied by about two orders of magnitude and 334 the latter by three orders of magnitude among mesocosms (Fig. 6a). The ratio of 335 zooplankton to phytoplankton biomass (Z:P) was significantly and negatively correlated 336 with phytoplankton biomass (Fig. 6b; Table 1). Therefore, zooplankton biomass exceeded 337 phytoplankton biomass (i.e. Z:P >1) when phytoplankton biomass was low and vice versa 338 (i.e. Z:P <1) when phytoplankton biomass was high. Warming significantly increased the 339 ratio of Z:P biomass (Table 2). Furthermore, the ratio of Z:P biomass was strongly and 340 positively correlated with the turnover rates of the phytoplankton assemblages, which 341 exhibited distinct variation between warmed and ambient mesocosms (Fig. 6c; Table 2). 342

In summary, the warmed mesocosms were characterised by phytoplankton assemblages 343 comprised of small individuals with low standing stocks of biomass and rapid turnover 344 there is an increasingly urgent need to explore the effects of the principal components of 353 climate change (e.g., warming) on community structure and ecosystem functioning 354 (Tylianakis et al. 2008[START_REF] Montoya | Climate change, biotic interactions and ecosystem 632 services[END_REF]. Our results broadly supported our 355 experimental hypotheses: i.e., that warming would increase the steepness of the size 356 spectrum slope, reduce total community biomass, and increase the zooplankton to 357 phytoplankton biomass ratio. These findings could provide some novel insights into how 358 future warming might change the distribution of body size and biomass in aquatic 359 ecosystems. The size structure of plankton communities in aquatic ecosystems is a key 360 driver of rates of carbon sequestration and nutrient cycling [START_REF] Laws | Temperature 619 effects on export production in the open ocean[END_REF], and 361 therefore changes in the distribution of planktonic body size and biomass could alter the 362 regulation of biotic feedbacks with warming on a potentially global scale (Falkowski et 363 al. 1998). 364

The general increase in the prevalence of small organisms with increases in 365 environmental temperature that we observed experimentally agrees well with recent 366 studies that have either focused on specific taxa, or subsets of taxa (Atkinson et al. 2003, 367 F o r R e v i e w O n l y [START_REF] Finkel | Climatically 583 driven macroevolutionary patterns in the size of marine diatoms over the 584 cenozoic[END_REF][START_REF] Daufresne | Global warming benefits the small in 568 aquatic ecosystems[END_REF], Winder et al. 2009), or analysed correlational 368 trends in community structure across latitudinal gradients in temperature (Moran et al. 369 2010). However, here we have developed this understanding further by documenting the 370 effects of warming on the body size, biomass and taxonomic structure of entire 371 planktonic food webs subjected to experimental warming. Experimental mesocosm 372 studies, although inevitably an abstraction of natural ecosystems, afford us the 373 opportunity to isolate the effects of temperature from other potentially confounding 374 variables (e.g. latitudinal and biogeographical effects) whilst studying entire replicated 375 plankton communities. 376

The increase in the dominance of small phytoplankton and the truncation of the 377 larger size classes in their size spectrum resulted in a general increase in the steepness of 378 the slope of the community size spectrum in the warmed mesocosms. Changes in the 379 distribution of organism size might arise from at least two broad mechanisms, which are 380 not necessarily mutually exclusive. Firstly, organisms might exhibit a degree of 381 phenotypic plasticity to changes in temperature. This hypothesis has been termed the 382 temperature-size rule [START_REF] Atkinson | Protists decrease in size linearly with 556 temperature: ca. 2.5% degrees C-1[END_REF] and posits that reduced organism size at 383 higher temperatures is an adaptive plastic response that results from selection for earlier 384 reproduction as population growth rate increases. The accelerated completion of the life 385 cycle occurs at the expense of maturation size [START_REF] Atkinson | Protists decrease in size linearly with 556 temperature: ca. 2.5% degrees C-1[END_REF]). In the second 386 mechanism, changes in the physicochemical environment created by warming select for 387 smaller sized species. In this case, changes in community size structure occur as an 388 indirect effect of warming, mediated for example, by concomitant nutrient limitation, 389 resulting in the competitive exclusion of larger species (Finkel et al. 2005, Irwin et [START_REF] Falkowski | Mix and match: how climate selects phytoplankton[END_REF], Winder et al. 2009[START_REF] Finkel | Phytoplankton in 580 a changing world: cell size and elemental stoichiometry[END_REF]. Here, small cell 391 size increases the efficiency of the acquisition of limiting nutrients because of a higher 392 surface area to volume ratio and is therefore competitively advantageous under conditions 393 of nutrient limitation [START_REF] Litchman | Contrasting size evolution in marine 626 and freshwater diatoms[END_REF]. 394

Our results support the second mechanism. Redundancy analysis revealed that 395 warming dramatically shifted the taxonomic composition of the phytoplankton 396 assemblages. Moreover, warming favoured smaller phytoplankton genera, resulting in a 397 reduction in mean and maximum body size by almost an order of magnitude. For 398 example, the large cholorophyte Botryococcus dominated the biomass of the ambient 399 mesocosms in both April and October, but was almost entirely absent from the warmed 400 mesocosms. Similarly the small cyanophyte Synechocystis and the small chlorophyte 401

Monoraphidium were strongly associated with the warmed mesocosms but were only 402 peripheral members of the assemblages in the ambient mesocosms. Warming therefore 403 resulted in the establishment of phytoplankton assemblages dominated by small species, 404 rather than reducing the body size of the same species composition present in the ambient 405 mesocosoms. 406

Our experimental design adopted a space-for-time substitution approach to 407 attempt to understand the consequences of warming on the structure of plankton 408 communities. The relatively infrequent but highly replicated sampling regime adopted in 409 our study was a necessary compromise. For example, we documented the size, biomass 410 and taxonomic structure of 20 replicated experimental ecosystems on two separate 411 sampling occasion at the beginning and end of the growing season (identified from 412 measures of primary production; see [START_REF] Yvon-Durocher | Warming 103 alters the metabolic balance of ecosystems[END_REF] for details) rather than 413

F o r R e v i e w O n l y
focusing on the complex temporal dynamics of the plankton assemblages of one or two 414 systems, as would typically be logistically feasible within such a study. As a result, our 415 results come with an associated caveat: we are unable to discern the effects of warming 416 on the temporal succession of the plankton communities. However, analysis of the 417 phytoplankton taxonomic composition suggests that a large, core contingent of these 418 assemblages are present in both April and October but which differ markedly between 419 treatments in both months. These results suggest that temporal succession in the plankton 420 communities was less important than the effect of treatment (i.e. warming) in determining 421 the taxonomic and therefore the body size and biomass structure of these assemblages. 422 Inorganic nitrogen was limiting in our experiment (N:P ratios were ≈11:1, and 423 were below the 16N:1P expected at Redfield; see S3 & S4 in supplementary material for 424 further details) but to the same extent in both warmed an ambient treatments: i.e., 425 warming did not exacerbate nutrient limitation. Therefore, it is unlikely that a direct 426 effect of nutrient limitation induced by warming caused the observed shifts in 427 phytoplankton size structure that have been frequently documented in the open ocean and 428 in lake ecosystems [START_REF] Finkel | Climatically 583 driven macroevolutionary patterns in the size of marine diatoms over the 584 cenozoic[END_REF][START_REF] Falkowski | Mix and match: how climate selects phytoplankton[END_REF], Winder et al. 2009, 429 Finkel et al. 2010). Furthermore, redundancy analysis revealed that inorganic nutrient 430

concentrations (NO 3 - , NO 2 - , NH 4 + , PO 4 3-
, and total inorganic N:P) were not significantly 431 correlated with phytoplankton taxonomic composition. Therefore, the shift in 432 phytoplankton size and taxonomic structure in the warmed treatments might simply 433 reflect the fact that smaller phytoplankton have lower specific nitrogen requirements than 434 large phytoplankton [START_REF] Litchman | The role of functional 623 traits and trade-offs in structuring phytoplankton communities: scaling from 624 cellular to ecosystem level[END_REF]. [START_REF] Litchman | The role of functional 623 traits and trade-offs in structuring phytoplankton communities: scaling from 624 cellular to ecosystem level[END_REF] found that the 435 minimum nitrogen quota required to support growth, Q min , across a wide range of 436 cellular nitrogen quota with size. Because metabolic rates and nutrient uptake rates 438 increase with temperature and size [START_REF] Gillooly | Effects of size and 593 temperature on metabolic rate[END_REF][START_REF] Allen | Towards an integration of ecological stoichiometry and the 553 metabolic theory of ecology to better understand nutrient cycling[END_REF], under 439 conditions of nutrient limitation, small cell size should provide a competitive advantage 440 as environmental temperatures rise. This is because species with lower Q min will be better 441 able to balance the increased demand for limiting nutrients imposed by temperature 442 driven elevated metabolic rates. 443

An alternative mechanism for the shifts in phytoplankton size and taxonomic 444 structure in the warmed mesocosms is that warming served to increase "top down" 445 control of the phytoplankton community by increasing zooplankton grazing rates. We 446 have previously demonstrated that heterotrophic metabolism increased more rapidly than 447 autotrophic metabolism with increasing temperature in the same experimental system 448 (measurements made simultaneously; see [START_REF] Yvon-Durocher | Warming 103 alters the metabolic balance of ecosystems[END_REF]

for details). 449

Therefore, because ingestion rates increase in proportion with metabolic rates (Berlow et 450 al. 2009), warming might have increased the strength of top down control of 451 phytoplankton populations by zooplankton grazing. Moreover, zooplankton are often size 452 selective when feeding on phytoplankton, typically consuming the largest size classes 453 possible [START_REF] Porter | Selective grazing and differential digestion of algae by zooplankton[END_REF][START_REF] Hall | Size efficiency hypothesis and the 597 size struture of zooplankton communities[END_REF][START_REF] Katechakis | Changes in the phytoplankton 612 community and microbial food web of Blanes Bay (Catalan Sea, NW 613 Mediterranean) under prolonged grazing pressure by doliolids (Tunicata), 614 cladocerans or copepods (Crustacea)[END_REF]. Warming might therefore 454 have increased the prevalence of small sized phytoplankton indirectly, by elevating 455 grazing pressure on the larger size classes of the phytoplankton community due to the 456 elevated metabolic demands of zooplankton at higher temperature. Importantly, both the 457 "top down" and "bottom up" hypotheses stated here are not mutually exclusive: both 458 bottom up regulation of phytoplankton competitive ability for limiting nutrients, and top 459 Warming reduced total standing community biomass, largely via a reduction in 463 phytoplankton biomass. These results confirmed our qualitative theoretical predictions. 464

For example, because the potential resource supply rate (i.e. the concentrations of 465 limiting inorganic nutrients) remained constant, we predicted that elevated metabolic 466 demands at higher temperatures should have resulted in a decline in standing community 467 biomass in the warmed mesocosms. Assuming B tot = r 0 e -E/kT M 1/4 and that r 0 (i.e. the 468 resource supply rate) and M 1/4 (i.e. the allometric scaling of biomass with body mass) are 469 constant with temperature we can predict that for ≈4˚C warming (i.e. the average annual 470 temperature increase in our experiment) standing community biomass should decline 471 approximately 1.54 fold according to: e -E/kTh / e -E/kTa where T h and T a are the mean annual 472 temperatures of the heated and ambient mesocosms (290.9 and 286.1 K, respectively) and 473 E is the activation energy of metabolism ≈0.65eV [START_REF] Gillooly | Effects of size and 593 temperature on metabolic rate[END_REF]). In our 474 experiment average total community biomass declined 2.53 fold (i.e. the ratio of mean 475 biomass in the heated and ambient mesocosms), almost double that predicted by 476 metabolic costs alone, suggesting that additional factors may be operating. 477

The large shift in the distribution of body size from large to small phytoplankton 478 might further reduce standing biomass. For example, the above prediction assumes that 479 the allometric scaling of biomass with body mass (i.e. B tot = M 1/4 ) remains constant with 480 warming. However, we have demonstrated that the slope of the community size spectrum 481 (i.e. the log-log relationship) which is equivalent to the exponent (i.e. -α) of N = M -α , 482

F o r R e v i e w O n l y 22
where N is abundance (White et al. 2007[START_REF] Reuman | Three allometric relations of 653 population density to body mass: theoretical integration and empirical tests in 149 654 food webs[END_REF], White et al. 2008), 483 changes from -0.86 to -0.95 in response to warming. Therefore, because B tot = N×M the 484 allometric scaling of B tot declined from B tot = M 0.14 in the ambient mesocosms to 485 B tot = M 0.05 in the warmed mesocosm: i.e., more standing biomass was retained in larger 486 body size classes in the ambient relative to the warmed mesocosoms. We suggest that the 487 effects of increased metabolic costs, associated with warmer temperatures and the shift in 488 the distribution of body size and taxonomic composition of the phytoplankton 489 assemblage, could have acted synergistically to reduce total community biomass in the 490 warmed mesocosms. 491

The ratio of zooplankton to phytoplankton biomass, Z:P, declined as a function of 492 phytoplankton biomass, in line with our third experimental hypothesis. Our results are 493 qualitatively similar to the findings of [START_REF] Gasol | Biomass distribution in marine planktonic 591 communities[END_REF] who also demonstrated that the 494 ratio of heterotroph to autotroph biomass (H:A) was a declining function of autotroph 495

biomass in the open ocean and coastal seas, although they attributed the relationship to a 496 nutrient gradient rather than temperature. In our case, the large shifts in community size 497 structure and the distribution of biomass between zooplankton and phytoplankton were 498 independent of the inorganic nutrient status of the mesocosms and appear to have been 499

driven largely by the effects of temperature on metabolism and the relative competitive 500 abilities of large and small phytoplankton. 501

We found a strong, positive correlation between the Z:P biomass ratio and the 502 turnover rate of the phytoplankton assemblages, which differed profoundly between 503 warmed and ambient treatments. These results offer insight into how these communities 504 might function: the inverted pyramid or squared biomass distributions (i.e. Z>P or Z=P) 505

F o r R e v i e w O n l y
in the warmed mesocosms contrasted markedly with the pyramidal biomass structure (i.e. 506 Z<P) of the mesocosms at ambient temperature. This suggests that warming of ~4˚C 507 fundamentally altered the structure and functioning (i.e. energy transfer) of our 508 experimental ecosystems. For instance, in the heated mesocosms the high relative 509 biomass of zooplankton may have been supported by a fast turnover rate of the 510 phytoplankton assemblage. For example, for the low standing stocks of phytoplankton 511 biomass in the warmed mesocosms (2.93×10 5 µg C m -3 in heated; 1.12×10 6 µg C m -3 in 512 ambient) to sustain the equivalent biomass of zooplankton as the mesocosms at ambient 513 temperature (1.71×10 5 µg C m -3 in ambient; 1.36×10 5 µg C m -3 heated), the turnover rate 514 of the phytoplankton community would need to be elevated by a factor of ~4. The 515 average turnover rates of the phytoplankton community in the warmed treatments was 516 actually elevated by a factor of ~5 (i.e. 40.9 µg C m -3 d -1 / µg C m -3 in heated; 8.25 µg C 517 m -3 d -1 / µg C m -3 in the ambient) and was therefore sufficient to support the biomass of 518 zooplankton in these systems. Taken together, these results suggest that warming 519 increases the rate of carbon flux between autotrophs and heterotrophs. This effect appears 520 to be driven by the relative increase in small phytoplankton, which have faster turnover 521 times due to the -1/4 allometry of mass specific metabolic rate and generation time 522 [START_REF] Gillooly | Effects of size and 595 temperature on developmental time[END_REF][START_REF] Brown | Toward a metabolic 562 theory of ecology[END_REF], and also the direct stimulation of metabolism 523 and generation time by temperature [START_REF] Gillooly | Effects of size and 595 temperature on developmental time[END_REF]. 524 525

Conclusion 526

In general, the results of our experiment reflect patterns in empirical surveys that 527 have analysed phytoplankton communities over macroevolutionary time (Finkel et [START_REF] Moran | Increasing importance of 635 small phytoplankton in a warmer ocean[END_REF], 529 and across gradients of nutrient regime and productivity [START_REF] Del Giorgio | Biomass distribution in freshwater plankton 571 communities[END_REF], 530 Gasol et al. 1997). Our results, however, represent the first experimental evidence for a 531 shift in the distribution of body size and biomass of whole plankton communities that can 532 be attributed directly to the effects of warming via a controlled and replicated whole 533 ecosystem manipulation. Although we now have some tantalising hints, the precise 534 mechanism behind the size shifts we observed requires further research. Also, the 535 consequences of such shifts in community size structure for the functioning (e.g. carbon 536 sequestration capacity) of aquatic ecosystems remains an unexplored avenue in 537 ecological research, though with no doubt one that will prove fundamental in addressing 538 size spectrum in the ambient mesocosoms (n=20), (c) frequency distribution of the slope 686 of the community size spectrum in the warmed mesocosoms (n=20). On average the 687 slope of the community size spectrum in the warmed mesocosms was significantly 688 steeper than the ambient mesocosms (Table 1). ( d treatment. The mean cell mass of phytoplankton is significantly reduced in response to 699 warming while there is no significant difference in the mean body mass of zooplankton 700 between heated and unheated treatments (table 1). 701 702 Figure . 3. Redundancy analysis (RDA) biplot for sites (i.e. mesocosms) and species 703 scores for phytoplankton taxa recorded in the mesocosm experiment in April (a) and 704 October (b). In both cases RDA 1 was constrained by treatment and accounted for 24.1% 705 and 24.6% of the variation in the taxonomic composition of the mesocosms in April and 706 October respectively. In the plot the dotted lines denote the 95% confidence ellipses 707 around the centroids for both treatments. In both April and October these ellipses do not 708 warmed and ambient treatments. The solid lines enclose all mesocosms that belong to a 710 particular treatment; in both cases heated treatments (1,4,6,8,9,12,14,15,17,19) 711 cluster to the left, while ambient treatments (2,3,5,7,10,11,13,16,18,20) presented as the averages of the total biomass of either phytoplankton and/or zooplankton 726 across the mesocosms for each treatment (n=20 per treatment for the overall mean; n=10 727 per treatment for each sampling occasion). Total biomass is significantly reduced by 728 warming. This is mainly driven by a reduction in phytoplankton biomass, while there is 729 no significant difference in the biomass of zooplankton in response to warming (table 1) In both cases RDA 1 was constrained by treatment and accounted for 24.1% and 24.6% of the variation in the taxonomic composition of the mesocosms in April and October respectively. In the plot the dotted lines denote the 95% confidence ellipses around the centroids for both treatments. In both April and October these ellipses do not overlap indicating that the community composition was significantly different between warmed and ambient treatments. The solid lines enclose all mesocosms that belong to a particular treatment; in both cases heated treatments (1,4,6,8,9,12,14,15,17,19) cluster to the left, while ambient treatments (2,3,5,7,10,11,13,16,18,20) cluster ). Data are presented as the averages of the total biomass of either phytoplankton and/or zooplankton across the mesocosms for each treatment (n=20 per treatment for the overall mean; n=10 per treatment for each sampling occasion). Total biomass is significantly reduced by warming. This is mainly driven by a reduction in phytoplankton biomass, while there is no significant difference in the biomass of zooplankton in response to warming (table 1). S4). Furthermore, the stoichiometry of the inorganic nutrient pool exhibited 57 remarkable similarity between treatments, with a mean annual ratio of total inorganic N to P of 58 ≈11:1 in both heated and ambient mesocosms. 59 60 Table S4. Results of the linear mixed effects model testing for differences in the concentration of 61 inorganic nutrients between heated and ambient mesocosms. A linear mixed effects model was 62 conducted with restricted maximum likelihood methods using the lme (linear mixed-effects 63 model) function in R, treatment (heated or unheated) was the fixed effect, and temporal pseudo-64 replication from repeated sampling of the mesocosms over the year was accounted for by 65 including mesocosm identity nested with sampling occasion as random effects. 66

Inorganic

N i ) = b * log (M i ) + a.
Where N i is the abundance of the size class i and is the 70 mass at the centre of the i th size bin, b and a are the slope and the intercept respectively. These 71 data highlight that the size spectrum was linear for each of the mesocosms and that the individual 72 size distribution was a power law.

  the "size spectrum"

  and in lakes (del Giorgio & Gasol 1995) 138 along large scale spatial gradients of nutrient limitation. 139 carried out between December 2005 and April 2008 at the 143 Freshwater Biological Association, River Laboratory (2°10`W, 50°13`N), East Stoke, 144 Dorset, UK. A detailed description of the experimental set-up has been described 145 elsewhere (Yvon-Durocher et al. 2010). The experiment consisted of twenty freshwater 146 mesocosms (~1 m 3 , 0.5 m water depth): ten replicates remained at ambient temperature, 147 whilst the other ten were warmed and maintained at 3-5°C (mean 4°C) above ambient. 148 The mesocosms were seeded in December 2005 with organic substrates and a suite of 149 organisms to include the main components of organismal composition and physical 150 structure of shallow lake ecosystems. The established communities contained 151 representative species from primary producers (phytoplankton, including: Botryococcus, 152 Chlorella, Volvox, Scenedesmus) to top predators (Roach, Rutilus rutilus. Linnaeus), and 153 a suite of zooplankton consumers (including cyclopoid and calanoid copepods, 154 caldocerans, and rotifers). The biota was left to establish for ten months prior to 155 experimental warming, which commenced in September 2006, thereby allowing time for 156 further, natural colonisation before the onset of the study in April 2007. Populations of 157 the introduced top predator, R. rutilus were maintained at a constant densities [two 158

  This was sufficient to estimate 95% of the variance in the distribution of 186 body size (Fig S1 in supplementary material) given that settlement of organisms followed 187 a Poisson distribution within the sedimentation chamber (Fig S2 in supplementary 188 material). 189

  the carbon in the assemblage turns over. Measurements of primary 209 production were made simultaneously using the dissolved oxygen change technique and 210

  spectrum (n = 40), which included phytoplankton and zooplankton, 218 and the phytoplankton assemblage size spectrum (n = 40) were constructed for each 219 mesocosm in April and October 2007. The size spectrum of the zooplankton assemblage 220 alone could not be constructed accurately due to the relatively small body mass range and 221 the low number of individuals present in some samples. Size spectra were constructed by 222 logarithmic binning of the body masses (M) of the individuals measured in each 223 mesocosm (either the entire community or just the phytoplankton). The total range of 224 log 10 (M) values was divided into 10 bins of equal width and the log 10 of the total 225

  . Consequently, it was used to assess the strength 255 of the trend and its significance was tested using permutation tests. The F-ratio of the first 256 RDA axis was compared with those of 999 permutations, to assess the statistical 257 significance of the linear trend. As well as treatment (warming)N:P (see S3 for details on nutrient measurements) were tested as 259 constraining environmental variables. Phytoplankton taxon biomass was transformed 260

-

  also tested for significant relationships between phytoplankton 300 taxonomic composition and other environmental variables (NO 3

  relatively high standing stocks of zooplankton, exemplified by 345 high Z:P biomass ratios. 346 347 DISCUSSION 348 There is ample evidence that ecological responses to recent climate change are already 349 occurring at the species (and therefore the population) level (Walther et al. 2002), but 350 scaling from populations to communities and ecosystems is challenging because of the 351 perceived indeterminacy of ecological interactions (Yodzis & Innes 1992). Therefore, 352

  allometrically, resulting in a disproportionate increase in 437

  large phytoplankters by zooplankton grazing could occur simultaneously, 460 and combine with the direct effects of warming on metabolism to produce the observed 461 shifts in size, biomass taxonomic structure. 462

Figure. 1 .

 1 Figure Legends 682

Figure. 2 .

 2 Figure. 2. Effects of warming on mean body mass (±1 s.e.m) of phytoplankton (a) and 696

  the community composition was significantly different between 709

Figure. 4 .Figure. 5 .

 45 Figure. 4. Mean biomass of the major zooplankton taxonomic groups documented in the 720

Figure. 6 .(

 6 Figure. 6. (a) Relationship between zooplankton and phytoplankton biomass. (b) 732

Figure. 1 .Figure. 3 .

 13 Figure. 1. The size spectrum. (a) The community size spectrum of a heated (red circles) and ambient (black circles) mesocosm, highlighting the increase in the steepness of the slope in the warmed mesocosm. (b) Frequency distribution of the slope of the community size spectrum in the ambient mesocosoms (n=20), (c) frequency distribution of the slope of the community size spectrum in the warmed mesocosoms (n=20). On average the slope of the community size spectrum in the warmed mesocosms was significantly steeper than the ambient mesocosms (Table1). (d) The phytoplankton size spectrum of a heated (red circles) and ambient (black circles) mesocosm, highlighting the increase in the steepness of the slope and the truncation of large sized individuals in the warmed mesocosm. (e) Frequency distribution of the slope of the phytoplankton size spectrum in the ambient mesocosoms (n=17), (f) frequency distribution of the slope of the community size spectrum in the warmed mesocosoms (n=18). 198x328mm (72 x 72 DPI)

Figure. 5 .

 5 Figure.3. Redundancy analysis (RDA) biplot for sites (i.e. mesocosms) and species scores for phytoplankton taxa recorded in the mesocosm experiment in April (a) and October (b). In both cases RDA 1 was constrained by treatment and accounted for 24.1% and 24.6% of the variation in the taxonomic composition of the mesocosms in April and October respectively. In the plot the dotted lines denote the 95% confidence ellipses around the centroids for both treatments. In both April and October these ellipses do not overlap indicating that the community composition was significantly different between warmed and ambient treatments. The solid lines enclose all mesocosms that belong to a particular treatment; in both cases heated treatments(1, 4, 6, 8, 9, 12, 14, 15, 17, 19) cluster to the left, while ambient treatments(2, 3, 5, 7, 10, 11, 13, 16, 18, 20) cluster to the right. Genus abbreviations are as follows: Aphanothece (Aph), Asterococcus (Ast), Botryococcus (Bty), Bumilleriopsis (Bum), C.dinobryonis (C.d), Chlorella (Chl), Chlorococcum (Coc), Chroococcus (Chr), Chroomonas (Cho), Coencococcus (Coe), Cosmarium (Cos), Cryptomonas (Cry), Goniochloris (Gon), Kirchneriella (Kri), Monoraphidium (Mon), Navicula (Nav), Nephrocytium (Nep), Rhodomonas (Rho), Scenedesmus (Sce), Synechococcus (Syn), Synechocystis (Syc), Spermatozopsis (Spe). 391x198mm (72 x 72 DPI)

  Figure.5. Effects of warming on mean total planktonic biomass (±1 s.e.m). Data are presented as the averages of the total biomass of either phytoplankton and/or zooplankton across the mesocosms for each treatment (n=20 per treatment for the overall mean; n=10 per treatment for each sampling occasion). Total biomass is significantly reduced by warming. This is mainly driven by a reduction in phytoplankton biomass, while there is no significant difference in the biomass of zooplankton in response to warming (table1). 144x252mm (72 x 72 DPI)

Figure S1 .Figure S3 .

 S1S3 Figure S1. Frequency distributions of individual body mass for (a) all individuals measured, (b) 22

Figure S7 .

 S7 Figure S7. Quotient of benthic to ecosystem metabolism. On average over the course of the year 84

  et al. 2005, Winder et al. 2009) and documented changes in body size across latitudinal 94 gradients where other factors (i.e. nutrient limitation) are potentially confounded with 95 temperature

	F o
	r
	R e v i e w
	O n
	l y
	93	Finkel

  [START_REF] Finkel | A universal driver of 587 macroevolutionary change in the size of marine phytoplankton over the Cenozoic[END_REF], across latitudinal gradients in temperature

		24
	2005,
	F o
	r
	R e v i e w
	O n
	l y
	528	al.

Table 1 .

 1 The effect of treatment (heated or ambient) on community-level properties. CSS 739 is the community size spectrum and PSS is the phytoplankton size spectrum. ANOVAs 740 were used to isolate treatment effects on individual community-level properties.

	In each

Table 2 .

 2 Analysis of covariance for the relationships between zooplankton and 748 phytoplankton biomass , the Z:P biomass ratio and phytoplankton biomass, and the Z:P 749 biomass ratio and phytoplankton turnover time. 750

	Relationship

1, 2 , Mark Trimmer 1 , and Guy Woodward 1

	6
	7
	8	1 School of Biological & Chemical Sciences, Queen Mary University of London, London E1 4NS.
	9	U.K.
	10	2 Institute of Marine Sciences (ICM-CSIC) Pg. Marítim de la Barceloneta, 37-49
	11	E-08003 Barcelona, Spain
	12
	13	Authors for correspondence: Gabriel Yvon-Durocher (g.yvon-durocher@qmul.ac.uk) and Guy
	14	Woodward (g.woodward@qmul.ac.uk)
	15	School of Biological & Chemical Sciences,
	16	Queen Mary University of London,
	17	London E1 4NS. U.K.
	18	TEL:+44 20 7882 3640
	19

Table S5 .

 S5 Regression statistics for the community size spectrum of each mesocosm for the 69 relationship: log (

				F o
					r
		NO 2 NO 3 NH 4	--+	Nutrient	DF 1, 120 1, 120 1, 120 R e v F 0.06 0.65 0.23 i e w P 0.812 (NS) 0.420 (NS) 0.632 (NS)
	67 68	Si PO 4 Total inorganic N to P 3-	1, 120 1, 120 1, 120	6.08 0.68 0.009	0.015 0.412 (NS) 0.922 (NS) O n l y

Table S6 .

 S6 Regression statistics for the phytoplankton size spectrum of each mesocosm for the 77relationship: log (N i ) = b * log (M i ) + a.Where N i is the abundance of the size class i and is the 78 mass at the centre of the i th size bin, b and a are the slope and the intercept respectively.

						7 8
		13 11	Ambient Ambient	October -0.78 5.30 October -0.32 7.90	0.88 0.77 0.000880 0.00010
		14 12	Heated Heated	October -0.94 3.75 October -0.45 7.09	0.82 0.87 0.000240 0.00080
		15 13	Heated Ambient	October -0.95 4.17 October -0.40 7.43	0.93 0.90 0.000099 0.00010
		16 14	Ambient Heated	October -0.79 5.00 October -0.35 7.41	0.87 0.58 0.010000 0.00020
		17 15	Heated Heated	October -1.01 4.25 October -0.57 6.25	0.93 0.80 0.000400 0.00010
		18 16	Ambient Ambient	October -0.95 3.77 October -0.25 8.20	0.93 0.60 0.023000 0.00009
		19 17	Heated Heated	October -0.85 4.70 October -0.60 6.70	0.89 0.91 0.000200 0.00010
	73 75	20 18 19	Ambient Ambient Heated	October -0.94 4.24 October -0.46 6.70 October -0.36 7.49	0.92 0.82 0.000300 0.00004 0.69 0.003000
	74 76	20	Ambient	October -0.38 7.38	0.86 0.000300
	81	Pond	Treatment Month Slope Intercept r 2	P-value
	80 79 82	1 2 3 4 5	Heated Ambient Ambient Heated Ambient	April April April April April r -0.92 4.64 -0.94 4.58 -0.93 4.80 -0.93 4.50 -0.79 5.28 r F o o F	0.91 0.81 0.86 0.90 0.84	0.00020 0.00040 0.00030 0.00020 0.00003
		6 7 8 9 10 11 12 13 14 Pond Treatment Month Slope Intercept r 2 Heated April -1.12 3.30 Ambient April -0.83 5.09 Heated April -0.90 4.39 Heated April -1.03 3.94 Ambient April -0.92 3.89 Ambient April -0.86 4.71 Heated April -0.90 4.52 Ambient April -0.98 4.21 Heated April -0.88 4.25 R e v i e w 0.78 0.84 0.80 0.85 0.80 0.78 0.97 0.74 0.91 1 Heated April -0.41 7.50 0.42 0.040000 0.00060 0.00020 0.00040 0.00040 0.00100 0.00200 0.00004 0.00100 0.00080 P-Value 2 Ambient April -0.31 8.20 0.70 0.005000 4 Heated April -0.50 6.89 0.90 0.000092 6 Heated April -0.35 7.70 0.71 0.002200 7 Ambient April -0.22 8.39 0.57 0.012000 8 Heated April -0.27 8.03 0.55 0.014000 9 Heated April -0.55 6.78 0.88 0.000160 10 Ambient April -0.47 6.72 0.91 0.000020 R e v i e w
	83	15 16 17 18 19 20 1 15 16 17 11 12 13 14	Heated Ambient Heated Ambient Heated Ambient Heated Heated Ambient Heated Ambient Heated Ambient Heated	April April April April April April October -0.87 4.58 -0.94 4.64 -0.91 4.90 -1.05 4.05 -0.71 5.58 -0.92 5.09 -0.75 5.49 April -0.57 6.86 April -0.45 7.28 April -0.52 7.20 April -0.30 7.82 April -0.76 5.08 April -0.34 7.77 April -0.65 5.52	0.80 0.93 0.88 0.81 0.97 0.90 0.94 0.87 0.000200 0.00100 0.00001 0.00050 0.00030 0.00010 0.00001 l y 0.75 0.001200 0.67 0.004000 y l 0.00000 O n 0.53 0.018000 0.62 0.011000 0.56 0.013000 0.70 0.004600 O n
		2 18	Ambient Ambient	October -0.94 4.15 April -0.27 7.90	0.95 0.48 0.030000 0.00001
		3 19	Ambient Heated	October -0.72 5.46 April -0.65 6.36	0.70 0.93 0.000006 0.00200
		4 20	Heated Ambient	October -0.94 4.02 April -0.34 7.60	0.90 0.77 0.000900 0.00001
		5 2	Ambient Ambient	October -0.94 4.10 October -0.48 6.65	0.81 0.82 0.000300 0.00040
		6 4	Heated Heated	October -1.06 3.68 October -0.50 6.41	0.85 0.78 0.000680 0.00100
		7 5	Ambient Ambient	October -0.97 4.12 October -0.34 7.70	0.83 0.85 0.000300 0.00020
		8 7	Heated Ambient	October -0.92 4.50 October -0.34 7.70	0.89 0.62 0.007000 0.00040
		9 8	Heated Heated	October -0.90 4.50 October -0.30 8.14	0.84 0.68 0.004000 0.00040
		10 9	Ambient Heated	October -0.84 5.09 October -0.42 7.16	0.87 0.94 0.000005 0.00070
		11 10	Ambient Ambient	October -0.80 5.27 October -0.43 7.50	0.83 0.79 0.001400 0.00020
		12	Heated	October -0.93 4.42	0.88	0.00006

mesocosms in (a) April and (b) October. Note that there is very little difference in the

Acknowledgements 542

We thank Brian Godfrey, Dan Perkins, and the Freshwater Biological Association for 543 their help with the experiment. Sarah Tuffin and Rebecca Stewart contributed to the 544 counting of phytoplankton G. Yvon-Durocher was supported by a Natural Environment 545

Research Council studentship (NER/S/A2006/14029). J. Montoya was funded by the 546 NERC Fellowship Scheme (NE/C002105/1), and a Ramon y Cajal Fellowship (RYC-547 2008-03664). 548 549