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Secondary production and consumer energetics • • • • • • The consumer energy budget Determinants of energy flow Ecological efficiencies Definition of secondary production Measurement of secondary production Predicting secondary production – For individual populations – For guilds of consumers – For the entire community of consumers → Ingestion (I) I=A+E → Ingestion (I) Assimilation (A) Egestion (E) → I=A+E A = R + P (+ U) Respiration (R) → Ingestion (I) Assimilation (A) Growth (G), or Production (P) Egestion (E) → (Excretion (U)) I=A+E A = R + P (+U) Respiration (R) =loss of useful energy Ingestion (I) =loss to prey population → Assimilation (A) =energy available to consumer Growth (G), or Production (P) =energy available to predators Egestion (E) =input to detritus → (Excretion (U)) What affects rates of energy flow? Temperature affects energetic rates (Q10 ~2) Peters 1983 Body size affects energetic rates (~M-0.25) Peters 1983 Homeothermy/heterothermy affects energetic rates Peters 1983 Metabolic rates are evolutionarily flexible Data on flatworms from Gourbault 1972 Ecological efficiencies A/I = assimilation efficiency P/A = net growth efficiency P/I = gross growth efficiency Typical values of ecological efficiencies Assimilation efficiency (%) Net growth efficiency (%) Gross growth efficiency (%) Plants 1–2 30 – 75 0.5 – 1 Bacteria - 5 – 60 - Heterotherms 10 – 90 10 – 60 5 – 30 Homeotherms 40 – 90 1–5 1-4 What affects ecological efficiencies (partitioning of energy)? Assimilation efficiency depends on food quality Valiela 1984 Bacterial growth efficiency depends on food quality Del Giorgio and Cole 1998 Bacterial growth efficiency depends on temperature Rivkin and Legendre 2001 Introduction to secondary production • “All non-photosynthetic production (growth), regardless of its fate” • NOT the same as biomass accumulation • NOT just the production of herbivores • Much better studied than other parts of the consumer energy budget – Easier to measure – Historically considered more important Secondary production is aquatic and empirical • • • • • 167 papers published on subject in 2005 52% marine or estuarine, 35% freshwater, 3% terrestrial 55% microbial, 39% invertebrate, 7% vertebrate Very little theoretical work Are generalizations about secondary production really generalizations about aquatic ecosystems? How do we estimate secondary production? • • • • Tracer methods Demographic methods Turnover methods Empirical methods How do we estimate secondary production? Organism Method Data requirements Limitations Bacteria tracers (radioactive nucleotides or amino acids) uptake of label subject to large errors because of (i) critical assumptions about fate and use of label and nonradioactive analogues, which may be hard to test; (ii) uncertain conversion factors to get from uptake of label to carbon production Fungi ergosterol synthesis (from radioactive acetate) uptake of label into ergosterol method still under development; potential problems similar to those for bacterial production animals with recognizable cohorts increment summation, mortality summation, Allen curve density and body size of animals at frequent intervals over the life of the cohort data intensive animals without recognizable cohorts growth increment summation, instantaneous growth density, body size, and growth rates of animals in various size classes throughout the year data intensive; growth rates often measured in the lab and extrapolated to the field egg ratio density and development time of eggs, body mass of animals at death suitable only in the special case in which the body mass at death is known size-frequency (“Hynes method”) density and body size of animals in various size classes throughout the year data intensive empirical models population biomass; perhaps body size, temperature, habitat type subject to large error; may be data intensive any organism Controls on/prediction of secondary production • Individual populations • Guilds of consumers • Entire communities Predicting secondary production: (1) individual populations Marine benthic invertebrates Log10(P) = 0.18 + 0.97 log10(B) - 0.22 log10(W) + 0.04 (T) – 0.014 (T*log10depth) R2 = 0.86, N = 125 Tumbiolo and Downing 1994 Predicting secondary production: (1) individual populations Marine benthic invertebrates Log10(P) = 0.18 + 0.97 log10(B) - 0.22 log10(W) + 0.04 (T) – 0.014 (T*log10depth) R2 = 0.86, N = 125 Tumbiolo and Downing 1994 Predicting secondary production: (1) individual populations Q10 ~ 2.5 Tumbiolo and Downing 1994 Predicting secondary production: (1) individual populations Tumbiolo and Downing 1994 Predicting secondary production of individual populations • Feasible if you know mean annual biomass, body size, and temperature • Very imprecise • If you’re going to measure mean annual biomass, why not just estimate production directly? Predicting secondary production: (2) guilds (aquatic bacterial production as a function of phytoplankton production – Cole et al. 1988) Predicting secondary production: (2) guilds (aquatic invertebrate production in experimentally manipulated streams (Wallace et al. 1999) Predicting secondary production: (2) guilds (terrestrial animal production as a function of primary production – McNaughton et al. 1991) (V=vertebrates, I=invertebrates) Activity of consumer guilds rises roughly linearly with food supply Ecosystem type Consumer activity RMA slope Source Lakes Zoobenthos production 0.8 Kajak et al. 1980 Aquatic ecosystems Bacterial production 1.1 Cole et al. 1988 Terrestrial ecosystems Aboveground production 1.8 McNaughton et al. 1991 Aquatic ecosystems Herbivore ingestion 1.05 Cebrian and Lartigue 2004 All ecosystems Herbivore ingestion 1.1 Cebrian 1999 Marine ecosystems Herbivore ingestion 1.0 Cebrian 2002 Nutrients affect production of guilds Cross et al. 2006 Predicting secondary production (or ingestion): (2) guilds Aquatic is white (left) or blue (center and right); terrestrial is black (left) or green (center and right) (Cebrian and Lartigue 2004) Terrestrial/aquatic differences • Herbivores ingest a higher proportion of NPP in aquatic systems (higher nutrient content of NPP) • Herbivore production possibly much higher in aquatic systems (higher ingestion, higher assimilation efficiency?, less homeothermy so higher net growth efficiency) Predicting secondary production of guilds • Predictable (and linear?) from resource supply • Too imprecise to be very useful as a predictor • Maybe strong terrestrial/aquatic differences arising from nutrient content of primary producers • Nutrients as well as energy affect guild production Predicting secondary production: (3) entire communities Predicting secondary production: (3) entire communities S = R + L, so R = S – L (S = net supply of organic matter, L = non-respiratory losses) Predicting secondary production: (3) entire communities S = R + L, so R = S – L εng = P/(P + R), so P = εng(P + R) (εng = net growth efficiency, S = net supply of organic matter, L = non-respiratory losses) Predicting secondary production: (3) entire communities S = R + L, so R = S – L εng = P/(P + R), so P = εng(P + R) Therefore, P = εng(P + S – L) Predicting secondary production: (3) entire communities S = R + L, so R = S – L εng = P/(P + R), so P = εng(P + R) Therefore, P = εng(P + S – L); Rearranging, P(1- εng) = εng(S – L) Predicting secondary production: (3) entire communities S = R + L, so R = S – L εng = P/(P + R), so P = εng(P + R) Therefore, P = εng(P + S – L); Rearranging, P(1- εng) = εng(S – L) And P = (S – L)εng/(1 – εng) Predicting secondary production: (3) entire communities P = (S – L) εng/(1 – εng) A = (S – L)/(1 – εng) I = (S – L)/(εa(1 - εng)) εa = assimilation efficiency, εng = net growth efficiency, S = net supply of organic matter, L = non-respiratory losses Predicting secondary production: (3) entire communities Predicting secondary production of entire communities • Secondary production is large compared to primary production (if NGE=30%, secondary production = 43% of NPP) • Decomposers see a lot of consumer tissue (not just plant tissue) • Secondary production is larger in systems dominated by heterotherms than in systems dominated by homeotherms • Energy available for ingestion and assimilation by consumers is greater than primary production (if NGE=30% and AE = 20%, A=143% of NPP, I = 714% of NPP) Conclusions • It’s easier to predict the secondary production of an entire community than a single population • Consumer activity is tightly linked with other processes that control the movement and fate of organic matter • When considered at the community level, secondary production (maybe) is controlled by the same factors that control primary production: supply of energy and nutrients, and their retention