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) →

→ Assimilation (A) I = A + E → Egestion (E)

Ingestion (I) → Assimilation (A) I = A + E A = R + P (+ U) → Egestion (E) Respiration (R) → Growth (G), or Production (P) (Excretion (U))

Ingestion (I) =loss to prey population → Assimilation (A) =energy available to consumer I = A + E A = R + P (+U) → Egestion (E) =input to detritus Respiration (R) =loss of useful energy → Growth (G), or Production (P) =energy available to predators (Excretion (U))

What affects rates of energy flow?

Temperature affects energetic rates (Q 10 ~2) Peters 1983

Body size affects energetic rates (~M ) 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 (%) Plants1 – 230 – – 1 Bacteria-5 – 60- Heterotherms10 – 9010 – 605 – 30 Homeotherms40 – 901 –

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 % 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? OrganismMethodData requirementsLimitations Bacteriatracers (radioactive nucleotides or amino acids) uptake of labelsubject to large errors because of (i) critical assumptions about fate and use of label and non- radioactive analogues, which may be hard to test; (ii) uncertain conversion factors to get from uptake of label to carbon production Fungiergosterol synthesis (from radioactive acetate) uptake of label into ergosterolmethod 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 ratiodensity 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 any organismempirical modelspopulation biomass; perhaps body size, temperature, habitat type subject to large error; may be data intensive

Controls on/prediction of secondary production Individual populations Guilds of consumers Entire communities

Predicting secondary production: (1) individual populations Marine benthic invertebrates Log 10 (P) = log 10 (B) log 10 (W) (T) – (T*log 10 depth) R 2 = 0.86, N = 125 Tumbiolo and Downing 1994

Predicting secondary production: (1) individual populations Marine benthic invertebrates Log 10 (P) = log 10 (B) log 10 (W) (T) – (T*log 10 depth) R 2 = 0.86, N = 125 Tumbiolo and Downing 1994

Predicting secondary production: (1) individual populations Tumbiolo and Downing 1994 Q 10 ~ 2.5

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 typeConsumer activityRMA slopeSource LakesZoobenthos production 0.8Kajak et al Aquatic ecosystemsBacterial production1.1Cole et al Terrestrial ecosystems Aboveground production 1.8McNaughton et al Aquatic ecosystemsHerbivore ingestion1.05Cebrian and Lartigue 2004 All ecosystemsHerbivore ingestion1.1Cebrian 1999 Marine ecosystemsHerbivore ingestion1.0Cebrian 2002

Nutrients affect production of guilds Cross et al. 2006

Predicting secondary production (or ingestion): (2) guilds ( Cebrian and Lartigue 2004) Aquatic is white (left) or blue (center and right); terrestrial is black (left) or green (center and right)

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

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 ε ng = P/(P + R), so P = ε ng (P + R) (ε ng = 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 ε ng = P/(P + R), so P = ε ng (P + R) Therefore, P = ε ng (P + S – L)

Predicting secondary production: (3) entire communities S = R + L, so R = S – L ε ng = P/(P + R), so P = ε ng (P + R) Therefore, P = ε ng (P + S – L); Rearranging, P(1- ε ng ) = ε ng (S – L)

Predicting secondary production: (3) entire communities S = R + L, so R = S – L ε ng = P/(P + R), so P = ε ng (P + R) Therefore, P = ε ng (P + S – L); Rearranging, P(1- ε ng ) = ε ng (S – L) And P = (S – L)ε ng /(1 – ε ng )

Predicting secondary production: (3) entire communities P = (S – L) ε ng /(1 – ε ng ) A = (S – L)/(1 – ε ng ) I = (S – L)/(ε a (1 - ε ng )) ε a = assimilation efficiency, ε ng = 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