Secondary production and consumer energetics

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)

→

Ingestion (I)

→Assimilation (A)

I = A + E

→Egestion (E)

http://science.mccneb.edu/pevans/Image_Data_Base/Zoom_Images/ZoomRabbitDroppings.htm

Ingestion (I)

→ Assimilation (A)

I = A + EA = R + P (+ U)

→Egestion (E)

Respiration (R)

→

Growth (G), or Production (P)

(Excretion (U))


Ingestion (I)=loss to preypopulation→ Assimilation (A)

=energy available to consumer

I = A + EA = 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(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 andCole 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 non-radioactive 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

any organism empirical models population 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

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


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




Q10 ~ 2.5



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)


(aquatic invertebrate production in experimentally manipulated streams (Wallace et al. 1999)


(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

(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)


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)


S = R + L, so R = S – L


Therefore, P = εng(P + S – L)


S = R + L, so R = S – L


Therefore, P = εng(P + S – L);

Rearranging, P(1- εng) = εng(S – L)


S = R + L, so R = S – L


Therefore, P = εng(P + S – L);

Rearranging, P(1- εng) = εng(S – L)

And P = (S – L)εng/(1 – εng)


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

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Secondary production and consumer energetics