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Secondary production and consumer
energetics
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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
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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?
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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