Ecological efficiency (n) for a consumer at the nth trophic level
Pn
n 
Pn  1
Ecological
efficiency of
zooplankton is
usually around
10% of NPP in
lakes
Variability??
80-95% of energy is lost at each trophic step, much of it as feces
Assimilation efficiency
Herbivores depends on diet
≈100% for sugary nectar
≈40-80% for small phytoplankton
and filamentous algae
<20% for mud and detritus
Carnivores
60-70% for aquatic insects
70-90% for meat
Fecal pellets
The undigested material in the zooplankton fecal pellets was not assimilated.
Assimilation efficiency depends on the digestibility of the diet
Cellulose, chitin, lignin or other undigestible material makes AE low
Ingested energy ─ egested energy = assimilated energy
Assimilation efficiency (AE, %)= assimilated energy/ingested energy x 100
Exploitation efficiency or Consumption Efficiency (EE)
In
EEn 
 100
Pn  1
Exploitation efficiency is the consumption rate at a given trophic level divided by
the productivity of the trophic level it feeds on.
Zooplankton will have low EE (CE) when phytoplankton are sedimenting rapidly
to the bottom before they are being eaten.
If EE(CE) is high then most of the sedimentation will be in the form of fecal
pellets, which sink more rapidly than individual cells.
Zooplankton fecal pellets are good food for benthic invertebrates
If EE for herbivorous zooplankton is low then dead (sedimenting) phytoplankton
will be readily available for detritivores (zoobenthos)
Activity is energetically expensive and high Metabolic rate means
low Production efficiency
Gross PE
Endotherms
≈5% or less
≈1% some birds
Ectotherms
≈10-30% for fish
≈ 5-15% insects
Otter swim about rapidly and spend large amounts of energy looking for fish to eat
Assimilated energy ─ respiration ─ excretion = production (growth)
Net Production efficiency (NPE, %)= growth/assimilation x 100
Gross PE (%)=[assim/ingest x growth/assim] x100=growth/ingest x 100
Pelagic fish like kokanee salmon
expend a huge amount of energy
actively searching for prey--they
have high basal metabolic rates low
conversion efficiencies
The deepwater sculpin sits
on the bottom and ambushes
unsuspecting prey. They
have very low basal
metabolic rates and high
conversion efficiencies
If these two species were fed the same amount of food, the sculpin
would grow more than twice as fast as the salmon
Copepod dominated communites have lower trophic efficiency than cladoceran
dominated communities—possible reasons?
Filter-feeding by a calanoid copepod
•Copepods are rapid swmmers and generate feeding currents as they swim
•Copepods filter-feed by generating currents with their 1st antennae and their thoracic
appendages..
•Water from small eddy currents around the mouthparts is drawn over the fine setae of the
maxillae, where small algae are collected and moved to the mouth.
http://www.ucmp.berkeley.edu/arthropoda/crustacea/images/copepoda03.jpg
Energy budget for herbivorous zooplantkon
NPP = rate of formation of
phytoplankton biomass
S = rate of production of
uneaten algae, mostly inedible
species (sedimentation)
F= rate of production of
fecal pellets (sedimentation)
 The Bioenergetic budget for an organism
C= G + M*A+ SDA+F+U
Metabolic costs include basal metabolism, activity costs
and specific dynamic action (costs of digestion etc)
Zooplankton production is the rate at which biomass (energy)
becomes available for consumption by zooplanktivores
Energetic losses in the food chain
Less than 1% of the incident light
energy is captured by
photosynthesis
as NPP.
Productivity declines by
about 10-fold for each
trophic level in the food
chain.
Most of the losses are
are in the form of waste
heat.
Some energy from each
trophic level winds up in
the detrital pool, and some
of this remains buried
as sediment (or soil) organic
matter (fossilized)
Pn
n 
Pn  1
In
An
Pn
Pn
EEn 
, AEn 
, PEn 
, GPEn 
Pn  1
In
An
In
Show
n  EEn  AEn  PEn
n  EEn  GPEn
Productivity at different levels in the food web
500 x (0.1)3 g/m /yr
2
500 x (0.1)2 g/m /yr
2
500 x 0.1
g/m2/yr
NPP around 500 g/m /yr
2
Zooplankton
Benthic & epiphytic
invertebrates
PhytoplanktonDiet shift
Benthic & epiphytic
algae plus detritus
Trophic link
Net productivity at level n = the rate of growth of biomass at that level
= [SGR +GSI] * Biomass
= NPP (TE) n-1
Pelagic fish like kokanee salmon
expend a huge amount of energy
actively searching for prey--they
have high basal metabolic rates low
conversion efficiencies
The deepwater sculpin sits
on the bottom and ambushes
unsuspecting prey. They
have very low basal
metabolic rates and high
conversion efficiencies
If these two species were fed the same amount of food, the sculpin
would grow more than twice as fast as the salmon
 The Bioenergetic budget for an organism
C= G + M*A+ SDA+F+U
A
Activity multiplier
5
4
Br3+
Mg3+
3
Mg2+
Me3+
2
Bmt2+
1
Wa2+
Me2+
Bmt3+
Wa3+
0
2.3
2.4
2.5
2.6
2.7
2.8
Log LDH activity
•The anaerobic capacity of fish muscles is closely linked to amount of energy
spent on Activity
•Lactate dehydrogenase (LDH) is an important enzyme for anerobic
respiration, and anaerobic respiration generates bursts of power--but is very
inefficient and builds up an oxygen debt.
There is a trade-off between power (the rate of energy consumption) and
efficiency.
(abs units per mg prot)
LDH activity
LDH vs body size for perch
600
500
400
300
200
100
fish
diet
inverts
zooplankton
0.1
1
10
100
1000
body size (g)
In order to keep growing carnivorous fish usually need to switch to larger and larger prey
If they do not, the activity costs escalate rapidly, and fish fail to grow (stunting)
Thus trophic position usually increases as the fish matures.
Trophic niches filled by yellow perch
In the foodweb of an unimpacted lake
Benthic & epiphytic
invertebrates
Zooplankton
Phytoplankton
Diet shift
Trophic link
Pelagic food chain
Benthic & epiphytic
algae plus detritus
Trophic ecology of yellow perch
In the foodweb metal impacted lake
X
bottleneck
Diet shift
Trophic link
X
Zooplankton
X
X
Benthic & epiphytic
invertebrates
Phytoplankton
Pelagic food chain
Benthic & epiphytic
algae plus detritus
Classenia, a predatory stonefly, and some of the stream insect
larvae that it preys on
Stoneflies prefer prey that
are near the energetically
optimum size, when they
are given the opportunity
to select from a variety of
sizes.
Yields of piscivorous fish are well correlated with primary productivity but are
several orders of magnitude lower than PP
Summarizing concepts on Secondary production
•The organic matter produced by primary producers (NPP) is used by
a web of consumers
•NPP is used directly by primary consumers (herbivores and detritivores), which are in
turn consumed by carnivores.
•Measurement of 2o Production is done by estimating the rate of growth of individuals
and multiplying by the number of individuals per unit area in the cohort (age or size group).
•The efficiency of secondary production ranges from 5-20% (Avg 10%)
at each trophic level.
•Efficiency depends on several factors--palatability, digestibility, energy requirements
for feeding (activity costs)(eg homeotherms vs poikilotherms , other limiting factors
eg water, and nutrient quality of food.
•Trophic efficiency can be represented as the product of CE*AE*PE, each of which
is dependent on one or more of the above factors.
•The yields of many important fisheries depends on a combination of NPP, the
length ofthe food chain leading to the fish being harvested, and the efficiency
of each step.
•Many of the species that we harvest or very high in the food chain, so a great deal
of NPP is required to support them.