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The food web

Primary producers

Primary consumers

D Detritus and associatedMicroflora (bacteria/fungi)

P

Death and sedimentation

herbivore detritivore

A1

inedible

Secondary Productivity:Primary production supportsa web of consumers—a simple example

Productivity

Biomass

ratedeath specific theis and rategrowth or production specific theis

,population theofty productivi thecalled is birth term The

formed. is biomass newat which rate theisty Productivi

lost. and formed isit at which rate the

between difference theis biomass of rategrowth net theisthat

balance mass a as written becan biomassfor equation rateA

mb

mBbBdt

dB

Defining some productivity terms

Birth (production) term

Death (loss) termB

bB/t

mB/t

The productivity is a combination of the birth of new organisms and the growth of the organisms already present

Similarly, the death process is a combination of death of organisms and weight loss by existing organisms.

If the productivity (birth term) exceeds the death term the biomass is increasing, and if the death term is larger, the biomass is decreasing

Time (t)

Biomass of a consumer

0dt

dB

B

t

0dt

dB

0dt

dB

Time (t)

RotiferBiomass

0dt

dR

R

t

0dt

dR

0dt

dR

So if we measure and B at any point in time and we can estimate the specific birth rate, we can then obtain the specific death rate by subtraction.

dt

dB

dt

dB

Bbm

1

mbdt

dB

B

BmbmBbBdt

dB

1

or

losses minus production

•For a tiny consumer like a rotifer the birth rate is easy to estimate since the adult females carry their eggs around until they hatch

•When they hatch they come out as full sized rotifers. •If we know the fraction of adults carrying egs and the average time it takes for eggs to hatch, we can calculate the birth rate. •Since the rotifers are born more or less full size, so there is no need to model or measure the growth of individuals.

A tiny organism like a rotifer is born at full size, so productivity amounts to measuring the rate at which new animals are born

Rotifers carrying eggs

1-d

rate hatching1

(d) hatchingfor required timeavg

,adults#

eggs#

T

Eb

T

T

E

dt

dB

BT

Em

1

Time (t)

RotiferBiomass

0dt

dR

R

t

0dt

dR

0dt

dR

Egg Ratio

For a large organism like a fish, biomass production occurs mostly from individual growth. New born fish are so tiny that birth of individuals makes a negligible contribution to biomass production

1W2W

3W

4W

t

tt

W

WSGR

1ln

Year classes

The Wt represent the Weights of each year class

•We can calculate the growth rate of biomass individual fish by weighing fish and determining their age and then seeing how much weight they gain each year.

•The productivity of each age class is the Specific growth rate (SGR) of that age class times the total biomass of that age class in the population.

category trophicin the species allover summed and classes, age ofeach for

present] biomass timesrategrowth [specific of sum Production

*

it

tt

i tBSGRP

This approach assumes that the size vs age relationship is relatively constant.

1W2W

3W

4W

t

tt

W

WSGR

1ln

The Wtrepresent the Weights of each year class

By this method the average SGR for the whole population can be calculated as the weighted average over all age classes

However there is a problem with this approach…???

1

t

T

t

t SGRwSGR

class ageth ' in the Biomass offraction the, where tB

Bw

tt

t

tt

W

WSGR

1ln

However there is a problem with this approach.

By considering only the gain in weight across age classes, this method ignores weight gained and lost within the same year, eg Gonad tissue Adult fish usually convert a considerable portion of their body mass to gonads and release it during spawning every year.Thus it does not add to next year’s weight and would not be recorded as growth

We can quite easily correct for this by factoring in gonad production (add GSI)

weighttotal

weightgonad matureindex) atic(Gonadosom where

GSI

GSISGRt

We would of course only make this GSI correction on adult age classes.

Scales of a chum salmon

2+

3+

4+

Measuredistances fromscale center to eachannulus along a chosenaxis

T

A

L

L

length scale total

annulus todistance

How can we tell how old a fish is?

LA

Age yr

Convert the growth curve based on length to weights usinga length-weight plot for the species

This allows us to construct a growth curve based on length and age.

Many types of bony structures are commonly used to determine age of fish

Scale Otolith Opercular bone

These three structures are all from the same 3+ year old 30 cm cutthroat trout

The specific death rates can also be estimated from the population structure. This time we assume that the age structure of the population is constant, and that the numbers of individuals of each age within a sample reflects the proportion of that age group in the population.Assume we have a sample of 215 pike from a population.

215

1101

t

tN

N

552 N

303 N

204 N

The Nt / Nt represent the proportion of the population in each year class

69.0110

55ln1 m

61.055

30ln2 m

41.030

20ln3 m

t

tt

N

Nm

1ln

Age1 3 50

*

*

*

*

110

30

55

20

#

0

50

100

The survivorship curve assuming stable age structure for the population looks like this

t

tt

N

Nm

1ln

m1 =0.69

150

m3 =0.41

m2 =0.61

equal. are terms two thepopulation stable aFor

biomassin decreasing is population theotherwise

biomassin growing is population thelosses, exceedsty productivi If

processes loss andgrowth itsbetween difference the

as modelledusually is species afor biomass of change of rate The

mSGRBGSImBGSISGRBdt

dB

Productivity term loss term

Summary

Phytoplankton

Zooplankton

Benthic & epiphytic algae plus detritus

Benthic & epiphyticinvertebrates

Diet shift

Trophic link

Net productivity at level n = the rate of growth of biomass at that level= [SGR +GSI] * Biomass= NPP (TE) n-1

Productivity at different levels in the food web

NPP around 500 g/m2/yr

500 x 0.1 g/m2/yr

500 x (0.1)2 g/m2/yr

500 x (0.1)3 g/m2/yr

Ecological efficiency of zooplankton is usually around 10% of NPP in lakes

Variability??

1

n

nn

P

P

Ecological efficiency (n) for a consumer at the nth trophic level

Zooplankton such as Daphnia filter-feed using currents generated bytheir thoracic appendages. Fecal pellets sediment rapidly to the bottom

Fecal pellets

80-95% of energy is lost at each trophic step, much of it as feces

The undigested material in the zooplankton fecal pellets was not assimilated.Assimilation efficiency depends on the digestibility of the dietCellulose, chitin, lignin or other undigestible material makes AE low

Ingested energy ─ egested energy = assimilated energyAssimilation efficiency (AE, %)= assimilated energy/ingested energy x 100

Assimilation efficiencyHerbivores depends on diet≈100% for sugary nectar≈40-80% for small phytoplankton and filamentous algae<20% for mud and detritus

Carnivores60-70% for aquatic insects70-90% for meat

Fecal pellets

Exploitation efficiency or Consumption Efficiency (EE)

1001

n

nn

P

IEE

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

Assimilated energy ─ respiration ─ excretion = production (growth)Net Production efficiency (NPE, %)= growth/assimilation x 100Gross PE (%)=[assim/ingest x growth/assim] x100=growth/ingest x 100

Gross PEEndotherms≈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

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 sculpinwould grow more than twice as fast as the salmon

http://www.ucmp.berkeley.edu/arthropoda/crustacea/images/copepoda03.jpg

•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.

Filter-feeding by a calanoid copepod

Copepod dominated communites have lower trophic efficiency than cladoceran dominated communities—possible reasons?

NPP = rate of formation of phytoplankton biomass

S = rate of production of uneaten algae, mostly inediblespecies (sedimentation)

F= rate of production offecal pellets (sedimentation)

Energy budget for herbivorous zooplantkon

Metabolic costs include basal metabolism, activity costsand specific dynamic action (costs of digestion etc)+ excretion

Zooplankton production is the rate at which biomass (energy)becomes available for consumption by zooplanktivores

The Bioenergetic budget for an organism C= G + M*A+ SDA+U+F

Energetic losses in the food chain

Less than 1% of the incident light energy is captured by photosynthesisas NPP.

Productivity declines byabout 10-fold for eachtrophic level in the foodchain.

Most of the losses are are in the form of waste heat.

Some energy from each trophic level winds up inthe detrital pool, and someof this remains buried as sediment (or soil) organicmatter (fossilized)

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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 sculpinwould grow more than twice as fast as the salmon

0

1

2

3

4

5

2.3 2.4 2.5 2.6 2.7 2.8

Log LDH activity

Act

ivity

mul

tiplie

r Br3+

Bmt3+Bmt2+

Wa3+ Wa2+

Mg3+

Mg2+

Me2+

Me3+

•The anaerobic capacity of fish muscles is closely linked to amount of energyspent on Activity

•Lactate dehydrogenase (LDH) is an important enzyme for anerobicrespiration, and anaerobic respiration generates bursts of power--but is veryinefficient and builds up an oxygen debt.

There is a trade-off between power (the rate of energy consumption) andefficiency.

The Bioenergetic budget for an organismC= G + M*A+ SDA+F+U

A

100

200

300

400

500

600

0.1 1 10 100 1000

LDH vs body size for perch

body size (g)

zooplankton

inverts

fish

LD

H a

ctiv

ity

(abs

un

its p

er

mg

pro

t)

die

t

In order to keep growing carnivorous fish usually need to switch to larger and larger preyIf they do not, the activity costs escalate rapidly, and fish fail to grow (stunting)Thus trophic position usually increases as the fish matures.

Benthic & epiphytic algae plus detritus

Diet shift

Trophic link

Phytoplankton

ZooplanktonBenthic & epiphytic

invertebrates

Trophic niches filled by yellow perchIn the foodweb of an unimpacted lake

Pelagic food chain

Benthic & epiphytic algae plus detritus

Diet shift

Trophic link

Phytoplankton

Zooplankton Benthic & epiphyticinvertebrates

Trophic ecology of yellow perchIn the foodweb metal impacted lake

Pelagic food chain

X XX

X bottleneck

Classenia, a predatory stonefly, and some of the stream insect larvae that it preys on

Stoneflies prefer prey thatare near the energeticallyoptimum 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

Total Phosphorus µg ● L-1

Fis

h co

mm

unity

bio

mas

s kg

●

ha-1

Log B = 0.94+ 0.52 (± 0.09) Log TP -0.18 (± 0.05) L/R, RMS=0.27, R2=0.71

Rivers

Lakes

Rivers support more fish biomass than lakes for the same TP Level? Why?

Total Phosphorus µg ● L-1

Fis

h co

mm

unity

bio

mas

s kg

●

ha-1

Oldman River, Alberta

Warta River, Poland

Comparing regulated vs unregulated rivers ?

50 m, 0.03 ha seine

•Intensive aquaculture can produce yields that are orders of magnitude beyond natural ecosystems

How to maximize energy flow to fishIncreased nutrient loading—fertilization + ammonia and anoxia tolerant speciesShortening the food chain—primary consumers (eg carps, tilapia or mullets)Don’t rely on natural recruitment and managing the life cycle—stocking/hatcheriesIncreasing consumption efficiency—small pens intensive feedingIncreased assimilation efficiency—feeding with easy to digest food pelletsIncreased production efficiency—low activity species that don’t mind crowding,

, highly turbid water

Many aquaculture proponents argue that aquaculture reduces harvesting pressure on wild fisheries.

Salmonid aquaculture not very trophically efficient, food pellets made from by-catch of wild species

Major water quality issues—nutrient pollution from cages, anti-fouling paint, antibiotics, habitat destruction

Transmit diseases to wild salmonids—bacteria, viruses, protozoans, fungi, “fish lice” –parasitic copepods and other Crustacea

Genetic problems when domestic escapees compete with or interbreed with wild fish

Argulus

Lepeophtheirus salmonis

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 inturn 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 whichis 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.

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If the productivity of a phytoplankton population is 4000 k J (kilo Joules) /yr / m2, If sedimentation rate of dead cells to the substrate constitutes 1600 kJ/m2yr, and the phytoplankton population is dB/dt=0. If the rain of zooplankton fecal pellets to the bottom is 1400 kJ/m2/yr. What is the assimilation efficiency of the zooplankton trophic level (assume that they are all feeding on phytoplankton).

1.0.42 or 42%2.0.60 or 60%3.0.35 or 35%4.0.25 or 25%5.None of these

What is the exploitation efficiency EE (or Consumption efficiency CE) of the zooplankton trophic level

1.0.42 or 42%2.0.60 or 60%3.0.35 or 35%4.0.25 or 25%5.None of these

If the net production efficiency of the zooplankton trophic level is 0.40 (40%) what is the ecological efficiency () of the trophic level 1.0.15 or 15%2.0.05 or 5%3.0.10 or 10%4.0.25 or 25%5.None of these

If the zooplanktivorous fish are consuming zooplankton at the rate of 400 kJ/yr/m2, their EE (CE) is 1.0.40 or 40%2.0.60 or 60%3.1.00 or 100%4.0.25 or 25%5.None of these

If the zooplanktivorous fish have an assimilation efficiency of 0.70 (70%) and Net production efficiency (NPE) of 0.20 (20%), the productivity at this trophic level is1.40 kJ/yr/m2

2.56 kJ/yr/m2

3.100 kJ/yr/m2

4.280 kJ/yr/m2

5.None of these

If in another lake with similar zooplankton productivity the planktivore fish productivity was 2 X higher, a possible explanation for this would be1.the AE of the fish in that lake was 2X as high2.the NPE of the fish in that lake was 2X as high3.the EE (CE) in that lake was 2X as high4.the AE*NPE in that lake was 2X as high5.both b and d are true6.both b and c are true

The standing stock of energy in the plankton is low but it is turned over rapidly, because the organisms are small, grow rapidly and don’t live long

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Residence time and turnover of energy by trophic levels

Turnover is slower at higher trophic levels, since larger organisms accumulate energy over a longer life span—longer residence time and slower turnover

PlanktonicHerbivore (50g) life span 1 month Benthic Detritivore

(0.1 g) life span 1yr

Phytoplankton (0.01g, life span, few days

Carnivorous fish (100g) life span 5-10 yr