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

n



P n P n

 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)

EE n



I n P n

 1  100 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 1 st 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)



n



P n P n

 1

EE n



P n I n

 1 ,

AE n

 Show 

n



n

 

EE n



AE n



PE n EE n



GPE n A n

,

PE n I n



P n A n

,

GPE n



P n I n

Productivity at different levels in the food web 500 x (0.1) 3 g/m 2 /yr 500 x (0.1) 2 g/m 2 /yr 500 x 0.1 NPP g/m 2 /yr around 500 g/m 2 /yr Zooplankton Phytoplankton Diet shift Benthic & epiphytic invertebrates 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 5 4 Br3+ Mg3+ 3 Mg2+ A Me3+ 2 Bmt2+ 1 Wa2+ 0 2.3

Bmt3+ Wa3+ 2.4

Me2+ 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.

600 500 400 300 200 100 LDH vs body size for perch fish inverts zooplankton 0.1

1 10 body size (g) 100 1000 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 Zooplankton Phytoplankton Pelagic food chain Diet shift Trophic link Benthic & epiphytic invertebrates Benthic & epiphytic algae plus detritus

Trophic ecology of yellow perch In the foodweb metal impacted lake Diet shift Trophic link

X

bottleneck

X X

Benthic & epiphytic invertebrates

X

Zooplankton 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 2 o 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.