Secondary production

1
Secondary production

• Energy fixed by green plants flows to
• Herbivores or detritus or
• lost in respiration
• Secondary production limited by
• Primary production
• Second Law of Thermodynamics
• Most animals important to humans play a trivial
  role in ecosystem energetics
• Plants and detritus are THE important components
  in all ecosystems.

2
Secondary Production Partitioning energy for
herbivores or predators
3
Estimating energy expenditure in free living
animals
Inject an animal with a known amount of the two
isotopes Wait 12-24 hours after injection (time
for isotopes to circulate through the body)
Blood sample taken to begin experiment Animal
released and recaptured after a appropriate time
(varies with metabolism of species) Blood sample
taken to end experiment. Isotope concentration in
blood samples determined 18O elimination 3H2
elimination CO2 production ? energy used
4
Field metabolic rates related to body size
Homeothermy energetically expensive Use gt 98 of
ingested energy to maintain body
temperature. Poikilotherms more efficient.
5
Problem estimating production for a whole trophic
level
Too much omnivore variation to classify. Generally
deal with taxonomic parts of food webs So
selected species generally examined.
6
Production efficiency within a single species
net productivity of species a
assimilation of species a
4 groups
3 groups
Do all taxa have the same production
efficiency? Within each group as respiration
goes up 1 kJ, production goes up 1 kJ Production
efficiencies are the same for all sizes of
animals within the same group
7
But, there is a way to measure of ecosystem
efficiency Trophic efficiency net production
at trophic level i 1 net production at
trophic level i
Energy not transferred Is lost in respiration or
detritus.
Frequency distribution of energy transfer
efficiencies herbivores to carnivores Estimates
from 140 examples from freshwater and marine
ecosystems
8
Aquatic ecosystems trophic efficiency 2-24
averages 10.1
How much production does it take to support a
fishery? 1990 2,975,000 tons of tuna For every
100 g of tuna, it requires 100,000 g of
phytoplankton
9
To support world fisheries
10
Fishing down food webs Overfishing Trophic
assignments Top predator Orcas (5) Second level
predators cod and tuna (4) First level predators
(3) Herbivorous fish (2)