Lecture energy flow in ecosystems

ENERGY FLOW IN ECOSYSTEMS

• All organisms require energy:
for growth, maintenance, reproduction, locomotion, etc.
• Hence, for all organisms there must be:
 A source of energy
 A loss of usable energy


Types of energy
heat energy
mechanical energy

(+gravitational energy, etc.)
chemical energy

= energy stored in molecular bonds



The distribution of sola radiation energy in the biosphere
0.8% 0.2%
Heating air, land,
ocean
Evaporation

30.0%
46.0%

Reflection
Photosynthesis

23.0%

Wave, wind


This pattern of energy flow among different organisms is
the TROPHIC STRUCTURE of an ecosystem


Transformations of energy
The transformations of energy from solar radiation
to chemical energy and mechanical energy and
finally back to heat of Ecosystem Ecology.


Energy and biomass pyramids


The concepts
• PG: Gross primary productivity
– = the total rate of photosynthesis
– = the rate of energy capture by producers (kcal/m2/yr)
– = the amount of new biomass of producers (g/m2/yr)

• PN = PG – R; Net primary production is thus the amount of
energy stored by the producers and potentially available to
consumers and decomposers
• B: Standing crop Biomass – the amount of accumulated
organic matter found in an area at a given time

The concepts
• NU: Not consumed
• NA: Undigested / Fecal wastes
• R: Respiration
•

P: Secondary productivity
– the rate of production of new biomass by consumers,
– the rate at which consumers convert organic material into new
biomass of consumers


The common method of measuring PN
 Terrestrial ecosystems
 To estimate the change in Standing crop Biomass over a given time
interval (t2 –t1)
 B = B(t2) – B(t1)
 PN = B + D + C
 D: loss of biomass due to the dead of plants from t1 to t2
 C: loss of biomass due to consumption by consumer


The common method of measuring PN
 Aquatic ecosystems
 To estimate the change in O2 concentration in light/dark bottle
 Water sample containing phytoplankton

O2 produced by photosynthesis

O2 consumed in respiration


Limiting Factors control PN in Terrestrial ecosystems


Limiting Factors control PN in Aquatic ecosystems
100

12
10
8
6

PN

10

Light intensity
(% of suface value)

50

4
2
0
0

20

40

60

80

100

120

Nitrogen concentration (mg/l)

140

160


Primary production varies with time


Primary production varies with time


Primary production varies with time


Primary production varies with time


Primary production varies with time

Net primary production (NPP) and standing biomass allocation for
a 90-year-old Michigan forest estimated from inventory-based
methods in which biomass growth is quantified over time
(Gough et al. 2008)



Primary productivity limits secondary production

Net primary productivity (kJ/m2/yr)


Primary productivity limits secondary production


 Trophic efficency (TE): the ratio of productivity in

a given trophic levelGrowth
(Pn) to trophic level it feeds
on (Pn-1Respiration
)
33J
Undigested
100J
67J
(P)
TE = Pn / Pn-1
 Growth efficency: the ratio of energy for growth to

total energy
200J (A)

Growth efficency (P/A) = 33/200 = 16,5%


Production efficiency (x100) of various animal group
(Humphrey, 1979)

Group

P/A (%)

Group

P/A (%)

Mice

4.10

Orthoptera

41.67

Voles

2.63

Hemiptera

41.90

Other mammals

2.92

All other insects

41.23

Birds

1.26

Mollusca

21.59

Fish

9.74

Crustacea

24.96

8.31

All other noninsect

invertebrates

27.68

Social insects


General patterns of energy flow through ecosystems
(Begon et al, 1986)
FOREST
Respiration

Respiration

GRAZER
SYSTEM

DECOMPOSER
SYSTEM

NET PRIMARY
PRODUCTIVITY

DEAD ORGANIC
MATTER