Townsend C.R., Begon M., Harper J.L. Essentials of Ecology

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Net primary productivity. The difference between GPP and R is known as

net primary productivity (NPP) and represents the actual rate of production

of new biomass that is available for consumption by heterotrophic

organisms (bacteria, fungi and animals).

Secondary productivity. The rate of production of biomass by heterotrophs

is called secondary productivity.

A proportion of primary production is consumed by herbivores, which, in

turn, are consumed by carnivores. These constitute the live consumer system. The

fraction of NPP that is not eaten by herbivores passes through the decomposer

system. We distinguish two groups of organisms responsible for the decomposi-

tion of dead organic matter (detritus): bacteria and fungi are called decomposers

while animals that consume dead matter are known as detritivores.

Chapter 11 The ﬂux of energy and matter through ecosystems

359

11.1 HISTORICAL LANDMARKS

11.1 Historical landmarks

A classic paper by Lindeman (1942) laid the founda-

tions of a science of ecological energetics. He

attempted to quantify the concept of food chains and

food webs by considering the efﬁciency of transfer

between trophic levels – from incident radiation

received by a community through its capture by green

plants in photosynthesis to its subsequent use by

bacteria, fungi and animals.

Lindeman’s paper was a major catalyst that stimu-

lated the International Biological Programme (IBP for

short). The subject of the IBP was ‘the biological basis

of productivity and human welfare’. Given the prob-

lem of a rapidly increasing human population, it was

recognized that scientiﬁc knowledge would be required

for rational resource management. Cooperative inter-

national research programs focused on the ecological

energetics of areas of land, fresh waters and the seas.

The IBP provided the ﬁrst occasion on which biologists

throughout the world were challenged to work together

towards a common end.

More recently, another pressing issue has galvanized

the ecological community into action. Deforestation,

the burning of fossil fuels and other human inﬂuences

are causing dramatic changes to global climate and

atmospheric composition, and can be expected in turn

to inﬂuence patterns of productivity and the composi-

tion of vegetation on a global scale. Among the prime

objectives of the International Geosphere-Biosphere

Programme (IGBP), established in the early 1990s,

was to predict the effects of changes in climate and

atmospheric composition on agriculture and food pro-

duction. The Food and Agriculture Organization (FAO)

of the United Nations reported recently that some of

the predicted changes seemed to be advancing at a

higher rate than anticipated, including:

1 A likely decline in precipitation in some food-

insecure areas such as southern Africa and the

northern region of Latin America.

2 Changes in seasonal distribution of rainfall, with

less falling in the main crop-growing season.

3 Higher night-time temperatures, which may

adversely affect grain production.

4 Disruption of food supply through more frequent

and severe extreme weather events.

We will see in this chapter why changes to water

availability and temperature, among other factors, can

have such profound effects on productivity.

Ecological energetics and the biological basis of productivity and

human welfare

live consumer systems and

decomposer systems

9781405156585_4_011.qxd 11/5/07 15:00 Page 359

11.2 Primary productivity

11.2.1 Geographic patterns in primary productivity

The functioning of the biota of the Earth, and of the communities across the

surface of the planet, depend crucially on the levels of productivity that plants are

able to achieve. The total NPP of the planet is estimated to be about 105 petagrams

of carbon per year (1 Pg = 10

g). Of this, 56.4 Pg C yr

−1

is produced in terrestrial

ecosystems and 48.3 Pg C yr

−1

in aquatic ecosystems (Table 11.1). Thus, although

oceans cover about two-thirds of the world’s surface, they account for less than

half of its production and most of the ocean is, in effect, a marine desert. On the

land, tropical rain forests and savannas account between them for about 60% of

terrestrial NPP, reﬂecting the large areas covered by these biomes and their high

levels of productivity.

In the forest biomes of the world, there is a general latitudinal trend of

increasing productivity from boreal (1019–1034 g C m

−2

−1

), through temperate

(1327–1499 g C m

−2

−1

) to tropical (> 3000 g C m

−2

−1

) forest (Falge et al.,

2002). A similar latitudinal trend has been reported for tundra and grassland

communities, various cultivated crops and lakes. Despite considerable varia-

tion, these general trends with latitude suggest that radiation (a resource) and

temperature (a condition) may be the factors usually limiting the productivity

of communities. Other factors can, however, constrain productivity within even

narrower limits. In the sea, where no latitudinal trend has been reported, pro-

ductivity is more often limited by a shortage of nutrients.

11.2.2 Factors limiting primary productivity

What, then, limits primary productivity? In terrestrial communities, solar radia-

tion, carbon dioxide, water and soil nutrients are the resources required for

primary production while temperature, a condition, has a strong inﬂuence on the

Part III Individuals, Populations, Communities and Ecosystems

360

Table 11.1

Net primary production (NPP) per year summed for each of the major biomes and for the planet in total (in

units of petragrams of carbon).

FROM GEIDER ET AL., 2001

MARINE NPP TERRESTRIAL NPP

Tropical and subtropical oceans 13.0 Tropical rain forests 17.8

Temperate oceans 16.3 Broadleaf deciduous forests 1.5

Polar oceans 6.4 Mixed broad/needleleaf forests 3.1

Coastal 10.7 Needleleaf evergreen forests 3.1

Salt marsh/estuaries/seaweed 1.2 Needleleaf deciduous forests 1.4

Coral reefs 0.7 Savannas 16.8

Perennial grasslands 2.4

Broadleaf shrubs with bare soil 1.0

Tundra 0.8

Desert 0.5

Cultivation 8.0

Total 48.3 Total 56.4

the open ocean is, in effect, a

marine desert

the productivity of forests,

grasslands, crops and lakes

follows a latitudinal pattern

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rate of photosynthesis. Carbon dioxide is normally present at a level of around

0.03% of atmospheric gases and seems to play no signiﬁcant role in determining

differences between the productivities of different communities (although global

increases in carbon dioxide concentration may bring big changes; Kicklighter

et al., 1999). On the other hand, the intensity of radiation, the availability of water

and nutrients, and temperature all vary dramatically from place to place. They are

all candidates for the role of limiting factor. Which of them actually sets the limit

to primary productivity?

Depending on location, something between 0 and 5 J of solar energy strike

each square meter of the Earth’s surface every minute. If all this were converted

by photosynthesis to plant biomass (that is, if photosynthetic efﬁciency was 100%)

there would be a prodigious generation of plant material, ten to a hundred times

greater than recorded values. However, only about 44% of incident shortwave

radiation occurs at wavelengths suitable for photosynthesis. Yet, even when this

is taken into account, productivity still falls well below the maximum possible.

For example, the conifer communities shown in Figure 11.1 had the highest net

photosythetic efﬁciencies, but these were only between 1% and 3%. For a similar

level of incoming radiation, deciduous forests achieved 0.5–1%, and, despite their

greater energy income, deserts managed only 0.01–0.2%. These can be compared

with short-term peak efﬁciencies achieved by crop plants under ideal conditions,

when values from 3% to 10% can be achieved.

There is no doubt that available radiation would be used more efﬁciently if

other resources were in abundant supply. The much higher values of community

productivity from agricultural systems bear witness to this. Shortage of water –

an essential resource both as a constituent of cells and for photosynthesis – is

often the critical factor. It is not surprising, therefore, that the rainfall of a region

is quite closely correlated with its productivity (Figure 11.2a). There is also a

clear relationship between NPP and mean annual temperature, but note that high

temperature is associated with rapid transpiration, and thus higher temperatures

increase the rate at which water shortage becomes important. Water shortage has

direct effects on the rate of plant growth, but it also leads to less dense vegetation.

Chapter 11 The ﬂux of energy and matter through ecosystems

361

AFTER WEBB ET AL., 1983

1,000,000 2,000,000 3,000,000 4,000,000

0.05

0.02

0.01

0.5

0.2

0.1

C Conifer forest

D Deciduous forest

De Desert

Photosynthetic efficiency (%)

Photosynthetically active radiation

reaching the community (kJ m

–2

–1

)

Figure 11.1

Photosynthetic efﬁciency

(percentage of incoming

photosynthetically active radiation

converted to above-ground net

primary production) for three sets

of terrestrial communities in the

United States. Desert ecosystems

receive the greatest levels of

radiation, but are much less

efﬁcient than forests in converting

it to biomass.

terrestrial communities use

radiation inefﬁciently

water and temperature as critical

factors

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Vegetation that is sparse intercepts less radiation (much of which falls on bare

ground), accounting for much of the difference in productivity between desert

vegetation and forest in Figure 11.1. Figure 11.2b plots the NPP for a variety of

ecosystem types against both temperature and annual rainfall – highest productivity

occurs where temperature and rainfall are both high.

The productivity of a community can be sustained only for that part of the year

when the plants bear photosynthetically active foliage. Deciduous trees have a

self-imposed limit on the period of the year during which they bear foliage, while

evergreen trees hold a canopy throughout the year. However, for much of the year

conifer forest may barely photosynthesize at all, a pattern that is particularly

marked in the colder boreal zones (Figure 11.3).

No matter how brightly the sun shines, how often the rain falls and how equable

the temperature, productivity must be low if there is no soil in a terrestrial com-

munity, or if the soil is deﬁcient in essential mineral nutrients. Of all the mineral

nutrients, the one with the strongest inﬂuence on community productivity is ﬁxed

nitrogen (in contrast to atmospheric nitrogen, which is not directly available for

use in photosynthesis; ﬁxed nitrogen occurs in inorganic ions such as nitrate).

There is probably no agricultural or forestry system that does not respond to the

application of nitrogen by increasing primary productivity, and this may well be

true of natural vegetation as well. The deﬁciency of other elements, particularly

phosphorus, can also hold the productivity of a community far below what is

theoretically possible.

In fact, in the course of a year, the productivity of a terrestrial community may

be limited by a succession of factors. The primary productivity of grasslands may

be far below the theoretical maximum because the winters are too cold and the

intensity of radiation is low, the summers are too dry, the rate of nitrogen supply

is too slow, or because heavy grazing reduces the standing crop of photosynthetic

leaves and much of the incident radiation falls on bare ground.

Part III Individuals, Populations, Communities and Ecosystems

362

(a) (b)

–5

–1

1500

300

600

900

1200

Total NPP ( tonnes ha

–1

)

Grass above-ground NPP

(kg ha

–1

)

5000

4000

3000

2000

1000

0 250 500 750 1000 1250 1500

Annual rainfall (mm)

Annual mean temperature (°C)

Annual mean

precipitation (mm)

Figure 11.2

(a) Above-ground net primary productivity (NPP) of grass in savanna regions of the world in relation to annual rainfall. (b) Total NPP in relation to

both annual precipitation and temperature on the Tibetan Plateau for ecosystems including forests, woodlands, shrublands, grasslands and desert.

(a) AFTER HIGGINS ET AL., 2000; (b) AFTER LUO ET AL., 2002

NPP increases with the length of

the growing season

NPP may be low because

appropriate mineral resources

are deﬁcient

a succession of factors may

limit primary productivity

through the year

9781405156585_4_011.qxd 11/5/07 15:00 Page 362

Chapter 11 The ﬂux of energy and matter through ecosystems

363

AFTER FALGE ET AL., 2002

(a) AFTER CARIGNAN ET AL., 2000; (b, c) AFTER SILULWANE ET AL., 2001

% maximum GPP

100

Time (days)

60 120 180 240 300 360

Temperate

coniferous

Boreal

coniferous

Figure 11.3

Seasonal development of maximum daily gross primary productivity

(GPP) for conifer forests in temperate (Europe and North America)

and boreal locations (Canada, Scandinavia and Iceland). The

different symbols in each panel relate to different forests. Daily GPP

is expressed as the percentage of the maximum achieved in each

forest during the 365 days of the year. Note the extended periods

with no photosynthesis in the colder boreal locations.

(a)

GPP (mg C m

–3

day

–1

)

Depth (mm)

3069151812

(c)(b)

1000

100

10 100

Total phosphorus (mg m

–3

)

Chlorophyll (mg m

–3

)

3069151812

Chlorophyll (mg m

–3

)

Figure 11.4

(a) The relationship between gross

primary productivity (GPP) of

phytoplankton (microscopic plants)

and phosphorus concentration in

some Canadian lakes. (b, c)

Examples of vertical chlorophyll

proﬁles recorded in the ocean off

the coast of Namibia. The biomass

of chlorophyll is an index of NPP of

ocean phytoplankton. (b) A location

associated with ocean upwelling:

the nutrient-rich water fuels very

high NPP by phytoplankton near the

surface, but the dense phytoplankton

cells reduce light penetration so that

NPP is not detectable in deeper

water. (c) A location where nutrient

concentrations are much lower:

NPP is thus low, but because light

can penetrate more deeply, NPP can

be detected to a greater depth. All

regression lines are statistically

signiﬁcant.

productive aquatic communities

occur where nutrient

concentrations are high

In aquatic communities, the factors that most frequently limit primary pro-

ductivity are the availability of nutrients (particularly nitrate and phosphate) and

the intensity of solar radiation that penetrates the column of water. Productive

aquatic communities occur where, for one reason or another, nutrient concentra-

tions are high (as for the lakes in Figure 11.4a). Lakes receive nutrients by the

9781405156585_4_011.qxd 11/5/07 15:00 Page 363

weathering of rocks and soils in their catchment areas, in rainfall and as a result

of human activity (fertilizers and sewage input; see Chapter 13); lakes vary con-

siderably in nutrient availability.

In the oceans, locally high levels of primary productivity are associated with

high nutrient inputs from two sources. First, nutrients may ﬂow continuously

into coastal shelf regions from estuaries. Productivity in the inner shelf region is

particularly high because nutrient concentrations are high and the relatively clear

water provides a reasonable depth within which net photosynthesis is positive

(the euphotic zone). Closer to land, the water is richer in nutrients but highly

turbid and its productivity is less. The least productive zones are in the open

ocean where, although the water is clear and the euphotic zone is deep, there are

generally extremely low concentrations of nutrients. Local regions of high pro-

ductivity occur in the open ocean only where there are upwellings from deep,

nutrient-rich water (compare Figure 11.4b and c).

11.3 The fate of primary productivity

Fungi, animals and most bacteria are heterotrophs: they derive their matter and

energy either directly by consuming plant material or indirectly from plants by

eating other heterotrophs. Plants, the primary producers, comprise the ﬁrst

trophic level in a community; primary consumers occur at the second trophic

level; secondary consumers (carnivores) at the third, and so on.

11.3.1 The relationship between primary and

secondary productivity

Since secondary productivity depends on primary productivity, we should expect

a positive relationship between the two variables in communities. Figure 11.5

illustrates this general relationship in aquatic and terrestrial examples. Secondary

productivity by zooplankton (small animals in the open water), whose main food

is phytoplankton cells, is positively related to phytoplankton productivity in

a range of lakes in different parts of the world (Figure 11.5a). The productivity

of heterotrophic bacteria in lakes and oceans also parallels that of phytoplankton

(Figure 11.5b); the bacteria metabolize dissolved organic matter released from

intact phytoplankton cells or produced as a result of ‘messy feeding’ by grazing

animals. Figure 11.5c shows how the abundance achieved by caterpillars (larvae

of moths and butterﬂies) is tightly linked to annual rainfall (and thus primary

productivity) on an island in the Galapagos Archipelago. One of Darwin’s famous

ﬁnches, the seed-eating Geospiza fortis (see Figure 2.14), also responds to

increased plant production in wet years by raising signiﬁcantly more broods of

young (Grant et al., 2000).

In both aquatic and terrestrial communities, secondary productivity by herbivores

is approximately one-tenth of the primary productivity upon which it is based.

Where has the missing energy gone? First, not all of the plant biomass produced

is consumed alive by herbivores. Much dies without being grazed and supports a

community of decomposers (bacteria, fungi and detritivorous animals). Second,

not all the plant biomass eaten by herbivores (nor herbivore biomass eaten by

Part III Individuals, Populations, Communities and Ecosystems

364

there is a general positive

relationship between primary

and secondary productivity

most of the primary productivity

does not pass through the

grazer system

9781405156585_4_011.qxd 11/5/07 15:00 Page 364

carnivores) is assimilated and available for incorporation into consumer biomass.

Some is lost in feces, and this also passes to the decomposers. Third, not all the

energy that has been assimilated is actually converted to biomass. A proportion

is lost as respiratory heat. This occurs both because no energy conversion process

is 100% efﬁcient (some is lost as unusable random heat, consistent with the

second law of thermodynamics) and also because the organisms do work that

requires energy, again released as heat. These three energy pathways occur at all

trophic levels and are illustrated in Figure 11.6.

11.3.2 The fundamental importance of energy

transfer efﬁciencies

A unit of energy (a joule) may be consumed and assimilated by an invertebrate

herbivore that uses part of it to do work and loses it as respiratory heat. Or it might

be consumed by a vertebrate herbivore and later be assimilated by a carnivore

that dies and enters the dead organic matter compartment. Here, what remains

of the joule may be assimilated by a fungus and consumed by a soil mite, which

uses it to do work, dissipating a further part of the joule as heat. At each consump-

tion step, what remains of the joule may fail to be assimilated and pass in the feces

to dead organic matter, or it may be assimilated and respired, or assimilated

and incorporated into growth of body tissue (or the production of offspring).

The body may die and what remains of the joule enters the dead organic matter

compartment, or it may be captured alive by a consumer in the next trophic level

where it meets a further set of possible branching pathways. Ultimately, each

Chapter 11 The ﬂux of energy and matter through ecosystems

365

(a)

(c)

(b)

3000

2500

2000

1500

1000

500

25 250 250020,000 25,000

600

100

Year

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

Number of caterpillars ( )

Annual rainfall (mm) ( )

1500

1000

500

Zooplankton production

(kJ m

–2

)

50000 10,000 15,000

Phytoplankton production per

growing season (kJ m

–2

)

Bacterial productivity

(mg C m

–2

day

–1

)

Net primary productivity

(mg C m

–2

day

–1

)

Sea water

Fresh water

possible pathways of a joule of

energy through a community

Figure 11.5

The relationship between primary

and secondary productivity

for: (a) zooplankton in lakes,

(b) bacteria in fresh and sea water,

and (c) caterpillars (numbers and

standard errors from a standard

census) in relation to a histogram

of annual rainfall on the Galapagos

island of Daphne Major. Caterpillar

numbers are an index of their annual

secondary productivity; the primary

productivity of plants, upon which

the caterpillars feed, is closely

correlated with annual rainfall.

Regression lines are signiﬁcant and

caterpillar abundance is signiﬁcantly

correlated with annual rainfall at

P < 0.05.

(a) AFTER BRYLINSKY & MANN, 1973; (b) AFTER COLE ET AL., 1988; (c) AFTER GRANT ET AL., 2000

9781405156585_4_011.qxd 11/5/07 15:00 Page 365

joule will have found its way out of the community, dissipated as respiratory heat

at one or more of the transitions in its path along the food chain. Whereas a

molecule or ion may cycle endlessly through the food chains of a community,

energy passes through just once.

The possible pathways in the herbivore/carnivore (live consumer) and decom-

poser systems are the same, with one critical exception – feces and dead bodies are

lost to the former (and enter the decomposer system), but feces and dead bodies

from the decomposer system are simply sent back to the dead organic matter

compartment at its base. Thus, the energy available as dead organic matter may

ﬁnally be completely metabolized – and all the energy lost as respiratory heat – even

if this requires several circuits through the decomposer system. The exceptions to

this are situations: (i) where matter is exported out of the local environment

to be metabolized elsewhere, for example detritus being washed out of a stream;

and (ii) where local abiotic conditions have inhibited decomposition and left

pockets of incompletely metabolized high-energy matter, otherwise known as oil,

coal and peat.

The proportions of net primary production ﬂowing along each of the possible

energy pathways depend on transfer efﬁciencies from one step to the next. We need

to know about just three categories of transfer efﬁciency to be able to predict the

pattern of energy ﬂow. These are consumption efﬁciency (CE), assimilation

efﬁciency (AE) and production efﬁciency (PE).

Consumption efﬁciency is the percentage of total productivity available at

one trophic level that is consumed (‘ingested’) by the trophic level above. For

Part III Individuals, Populations, Communities and Ecosystems

366

Not consumed

Dead organic matter

compartment of

decomposer system

Figure 11.6

The pattern of energy ﬂow through a trophic compartment

(represented as the maroon box).

consumption, assimilation and

production efﬁciencies determine

the relative importance of

energy pathways

9781405156585_4_011.qxd 11/5/07 17:17 Page 366

primary consumers, CE is the percentage of joules produced per unit time as

NPP that ﬁnds its way into the guts of herbivores. In the case of secondary con-

sumers, it is the percentage of herbivore productivity eaten by carnivores. The

remainder dies without being eaten and enters the decomposer system. Reason-

able average ﬁgures for CE by herbivores are approximately 5% in forests, 25%

in grasslands and 50% in phytoplankton-dominated communities. As far as

carnivores are concerned, vertebrate predators may consume 50–100% of pro-

duction from vertebrate prey but perhaps only 5% from invertebrate prey,

while invertebrate predators consume perhaps 25% of available invertebrate

prey production.

Assimilation efﬁciency is the percentage of food energy taken into the guts of

consumers in a trophic level that is assimilated across the gut wall and becomes

available for incorporation into growth or to do work. The remainder is lost as

feces and enters the decomposer system. An ‘assimilation efﬁciency’ is much less

easily ascribed to microorganisms, where food does not pass through a ‘gut’ and

feces are not produced. Bacteria and fungi digest dead organic matter externally

and, between them, typically absorb almost all the product: they are often said to

have AEs of 100%. AEs are typically low for herbivores, detritivores and micro-

bivores (20–50%) and high for carnivores (around 80%). The way that plants

allocate production to roots, wood, leaves, seeds and fruits also inﬂuences their

usefulness to herbivores. Seeds and fruits may be assimilated with efﬁciencies as

high as 60–70%, and leaves with about 50% efﬁciency, while the AE for wood

may be as low as 15%.

Production efﬁciency is the percentage of assimilated energy that is incorporated

into new biomass – the remainder is entirely lost to the community as respiratory

heat. PE varies according to the taxonomic class of the organisms concerned.

Invertebrates in general have high efﬁciencies (30–40%), losing relatively little

energy in respiratory heat. Amongst the vertebrates, ectotherms (whose body

temperature varies according to environmental temperature; see Section 3.2.6)

have intermediate values for PE (around 10%), whilst endotherms, which expend

considerable energy to maintain a constant temperature, convert only 1–2% of

assimilated energy into production. Microorganisms, including protozoa, tend

to have very high PEs.

The overall trophic transfer efﬁciency from one trophic level to the next is

simply CE × AE × PE. In the period after Lindeman’s (1942) pioneering work

(see Box 11.1), it was generally assumed that trophic transfer efﬁciencies were

around 10%; indeed some ecologists referred to a 10% ‘law’. However, there is

certainly no law of nature that results in precisely one-tenth of the energy that enters

a trophic level transferring to the next. For example, a compilation of trophic

studies from a wide range of freshwater and marine environments revealed that

trophic-level transfer efﬁciencies varied between about 2% and 24% – although

the mean was 10.13% (standard error 0.49) (Pauly & Christensen, 1995).

11.3.3 The relative roles of the live consumer and

decomposer systems

Given knowledge of NPP at a site, and CE, AE and PE for all the trophic group-

ings present (herbivores, carnivores, decomposers, detritivores), it is possible

to map out the relative importance of different pathways. Figure 11.7 does this,

Chapter 11 The ﬂux of energy and matter through ecosystems

367

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Part III Individuals, Populations, Communities and Ecosystems

368

(a) Forest

Respiration Respiration

LCS

NPP DOM

Decomposer

system

(b) Grassland

Respiration Respiration

LCS

NPP DOM

Decomposer

system

Respiration Respiration

LCS

NPP DOM

Decomposer

system

(d) Stream community

Respiration

LCS

NPP

DOM

Decomposer

system

From terrestrial catchment

Forests and shrublands

Mangroves

Grasslands

Marshes

Macroalgal beds

Benthic microalgal beds

Phytoplanktonic communities

40080

(b)(a)

Percentage of NPP

consumed by herbivores

Percentage of NPP channeled

to the DOM compartment

Seagrass meadows

Freshwater macrophyte meadows

Figure 11.7

General patterns of energy ﬂow

for: (a) forest, (b) grassland, (c) a

plankton community in the sea, and

(d) the community of a stream or

small pond. Relative sizes of boxes

and arrows are proportional to the

relative magnitude of compartments

and ﬂows. DOM, dead organic

matter; LCS, live consumer system;

NPP, net primary production.

in a general way, for a forest, a grassland, a plankton community (of the ocean

or a large lake) and the community of a small stream or pond. The decomposer

system is probably responsible for the majority of secondary production, and

therefore respiratory heat loss, in every community in the world (Figure 11.8).

The ‘live consumers’ have their greatest role in open-water aquatic communities

based on phytoplankton or in the beds of microalgae that occur in shallow water.

In each case, a large proportion of NPP is consumed alive and assimilated at quite

Figure 11.8

Box plots for a range of ecosystem types showing: (a) percentage of net primary production (NPP)

consumed by herbivores and (b) percentage of NPP entering the dead organic matter (DOM)

compartment. Boxes encompass 25% and 75% percentiles of published values and the central lines

represent the median values. Phytoplankton and aquatic microalgal communities channel the largest

proportions of NPP through herbivores and the smallest proportions through the DOM compartment.

AFTER CEBRIAN, 1999

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