BIOS 3010: Ecology Lecture 18: Community matter & energy...

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Dr. S. Malcolm BIOS 3010: Ecology Lecture 18: slide 1

BIOS 3010: Ecology Lecture 18: Community matter & energy flux:

•  Lecture summary: –  Matter and energy.

–  Primary productivity.

–  Trophic structure

–  Flux of matter.

–  Geochemical cycles.

–  Hubbard Brook.

The Hubbard Brook Ecosystem Study

http://www.hubbardbrook.org/


2. Matter and energy:

•  All organisms require matter for construction, and energy for activity, at individual, population and community levels of organization.

•  Communities interact with the abiotic environment as ecosystems which include:

–  “primary producers, decomposers and detritivores, a pool of dead organic matter, herbivores, carnivores and parasites, plus the physicochemical environment that provides living conditions and acts both as a source and a sink for energy and matter.”


3. Matter and energy:

•  The primary productivity of a community is: – The rate at which biomass is produced per unit

area by plants (primary producers) as energy (J·m-2·day-1) or dry organic matter (kg·ha-1·year-1).

•  Gross primary productivity (GPP) –  Total fixation of energy by photosynthesis

•  Net primary productivity (NPP) – GPP - energy lost to respiration

»  = actual rate of biomass accumulation available for consumption by heterotrophs.

•  Secondary productivity – Rate of biomass production by heterotrophs.

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4. Primary productivity:

•  Global terrestrial NPP: –  110 - 120 x 109 tonnes dry weight per year

•  Global marine NPP (Fig. 18.1, Table 18.1): –  50 - 60 x 109 tonnes per year

•  despite being 67% of the earth's surface

•  Productivity (P) and biomass (B) (Fig. 17.6): –  P:B ratios (kg/year/kg biomass) average:

•  0.042 for forests •  0.29 for other terrestrial systems •  17 for aquatic communities. •  Ratios also change with successional shifts (Fig. 18.6).


5. Community trophic structure:

•  Energy moves through communities via trophic (feeding) interactions.

•  Primary productivity generates secondary productivity in heterotrophic consumers once they consume autotrophs with a measurable efficiency:

–  The slope of Fig. 18.17 at about 0.1. •  Generates the classical view of a broad-based

productivity pyramid or biomass pyramid: –  After Elton (1927) and later Lindemann (1942).


6. Community trophic structure: •  Basic trophic structure of communities (Figs 17.21

& 17.22). •  Energy flow through different components of a

grassland community (Fig. 18.22). •  Predicted vs observed values of productivity

(Fig. 18.23). •  Energy flow & nutrient cycling links between

decomposer & grazer systems & return of free inorganic nutrients released by decomposers from dead organic matter (DOM) back to net primary production (NPP) (Fig. 18.1).

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7. NPP and global climate change

•  Climate models predict that increased greenhouse gases will lead to an increase in temperature of 1.5-4.5°C.

•  Altered CO2, temperature, cloud cover and

rainfall will dramatically change the NPP of earth's communities Table 18.6.


8. Flux of matter (chapter 19):

•  “If plants, and their consumers, were not eventually decomposed, the supply of nutrients would become exhausted and life on earth would cease.”

•  So the matter cycling (fueled by energy) of Fig. 18.1 is essential.


9. Biogeochemical cycles:

•  Terrestrial and aquatic ecosystems are linked much as in Fig. 18.2.

•  Within these links, the primary resources of

water, phosphorus, nitrogen, sulfur and carbon circulate as in Figs 18.19, 18.20 & 18.21.

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10. The Hubbard Brook experiments:

– Within a water catchment area how important is nutrient cycling within the terrestrial community in relation to the through-put of nutrients?

– The Hubbard Brook experiment in the temperate deciduous forest of the White Mountains in New Hampshire is the best test of this question:

•  6 small catchments with input and output measured (Table 18.1).

•  Most nutrients were held in biomass (like N2 in Fig. 19.5). •  But sulfur was released in excess of input because it was

a major pollutant in the area (acid rain).


11. The Hubbard Brook experiments:

•  Experimentally, one catchment was deforested: – The rate of nutrient loss rose x13 in comparison

with a control catchment. – Two reasons for the lost nutrients:

•  (1) through increased water flow (less water held by trees) - see Fig. 19.4

•  (2) within-system nutrient cycling was lost by uncoupling the decomposition process from the plant-uptake process

–  nutrients made available by decomposition were lost to leaching in the increased stream flow (Fig. 18.6).


Figure 18.1 (3rd ed.):

Distribution of global terrestrial and marine net primary productivity

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(3rd ed.)


Figure 17.6: Relationship between average net primary productivity and average standing crop biomass for communities in Table 18.1


Figure 18.6 (3rd ed.): Change in net primary productivity (P), standing crop biomass (B) and P:B ratio during forest succession on Long Island.

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Figure 18.17 (3rd ed.): Secondary productivity plotted against primary productivity in three communities.

(see Fig 17.20, 4th ed.)


Figure 17.21:

Energy flow through a trophic compartment.


Figure 17.22: Model of trophic structure and energy flow for a terrestrial community.

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Figure 18.22 (3rd ed.): Patterns of energy flow through the different trophic compartments of Fig. 17.22.


Figure 18.23 (3rd ed.): Predicted heterotroph productivity plotted against observed productivity in a range of communities.


Figure 18.1: Energy flow (pink) and nutrient cycling of organic matter (red) and inorganic matter (white).

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(3rd ed.)


Figure 18.2:

Components of nutrient budgets of terrestrial and aquatic systems.


Figure 18.19: Hydrological cycle.

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Figure 18.20: Major global pathways of nutrients between abiotic and biotic reservoirs.


Figure 18.21:

Four main pathways of nutrient flux (black arrows) and human perturbations (red arrows).


Table 18.1:

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Figure 19.5 (3rd ed.): Annual nitrogen budget for control forest at Hubbard Brook (kg N2/ha).


Figure 19.4 (3rd ed.): Annual loss of major nutrients in streamflow.


Figure 18.6:

Concentrations of ions in stream water from control and deforested watersheds at Hubbard Brook.

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The Hubbard Brook Ecosystem Study:

http://www.hubbardbrook.org/

BIOS 3010: Ecology Lecture 18: Community matter & energy...

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