DP Environmental systems and societies

Topic 2

The ecosystem

2.5 FUNCTION

Ecosystem function

• Producers, consumers, and decomposers all have their part to play in cycling materials and energy in the ecosystem

Energy cycles

Material cycles

• Refer to Topic 1 ppt

Also• Photosynthesis• Photosynthesis and respiration• Carbon cycle

Nitrogen inthe air

animal protein

dead plants & animalsurine & faeces

ammonia

nitrites

nitrates

plant madeprotein

dead rabbit

decomposition by bacteria & fungi

bacteria

(nitrifying bacteria)

nitrates absorbed

denitrifyingbacteriaroot nodules

(containing nitrogen fixing bacteria)

nitrogen fixing planteg pea, clover

bacteria

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Terminology

Primary productivity – the gain by producers (autotrophs) in energy or biomass per unit area per unit time

Secondary productivity – the biomass gained by heterotrophic organisms through feeding or absorption

Terminology

Gross productivity (GP) – the total gain in energy or biomass per unit area per unit time

Gross primary productivity (GPP) - GP of primary producers

Gross secondary productivity (GSP) – GP absorbed in consumers

Terminology

Net productivity (NP) – the gain in energy or biomass per unit area per unit time after allowing for respiratory losses (R).

Net primary productivity (NPP) – NP for producers NPP = GPP – R.

Net secondary productivity (NSP) – NP for consumers NSP = GSP – R.

• Would you consider open ocean or tropical rainforest to be the most productive? Why?

• (consider area)

Is this primary or secondary productivity?

Gross or net productivity?

Biomass or energy?

2.6 CHANGES

Limiting factors

• Temperature

Limiting factors

• Food source

Limiting factors

Density dependent(negative feedback)• Competition for

resources• Space• Disease• Parasitism• Predation• Population size

Density independent• Extremes of weather• Long-term climate

change• Volcanoes and

tsunamis

S and J curves - animation

r strategists

K strategists

r strategists K strategists

Initial colonizers Dominant species

Large numbers of a few species

Diverse range of species

Highly adaptable Generalists

Rapid growth and development

Slow development

Early reproduction Delayed reproduction

Short life Longer living

Small size Larger size

Very productive Less productive

2.6.5 Succession

Succession 繼承法Predictable changes in a community

Knowing what animals and plants will dominate next

Primary successionA series of changes that occurs where no organisms

exist

Pioneer speciesThe first species in primary succession

Pioneer species

Secondary successionA series of changes that occurs when there are

organisms to begin with

Secondary successionA series of changes that occurs when there are

organisms to begin with

Figure 53.18 Patchiness and recovery following a large-scale disturbance

Figure 53.18x1 Large-scale disturbance: Mount St. Helens

Figure 53.18x2 Forest fire

Figure 53.19 A glacial retreat in southeastern Alaska

Table 53.2 The Pattern of Succession on Moraines in Glacier Bay

Figure 53.20 Change in soil nitrogen concentration during succession after glacial retreat in Glacier Bay, Alaska

Figure 53.20 Alders and cottonwoods covering the hillsides

Figure 53.20 Spruce coming into the alder and cottonwood forest

Figure 53.20 Spruce and hemlock forest

Terminology

Zonation – different to succession – difference due to environmental gradient (eg. altitude)

Succession occurs over several seral stages where each sere is a set of communities.

Plagiosere – humans prevent a climax community – growing crops

Hydrosere (water)

Lithosere (rock) – one type of xerosere (land)

Psammosere (sand) – one type of xerosere (land)

Climax community• Greater biomass• Higher levels of diversity• Better soil conditions• Better soil structure• Lower pH• Taller and longer living plants• More K less r strategists• More complexity and stability• More habitat diversity• Steady state equilibrium• Production:respiration ratio P/R reaches 1

(not ideal for agriculture)

2.7 MEASURING CHANGES IN THE SYSTEM

Evaluating transects • Same time of day (abiotic and

biotic variables)• Samples taken througout the year

(seasonal variations)• Repeat transects for reliable data

(minimum 3 times)• Random number generator for

where to take transects to eliminate bias

Measuring changes – human activity

• Satellite images

eg. deforestation • Monitoring stations

eg. Taiwan EPA• Erosion rates

Environmental Impact Assessments (EIAs)• To decide if the project will be too

damaging or not, and to mitigate any damage.

1. Baseline study

2. Monitoring during and after development

Variables in EIA

• Habitat type and abundance• Species list and diversity including

endangered species• Land use – access and coverage• Water flow• Human population• Soil quality and fertility• Example EIA for a dam project