6.3 Ecosystems 6.3.1 Ecosystems By Ms Cullen

Try and define the following terms used when studying the environment. Terminology Try and define the following terms used when studying the environment.

Biosphere The biosphere is the outermost part of the planet's shell — including air, land, surface rocks, and water — within which life occurs.

Ecosystem Ecosystems are dynamic interactions between plants, animals, and microorganisms (biotic) and their physical environment (abiotic) working together as a functional unit.  The abiotic environment includes climatic and edaphic (soil or water composition). Ecosystems will fail if they do not remain in balance. eg a coral reef

Biotic factors: these involve other living organisms

Abiotic factors:

Habitat Is the place where a particular species lives and grows. It is essentially the environment—at least the physical environment—that surrounds (influences and is utilized by) a species population.

Producer (autotroph) An organism that produces complex organic compounds to form biomass from simple molecules and an external source of energy, such as light . Autotrophs are considered producers in a food chain. Plants and other organisms that carry out photosynthesis are phototrophs. from the Greek autos = self and trophe = nutrition Can you remember the balanced equation for photosynthesis? 6CO2 + 6H20 C6H12O6 + 6O2

Consumer (heterotroph) A heterotroph is an organism that requires organic substrates to get its carbon for growth and development. A heterotroph is known as a consumer in the food chain. All animals are heterotrophic, as well as fungi and many bacteria. Greek heterone = (an)other and trophe = nutrition

Decomposer (saprotrophs) Organisms that require organic substrates to get their carbon for growth and development. They obtain their biomass from deceased organisms. Decomposers themselves are organisms (often fungi, bacteria, or earthworms) that break down organic materials to gain nutrients and produce ATP. Decomposers accelerate the natural process of decomposition.

Trophic Level the position that an organism occupies in a food chain.

Food Chain and Food Web Food chains and food webs describe the feeding relationships between species in an ecological community. They graphically represent the transfer of material and biomass from one species to another within an ecosystem. Organisms are connected to the organisms they consume by arrows representing the direction of biomass transfer.

Pyramids of Numbers Oak trees are very large, but caterpillars are very small. One oak tree can feed many caterpillars, but many caterpillars are needed to feed a blue tit, and many blue tits are needed to feed a sparrow hawk. Draw a pyramid of numbers for this food chain. It should look like this:                                         

Pyramids of Biomass The dry mass of all organisms per unit area of ground (or water) is called biomass. The total biomass at a particular step in a food chain is always less than the total biomass at the step before it. Note the large biomass of the one oak tree, compared with the small biomass of lots of caterpillars, indicated by the shape of the pyramid. The wider the bar, the more biomass there is. Pyramids of biomass always have this shape (but pyramids of numbers can be any shape).

The circle represents the producer The circle represents the producer. All of the stored chemical energy in the body of the producer organism is eaten by the primary consumer. This circle represents the primary consumer. Only the stored chemical energy in biomass is eaten by the secondary consumer. This circle represents the secondary consumer. Only a very small fraction (shown in green) of the producer's original store of chemical energy is stored by the secondary consumer. This stored energy is taken into the body of the tertiary consumer as biomass.

Biomass Flow in Food Chains As you can see from the previous diagrams, only about 10% of the biomass which the plant used for growth is taken into the body of the carnivore. The second consumer uses some of this biomass for its own body activities and some of the energy produced from these processes will be transferred to surroundings. Therefore, the amount of biomass available for the tertiary consumer is only 1% of the biomass which the primary consumer gained from the plant. As the biomass is passed along the food chain much of it is either used or lost. Therefore there is a limit to the number of organisms in a food chain. The top carnivore is usually the third or fourth consumer. Only around 0.001% of total original energy present in sunlight is finaly embodied as biomass in the tertiary consumer.

Ecological Efficiency Consumers at each trophic level convert at most 10% of the biomass in their food to their own organic tissue Can you explain reasons why?

Ecological Efficiency The following equation calculates the energy transfer between each trophic level (approx equivalent to biomass transfer) Ecological Efficiency = energy or biomass available after transfer x100 energy or biomass available before transfer

Pyramids of Energy Pyramids of energy show us the amount of stored energy transferred between each trophic level. It is measured in kJ per m2 per year, as there are seasonal variations. Pyramids of energy include the initial transfer of energy from the sun.

NB these figures are in Joules – convert to kJ

Productivity The Primary Productivity of an ecosystem is It can be divided into 2: Gross Primary Production (GPP) Net Primary Production (NPP)

Temperate deciduous forest 26000 Ecosystem Mean NPP (kJm-2 yr-1) Extreme desert 260 Open ocean 4700 Temperate grasslands 15000 Temperate deciduous forest 26000 Intensive agriculture 30000 Tropical rainforest 40000 Mean values for NPP in a range of ecosystems

Recycling of Nutrients

The Carbon Cycle

The Carbon Cycle involves:

The Carbon Cycle

Carbon sinks The concept of carbon sinks is based on the natural ability of trees, other plants and the soil to absorb carbon dioxide and temporarily store the carbon in wood, roots, leaves and the soil.

The Nitrogen Cycle

The nitrogen cycle. Yellow arrows indicate human sources of nitrogen to the environment. Red arrows indicate microbial transformations of nitrogen. Blue arrows indicate physical forces acting on nitrogen. And green arrows indicate natural, non-microbial processes affecting the form and fate of nitrogen.

Role of bacteria in the nitrogen cycle Decomposers (saprophytic bacteria)

Role of bacteria in the nitrogen cycle Nitrifying Bacteria

Role of bacteria in the nitrogen cycle Nitrogen Fixing Organisms (diazotrophs)

A symbiotic relationship Part of a clover root system bearing naturally occurring nodules of Rhizobium, bacteria that can fix atmospheric nitrogen. Each nodule is about 2-3 mm long

Role of bacteria in the nitrogen cycle Denitrifying bacteria

Recent increases in anthropogenic N fixation in relation to “natural” N fixation. Modified from Vitousek, P. M. and P. A. Matson (1993). Agriculture, the global nitrogen cycle, and trace gas flux.