AN INTRODUCTION TO ECOSYSTEMS
Ecosystems
Basic definition:
"An ecosystem is a basic functional unit of nature, consisting of living organisms (plants and animals) and their non-living environment (air, water, soil and rock) - it functions as a whole unit and is self-sustaining"
There are many SCALES of ecosystem: from a garden pond to the Amazon rain forest... Even a teaspoon of sea water or soil contains life in abundance....
3 components to ecosystems:
BIOTIC: living - plants and animals / flora and fauna (and things in-between)
ABIOTIC: non-living environment
DOM
Does DOM live in 'da bungalow' with Dick ? No DOM is 'Dead Organic Matter' - this is particularly important to some ecosystems as it is here that the nutrient are stored and re-cycled - more on that later....
Consider a bare patch of earth. Does such a thing exist ?
There are occasions when a new patch of earth is created which has no chance of seeds already existing. In 1963, off the coast of Iceland, volcanic activity produced the island of Surtsey: it's as old as me.... this was entirely new land with no chance of pre-existing seeds etc. sprouting... Other places where this could occur might be on a new sand dune system, in volcanic ash, or in an alluvial or aeolian deposit which is revealed perhaps by sea level change...
Within a few years, seeds started to arrive - perhaps carried by the wind, perhaps or deposited in bird faeces, or washed by the sea. Perhaps seeds were caught on the clothing or embedded in mud in the treads of the boots of scientists who visited the island. It is hard for people to visit a place without 'contaminating' it in some small way.
The first plants to arrive are the PIONEERS or COLONISERS (r species) - these are able to cope with STRESS:
They are tolerant of something that prevents other plants living there, and can cope with a small amount of nutrient availability. Perhaps they are XEROPHYTIC, or HALOPHYTIC or HYDROPHYTIC...
The PIONEER species include weeds such as the rose-bay willow herb which colonised bomb sites in London after the Blitz...lichens, mosses, thistles etc.
These plants contribute to the weathering of the parent material (regolith) and contribute organic material, and DOM... this leads to the development of SOIL and HUMUS which is able to hang on to WATER and NUTRIENT.
Over time, other plants start to arrive and become dominant, the HIGHER SPECIES such as trees are the last to arrive, and the whole process is know as a SERE or SERAL STAGE or PRISERE. The resultant vegetation depends on the climate of the area, and so is known as the CLIMATIC CLIMAX vegetation, because it is what comes at the end of the succession: the climax of the whole process....
This assumes of course that people don't come along and interrupt the succession, or ARREST it: stop it at an earlier stage to suit them. So if you want to breed grouse on a heather moorland so that come August 12th you can shoot them, you need to ensure a lot of young heather shoots for them to eat, so you use MUIRBURN to keep the heather moorland at a particular stage, and trees never get a chance to grow - this is also the case with any pasture land.
The PLANTS are known as PRODUCERS, as they get their energy directly from the sun. Also known as AUTOTROPHS. Other organisms are CONSUMERS: either PRIMARY consumers or HERBIVORES, or SECONDARY consumers which may be CARNIVORES or OMNIVORES.
At each level of the FOOD CHAIN or FOOD WEB, energy is transferred as one organism eats another.
Other LIFELESS SURFACES which may be colonised include:
SCREE
ICE MARGINS and PERMAFROST CONDITIONS
BOMB SITES
A good quote from G. Tyler Miller, an American chemist.
"Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off 1000 tons of grass."
Characteristics of a HIGH PRODUCTIVITY ECOSYSTEM
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Low stress and disturbance (warm temperatures, high light intensity and adequate rainfall...) |
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leads to |
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Good growth conditions
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leads to |
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Competition from other plants
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leads to |
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High rate of resource depletion
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THIS OCCURS IN TROPICAL & TEMPERATE FOREST BIOMES |
BIODIVERSITY leads to COMPETITION: "the negative effects which one organism has upon another by consuming, or controlling access to, a resource that is limited in availability"
Nutrient: plants need the following MINERALS: C, H, N, O, P, S, Ca, Mg, K, Cl and the following MICRONUTRIENTS: Fe, Mn, Zn, Cu, B, Mo
Humans also need to ensure that they get the corrent nutrients, vitamins etc to sustain good health.
A major input is SOLAR ENERGY: controls the whole BIOSPHERE.
An output is HEAT: people in a room like a classroom will make the room warmer by the end of the lesson.
When a plant is eaten by a herbivore, some energy is stored as living tissue in the animals body, but the rest is lost as the animal respires, moves, and maintains its body temperature.
If the herbivore is then eaten by a carnivore, the energy is transferred along the food chain, but at each step or TROPHIC LEVEL/STAGE energy is lost.
The shorter the food chain, the less energy is lost.
Nutrients are also recycled. When fallen branches and leaves decay, the energy from the sun that was stored during photosynthesis is released and escapes from the ecosystem. The chemicals obtained from water, air and minerals in the soil are constantly recycled. Before they can be recycled, they need to be converted to simpler chemical forms by decomposers or DETRITIVORES.
E.g: a tree falls in a forest
wood destroying fungi and beetles colonise the wood
spores incubate in the wood and threads spread through the trunks
other decomposers are able to move in as the wood starts to be broken down
these insects attract woodpeckers and other creatures that eat insects
eventually, over many years, the trees break down to humus