Soil Organism Project

 

Theory and Methods

An ecosystem is a community of living organisms and their non-living environment. Every ecosystem has both living (biotic) and non-living (abiotic) components. The biotic components consist of producers that synthesise food, consumers that eat the food and decomposes that break down dead organic material. The most important abiotic factors, which have ecological effects on organisms are temperature, light, humidity, oxygen concentration, pH and physical and chemical nature of soil.

In this experiment two abiotic factors will be measured i.e. temperature and soil moisture content, of two communities selected for this experiment. Biotic factors, such as predators and availability of food to organisms in each habitat, will also be considered.

As stated above, the communities selected for this investigation are woodland and grassland. Grasslands are usually wide open land. The main vegetation is grass of varied length with other small seasonal weeds, shrubs, mushrooms, etc. Because of its ground-level vegetation, grasslands often get direct sunshine, greater exposure to wind and rain than woodland. Woodland is well distinguished from grassland by its vegetation. Plant profile range from ground level to several metres high. It has dense tall mature trees like ash, beech, oak and pines which prevent light reaching ground level. Small plants, chiefly mosses and fungi cover the floor area while the herb layer contain shade tolerant, moisture requiring species such as ferns and flowering plants. Woodlands usually have greater amount of litter and dead organic matter than grassland.

For this investigation, communities to be used are located next to each other in the Schools’ parkland. Both are exposed to the same climatic conditions of rainfall, temperature and sunshine. They are on the same altitude and easily accessible for experimental work.

Method:
The plastic tubs were used as pitfall traps. A cover was placed over the tub as in the diagram, propped up by large pebbles. The purpose of the cover is to keep the rain from flooding the tub and leaves and other debris falling into it. The insects fall into the trap from under the cover. The traps were set for one week after which they were removed and the organisms caught were classified, counted and tabulated.

Four sets of traps were set in the grassland and four in the woodland simultaneously. Organisms were collected and studied in winter and in summer. Daily the maximum and minimum temperatures and the moisture content of the soil were measure and tabulated.

Each tub was labelled and coded accordingly, for identification and differentiation in the lab. The maximum-minimum thermometers were put firmly along one of the traps in each area. The traps were left for a week. Thermometer readings and moisture contents of soil by Ecometer were measured at a set time each day throughout the week. The temperature and moisture readings obtained were averaged to get the mean temperature and moisture readings of both habitats. It will be these averaged results which will be used in statistics and discussion.

Tables were drawn up for the number of organisms and the species diversity in the winter and in the summer in the grassland and in the woodland. The average maximum and minimum temperatures and the average moisture content for the corresponding periods in the two communities were also drawn up. Correlations were made between the temperature and numbers of organisms, temperature and species diversity, moisture content and number of organisms, moisture content and species diversity in both communities to ascertain which abiotic factor is affecting the species diversity and number of organisms the most. It is also hoped that the study will show which community resists the effect of the abiotic factor more efficiently.

 

Apparatus:

Plastic ice-cream tubs – for pitfall traps
Ecometer – to measure moisture content of soil
Maximum-minimum thermometer
Alcohol (50%)
Forceps
Small specimen jars
Labels and dark markers
Spade and trowel
Heat proof mat 

Note: Additional material such as plastic boots, raincoat and safety glasses might be needed.

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