Species, communities and ecosystems

Nature of science:

Looking for patterns, trends and discrepancies—plants and algae are mostly autotrophic but some are not. (3.1)

• Species are groups of organisms that can potentially interbreed to produce fertile offspring.
• Members of a species may be reproductively isolated in separate populations.
• Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
• Consumers are heterotrophs that feed on living organisms by ingestion.
• Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
• Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
• A community is formed by populations of different species living together and interacting with each other.
• A community forms an ecosystem by its interactions with the abiotic environment.
• Autotrophs obtain inorganic nutrients from the abiotic environment.
• The supply of inorganic nutrients is maintained by nutrient cycling.
• Ecosystems have the potential to be sustainable over long periods of time.

• The need for sustainability in human activities could be discussed and the methods needed to promote this.

Utilization:

• Syllabus and cross-curricular links:
• Geography
• Part 2A: Fresh water-issues and conflicts
• Environmental systems and societies
• Topic 2.1 Species and populations

Aims:

• Aim 6: It would be best for students to obtain data for the chi-squared test themselves, to give first-hand experience of field work techniques.

• Skill: Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
• Skill: Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
• Skill: Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
• Skill: Recognizing and interpreting statistical significance.

Guidance:

• Mesocosms can be set up in open tanks, but sealed glass vessels are preferable because entry and exit of matter can be prevented but light can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones.
• To obtain data for the chi-squared test, an ecosystem should be chosen in which one or more factors affecting the distribution of the chosen species varies. Sampling should be based on random numbers. In each quadrat the presence or absence of the chosen species should be recorded.