Click the headline below to read an article on the ecological and scientific importance of Napenthes pitcher plants.

2.1.7 Describe and explain population interactions/relationships using named species

Apart from herbivory and predation and feeding relationships in food chains structures, animal populations also interact by competition, parasitism and mutualism. This is another way in which communities are similarly structured and organised – through population interactions. There are many ways in which organisms interact, apart from the basic ‘X’ eats ‘Y’ relationship. Consider the following information, which refers to the organisms which live inside the Napenthes pitcher plants. (Pitcher plants are insectivorous plants with a world distribution centered on SE Asia; they are usually found in nutrient-poor soils, and have leaves modified to form ‘pitchers’ which attract and digest invertebrate visitors)

Nepenthes species of tropical pitcher plant is a true bizarre jewel of the plant kingdom.

Phorid fly larva (maggots) are filter feeders & are parasitised by small wasps which also live in the pitchers. Phorids are flightless – they are unusual flies as most species have tiny wings

The Napenthese pitcher plant and Phorid flies

The drowned insects represent the main energy source in our Napenthese open system; digestive enzymes produced by the pitcher and the decomposer microorganisms will break down the bodies of the dead insects, releasing minerals into the surrounding solution. These minerals represent a resource, both to the decomposers and to the pitcher plant- both require these minerals, and so there will be competition for them. The phorid flies are parasitised by the small wasps- the adult female wasp stings a phorid larva (maggots) and paralyses it, then lays one egg on the phorid; when the wasp egg hatches it feeds on the (still alive but paralysed) phorid. The thomasiid spiders prey on insects entering and leaving the pitcher- they are an example of a predator. Any insect which feeds on the normal photosynthetic leaves of the pitcher plant would be considered a herbivore. Interestingly, pitcher plants are insect-pollinated; this means they rely on insects to complete their reproductive process. Flying insects are attracted to the flowers of a pitcher plant and in exchange for a nectar meal, they transfer pollen to another flower; both organisms benefit from this relationship, which we describe as an example of mutualism.

TASK: On your class handout (section E) – Give named examples for each of the interactions terms to apply your understanding; complete the two tables & create a food chain / web.

Class work during lesson – what could we add or change to improve?

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TASK – Tying it all together: Constructing a food web from written information 

Textbook: J. Rutherford p. 55 “To Do” box at the at the top of pg

1. Create a list of all the organisms described in the reading.
2. Sort the organisms into producers and add them to trophic level 1; then sort the herbivores and add them to trophic level 2….
3. On an A4 plain paper (no lines), use a ruler and pencil to neatly construct a food web diagram showing feeding relationships and energy flow. You can add colour or ink if you wish afterwards and/or use a key.
4. In addition to this, on a separate line page (or typed on computer) complete the following:

• a. List the significant abiotic factors.
• b. List the significant biotic factors.
• c. Describe one food chain operating within.
• d. Describe the community. Is it diverse or dominated by one species? Is it complex or quite simple? Explain (give reason or cause).
• e. Choose one species and describe its habitat and its niche
• f. Suggest an example of (i) Herbivory; (ii) Predation; (iii) Competition; (iv) Parasitism; and (v) Mutualism; if they exist.

Sample Work –

How does each one compare to your own? What should be added, removed             or change?

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Check your understanding: