ESS – The ecosystem - structure

ESS – The ecosystem - structure Syllabus points 2.1.1, 2.1.2, 2.1.3, 2.1.4.

Edaphic factors Abiotic Biotic Light intensity Number of predators Topography pH Humidity Age of population Light Temperature Air Parasites Microbial community Minerals

Summary • The living parts of an ecosystem are called biotic. • The non-living parts of an ecosystem are called abiotic. • Biotic + abiotic = ecosystem NB the word environment refers to the non-living part of the ecosystem

Learning objectives 2.1.1 distinguish between biotic and abiotic components of an ecosystem. 2.1.2 define the term trophic level. 2.1.3 Identify and explain trophic levels in food chains and food webs selected from the local environment. 2.1.4 explain the principles of pyramids of numbers, pyramids of biomass and pyramids of productivity, and construct such pyramids from given data.

Module 2: The Ecosystem

Food Chains The flow of energy and matter from one organism to another can be shown using a food chain. Lets try to draw one for the following organisms: - stinging nettles - peacock butterflies (caterpillars) - blue tits - sparrow hawks

Terminology • Now lets try to add the following terminology • Producer and consumers (1o, 2o, 3o and 4o). • Herbivore/carnivore/omnivore • Decomposers • Trophic levels Extension: • Top carnivores

Practice • Food chains are a very simplified model, but can be made more realistic by combining them into food webs. Produce a food web for an ecosystem of your choice (ideally local) and then label it with as much detail as you can. Extension: what components of systems can you identify?

Quick check questions • Are primary consumers always herbivores? • What is meant by the term trophic level? • Which trophic level do decomposers feed at?

Ecological Pyramids Use the blue books to research about pyramids of number, biomass and productivity. Areas to focus: • What does each pyramid show. • What are the advantages and disadvantages of each • What are the units for each • The ‘to do’ task on page 51. NB This information could be presented in a table. Extension: complete the ‘to do’ task on page 55.

Questions • Why are food chains generally short? (Think thermodynamics). • How does this support claims for vegetarianism? • What are the implications for the conservation of top carnivores? • The amount of energy (KJ/m2/year for each trophic level is as follows Plankton (8869)  Copepod (892)  Herring (91) • Sketch a pyramid of productivity. • Calculate the percentage of energy entering the plankton that passes to the copepod. • Calculate the energy entering the copepod that passes to the herring. • Calculate the amount of energy entering the food chain per year if the plankton use 0.1% of the available energy.

Reading • http://www.bbc.co.uk/news/science-environment-22425219 • Mercury exposure linked to dramatic decline in Arctic foxes – BBC News

ESS – The ecosystem - structure Syllabus points 2.1.5, 2.1.6, 2.1.7

Pyramids review Pyramids are a graphical way of representing data. There are three types: • Pyramids of numbers • The number of individuals at each trophic level. • Pyramids of biomass • Biological mass of standing stock at each trophic level at a particular point in time. • Pyramids of productivity • This shows the flow of energy or the rate at which stock is regenerated. Each of these representations has advantages and disadvantages.

Syllabus points 2.1.5 Discuss how the pyramid structure affects the functioning of an ecosystem. 2.1.6 Define the terms species, population, habitat, niche, community and ecosystem with reference to local examples. 2.1.7 Describe and explain population interactions using examples of named species.

How long can food chains be? • Discuss with your partner. • What’s the longest food chain you can think of?

Concentration of toxins Some toxins do not break down naturally. Instead they are stored in the tissues of organisms. As there are fewer organisms in each successive trophic level the toxins accumulate. This problem can be averted by only using biodegradable toxins.

Vulnerable carnivores • Read the case study of the snow leopard on page 18. • Taking a systems approach what would you do to help conserve the snow leopard? • Explain how it would help.

Definitions • Species: a group of organisms that interbreed and produce fertile offspring. • Niche: where, when and how an organism lives. No two different species can have the same niche because a niche completely defines the species. • Population: a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding. • Community: a group of organisms living and interacting with each other in a common habitat. • Habitat: the environment in which a species usually lives. • Ecosystem: a community of interdependent organisms and the physical environment they inhabit.

Activities • Research an example of each of the four species interactions. (Mutualism, parasitism, predation and competition). • What is meant by a symbiotic relationship? Extension: are there any other types of interaction that could be possible?

Discuss in pairs • What is the difference between predators and scavengers? • Do parasites kill their hosts? • Are these types of relationships ‘fixed’ over evolutionary time? • What is the relationship between an elephant and plants it tramples on? • How would we classify what happens if a lion kills a hyena but doesn’t eat it?

ESS – The ecosystem - structure