ESS – The ecosystem - structure

Syllabus points 2.1.1, 2.1.2, 2.1.3, 2.1.4.

BioticAbiotic

pH

Light

Air

Humidity

Minerals

Edaphic factors

Topography

Microbial community

Age of population

Number of predators

Light intensity

Parasites

Temperature

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

1. Why are food chains generally short? (Think thermodynamics).a) How does this support claims for vegetarianism?b) What are the implications for the conservation of top carnivores?

2. The amount of energy (KJ/m2/year for each trophic level is as follows

Plankton (8869) Copepod (892) Herring (91)a) Sketch a pyramid of productivity.b) Calculate the percentage of energy entering the plankton that passes to

the copepod.c) Calculate the energy entering the copepod that passes to the herring.d) 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.

Pyramid type What it shows Advantages Disadvantages Units

Numbers(store)

The number of individuals at each trophic level

Easy to measure Doesn’t provide very useful information about feeding relationships.

None

Biomass(store)

Biological mass of standing stock at each trophic level at a particular point in time.

Results in fewer inverted pyramids and still not too difficult to measure.

Can sometimes be inverted because they only provide a snapshot in time- they take no account of productivity

Grams of biomass per metre squared (g m-2) or in joules per metre squared (J m-2).

Productivity(flow)

The the flow of energy or the rate at which stock is regenerated.

Shows the flow of energy rather than a ‘snapshot’. Overcomes the problem of species having different energy content per unit of mass.

Very hard to calculate.

Grams per metre squared per year (g m-2 yr-1) or joules per metre squared per year (J m-2 yr-1)

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.

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.

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.

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.

Species Interactions

Species B

Positive Negative

Species A

Positive Mutualism Parasitism

Negative Predation Competition

Species Interactions

Species B

Positive Negative

Species A

Positive

Mutualism

A symbiotic relationship in which both species

benefit.

Parasitism

One organism benefits at the expense of the other.

Ectoparasites and endoparasites.

NegativePredation

When one animal hunts and eats another.

Competition

This occurs when resources are limited.

Intraspecific and interspecific.

Activities

1. Research an example of each of the four species interactions. (Mutualism, parasitism, predation and competition).

2. What is meant by a symbiotic relationship?

Extension: are there any other types of interaction that could be possible?

Discuss in pairs

1. What is the difference between predators and scavengers?

2. Do parasites kill their hosts?3. Are these types of relationships ‘fixed’ over

evolutionary time?4. What is the relationship between an elephant

and plants it tramples on?5. How would we classify what happens if a lion

kills a hyena but doesn’t eat it?

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.