Ecosystems

Learning ObjectivesState key terms and definitionsState that ecosystems are dynamicDescribe how energy is transferred through

ecosystems

Starter: Card sort

Ecosystem –All the living organisms and non living components in a specific habitat, and their interactions

Habitat – the place where an organism or population of organisms lives eg a woodland, rocky shore.

Microhabitat – an area within a habitat with specific conditions eg a rotting log.

Niche – The ‘role’ an organisms has in it’s environment – where it lives, what it eats, where and when it feeds, when it is active. Every species has its own unique niche.

Key definitions

Community – All the populations of different species that live in the same place at the same time, and who can interact with each other.

Population - all of the organisms of one species, who live in the same place at the same time, and can breed together

Environment – The conditions surrounding an organism, including both abiotic factors and biotic factors

Key definitions

Key definitionsAbiotic factor – the effects of the non-living

components of an ecosystem eg temperatureBiotic factor – the effects of the living parts of the

ecosystem eg competition, predationAutotrophs – organisms that can make their own

food.Heterotrophs - organisms that can’t make their own

food.Trophic level – the level at which an organisms feeds

in a food chain

Producers - autotrophic organisms that convert light energy to chemical energy, which they then supply to consumers

Consumers – living organisms that feed on other living organisms

Decomposer – An organism that breaks down complex organic molecules into simple inorganic molecules that can be recycled. Also know as a saprophyte.

Detritivore – An organism that feed on dead organic matter.

Key definitions

Dynamic ecosystemsMatter is constantly recycled within an

ecosystem eg carbon and nitrogen cyclesEnergy is not recycled it flows through

ecosystems

Light energy Heat energyBiotic

component

Abiotic component

Photosynthesis

Respiration

Nutrients

Simple Food Chain

Producer First Consumer Second Consumer

• The arrows in a food chain show the transfer of food energy from organism to organism

• Food chains always begin with a PRODUCER. This is a green plant which is able to make food using the energy of sunlight in photosynthesis

• Each stem in the food chain is known as a TROPHIC LEVEL

• In this case the TOP CARNIVORE is the fox. Top Carnivores are not eaten by anything else except decomposers (bacteria and fungi) after they die.

Food WebSimple food chains are not very realistic. In practice very few animals eat just one thing. Most of them can eat several other animals or plants. A more realistic picture is given by a FOOD WEB which is made up of interconnected food chains.

Falcon

Fox

Barn Owl

Thrush

Rabbit

Pigeon

Dormouse

Cabbage

Grain

Snail

Energy transfer in the food chain

Pyramids of numbers only give an accurate impression of the flow of energy in a food chain if the organisms are of similar size. Measuring the biomass at each trophic level can give a more accurate picture.

Pyramids of numbers are a quantitative way of representing food chains.

What are the problems of representing food chains in pyramids of numbers?

They record the number of organisms at each trophic level in a specified area.

What are pyramids of numbers?

Numbers or biomass?

In a pyramid of numbers, the length of each bar represents the number of organisms at each trophic level in a specified area.

As a single tree can support many organisms, this food chain produces an unbalanced pyramid.

Understanding pyramids of numbers

Understanding pyramids of biomassIn a pyramid of biomass, the length of each bar represents the amount of organic matter – biomass – at each trophic level in a specified area.

At each trophic level, the amount of biomass available is reduced, giving a pyramid shape.

Drawbacks of pyramids of biomass Fresh mass is quite easy to assess, but the

presence of varying amounts of water makes it unreliable.

The use of dry mass measurement overcomes this problem but, because the organisms must be killed, it is usually only made on a small sample and this sample may not be representative.

Different species can release different amounts of energy per gram

Pyramids of energyMeasures the amount of energy in the

organism in kilojoules per square metre per year (kJm-2yr-1).

These pyramids are very difficult to measure but are always true pyramids

Drawbacks of pyramids of biomass It’s a ‘snapshot in time’ - Biomass can vary with

the seasons.Also, when the producer is a small organism

which multiplies very rapidly, the total biomass of the producers present at any one time may be less than the total biomass of the primary consumers.

Over the course of a whole year, the mass of phytoplankton (plants) must exceed that of zooplankton (animals), but at certain times of the year this is not seen. e.g. In early spring around the British Isles, zooplankton consume phytoplankton so rapidly that the biomass of zooplankton is greater than that of phytoplankton.

Measuring Energy TransferPyramid of Biomass

Bars represent dry massDry mass: evaporate all water at 80oCScientists often measure wet mass and

calculate using prior dataPyramid of Energy

Different species produce different amounts of energy

Use calorimeter to calculate heat released per gram

Too destructive for most scientists

Plenary: Summary questions1. State 2 advantages of using a pyramid of biomass rather

than a pyramid of numbers when representing quantitative information on a food chain (2 marks).

2. Explain how a pyramid of biomass for a marine ecosystem may sometimes show producers (phytoplankton) with a smaller biomass than primary consumers (zoo plankton) (1 mark).

3. Name suitable units for the measurement of biomass (2 marks).

In a pyramid of numbers: no account is taken of size (1 mark)The pyramid of individuals of one species may be so great that it is impossible to represent them on the same scale as other species in the food chain (1 mark).

At certain times of year (e.g. Spring) zooplankton consume phytoplankton so rapidly that their biomass temporarily exceeds that of phytoplankton (1 mark).

Grams per square metre (gm-2) (1 mark)Grams per cubic metre (gm-3) (1 mark)