1

UNIT 3: ECOSYSTEMS

STRUCTURE AND FUNCTION

WHICH ARE COMPONENTS OF AN ECOSYSTEM?

Ecosystems are functional units composed of all the living things in a place, their biotic components, and the physical and chemical factors which make up its non-living things, which are their abiotic components. There are different interactions between the biotic and abiotic factors as well as between the organisms living in a ecosystem.

The ecosystem is the higher level in the organisation and complexity of life. An organism from a species is an individual. All individuals of one species which live in the same place and at the same time are called population. And populations of different living things that live in the same ecosystem and interact between them are called community.

All the ecosystems on Earth can be considered as an only functional unit called Ecosphere, where the biotic components are all the living things living in our planet, which we call Biosphere, and the abiotic components are the Geosphere, the Atmosphere and the Hydrosphere.

The habitat of a population is the place that supplies the needs of this population, such as water or food. The habitat where a population lives and the range of environmental conditions that are suitable for the survival of the population determine the ecological niche. Each species occupies a specific niche in the ecosystem. If two different populations have the same ecological niche, they will compete for it.

They are different interactions between the members of a community that keep the functionality of the ecosystem. Some of them are: competition, when two living things need the same resource; predation, an individual kills and eats another individual of a different species; symbiosis, two or more individuals of different species live in close proximity to each other and interact regularly in such a way as to benefit them; or cooperation.

HOW ABIOTIC FACTORS INFLUENCE ON LIVING THINGS?

There are two main types of environment, terrestrial and aquatic. The influence of the abiotic factors is different in each one. These factors are important because they determine the living things that live in an ecosystem. The main abiotic factors are water, light, temperature, precipitation, salinity or soil chemistry.

Living things have limits of tolerance to abiotic factors to survive. The abiotic factor’s range in which a population can live is called tolerance range. This range is different for each population, and everyone has a level or optimum, inside the tolerance range, at which the population grows and lives better.

Temperature and water are the most influential abiotic factors in the development of a population in a terrestrial environment. On the contrary, in aquatic environments, as well as temperature, other factors such as light, salinity or dissolved oxygen level limit life.

2

UNIT 3: ECOSYSTEMS

ACTIVITIES

1. Answer the following questions.

a) What is the difference between an ecosystem and the Ecosphere?

b) What is the difference between population and community?

c) What is the difference between habitat and ecological niche?

d) What is the difference between biotic and abiotic components?

e) What is the difference between limits of tolerance and tolerance range?

2. Look at the picture and write four biotic components and four abiotic components.

http://4.bp.blogspot.com/_mYcBoE9RZdU/TS8NhyPHznI/AAAAAAAACNM/OoTWYNAzJtA/s1600/ecosystem.jpeg

3. Look at the picture in activity 2 and write two interrelationships between different biotic components and write what abiotic factor is more limiting in the ecosystem. Give reasons for your answer.

4. W.orking W.ith the W.eb: Plant and Animal Adaptation Research

Adaptations are behavioural and physical characteristics that organisms develop to survive and reproduce in their environment. Choose a plant and an animal to study how they adapt to abiotic factors in an ecosystem. Use the information on the Internet to write and illustrate a fact sheet explaining how your plant and animal adapt to their habitats. Include images and information about their habitat and behavioural or physical traits related to each abiotic factor.

http://resources.education.tas.gov.au/item/edres/68652f50-0e7f-5e01-321a-5680ee051f0d/1/I_eat_them.zip/bio.swf http://bioactive.mrkirkscience.com/Part6Sim/swfs/Sim_06.swf http://www.phs.d211.org/science/dahljl/Bio%20138/PPTs/flash%20unit%2011/Biomes.swf http://www.biologyreference.com/A-Ar/Adaptation.html

3

UNIT 3: ECOSYSTEMS

FOOD CHAINS AND FOOD WEBS

HOW ARE LIVING THINGS RELATED IN AN ECOSYSTEM?

Living things need matter and energy for their life processes. Matter and energy appear in the ecosystem when autotrophs get them from soil, air and light. Then, matter and energy are transferred to heterotrophs by trophic relationships. Thus, living things can be classified according to the trophic level they occupy:

Producers are autotrophic organisms that transform the inorganic matter into organic by photosynthesis.

Consumers are heterotrophic living things that feed on other organisms. The consumer trophic level can subdivide depending on the type of organisms included. First-order consumers eat producers, whereas second-order consumers obtain food from first-order consumers.

Decomposers transform organic matter into inorganic substances which are used by producers.

A food chain is a sequence of organisms that shows the feeding relationships between them. A food chain always begins with producers. But, these relationships are not always so simple because a consumer can feed from several lower levels. This means that several food chains become connected forming complex food webs.

Higher trophic levels have fewer organisms than lower levels. This is because when nutrients are recycled within an ecosystem, energy is lost with each transfer to a higher trophic level. So, energy must be continually generated in an ecosystem by photosynthesis.

HOW ARE TROPHIC RELATIONSHIPS REPRESENTED?

As well as food chain or food web, the relationships between living things can be represented by trophic pyramids. These pyramids show the amount of energy, biomass or the number of organisms there are in every trophic level.

An ecological pyramid places the producers at the base, the next higher level consist of first-order consumers, the next higher level of second-order consumers, and so on. There are different types of ecological pyramids:

The energy pyramid shows the total amount of energy present in each trophic level. This is the only representation that always has a pyramidal form, because of the progressive energy loss.

A biomass pyramid represents the biomass or amount of organic matter at each trophic level of a food web. Usually these pyramids have a pyramidal form, but some of them can be inverted. This pattern is often attributed to different sizes of producers, such as plankton producers in some aquatic ecosystems.

A pyramid of number shows the number of organisms at each trophic level. This pyramid also can be inverted, such as the number of insects living on a tree.

4

UNIT 3: ECOSYSTEMS

ACTIVITIES

1. Match each concept with its definition.

- They are herbivores - Food chain

- They do photosynthesis - Energy pyramid

- It is a sequence of feeding relationships - Producers

- It never is inverted - Decomposers

- It can be inverted - Food web

- It is formed by several food chains - Biomass pyramid

- They produce inorganic matter - Second-order consumers

- They eat herbivores - First-order consumers

2. Look at the following food web and give reasons for your answer.

(http://king.portlandschools.org/files/houses/y2/animalmaineia/files/species/wfrogkm/foodweb/foodwebexample.gif)

a) What do you think will happen if you take the foxes out of the food web?

b) Which are the producers?

c) Which are the first-order consumers?

d) Which are the second-order consumers?

e) What is the biggest order of consumers in the food web? What animal/s occupy/ies this order?

f) Write the biggest food chain you can find.

3. Complete the sentences with the words below.

autotrophs – herbivore – carnivore – plants – heterotrophs – omnivore – produce

a) Plants _____________ their own food.

b) A __________ eats only plants.

c) __________ provide food for all the animals in the world.

d) __________ are animals that do not produce their own food.

e) Plants are called producers or _____________.

f) An animal or human being that eats meat and plants is an ______________.

g) A ______________ eats only meat.

4. W.orking W.ith the W.eb: Food chain game Play one of the following on-line games and write two different food chains. Identify the second-order consumer in each chain and explain what would happen if they disappeared. http://www.ecokids.ca/pub/eco_info/topics/frogs/chain_reaction/index.cfm http://www.sheppardsoftware.com/content/animals/kidscorner/games/foodchaingame.htm http://www.bbc.co.uk/schools/ks2bitesize/science/living_things/food_chains/play.shtml

5

UNIT 3: ECOSYSTEMS

WORLD’S BIOMES

HOW ARE ECOSYSTEMS DISTRIBUTED AROUND THE WORLD?

There are many similarities between the different ecosystems around the world. Scientists classified ecosystems into categories called biomes. The American scientist Neil Campbell defined biome as “the world’s major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment”. The terrestrial biome distribution is determined by temperature and precipitation patterns. Thus, the world’s biomes can be classified according to three climate zones: low-latitude climates (tropical rainforest, savanna, desert), mid-latitude climate (Mediterranean biome, grasslands, deciduous forest) and high-latitude climates (taiga, tundra, alpine biome).

These are the characteristics of the main world’s biomes:

The tropical rainforest has the greatest diversity of species. It occurs near the equator. Temperature and humidity are relatively high through the year.

The savanna is a grassland ecosystem with scattered individual trees. This biome has only two very different seasons: a very dry season and a very wet season. The savanna is located on extensive areas on either side of the equator on the edges of tropical rainforest.

Desserts cover about one fifth of the Earth’s surface and occurs where annual rainfall is less than 25 cm and, in some years, zero. Desserts are classified into hot and dry, semiarid, coastal and cold. This last type of dessert occurs in the high-latitude such as Antarctic or Greenland.

The Mediterranean biome is found between 32º and 40º latitude North and South on the west coast of the continents. The annual rainfall averages from about 300 to 1000 millimeters. Summers are dry and winters are wet.

Grassland biomes are areas dominated by grass or grasslike vegetation. There two main kinds of grassland: prairies, with tall grasses, and steppes, with short grasses.

The deciduous forest is characterised by a moderate climate and deciduous trees. Normally, large areas are dominated by a single species. Abundant precipitation falls throughout the year, increasing in the summer season. There is not a dry season.

The taiga or boreal forest represents the largest terrestrial biome. It occurs between 50º and 60º North latitude and it is dominated by conifers. It has long, very cold winters and short, cool summers. Precipitation is small, increasing during summer months.

The tundra is located in the northern hemisphere, poleward of 60º North latitude. The climate is so cold in winter that soils of this biome are usually permafrost.

The alpine biome is quite similar to the tundra but there are not permafrost and it presents a better drainage. Alpine biomes are found in the mountain regions all around the world.

The world’s aquatic ecosystems can be classified into freshwater (ponds and lakes, rivers) and marine (oceans, coral reefs).

6

UNIT 3: ECOSYSTEMS

ACTIVITIES

1. Tick the sentences T (true) or F (false). Then correct the false sentences.

T F

a. Aquatic biomes are distributed according to climate.

b. Steppes are a type of Mediterranean biome.

c. The tropical rainforest occurs near to equator.

d. There are desserts in Greenland.

e. The coral reef is a type of freshwater biome.

2. Answer the following questions.

a. Which terrestrial biome occupies one fifth of the Earth’s surface?

b. What is the difference between prairies and steppes?

c. Which terrestrial biome is between 50º and 60º North latitude?

d. In which hemisphere is the tundra located?

e. In which latitude can the Mediterranean biome be found?

3. Identify the type of biome. What animals can you see in each ecosystem?

savanna desert coral reef Mediterranean forest tundra desert

W.orking W.ith the W.eb: My favourite aquatic ecosystem

In groups, design a poster about your favourite aquatic ecosystem using information on the Internet. Include a map where you can locate the ecosystem in the world and a fact file of its characteristics: climate, animals and plants. Write a possible food chain or food web in the ecosystem.

Suggested websites: http://www.mbgnet.net/fresh/ http://www.ucmp.berkeley.edu/exhibits/biomes/index.php http://www.schools.indiawaterportal.org/sites/schools.indiawaterportal.org/files/ppt/cp/Aquatic_Ecosystems/Aquatic_Ecosystems.swf http://www.limpoporak.com/UserFiles/Interactive/en/FoodWeb/food_web3.swf

a. b. c. d. e.

7

UNIT 3: ECOSYSTEMS

KEY POINTS

What is an ecosystem

made up of?

Biotic

components

Abiotic

components

What are the

world’s

ecosystems?

ECOSYSTEM

How are the

relationships in an

ecosystem

represented?

Organism – Population – Community Temperature – Light – Water – Salinity –

Precipitation – Soil chemistry

Food chain

Food web

Ecological

pyramids

Energy

Biomass

Number

Terrestrial

ecosystems

Aquatic

ecosystems

Low-latitude: tropical rainforest,

savanna, desert

Mid-latitude: Mediterranean biome,

grasslands, deciduous forest

High-latitude: taiga, tundra, alpine

biome

Freshwater:

ponds and

lakes

Marine:

oceans and

coral reefs.

8

UNIT 3: ECOSYSTEMS

PROGRESS CHECK

Choose the correct answer:

1. _________ is all the individuals of the same species that live in an ecosystem. a) Organism b) Community c) Population 2. _________ are limiting factors in a terrestrial environment. a) Water and temperature b) Light and water c) Light and temperature 3. The interaction between two populations for the same resource is called ________. a) Cooperation b) Symbiosis c) Competition 4. The living things that make their own food by photosynthesis are called __________. a) Producers b) Consumers c) Decomposers 5. A food chain always starts with a __________. a) Producers b) Consumers c) Decomposers 6. The true sentence is ___________. a) The food chain is formed by several food webs b) The food web is formed by several food chains c) The food web is formed by one food chain. 7. A __________ pyramid shows how many organisms there are at each trophic level. a) Biomass. b) Number. c) Energy. 8. The Mediterranean biome is located in the ___________ climate zone. a) Low-latitude b) High-latitude c) Mid-latitude 9. The taiga biome is located in the ___________ climate zone. a) Low-latitude b) High-latitude c) Mid-latitude 10. The tropical rainforest is located in the ___________ climate zone. a) Low-latitude b) High-latitude c) Mid-latitude

ANSWERS: 1-c; 2-a; 3-c; 4-a; 5-a; 6-b; 7-b; 8-c; 9-b; 10-a.

9

UNIT 3: ECOSYSTEMS

Figure 1:

http://www.exploringnature.org/graphics/ecology/ecology_vocabulary.jpg

Figure 2:

http://3.bp.blogspot.com/_sob8E7nEtu0/SlVVhzbMrLI/AAAAAAAAAfo/3VxEnHANBT0/s320/tolerance+limits.jpg

Figure 3:

http://media-2.web.britannica.com/eb-media/99/95199-036-D579DC4A.jpg

Figure 4:

http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/life-in-the-sea/sci-media/images/marine-trophic-pyramid/169349-5-eng-NZ/Marine-trophic-pyramid.png

Figure 5:

http://luchipaiz.blogspot.es/img/biome.jpg