Ecosystems

Question 1

What is an ecosystem?

Answer 1

A natural unit consisting of living biotic components, non-living abiotic components and their interactions.

Question 2

What is a habitat?

Answer 2

The place where an organism lives.

Question 3

What is a population?

Answer 3

All of the organisms of one species that live in the same place at the same time, and that can breed together.

Question 4

What is a community?

Answer 4

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

Question 5

What is a niche?

Answer 5

• The role of a specific species in an ecosystem, in terms of their interactions with each other and other components in the ecosystem.
• This includes: Feeding habits, excretion, reproduction…- No two species can occupy the same niche.

Question 6

What are biotic factors in an ecosystem?

Answer 6

The ways in which different organisms interact with each other in an ecosystem.

Question 7

What are examples of biotic factors?

Answer 7

• Feeding/predation.
• Competition.
• Pollination/seed dispersal.
• Camouflage.- Mimicry.
• Symbiosis.
• Disease.

Question 8

What types of symbiosis are there?

Answer 8

1. Mutualism: Relationship where both organisms benefit. E.g. Tick birds and cattle.
2. Parasitism: Relationship where one organism benefits and the other suffers. E.g. Humans and tapeworms.
3. Commensalism: Relationship where one organism benefits and the other is unaffected. E.g. eyelash mites.

Question 9

What are abiotic factors in an ecosystem?

Answer 9

The ways in which different organisms interact with non-living components of an ecosystem.

Question 10

What are examples if abiotic factors?

Answer 10

• Soil pH.
• Temperature.
• Availability of water.
• Light intensity.
• Soil mineral content.

Question 11

Why are ecosystems dynamic?

Answer 11

• Organisms interact with each other and the environment very closely in an ecosystem. A small change may have a profound effect on one or may different populations.
• If the number of primary consumers go up, the number of producers would go down but number of secondary consumers would go up.
• Certain plants may influence nitrogen content of soil and thus other plants that grow (nitrogen fixing plants for example).

Question 12

What are the components of a food-chain?

Answer 12

1. Producers: Autotrophic plants/algae that rely on photosynthesis/chemosyntheis to make their own food and nutrients.
2. Primary consumers: Heterotrophic herbivores that feed off plants to obtain their energy and nutrients.3. Secondary consumers: Carnivores/omnivores that feed off primary consumers to obtain energy and nutrients.4. Tertiary consumers: Carnivores/omnivores that feed off secondary consumers to obtain energy and nutrients.5. Decomposers: Bacteria and fungi that feed off waste material and dead matter in the environment.

Question 13

What is a trophic level?

Answer 13

The level in a food-chain at which an organism feeds in.

Question 14

How is energy lost from trophic level to trophic level?

Answer 14

• Energy is used up by the organisms in each trophic level for respiration which is eventually lost as heat.
• Energy is trapped in excretion and dead matter (stored in the indigestible or inedible parts of an organism).
• About 10% of the energy available at a trophic level gets passed onto the next level.

Question 15

What are pyramid of numbers?

Answer 15

• Pyramid of numbers are visual representations of population size in a food-chain.
• Pyramid of numbers are usually pyramid shaped because energy is lost at each trophic level. As you go up the pyramid, less energy is available per trophic level to support the next. This means that population size shrinks.
• This is also why there are usually finite levels in pyramid of numbers. There will be a point where the energy available in a trophic level is not enough to support another, so it becomes the top trophic level.

Question 16

What are the problems with pyramids of numbers?

Answer 16

1. They do not take into account size of organisms. A large organism (e.g. a tree) can support many small organisms (e.g. birds). This may give a top heavy pyramid.
2. Numbers may be very large so pyramid difficult to draw.

Question 17

What are pyramids of biomass?

Answer 17

• Pyramids of biomass are visual representation of the total biomass available at each trophic level.
• This can be wet mass or dry mass (organisms need to be killed and dried).
• This pyramid takes into account the size of organisms.

Question 18

What are the problems with pyramids of biomass?

Answer 18

1. Pyramid of biomasses are only measures of standing crop. I.e. the biomass present at any one time.
2. An inverted pyramid of biomass may occur if a supporting level has a higher turnover rate and greater productivity than the level above. This means that there would be more biomass over time (which is not measured).

Question 19

What are pyramids of energy?

Answer 19

• Measure the flow of energy through a food-chain over a fixed time period, usually over a year.
• Productivity is taken into account as time is incorporated.
• Biomass may not be directly proportional to energy transferred depending on composition of organism. Such problems are eliminated- Solar input may be incorporated.
• No possibility of an inverted pyramid.

Question 20

What are the problems with pyramids of energy?

Answer 20

• Too time consuming to carry out.
• Data obtained through calorimitry which requires the burning of organism. This would kill the organism and is thus too destructive.

Question 21

What is Gross Primary Production (GPP)?

Answer 21

The rate at which plants convert light energy into chemical energy by photosynthesis.

Question 22

What is Net Primary Production (NPP)?

Answer 22

• The energy passed onto primary consumers by plants after respiratory losses (Rs_a) etc.
• Determined by: NPP = GPP - Rs_a.

Question 23

How can NPP be increased?

Answer 23

• Increasing light intensity increases the rate of photosynthesis in plants, thus increasing their GPP and NPP. This can be done by planting crops early or artificial lighting.
• Improving availability of water can increase NPP. This can be achieved through better irrigation or drought resistant crops.
• Temperature limits speed of chemical reactions in plants. Increasing it increases rate of photosynthesis and NPP. This is done through greenhouses.
• Lack of nutrients limits rate of photosynthesis and NPP. Increasing availability of nutrients increases NPP. This can be done through crop rotation or fertilisers.
• Diseases and pests decrease biomass and thus NPP. Pesticides and genetically modified pest resistance can be used to increase NPP.
• Competition with weeds for water, nutrients and light decreases NPP. Using herbicides can increase NPP.

Question 24

How can secondary productivity be increased?

Answer 24

• Younger animals convert more energy into biomass than older animals. Harvesting before adulthood minimises loss of energy.
• Growth enhancers such as steroids increase proportion of energy converted into biomass.
• Selective breeding can be used to maximise production.
• Antibiotics are used to treat animals to minimise energy loss while fighting infection.
• Keeping animals in warm and confined spaces, although inhumane, means that less energy is wasted for movement and maintaining body temperature.

Question 25

What is succession?

Answer 25

Changes in the community due to some event may change the habitat which may subsequently impact the community, causing the gradual directional change of an ecosystem over time.

Question 26

How does succession occur?

Answer 26

1. Initial conditions in an ecosystem are usually hostile. Only extremophiles are able to survive. In the case of sand dunes, these plants are adapted to living in salt water conditions, so settle, and are called the pioneer community.
2. As time passes, these plants die and organic matter is deposited. This encourages the growth of new plants like sea sandwort and sea couch grass, which eventually take over. Because these plants have underground roots, they hold sand together and stabalises it.
3. With more stability and further accumulation of nutrients, more plants begin to grow, trapping more sand and building up the dune.
4. Eventually, plants like hare’s-foot clover settle which are legumes with nitrogen-fixing bacteria, this further improves nutrient content in the soil by increasing nitrate level.
5. Eventually, the community of plants stabalise and no more major changes occur. This is called the climax community. In the sand dunes, plants like the sand fescue settle whereas in most inland ecosystems, a woodland is formed.
6. Each stage in the succession is called a sere.

Question 27

What factors can affect succession?

Answer 27

1. Sub-climaxes: When an event prevents ecosystem from developing further but doesn’t necessarily destroy the current ecosystem.
2. Diverted/deflected succession: When an environmental change destroys a current community and makes way for a better adapted community.
3. Secondary succession: When current community is destroyed and conditions returned to pre-pioneer community conditions, making way for same succession cycle.

Question 28

What are decomposers?

Answer 28

Microorganisms such as fungi and bacteria that feed off dead and waste organic matter by means of saprotrophic nutrition.

Question 29

Why are decomposers important?

Answer 29

Without decomposers, nutrients would be trapped in dead organic matter and become unusable. Decomposers break down dead organic matter and return nutrients to the soil or air, which is vital in nutrient recycling. Without decomposers, usable nutrients would eventually run out.

Question 30

What is nitrogen fixation?

Answer 30

The process of converting nitrogen in the air to usable nutrients such as nitrates and ammonia. This can be done through the Haber process, lightning and nitrogen fixing bacteria.

Question 31

What are nitrogen fixing bacteria?

Answer 31

Bacteria that convert nitrogen gas into nitrates and ammonia. Many live freely in soil, but most (such as Rhizobium) live in root nodules of legumes as part of a mutualistic relationship; with the bacteria providing nitrogen based nutrients to the plant and the plant providing carbohydrates to the bacteria.

Question 32

What is nitrification?

Answer 32

The process of converting ammonium ions into nitrites and nitrates.Ammonium ions —> Nitrites —> Nitrates

Question 33

What are nitrifying bacteria?

Answer 33

• Nitrifying bacteria are chemoautotrophs.
• They absorb ammonium ions released by decomposers and oxidise them into nitrites and then nitrates.- This process gives them energy.
• Oxidising ammonium ions requires oxygen, so nitrifying bacteria work best under aerobic conditions.
• Nitrosomonas converts ammonium into nitrites. Nitrobacter converts nitrites into nitrates.

Question 34

What is denitrification?

Answer 34

The process of converting ammonium, nitrates… back into nitrogen gas in the air.

Question 35

What are denitrifying bacteria?

Answer 35

Bacteria that carry out denitrification. They work best under anaerobic conditions (such as waterlogged soil) where they use the oxygen from nitrates for respiration.

Question 36

Why do samples need to be random?

Answer 36

Conditions may be slightly different across an ecosystem which may slightly affect the distribution of populations. Random samples ensure that the whole ecosystem is taken into account when data is being collected.

Question 37

How are samples taken randomly?

Answer 37

1. Samples are taken across the habitat at regular intervals.
2. A grid is laid over the habitat and random numbers are generated with a random number generator that are used to obtain random sampling coordinates.
3. Alternatively, the grid can be one found on a map. The sampling spot is then found with a GPS.

Question 38

How is sampling size determined?

Answer 38

Pilot studies are used to determine the minimum sample frequency, by looking at cumulative frequency, and the actual sample size is usually double that.

Question 39

How is species richness determined?

Answer 39

Using a quadrat. The number of different species that can be seen within the quadrat are usually counted and noted.

Question 40

What limitations are there with this method?

Answer 40

1. It may be difficult to distinguish between different species if they have similar appearances.
2. Smaller, more insignificant plants may be missed.
3. Seasonality may affect the number of species that can be seen within the sampling area.

Question 41

What is species evenness?

Answer 41

A measure of the species richness taking into account the number of individuals of that species (population) within a given habitat.

Question 42

How can species evenness be determined?

Answer 42

1. The number of individuals of a species can be counted within a quadrat.
2. A visual survey can be done of the quadrat and a measure of abundance can be giving using the ACFOR scale.

Question 43

What are the limitations with this method?

Answer 43

1. Difficult to distinguish between different species and indeed different individuals.
2. There may be too many individuals to count.
3. Smaller, more insignificant plants are harder to see and therefore their numbers are usually underestimated.

Question 44

How can % coverage be determined?

Answer 44

1. The quadrat can be split into smaller squares, % coverage can be estimated within these smaller squares and totalled at the end.
2. A point frame can me used. These are frames with usually a series of 10 needles/ pointers mounted onto them (with the same width as the quadrat). These are moved across the quadrat 10 times and plants touching the pointers are recorded.

Question 45

What is a transect?

Answer 45

• A line that stretches across a habitat used to determine the biodiversity and change in biodiversity throughout a habitat.
• The line can be a physical rope across the habitat or a line drawn across a map along which samples are taken.
• Samples may be taken at set intervals along the transect. This is called an interrupted belt transect and is used to sample biodiversity quantitatively across a habitat.
• Samples may be taken one after another along the transect. This is called a continuous belt transect and is used to record actual biodiversity quantitatively across the habitat.