Functioning Ecosystems

Question 1

Define ecological niche in terms of habitat, feeding relationships and interactions with other species

Answer 1

The role and space that an organism fills in an ecosystem, including all its interactions with the biotic and abiotic factors of its environment.

Question 2

Fundamental and realised niche

Answer 2

A fundamental niche: the potential niche that a species would occupy if there were no competition from other species (the full range of resources in which a species could survive and reproduce).

A realised niche: the actual use of resources of an organism ie. the actual range of resources that a species uses - constrained due to biotic interactions (competition) for resources.

Question 3

Competitive exclusion principle

Answer 3

Two species can’t coexist if they occupy exactly the same niche (competing for identical resources).
The competitive exclusion principal often leads to niche or resource partitioning. Niche partitioning is a process in which competing species become specialised in different ways in order to co-exist.

Question 4

! Analyse data to identify species (including microorganisms) or populations occupying an ecological niche !

Question 5

Define keystone species and understand the critical role they play in maintaining the structure of a community

Answer 5

A plant or animal that plays a unique and crucial role in the way an ecosystem functions.

Some features that are used to identify a keystone species are:

1. Its influence on other species is disproportionate to its abundance.
2. Its removal from the ecosystem has negative effects on the ecosystem.
3. It may eat a variety of organisms in the ecosystem and therefore keep their populations under control.

NOTE: If keystone species are removed from the ecosystem, the ECOSYSTEM WILL COLLAPSE

Question 6

! Analyse data (from an Australian ecosystem) to identify a keystone species and predict the outcomes of removing the species from an ecosystem. (Some Australian examples: Cassowary, Northern Quoll) !

Question 7

Predation

Answer 7

An interaction between two species in which one organism, the predator, captures and feeds on another organism, the prey.

Question 8

Competition

Answer 8

A negative interaction that occurs among organisms whenever two or more organisms require the same limited resource.

Question 9

Mutualism

Answer 9

Association between two or more species where each species benefits.

Question 10

Commensalism

Answer 10

Association between two species in which one species benefits and the other derives neither benefit nor harm

Question 11

Parasitism

Answer 11

An association between species, where one species, (the parasite living on or in another organism) benefits while the other (the host) is harmed.

Question 12

Ammensalism

Answer 12

An association between two different species in which one is inhibited or destroyed and the other is unaffected (eg. occurs in Australian rainforests. Tall trees reduce the available sunshine at ground level, and numerous plants cannot find adequate light in the shade).

Question 13

Sequence and explain the transfer and transformation of solar energy into biomass as it flows through biotic components of an ecosystem, including:

• converting light to chemical energy (photosynthesis)
• producing biomass (reproduction, growth and assimilation)

Answer 13

The ultimate source of energy for ecosystems is light (solar energy). Not all solar energy that strikes a leaf is used in photosynthesis (some is reflected, transmitted or not absorbed by photosynthetic pigments) Energy flows through ecosystems via process such as photosynthesis, consumption. Energy is lost from each consumer trophic level via respiration and decomposition. Thus, the energy contained in biomass at each successive trophic level is reduced. Ecosystems require a continuous supply of energy to replace the energy that is ‘lost’ as heat at each trophic level.

Cellular respiration supplies the energy needs for life processes such as growth, movement.

Plants convert only about 3% of the suns energy falling on them into organic molecules. At higher trophic levels, only about 10% of an organism’s energy is passed on to the organism that consumes it. The rest is used up in growth, reproduction, repair and movement, to name a few.

Question 14

Heterotrophs

Answer 14

Use chemical energy in organic molecules that they eat (consumers)

Named in a variety of ways:
1. By their specific trophic (or feeding) levels-

First order (or primary) consumers (herbivores): consume producers.

Second order (or secondary) consumers: consume first order consumers.

Third order (or tertiary) consumers: consume second order consumers.

2. By the specific type of food that they feed upon-

Herbivores: consume plants or algae

Carnivores: consume animals

Omnivores: consume both plants and animals

Detritivores: consume detritus (dead and decomposing particulate matter and organic waste) eg. earthworms

3. Other terms that are commonly used to describe consumers are:

Predators: consume organisms(prey) that they actively kill (Apex predators are the predators occupying the highest trophic level).

Prey: organisms that are killed by predators

Scavengers: consume food killed by other organisms

Decomposers break down energy rich molecules in dead organisms and the wastes of organisms into simple molecules and so help to recycle matter. eg. Bacteria and fungi.

Question 15

Autotrophs

Answer 15

Use chemical or solar energy to convert inorganic molecules into larger energy rich organic molecules (producers)

Can be either chemosynthetic or photosynthetic

Question 16

Food chains

Answer 16

Represent the energy flow between a few members of a community

Producer –> primary consumer –> secondary consumer etc

Question 17

Food webs

Answer 17

Represent the energy flow between many members of a community.

Question 18

As energy flows through an ecosystem

Answer 18

it is transformed from one form to another.

Only a small amount of the energy contained in light (<1% - 3%) that strikes a leaf is used in photosynthesis to make chemical energy in the form of plant biomass (the dry mass of living tissue at each trophic level).

Energy transfer in ecosystems is inefficient. Normally only 10% of the available energy from one trophic level becomes biomass (used in growth & reproduction) in the next trophic level. (This is called the 10% rule). Most of the energy consumed is mainly used during cellular respiration and is often converted to heat.

As the trophic level in a food web increases, the biomass and energy available decreases as energy is lost between trophic levels due to

not all the organic matter in a trophic level being consumed and

respiration (eg. heat production),

excretion (eg. urea) and egested waste (eg. undigested food / cellulose in faeces).

Higher trophic levels are often less efficient than lower levels as more energy is often spent on finding prey / food).

The energy available to consumer trophic levels equals the amount entering minus the amount lost to metabolic activity (respiration, heat and that lost to detritus (death, defecation, excretion)

Question 19

Pyramid of Numbers

Answer 19

A pyramid drawn with bar lengths proportional to the numbers of organisms present.

Question 20

Pyramid of Biomass

Answer 20

A pyramid drawn with bar lengths proportional to the dry mass of plants/animals.

Question 21

Pyramid of Energy

Answer 21

A pyramid drawn with bar lengths proportional to the energy stored in organisms.

Question 22

Energy and Biomass pyramids

Answer 22

Often look similar for the same food chain as energy is stored in the biomass. Also, as trophic levels increase, usually smaller amounts of biomass / energy are available. So biomass and energy pyramids often do look like pyramids (they are broad at base and narrow at the top).

Question 23

Numbers pyramids

Answer 23

Depict the number of organisms at each trophic level and are not always shaped like a pyramid. (eg. a food chain with parasites in it)

Question 24

Biomass

Answer 24

The total mass of organic matter making up a group of organisms in an area. Biomass consists of organic molecules ( eg. carbohydrates, proteins and lipids) and is a store of energy. (It is often measured as the total dry mass of organisms present)

Question 25

Productivity

Answer 25

The rate of biomass production in an ecosystem. Units used is often: units of mass, per area, per time (e.g. kg m–2 day–1)

Question 26

Primary productivity

Answer 26

The production of organic molecules by producers (mainly via photosynthesis).

Different ecosystems vary in their levels of primary productivity depending on types of producer, nutrient levels available, temperature range etc.

Question 27

Gross Primary Productivity (GPP)

Answer 27

The rate at which light energy is converted into chemical energy (as glucose)

Question 28

Net Primary Productivity (NPP)

Answer 28

The glucose that is stored as biomass after producers respire (R)

NPP = GPP - R

Question 29

Secondary productivity

Answer 29

The production of organic matter (biomass) by consumers. (It involves assimilation of food and production of new cells and tissues)

Question 30

Gross Productivity (GP)

Answer 30

In consumer trophic levels, the amount of biomass that enters the trophic level from a previous level.

GP = NPP - D (Detritus & waste from previous trophic level).

Question 31

Net Productivity (NP)

Answer 31

The portion of GP available for consumption by the next consumer trophic level.
NP is the amount of biomass / energy that enters a consumer trophic level minus the energy lost to metabolic activities (respiration (R) / heat).

NP = GP - R.

Question 32

Trophic efficiency

Answer 32

The percentage of energy transferred from one trophic level to the next (varies between 5 and 20%). The 10% rule refers to this concept.

Efficiency of transfer between trophic levels can be calculated for either biomass or NP energy (different units are used but the same basic equation as energy is stored in biomass).

Question 33

Percentage transfer

Answer 33

(Biomass in higher trophic level/biomass in lower trophic level) X 100

(NP energy of higher trophic level/NP energy of lower trophic level) X 100

Question 34

Photosynthetic efficiency (instead of calculating efficiency of transfer for producers from solar energy)

Answer 34

(Biomass of producers or GPP/ solar energy striking producers) X 100

Question 35

Predator-prey cycle

Answer 35

The total number of prey is greater than the total number of predators. The predator cycle follows the prey cycle (as the prey numbers increase, there is more food for the predators, so predator numbers will begin to increase which then eat more prey so prey numbers then decrease and so on….). Note: Prey are normally animals but may also be plants (predators in this case can be herbivores).

Normally the prey population increases before the predators population does.

Question 36

Three major cycles

Answer 36

Water, Nitrogen, Carbon

Question 37

Water cycle

Answer 37

The Water (H20) cycle is largely driven by solar energy and involves 4 major processes:

Transpiration which is the loss of water in the form of water vapour from plant surfaces (eg. Leaves)

Evaporation which is the conversion of liquid water into gaseous water vapour (largely from water bodies and soil).

Condensation which is the conversion of atmospheric water vapour into tiny liquid water droplets (in clouds).

Precipitation which is the falling of water (eg. rain, snow) to the earths surface.

Question 38

Carbon cycle

Answer 38

Carbon is transformed inside organisms via chemical reactions (eg. photosynthesis)

Carbon enters food chains via photosynthesis in producers (carbon dioxide is combined with hydrogen to make sugar in the light-independent reaction). It then is transferred between organisms (passes along food chains in organic matter (food)) via feeding. Carbon molecules leave organisms as a result of respiration (excreted as carbon dioxide) and also during decomposition (C02 and CH4). Some carbon leaves organisms in the faeces (undigested food substances such as cellulose).

Human Activity (farming animals, burning carbon containing fossil fuels, burning and clearing forests can enhance carbon addition to the atmosphere (eg. via methane, carbon dioxide or carbon monoxide release)

NOTE: As methane and carbon dioxide in the atmosphere trap heat, they are also considered ’green house gases’.

Question 39

Nitrogen cycle

Answer 39

To enter food chains nitrogen is absorbed or produced by plant roots or algae in the form of nitrate (NO3). Nitrate is produced by nitrogen fixing bacteria or through volcanic activity or lightning strikes.

Nitrogen also leaves organisms during excretion (eg. urea, uric acid or as ammonia) or in death via decomposition.

There are four processes involved in the Nitrogen cycle:

Ammonification is the production of ammonia (NH3) from proteins in dead organisms and urea in urine.

Nitrogen fixation is the conversion of nitrogen gas into nitrogen compounds eg. ammonia and nitrate (NO3).

Nitrification is the conversion of ammonia into nitrites and then into nitrates.

Denitrification is the conversion of soil nitrates and ammonia into nitrogen gas (N2).

There are three groups of bacteria that are involved in cycling Nitrogen:

Nitrogen fixing bacteria: which convert atmospheric nitrogen into ammonia or nitrates. They are located in soil or live symbiotically in the root nodules of some plants eg. Rhizobium sp. bacteria in Legume (Peas and Acacia spp.) root nodules and Azobacter sp. live in soil).

Nitrifying bacteria: which convert ammonia (NH3) and nitrites (NO2) into nitrates (NO3) (eg. Nitrococcus and Nitrobacter).

Denitrifying bacteria: which convert nitrates and nitrites back into atmospheric nitrogen (N2). (eg. Pseudomonas)

Question 40

Human impact issues linked to food webs and cycles

Answer 40

Salinisation of soil, eutrophication, enhanced global warming and biomagnification.

Question 41

Salinisation of soil

Answer 41

This environmental problem is linked to the water cycle.
Irrigating land (farming) and clearing land has lead to salt rising to the upper soil layers which affects seed germination and plant growth. When trees are removed there is less transpiration from plant surfaces, as a result the water table rises bringing salt in groundwater to the soil surface.

Question 42

Eutrophication

Answer 42

This environmental problem is linked to the nitrogen cycle and affects aquatic food webs.

Eutrophication involves a build up of nutrients (nitrates or phosphates) in the water which may lead to oxygen depletion.

It often occurs as the results of fertilisers entering waterways via runoff, causing a bloom of producer organisms (aquatic plants or algae) that then respire at night and deplete oxygen levels in the water, causing death and decomposition.

Question 43

Enhanced global warming

Answer 43

This environmental problem is linked to the carbon cycle. Gases (eg. carbon dioxide and water vapour) trapping heat in our atmosphere is essential for providing a temperature range that supports life.

As the human population grows, human activities that require burning fossil fuels and land clearing for urban development or agricultural use has increased resulting in an increase in levels of greenhouse gases (eg. carbon dioxide, methane, nitrous oxides, CFC’s) in the atmosphere. These gases are trapping extra heat which has a number of environmental consequences.

Question 44

Biomagnification

Answer 44

This environmental problem affects the health and reproductive ability of top order consumers in food webs. This is where non biodegradable chemicals (often fat soluble) accumulate in higher concentrations at higher trophic levels in a food web. This can lower fertility and egg shell hardness in top predatory birds.

Some examples of non-biodegradeable chemicals are: DDT, Dieldrin, Mercury.