Ecosystems Flashcards
(a) Define the term ecosystem;
A self-contained community together with all the physical features that influence the community, and the interactions between organisms (biotic factors, e.g. competition for mates, food) and their environments (abiotic factors – physical; changes in salinity, temperature, altitude (examples for salmon)).
Ecosystems are dynamic systems; in which the organisms (biotic factors) are affected by one another and by factors such as light intensity and temperature (abiotic factors). Population sizes vary due to different factors; e.g. increased predators population = prey population decreasing.
(b) Define the terms biotic factor and abiotic factor, using named examples;
Biotic factor; how living organisms affect each other; the living components of an ecosystem.
E.g. Food supply, predation, disease.
- *Abiotic factor;** the effects of non-living components of the ecosystem
e. g. water/soil pH, temperature, soil type, water availability
(a) Define ‘producer’
An organism that converts simple inorganic compounds (e.g. carbon dioxide, water and ions) into complex organic compounds. Most use light to provide the energy to drive the reactions involved. They are autotrophic (photoautotrophic; uses light, e.g. photosynthesis, chemoautotrophic; uses redox reaction, e.g. ammonia > nitrates in nitrifying bacteria), found on the first trophic level, and convert light energy into chemical energy.
(b) Define ‘consumer’
An organism that gains energy from complex organic matter (e.g. herbivores, carnivores, omnivores, detritivores, decomposers, parasites). Eats other organisms (e.g. animals and birds).
Primary consumers are found on the second trophic level, and feed upon producers; heterotrophic nutrition (breaks down complex organic compounds to simple inorganic compounds, releasing energy), usually herbivorous.
Secondary consumers are found on the third trophic level, and feed upon primary consumers; heterotrophic nutrition, usually carnivorous.
(c) Define ‘decomposer’
An organism that feeds on waste from other organisms, or on dead organisms, and waste products. It breaks down dead or undigested organic material, e.g. bacteria and fungi. Saprotrophic nutrition (type of heterotrophy). Digests shit extracellularly, e.g. enzymes are secreted onto bread, digested to starch, digested to sugars.
(d) Define ‘trophic level’
A stage in a food chain occupied by a particular group of organisms; each feeding level in a food chain.
(e) Describe how energy is transferred though ecosystems;
Main route of energy entering an ecosystem is via photosynthesis. Some sea ecosystems have energy entering where bacteria use chemicals from deep sea vents as an energy source.
Energy is transferred by organisms consuming each other; each trophic level consumes the one above. This is shown in a food chain/web, with the arrows representing the flow of energy between organisms.
Energy locked up in things that can’t be eaten (e.g. bones, faeces) are recycled back into the ecosystem by decomposers.
(f) Outline how energy transfers between trophic levels can be measured;
The energy content of samples of organisms from each trophic level is measured:
- The sample is dried to constant mass in an oven
- The sample is weighed (constant mass bit)
- Burned in oxygen in a bomb calorimeter
- The heat energy produced by the oxidation passes to a known mass of water, and the temperature rise(change) of the water is measured
- How much energy released per gram is calculated; given that 4.12J of heat energy raises the temperature of 1g of water by 1oC.
(g) Discuss the efficiency of energy transfers between trophic levels;
Relatively inefficient; rarely greater than 10% of energy is transferred to the next trophic level. Not much energy reached animals at the top of food chains, hence their rarity.
Energy is lost in food chains, between trophic levels, because animals:
- Never eat all the available food
- Cannot digest all the food they eat
- Use energy in their respiration so they can move, hunt, chew, reproduce, etc.
- Lose heat energy to their surroundings
- Lose energy in urine and faeces: but this energy may pass to decomposers.
Energy is lost in producers, plants, because:
- Plants respire
- Leaf fall = dead leaves are wasted energy
- Active transport
- *Producers**: Respiration, Leaf fall, Active transport.
- 10% energy available to next trophic level*
- *Primary consumer**: Respiration, Excretion, Movement, Creation of gametes, Cellulose hard to digest; not all parts of a plant are eaten.
- 10% energy available to next trophic lev*el
- *Secondary consumer**: Respiration, Excretion, Movement, Creation of gametes, bones + fur not eaten; not all of the primary consumer is consumed.
Net productivity = gross productivity – respiratory loss
= 8000 – 6000
= 2000 kJm-2yr-1
(h) Explain how human activities can manipulate the flow of energy through ecosystems;
Human activities in farming, forestry and fishing manipulate the flow of energy through an ecosystem by altering the productivity of one or more trophic levels. E.g:
- Replacing natural vegetation and fauna with crops and livestock
- Deflecting natural succession to maintain grassland
- Increasing productivity of producers through soil improvement, irrigation (the artificial application of water), fertilisers, and removal of competing weeds, damaging pathogens, and pests (herbicides; crops receive more energy as don’t have to compete with weeds for energy/fungicides; more energy for growth instead of fighting infection/insecticides; less biomass lost).
- Increasing productivity or producers an consumers through selective breeding or genetic engineering
- Sheltering organisms for damaging environmental factors
(i) Describe one example of primary succession resulting in a climax community;
Primary succession: A type of succession that involves the change from bare ground towards a climax community (The final, stable community of k-strategists at the end of succession).
A sand dune:
- Pioneer species such as sea rocket and prickly sandwort colonise the sand just above the high water mark. These can tolerate salt water spray, lack of fresh water, and unstable sand.
- Wind-blown sand builds up around the base of these plants, forming a ‘mini’ sand dune. As plants die and decay, nutrients accumulate in this mini dune. As the dune gets bigger, plants like sea sandwort and sea couch grass colonise it. Sea couch grass has underground stems to help stabilise the sand.
- With more stability and accumulation of more nutrients, plants like marram grass and sea spurge start to grow. Marram grass is special: it shoots trap wind-blown sand and, as the sand accumulates, the shoots grow taller to stay above the growing dune. This traps more sand.
- As the sand dune and nutrients build up, other plants colonise the sand. Many, such as hare’s-foot clover and bird’s foot trefoil are members of the legume family (beans). Bacteria in their root nodules convert nitrogen into nitrates; with nitrates available, more species like sand fescue and viper’s bugloss colonise the dunes. This stabilises them further.
- Fescues and ragwort colonise the sand due to deeper soil created from marram grass growing and dying; improving water availability. Shrubs then take over; e.g. scrub willow.
- The roots stabilise the soil, and gradually the plants get larger becoming trees; species richness/diversity increases, eventually reaching a climax community such as oak woodland. A climax community is the final stage in succession and is in equilibrium with its environment.
- Grazing, trampling, burning, mowing or application of a selective herbicide will prevent succession as it stops the development of the next sere; deflected succession.
Bare rock to woodland:
- Algae, lichens and mosses are the first colonisers on bare rock; the pioneer community. Lichens grown on and break down rocks, releasing minerals.
- Erosion of the rock and a build-up of dead and rotting organisms produces enough soil for larger plants like mosses and ferns to grow; vascular plants, replacing/succeeding the algae and lichens. Colonisation is faster now as vascular plants can take root without the lichen and moss stage.
- Eventually, larger plants succeed the small plants; soil is deep enough (thickens with dead organic matter, deeper it is the more water can move in, larger plants out-compete and succeed the previous) to support shrubs, and then trees, until a climax community is reached
Pioneer species:
- Are able to tolerate extreme conditions, e.g. low nutrient levels
- Have a very good means of dispersal, usually by wind
- Are not able to compete for resources, e.g. light
- Are not influenced by or dependent on animal species
- May be able to fix nitrogen (e.g. legume) and build up soil nutrients
Climax community species:
- Have large seeds (w/large energy store) so that seedlings can survive low light intensity
- Have a specialised niche, e.g. as an epiphyte
- Are unable to tolerate great fluctuations in the water content of soil
- Are strongly influenced by other organisms (biotic) e.g. competitors, herbivores, pollinators, seed-dispersal agents and soil microorganisms.
(i) Describe how the distribution and abundance of organisms can be measured using line transects:
• Lines across a habitat; all the species touching the line are identified and the position is recorded.
(j) Describe how the distribution and abundance of organisms can be measured using belt transects:
• Quadrats placed sequentially (in a sequence) along a line transect; making the transect wider.
(k) Describe how the distribution and abundance of organisms can be measured using Quadrats:
• A square frame of appropriate size for the area to be surveyed placed at random in the habitat, within you which identify what species are present and estimate the abundance of each by: percentage cover, counting the number of individuals, finding the species frequency (proportion of quadrats with a particular species in them), or subjective scales.
(l) Describe how the distribution and abundance of organisms can be measured using point quadrats;
• Frames with long pins that are lowered vertically; each species that touches a pin is recorded, together with the total number of times it is touched.
