Chapter 23 Ecosystems

abiotic factors

light intensity

temperature

water availability

oxygen availability

clay

fine particles

easily waterlogged

forms clumps when wet

loam

different sized particles

retains water

does not waterlog

sand

coarse, well separated particles

does not retain water

energy available units

kJ m^-2yr^-1

biomass

the mass of living material present in a particular area or in particular organisms

biomass formula

biomass present in each organism x total number of organisms in that trophic level

ecological efficiency

the efficiency in which biomass or energy is transferred from one trophic level to the next

why do producers only convert 1-3% of sunlight they receive into chemical energy

most is reflected

some is transmitted though leaf

some energy lost used for photosynthetic reactions

net production formula

gross production - respiratory losses

why do consumers convert max 10% of biomass to organic tissue

not all biomass of an organism is eaten/ digested

some energy is transferred to the environment as metabolic heat

urine

ecological efficiency formula

(energy available after transfer/ energy available before transfer) x 100

decomposition

chemical process in which a compound is broken down into smaller molecules

saprotrophs

organisms which obtain energy from waste organic material and digest externally by excreting enzymes onto waste matter

detritivores

organisms which speed up decay processes by feeding on dead material and breaking it down into smaller pieces of organic material, increasing surface area

examples of decomposers

microscopic fungi

bacteria

examples of detritivores

woodlice

earthworms

nitrogen fixation

fixing bacteria containing nitrogenase combine atmospheric nitrogen with hydrogen to make ammonia which is absorbed by plants

N₂ + 3H₂ = 2NH₃

Azotobacter

free-living soil bacterium

Rhizobium

bacterium inside root nodules

how do nitrogen-fixing bacteria have a symbiotic relationships with plants

plant gains amino-acids from Rhizobium (produced by fixing nitrogen gas in air into ammonia)

bacteria gain carbohydrates produced by the plant during photosynthesis which they use as an energy source

nitrification

process in which ammonium compounds in soil are converted into nitrogen-containing molecules that can be used by plants. oxidation reaction

steps of nitrifcation

1) nitrifying bacteria (Nitrosomonas) oxidise ammonium compounds into nitrites NO₂^-

2) Nitrobacter oxidise nitrites into nitrates NO₃^-

denitrification

denitrifying bacteria convert nitrates in soil back to nitrogen gas. happens under anaerobic conditions

ammonification

process in which decomposers convert nitrogen-containing molecules in dead organisms, faeces, and urine into ammonium compounds

diagram of nitrogen cycle

carbon cycle

removed from environment through photosynthesis

some returned to atmosphere by respiration

some transferred to animals that eat plants

released as decomposers feed on dead plants/ animals

released from combustion of fossil fuels

succession

occurs as a result of changes to the environment (abiotic factors) causing the plant and animal species present to change

primary succession

occurs on newly formed/ exposed land

no soil or organic material present to begin with

secondary succession

occurs on land where soil is present but it contains no plant or animal species

examples of when primary succession takes place

volcanoes erupting creates igneous rock

sand blown by wind to create sand dunes

silt and mud deposited at river estuaries

retreating glaciers deposit rubble and expose rock

seral stages

1) barren land

2) pioneer community (colonisers)

3) intermediate community (secondary colonisers, tertiary colonisers, shrubland)

4) climax community (dominant species)

5) land altered (eg fire, disease, grazing, agriculture)

examples of colonisers

lichen

examples of secondary colonisors

mosses

examples of tertiary colonisers

grasses

examples of shrubland

shrubs

small trees

examples of dominant species

woodland

diagram of seral stages

pioneer species adaptions

able to produce large quantities of seeds/ spores

seeds that germinate rapidly

able to photosynthesise to produce own energy

tolerance to extreme environments

able to fix nitrogen from atmosphere and add to the mineral content of the soil

humus

organic component created when organisms of the pioneer species die and decompose small organic products into the soil

tertiary colonisers adaptations

waxy cuticle to prevent water loss

plagioclimax

stage in which human activities have prevented the ecosystem from reaching a climax community

how does agriculture deflect succession from occuring

grazing of vegetation results in large areas remaining as grassland

removing existing vegetation to plant crops = plant becomes final community

burning to clear forests increases biodiversity = provides space and nutrient-rich ash for other species to grow

estimated number in population m² formula

number of individuals in sample/ area of sample m²

steps of capture-recapture

1) capture as many individuals as possible in sample area

2) tag each individual

3) release tagged individuals back into sample area and allow time for them to redistribute themselves throughout the habitat

4) recapture as many individuals as possible in the original sample area

5) record the number of tagged and untagged individuals present in the sample

6) use Lincoln index to estimate population size

Lincoln index formula

(number of individuals in first sample x number of individuals in second sample) / number of recaptured marked individuals

Simpson’s Index of Diversity formula

D = 1 - ∑ (n/N)²