Population size and ecosystems. Flashcards
Population definition.
A group of organisms of the same species.
Factors affecting population fluctuation.
-Births
-Deaths
-Immigration
-Emigration(decreases).
Birth+immigration=deaths+emigration(in a stable population).
Density independent factors.
Abiotic
Affect death rate
Kill members of small and large populations to the same extent
E.g. Wildfires.
Density dependent factors.
Biotic
Affect population more greatly(proportionally) if population is larger & denser
E.G. Larger pop=more food comp, more predation, more diseases, higher spreading of parasites etc.
Phases of a population growth curve for bacterium/yeast grown in nutrient broth.
Lag- Enzymes synthesised, DNA replicated
Exponential- Population doubles every unit of time, nutrients abundant
Stationary- Competition of nutrients=death and cell reproduction are equal rates
Death/decline- Nutrient depletion, toxin accumulation=death rate higher than cell reproduction.
Carrying capacity meaning.
The maximum number of individuals of a species that the environment can support indefinitely.
Phases of a population growth curve for a more complex organism e.g. grey squirrel.
Lag- Population limited by the low numbers to reproduce
Exponential- Doubling of numbers with abundant resources and low predation
Stationary phase- Fluctuation as increase in competition for resources, predation= death rate can become higher than birth rate(when pop increases
When pop decreases, competition reduced–> increases again
Continues indefinitely
Set point of fluctuation=carrying capacity of the environment.
Ecosystem definition.
An area that has a particular community of plants and animals interacting with their environment.
Community definition.
All of the organisms of all species in an ecosystem.
Habitat definition.
The place in an ecosystem where an organism lives.
Niche definition.
An organism’s role in an ecosystem
Applies particularly to it’s feeding role.
Direction of energy flow along food chains in an ecosystem.
Sunlight
Producers (autotrophs)
Primary consumer (herbivores)
Secondary consumers (carnivores)
May be more trophic levels.
Photoautotrophs meaning.
Use light energy from the sun
To fix CO2 into organic molecules (via photosynthesis)
Gross Primary Production (GPP)= rate at which this happens.
Net Primary Production (NPP).
Some organic molecules made during photosynthesis used in respiration
What is left=NPP
NPP=plant’s biomass that can be consumed by the next trophic level (herbivores).
NPP=GPP-R.
Why is not all sunlight used in photosynthesis?
May be wrong wavelength
Transmitted through leaf
Reflected
Energy is lost at every level due to respiration.
What do decomposers feed on?
Dead organism
Faeces
Urine.
Why is the number of trophic levels limited?
Because of energy losses
Eventually will not be enough left to sustain another level.
Efficiency of a transfer calculation.
little number/big number
x100.
General efficiency transfers facts.
Sun–>plant=0.2%
Plant–>herbivore=10%
Why do herbivores lose a lot of energy as faeces?
High cellulose levels
Relatively indigestible.
Why are endotherms less efficient than ectotherms?
Higher respiratory rates to produce heat
So more energy lost because of this
One reason why aquatic food chains tend to be longer.
Methods used in agriculture to reduce energy losses.
Keeping animals warm
Reducing movement
High protein feed.
Succession definition.
Change in a community and species composition over time.
Stages of primary succession.
Starts from bare rock- no organism living
Pioneer species colonise bare rock- blown in as spores
Lichens erode rock
Die then decay
Eroded rock builds up in cracks= mosses colonise (blown in as spores)
Soil accumulates= grasses, herbaceous plants, shrubs, woodlands(climax community) become established.
Climax communities.
Stable, end point of succession- no further changes
High species diversity.
Factors affecting speed of succession.
Temperature
Proximity to a source of seeds and spores to be blown in.
Sere meaning.
A stage of succession
Characterised by particular communities.
How can succession be deflected?
Grazing
Mowing
Burning
Maintaining particular sub climax communities.
Secondary succession.
Starts from cleared land
Where communities have lived before
Faster due to seeds, roots and soil to support the plants
After forest fires.
Random sampling method.
Used on a uniform area
Grid area
Generate random numbers to select co-ords
Place quadrats at co-ords
Use to asses cover %/number of organisms.
What to measure in fieldwork?
Abiotic factors that may affect results
E.g. pH, light intensity, soil, water
Use Simpson’s diversity index (counted species/organisms).
Method w/ transects.
Use when there is a change in conditions
Place quadrats at regular intervals along a line
Count/use % cover
Present data as a kite diagram.
Practical work- risks.
Biting/stinging insects
Slippery conditions
Sunburn
Hypothermia.
Methods to insure fairness/ accuracy of fieldwork.
Use correct sized grid
preliminary investigation to determine this
Carry out enough repeats
Different times of year
Successive years?
What recycles nutrients in a nutrient cycle?
Decomposers- bacteria/fungi
Use organic molecules and convert them to inorganic compounds.
Autotrophs function.
Use energy from sunlight/chemicals
Convert inorganic compounds to organic ones
Then passed along food chain.
Carbon cycle steps.
1) Plants take in CO2, use it in photosynthesis, make organic molecules, passed through food chain
2) Plants and animals respire and secrete CO2
3) Combustion releases CO2
4) Decomposers respire= releases CO2.
Carbon footprint definition.
Total amount of CO2 released attributable to an individual, product or service over the course of a year.
Human impacts on the carbon cycle.
Deforestation- less CO2 absorbed
Combustion of fossil fuels- releases ‘locked in’ CO2 to atmosphere.
Effect of CO2.
Traps heat
Raises global temperatures
Global warming.
Effects of global warming.
Species distribution- species pushed further north and south as equator gets warmer
Agricultural practices- may need to have drought resistant crops, may need crops that can survive w/ excess rain.
Factors affecting rate of decomposition.
Colder= slower
pH, more acidic= slower
O2 availability: slower when less oxygen available.
Nitrifying bacteria.
Nitrosomonas-converts ammonium to nitrite
Nitrobacter-convert nitrite to nitrate.
Nitrogen fixing bacteria.
Convert nitrogen gas to ammonium:
Azotobacter-free living in soil
Rhizobium-in root nodules of legumes, symbiotic.
Dentrifying bacteria.
Convert nitrate to nitrogen gas
Pseudomonas-thrive in water logged soils.
Rhizobium.
-Symbiotic relationship w/ legumes
-Fixes N gases to ammonium ions
-Makes amino acids
-Exports them to legumes
-Legume makes root nodule for Rhiz
-Gives it carbs, micro-anaerobic conditions(for nitrogen fixation).
Dentrification.
Nitrogen released back into atmosphere
From dentrifying bacteria
Nitrate to N gas
Anaerobic conditions, water-logged soils
Slows nitrification=nitrate poor soil.
Insectivorous plants.
Water-logged areas
Insect proteins–>amino acids.
Ploughing in agriculture.
Introduces air to soil
Encourages nitrification.
Drainage in agriculture.
Reduces water logging
Reduces dentrification.
Leaching meaning.
Soluble ammonium, nitrite and nitrate ions dissolve in ground water and drain away
Loss in nitrites.
Eutrophication.
Excess nutrients in lakes and rivers from leaching.
Algal bloom.
Microscopic algae undergoing a population bloom
As a result of eutrophication
Blocks light from bottom-dwelling plants=die
Algae die=decomposer increase=use more oxygen in water=increased biological oxygen demand
Fish and invertebrates die and are decomposed.
What do plants do with nitrates and ammonium ions?
Absorb them and use to synthesise nitrogen containing compounds
Key components in amino acids, proteins, nucleic acids, chlorophyll=photosynthesis(CO2+water).
Negatives of draining land.
Loss in species rich wetlands
Reduces species diversity.
Benefit of using wide borders around fields.
Support wild flowers(favour poor soil), pest predators, pollinators
Fertiliser=reduction in wild flowers&pollinators–>reduce species diversity.
