population size and ecosystems Flashcards
how are ecosystems dynamic?
- intensity of energy flowing through varies
- biological cycles vary mineral availability
- habitats change as succession occurs
- species arrive and leave
what determines population size?
- birth rate (hatching, binary fission)
- death rate
- immigration
- emigration
fugitive species
- poor at competition
- rely on large scale reproduction and dispersal
- invade new environments rapidly
e.g. algae colonising bare rock
equilibrium species
- control population by competition in a stable habitat
- sigmoid (s-shaped) curve of growth = one-step growth curve
e.g. bacteria in fresh nutrient solution
lag phase
- period of slow growth, adaption or preparation for growth
- cells adjust to new conditions
- intense metabolic activity for enzyme synthesis
- the time to reach sexual maturity, find a mate and gestate young in sexually reproducing organisms
log/exponential phase
- numbers increase, more individuals available for reproduction
- no factor limiting growth
- bacterial population doubles per unit time
- cell numbers increase logarithmically
stationary phase
- birth rate = death rate
- maximum population, fluctuates around carrying capacity in response to environmental changes
death phase
- factors that slow population growth become more significant
- negative gradient
environmental resistance
environmental factors that slow population growth
environmental resistance examples
- food availability
- overcrowding (not enough space or nesting sites)
- competition
- accumulation of toxic waste
biotic
a part of the environment of an organism that is living
biotic factors examples
- predation
- parasitism, disease (infection spreads rapidly)
- competition for other species for nesting sites and food
abiotic
a part of the environment of an organism that is non-living
abiotic factors examples
- temperature
- light intensity
- oxygen availability
predator prey relationships
- negative feedback
- abundance of prey limits the number of predators that can survive, and the number of predators controls the number of prey
- e.g. snowshoe hare and lynx
density dependent factors
environmental factors that affect a greater proportion of the population if the population is denser
- biotic factors (disease)
e.g. parasites are transmitted more efficiently so a larger number are effected
e.g. higher prey density = predators encounter more prey = more prey eaten
density independent factors
abiotic factors (suddenly change) in the environment that don’t depend on population density
same effect regardless of population size
e.g. flood, fire
carrying capacity
the maximum number around which a population fluctuates in a given environment.
around a set point
why are physical features in a habitat described first?
physical features (soil type, temp) determine the number and types of plants
animals present depend on the types of plants
abundance
the number of individuals in a species in a given area or volume
a measure of how many individuals exist in a habitat
measuring animal abundance
- capture-mark-recapture for moving organisms, using lincoln index
- kick sampling in a stream and counting invertebrates. unreliable if misidentified, escaped or miss the net
capture mark recapture assumptions
- few/no deaths or births
- no immigration or emigration
- marked individuals redistribute themselves evenly among the population
- all organisms have equal chance of capture/recapture
- marking method is not toxic / doesn’t make more conspicuous to predation
- marking is not lost
measuring plant abundance
- quadrat. calculate mean no. individuals in known area to find density
- estimate % cover with individuals hard to recognise
- estimate % frequency
distribution
the area or volume of which the organisms of a species are found
line transect
shows the organisms that lie on a line, at measured intervals
belt transect
shows abundance data for a given area at measured distances along the transect.
a quadrat is placed at each coordinate
e.g. shown in a kite diagram but rounded numbers reduce accuracy
readings taken from a belt transect
- density of chosen species
- % frequency of chosen species
- % area cover for all species
what can’t be measured by a transect
motile animals as they move
instead done by direct observation of individuals or nests, faecal deposits or vegetation markings
ecosystem
a characteristic community of interdependent species interacting with the abiotic (soil, air) components of their environment
components linked by energy flow and nutrient cycling
community
many species living and interacting together
types of ecosystems
- small (human large intestine)
- large (ocean)
- temporary (puddle)
- permanent (lake)
energy
the ability to do work
allows changes to occur
law of thermodynamics
a sequence of energy changes allow the functioning of an ecosystem
energy flows through the components of the ecosystem
habitat
the place in which an organism lives
an ecological or environmental area inhabited by a living organism
provides the means of survival (food, water, soil, temp, pH)
may be inside an organism
microhabitat
a very small area that differs from its surroundings
features suitable for a particular species
community
interacting populations of 2+ species in the same habitat at the same time
- relates to distribution, abundance, genotypic/phenotypic differences, food web structure, predator-prey relationships
biomass
the mass of biological material in living / recently living organisms
ultimate source of energy for ecosystems
photosynthetic organisms convert sunlight energy into chemical energy, passes down organisms through a food chain
trophic level (feeding level)
the number of times that energy has been transferred between the Sun and successive organisms along a food chain
food chains
a means of transferring biomass
shown as a linear sequence of organisms in a food chain
food chain steps
- producers (simple inorganic compounds to complex organic molecules) incorporate sun’s energy into carbs
- they trap solar energy and synthesise sugars by photosynthesis
- little incorporated into plant tissues
decomposition
when producers and consumers die energy remains in the organic compounds
dead tissues breakdown and are converted into simpler organic compounds
saprobiont
microorganism that obtains its food from the dead / decaying remains of other organisms
detritivores and decomposers feed as saprobionts
- contribute to recycling of nutrients
detritivores
organisms which feed on small fragments of organic debris (remains of dead organisms and fallen leaves - detritus)
e.g. earthworm, woodlice
decomposer
microbes that obtain nutrients from dead organisms and animal waste
complete process of decomposition started by detritivores
e.g. bacteria, fungi
food web
shows how organisms in a community interact with each other through the food they eat
why are food chain lengths limited?
no more than 4 or 5 trophic levels
energy is lost at each link and there is not enough to support another
inefficient transfers due to undigestible material (bones), lost as heat, lost via respiration
factors determining the length of a food chain
- the more energy entering the 1st trophic level = longer, e.g. tropical (light all year round) food chains longer than Artic
- energy transferred more efficiently = longer
- predator prey populations fluctuate, so relative abundance affects length
- larger ecosystem = supports longer chain
- 3D environment (aquatic, forest canopy) = longer than 2D (grassland)
why does 60% of light energy falling on a plant not be absorbed by photosynthetic pigments?
- wrong wavelength
- reflected
- transmitted through leaf
- strikes non-photosynthesising parts
- only small % utilised
photosynthetic efficiency (PE)
measure of ability to of plant to trap light energy
higher in crop plants
- depends on: plants genotype, environmental factors, if selectively bred for high productivity
PE equation
quantity of light energy incorporated into product (divided by )
quantity of energy falling onto plant
(times 100)
gross primary productivity (GPP)
amount of chemical energy stored in the carbohydrates within plants
-the rate of production of chemical energy in organic molecules by photosynthesis, in given area and time
- large proportion released by respiration of plant (for protein synthesis)
- 1%
net primary productivity (NPP)
energy in the plants biomass available to primary consumers
- food available to primary consumers / crop yield
- GPP - respiration
- 0.5%
primary productivity
the rate at which energy is converted by producers into biomass
10% efficiency
secondary productivity
rate at which consumers convert chemical energy of food into biomass
- accumulation of assimilated food in biomass in cells/tissues
- occurs in heterotrophs (animals, fungi, bacteria, Protoctista)
20% efficiency
how is energy lost along a food chain?
- energy in egested molecules.
- energy lost as heat. after processes fuelled by energy generated in respiration (muscle contraction)
-energy remains in molecules uneaten (horns, bones, fur)
herbivore vs carnivore energy transfer
- cows feed on plants (cellulose) digested by mutualistic micro-organisms, remains pass out as faeces (undigested material), provides energy for decomposers. 60% energy lost as waste products.
- carnivore protein-rich diet is readily and efficiently digested. 20% energy lost as waste products.
efficiency down food chain
- herbivores have 10% conversion efficiency of ingested energy into biomass and they don’t eat all the vegetation
- carnivores have 20% efficiency, food easier to digest
efficiency of energy transfer equation
energy incorporated into biomass after transfer
(divided by)
energy available in biomass before transfer
(times 100)
ecological pyramid
a diagram that shows the a particular feature of each trophic level in an ecosystem
but don’t take into account some organisms operate at multiple levels
pyramid of numbers
- how many organisms at each level
- easy to construct
- but: doesn’t consider organism size, difference between old and young, large number range (scale issue), may be inverted
pyramid of energy
- shows how much energy is transferred between levels (organisms burned in calorimeter)
- most accurate
- as material passes up, energy is lost, so bars decrease
- never inverted
- easy to compare efficiency of energy transfer between levels
pyramid of biomass
- mass of living material at each level
- but: difficult to measure accurately (plant roots), don’t indicate productivity, may be inverted, not representative (not all mass transferred like bones), species with similar biomass may have different life spans (not comparable)
standing crop
the mass of individuals present at a given time
succession
the change in structure and species composition of a community over time
- over decades (after wildfire)
- over 10000s years (after mass extinction)
(climatic) climax community
a stable, self-perpetuating community that has reached equilibrium with its environment, no further change
- stable community
- complex food web
- species diversity
primary succession
change in structure and species composition of a community over time in an area not previously colonised
- sequence of changes following introduction of new species
primary succession stages
- pioneer species colonise bare rock
- plants change the environmental conditions
- better adapted plants colonise
- rock weathering / erosion / decaying matter = primitive soil forms
- animals can survive (ants, spider)
- wind-blown spores allow moss growth
- outcompeted by small plants / grasses
- tall grass = shade-tolerant species established
- death/decay = thick soil, minerals, humus
- effectively holds water
- soil builds = deep rooted plants (shrubs, trees)
- soil deepens
- large trees outcompete small ones = stable, climax community
- tree canopy limits light = floor diversity decreases
pioneer species
the first species to colonise a new area in an ecological succession, e.g. algae, lichen
form a pioneer community
sere
sequence of communities, with different species and structures
xerosere
sere in a very dry environment
seral stages
stages in succession when particular species dominate
each change the environment = more suitable for other species
climax community is balanced with equilibrium between:
- GPP + total respiration
- Energy used from sunlight + released by decomposition
- soil nutrient uptake + return by plant / animal decay
- new growth + decomposition
as xerosere progresses, the following increases:
- soil thickness
- water availability
- humus
- minerals
- biomass
- biodiversity
- resistance to new species invasion
- stability to disruption by environmental challenges
secondary succession
changes in a community following disturbance/damage to a colonised habitat.
rapid recolonisation of a habitat after fire/tree felling
- seeds/spores may remain in soil
disclimax
prevention of development of a climatic community due to human interference
causes of a disclimax
- grazing sheep / cattle, good for grass but prevents tree growth
- farming removes species
- deforestation removes tree communities
factors affecting succession
- migration
- competition (inter/intraspecific)
migration affecting succession
arrival of new species (spores, seeds, animals) is vital
- non-native species affect community and soil
competition affecting succession
- plant compete for light, space, water, nutrients. animals for food, shelter, space, mates.
- operates at seral stages
- species with competitive advantage survive
intraspecific competition affect on succession
individuals of same species, density dependent
- higher population = higher competition
- organisms produce more offspring than habitat can support = regulates numbers
- best suited alleles = successfully reproduce
interspecific competition affect on succession
different species
- each has own niche
- occupy a particular area and a particular role in community
- less competitive species replaced
niche
describes an organisms way of life
- the role/position a species has in an environment
- all interactions with biotic and abiotic factors
competitive exclusion principal
when 2 species occur in the same niche, 1 will outcompete the other
facilitation
to enable something to happen
- positive interactions
- significant as succession progresses = complex communities
- provides better resource availability
- provides refuse from physical stress, predation, competition
e.g. mutualism, commensalism
symbiosis
the association between individuals of 2 species.
highly interdependent or loose association
mutualism
- an interaction between 2 species, beneficial to both
e.g. flowing plants + pollinators, close association of fungi + plant roots
commensalism
- interaction between 2 species, 1 benefits, 1 unaffected
e.g. squirrel sheltered in a tree ( tree not affected) - over time species evolve = relationships change, e.g. parasite may become useful, providing nutrients = commensal
why has carbon dioxide concentration increased in the atmosphere?
- burning fossil fuels releases locked up CO2
- deforestation removes photosynthesising biomass, so less CO2 is removed
3 major biological processes in the carbon cycle
- respiration: CO2 added to atmosphere by living organisms and combustion of fossil fuels
- photosynthesis: takes in CO2 from atmosphere, large scale
- decomposition: decomposers break down detritus releasing CO2.
compression of carbon in consumers in the sea
- in aquatic ecosystems CO2 (as bicarbonate) is combined with minerals, = calcium carbonate shells and sea creature exoskeletons (sink after death)
- carbonates become components of chalk, limestone, marble. lost from the biosphere. if exposed to atmosphere = eroded = release CO2
human impact on carbon cycle
- deforestation
- climate change
- greenhouse effect
- global warming
deforestation and carbon cycle
- rate of CO2 atmospheric removal by photosynthesis reduced
- global scale = massive reduction, contributes to global warming
- trees felled = burned or decayed = releases CO2
- increases CO2
climate change (temp ,rain, wind) and carbon cycle
- rise in CO2 and greenhouse gases
- burn fossil fuels: increased industrialisation and global transport = steep increase in emissions
- deforestation: forests affects maintenance of CO2 balance
- more greenhouse gases absorbing radiation = global warming
global warming
the increase of average global temps in excess of greenhouse gas effect cause by atmospheres historical CO2 concentration
greenhouse effect and carbon cycle
- gases include: CO2, methane, water vapour, nitrous oxide)
- allow high energy, short wavelength solar radiation to reach earth surface
- absorbed by earth = warms up, re-radiates low energy, low wavelength IR radiation, then absorbed and trapped by gases = then reabsorbed = warming
- natural process to sustain life
global warming and carbon cycle
enhanced greenhouse effect caused by high CO2 due to human activities
consequences:
- polar ice melt = coastal flooding
- increased extreme weather and forest fire frequency
- decreased water in tropical areas = deserts expand/form
- animals move (slow to adapt), plants move slower = extinction = extinct animals depending on plants = ecosystems collapse
- fishing / crop-growing belts move
- increased crop yields, higher photosynthesis
- decreased food production = economic issues
- higher ocean CO2 = lower pH = threatens organisms. coral reefs soluble in acid.
farming and global warming
affected by temp changes and timing/quantity of rain.
more flooding/droughts, less water to sustain production
reduced water supply depletes yields
how to improve soil quality
- conservation tillage: leave crop residue on soil surface, reduces erosion. improve water use.
- add organic matter to top soil
- cover crops: enhances soil structure.
- crop rotation: reduce pests and mineral repletion
how to reduce effects of methane from dairy/meat farming
- reduce meat / dairy dietary intake
- high-sugar grass, oats in cow diet reduces methane release
how to reduce methane release from decomposition of wet soils (rice paddies)
- use rice varieties that grow in drier conditions
- ammonium sulphate added favour non-methane producing microorganisms
how to reduce nitric/nitrous oxide released from anaerobic and waterlogged soils
- improve drainage
- remove water
- aerate soil (ploughing)
how to improve water supply due to low rain and high temps
- use drought tolerant crops
carbon footprint
the total amount of CO2 generated by an individual, product or service in 1 year.
measures a contribution to greenhouse gases in atmosphere
indirect sources of greenhouse gases from crop farming
- farming tools production
- insecticide, herbicide, fertiliser production
- farm machinery powered by fossil fuels
- transport of produce
how to reduce greenhouse gas production
3 Rs: reduce, reuse, recycle
- recycle packing material
- drive less
- use less air conditioning and heating (dress appropriately)
- reduce animal protein, rice, imported food, packed/processed food intake
- avoid food waste (compost)
- plant trees in deforested regions
the nitrogen cycle
the flow of nitrogen atoms between organic and inorganic compounds, and atmospheric nitrogen gas in an ecosystem
nitrogen fixation steps
- nitrogen = triple bond = stable. few have the enzyme to break bond.
- reduction of nitrogen molecules (N2 gas) in atmosphere) to ammonium ions
- azotobacter (to ammonium ions) and rhizobium (to ammonia used by plants)
- N2 gas diffuses into legume root nodule, nitrogenase catalyses reduction to ammonium ions (ATP, aerobic)
- poisoned by oxidising conditions
- root nodules contain leg-haemoglobin = pink
- ammonium ions to organic acids to amino acids (incorporated into proteins), some used for plant metabolism
azotobacter
free living nitrogen fixing bacteria in soil
- atmospheric nitrogen to ammonia, taken up by plants
rhizobium
bacteria in roots of legumes, symbiotic with plants
- atmospheric nitrogen to ammonium ions in soil
ammonification / putrefaction steps
- decomposers secrete enzymes to decay dead organisms / animal products
- proteases digest proteins into amino acids
- deaminases remove NH2 group from amino acids = reduced to ammonium ions
-Nitrogen compounds in waste products (e.g. urine and faeces) and dead organisms are converted into ammonia by saprobionts (a type of decomposer including some fungi and bacteria)
This ammonia forms ammonium ions in the soil
how are nitrogen fixing bacteria symbiotic with plants?
- bacteria provide plants with nitrogen containing compounds
- plants provide bacteria with organic compounds (carbohydrates)
nitrification steps (addition of nitrogen to soil)
- ammonium ions converted to nitrites, then nitrates
- nitrifying bacteria require aerobic conditions for oxidation reactions
- nitrosomas and nitrobacter
nitrosomonas
convert ammonium ions to nitrites
nitrobacter
convert nitrites into nitrates
denitrification steps (loss of nitrogen from soil)
- Denitrifying bacteria (anaerobic bacteria - pseudomonas) use nitrates in the soil during respiration
- producing nitrogen gas, which returns to the atmosphere
- occurs in anaerobic conditions (little or no oxygen available, waterlogged soil)
nitrogen fixation definition
reduction of nitrogen atoms in nitrogen molecules to ammonium ions, by prokaryotic organisms
non-biological processes that impact the nitrogen cycle
- agricultural fertilisers add nitrogen to soil
- lightning adds nitrogen to soil
- leaching of minerals removes nitrogen from soil
ways to improve nitrogen circulation
- ploughing
- drainage
- artificial nitrogen fixation
- animal waste
- slurry
- treated sewage sludge
- planting legumes
how does improve ploughing nitrogen circulation?
improves soil aeration, favouring:
- aerobic organisms (nitrogen fixers) enhancing NH3 formation
- nitrifying bacteria, enhances NH3 to nitrites + nitrates
- roots respiring aerobically = ATP, fuels uptake of minerals
how does drainage improve nitrogen circulation?
removal of water = air enters soil
reduces anaerobic conditions = inhibits denitrifying bacteria
reduces nitrate loss
how does artificial nitrogen fixation improve nitrogen circulation?
e.g. Haber process (forms ammonia)
- industrial processes convert nitrogen to fertilisers to produce food.
- fertilisers contain NH3 and nitrate ions = increases ions produced by nitrogen fixing and nitrifying bacteria
how does animal waste (collected from farms) improve nitrogen circulation?
- manure contains nitrogen and nutrients for plant growth
- improves soil structure = holds more nutrients and water = more fertile
- encourages microbial activity = promotes mineral supply = improved plant nutrition
- nitrogen compounds gradually released to soil
how does slurry (manure + water) improve nitrogen circulation?
- produced by livestock rearing systems
- injected into soil
- preserves soil structure
but smelly (herbivore manure less so)
how does treated sewage sludge improve nitrogen circulation?
- biosolids
- sustainable alternative to inorganic fertilisers
how does planting legumes improve nitrogen circulation?
- enhances nitrogen fixation
- crops die = ploughed back into soil as green manure (high nitrogen content)
oligotrophic
few dissolved minerals in upland streams
eutrophic
water enhanced with minerals
dystophic
mineral concentration so high that organisms die
eutrophication
processes / artificial enrichment of aquatic habitats by excess nutrients, caused by fertiliser run off
- nitrogen containing fertilisers leach from agricultural land, increasing mineral content of water
eutrophication stages
- mineral ions (nitrates) from excess fertiliser leach into waterways
- causes rapid growth of algae = algal bloom
- blocks sunlight and water becomes green. light can’t penetrate
- plants below the surface die as can’t photosynthesise
- algae die when competition for nutrients increases
- aquatic plants and algae die = decomposing bacteria feed on dead organic matter
- animal species diversity decreases
- decomposers respire aerobically using up dissolved oxygen
- dissolved O2 content in water decreases
- aquatic organisms die
- anaerobic bacteria release gases
biochemical oxygen demand (BOD)
- created by decomposers
- represents the amount of oxygen consumed by bacteria / microorganisms while they decompose organic matter under aerobic conditions
how to reduce the quantity of nitrogen entering waterways
- restrict amount of fertiliser applied
- only apply fertiliser during growing season = readily used, not leached
- leave area 10m from water untouched
- dig drainage ditches (mineral concentrate in them and undergo eutrophication = protects natural watercourse)
