populations Flashcards
population
the total number of organisms of a single species interbreeding within a habitat
habitat
the physical place where an organism lives
birth rate
the number of new indivduals derived from reproduction per unit time
immigration
the moment of individuals into a population
What is the equation for population size
- birth rate + immigration - death rate + emmigration
What are the four phases for population change
- lag phase
- exponential phase
- stationary phase
- death phase
decribe what happens during the lag phase
- period slow growth
- sexually reproducing organisms eg rabbits this represent the time takes to reach sexual maturity in gestating young
Describe what happens during the log phase
- growth phase
- number increase logarthimically as there are no factors limiting growth
- this cannot be maintinained indefinitley as environmental resitstance reduces growth from the avaiiabikity of food and space and other biotic factors such as predation competition, parasitism and disease and abiotic factors such as soil Ph light intensity and temperature which also reduce population growth
Describe what happens during the stationary phase
- birth and death rates are equal and the population has reached its maximum size or carrying capcity
- numbers will fluctuate around this in response to environmental changes
- often due to predator prey relationships where negative feedback regulates
- eg number of prey decrease so there is less food so number of predators decrease which reduces predation so prey number increase and so on
- these fluctuations exist over months even years as population responses are slow
What happens during the death phase
- factors that have reduced population growth become more significant and the population size decreases
- death exceeds births
Biotic factor
living factor
eg a predator or pathogen which can influence the population
abiotic factor
a non living factor
eg oxygen availability or air temperature which can influence the population
carrying capacity
the maximum numer around which a population fluctuates in a given environement
negative feedback
occurs in an equilibrium where the corrective mechanism is in the opposite direction to the direction of change eg if population number increae negative feedback results in a decrease and vice versa
What are density dependent factors and give two examples
- some factors have an increased effect on larger population sizes
- are biotic factors eg predation and disease
- in large populations disease is more easily spread and a predator can find prey more easily
What are density independent factors an give two examples
- are abiotic
- light intensity or temperature
- therefore their effect is the same regardless of the population density
- eg fire it will kill all life in its path wherther it is one tree of hundreds
Describe what an abundance of species is
- measure of how many individuals exist in a habitat
How can an abundance of a species be assessed
- physical features - soil type Ph and temperature will influence the range of organims that can live
Why should sampling me bias
to eliminate sampling bias
]Describe how you can sample terrestrial animals and what are the assumptions
- mark release recapture
- animals are captured and marked (not harmed or made more visible to predators) and then released
- once animals have had chance to reintegrate with the population the traps are reset
- the total population size can be estimated using the number of individuals captured in the second sample and the number in that sample are marked
- (no sample 1 x no sample 2)/no marked in sample
- have to assume no briths/deaths/immigration/emmigration have occurred during the time between collecting both samples
Describe how samples are taken of freashwarer invertebrates
- use kick sampling and simpsons index
- collect and identify invertebrates from a given area using a quadrat and a net
- kick or rake the area for a set period and collect invertebrates in a net downstream
- release invertebrates carfully and use simpsons index to calculate diversity
Describe how plants can me sampled
- quadrats and transects
- estimate percentage area cover of different plants using a quadrat divided into 100 sections
- measure plant density by counting number of plants in a quadrat
- a transect is a tap measure that is used to measure intervals along an environmental gradient eg distance from a woodland along which quadrats can be placed
ecosystem
a community in whcih energy and matter are transferred in complex interactions between the environment and organisms involving abiotic and biotic elements
producer
the autotrophic organism at the start of a food chain converts light energy into chemical energy
trophic level
the feeding level within a food chain and shows the number of times that energy has been transferred to successive organisms along a food chain
biomass
the mass of biological material in living or recently living organisms
What does an ecosystem represent and what varies between them
- the total number of different organisms of all species present in a habitat in which energy and matter are transferred in complex interactions between the environment and organisms
- abiotic and biotic features vary from ecosystem to ecosystem
Give examples of ecosystems
- tropical rainforest, temperature decidueous forest, tundra and desert
What does a food chain represent
the enrgy flow through an ecosystem
describe the flow of energy through a food chain
- the ultimate source of energy for a food chain is sunlight whcih is converted into chemical energy by producers via photosyntheis
- most of the nergy available at each trophic levels is released in respiration and incorporated into other molecules or into electrochemical gradients
- this means that often less that 10 % is incorporated into biomass and is available to thge next trophic level which limits the length of food chains
What are primary consumers
herbivores and feed on producers
What are secondary and tertiary consumers
- include carnivores and feed on the trophic level below
What does decomposition involve and what do decomposers feed on
- detritivores eg earthworms and woodlice
- these feed on detritus (the remenants of dead orgnaisms and fallen leaves)
- decomposers eg bacteria and fungi that feed via external digestion(saprotrophism) completing the process started by detritivores
- on all trophic levels and other decomposers
Why is the majoirty of light not absorbed by pigments in chloroplasts
- wrong wavelength
- reflected by leaf surface
- transmitted through the leaf without striking a chlorophyll molecule
How is photosynthetic efficiency calculated
quantity of light energy fixes on plant/quantity of light energy falling on plant x 100
gross primary productivity
the rate of production of chemical energy in organic molecules by photosynthesis in a given area in a given time measured by KJM-1Y-1
net primary productivity
the energy in plants biomass which is available to primary consumers measured in KJM-1y-1
how is net primary productviity calculated
GPP - respiration
Why is the true value of NPP lower than usual
- some of the biomass is used to form inedible material eg bark or is biomass in roots which is out of reach or primary consumers therefore the true value available is even lower
Describe one place that has a very high NPP and a lower NPP
- High NPP inclue tropical rainforests due to plentiful rainfull, high light intensities and warm temperatures
- tundra as a much lower NPP due to the environment being cold with much lower light intensities
Describe the energy glow through food chains
- transfer of energy in the form of biomasss from one trophic level to the next is relativley low at around 10 % or less
- in a primary producer up to 60 % is lost typically in excretion and egestion (urine and faecres)
- 30% is lost as heat in respiration
- proportion of chemical energy of food which consumers covert into biomass is referred to as the secondary production
Why is the transfer of energy higher in carnivores than herbivores
- around 20% due to the fact that they can digest their protein rich diet more efficiently and is important because the energy available at the end of a food chain is very small
- up to 60% is lost in faeces and urine from a primary consumer in a top carnivore it is 20% due to cellulose rich diet in herbivores which despite several adaptations much energy is not obtained
what is the equation to calculate the efficieny of energy transfer
energy fixed as biomass/energy available to the next trophic level x100
What do pyramid of number represent and what does it not account for
- relativley easy to construct and shows the energy flow through a food chain as energy is lost at each stage fewer individuals can be supported
- doesn’t take account the size of the organisms
Describe what a pyramid of biomass represent
- is more accurate but difficult to measure
- may also be inverted which can happen when organsims have a rapid life cycle and so numbers are replenished very quickly eg phytoplankton where total biomass over a year is considerable higher than at any given time
- difficult to calculate (measure mass of tree rotts)
WHat is the most accurate way of representing feeding relationsips
- pyramids of energy
- show more clearly the energy lost at each level but are difficult to calculate
What can no pyramid show
some organisms operate at serveral trophic levels
succession
the progressive changes in the structure and species composition in a commiunity over time
What does each satge of succession show
- known as the seral stage where different communities cominate as they outcompete pre existing species as conditions are more favourable for them
Describe the features of ecosystmes
dynamic and subject to change over time
How long for succession occur for
tens to thousands of years
Describe what does succession mean
change in the composition of community over time
When does primary succession occur give examples
when organism invade spaces that did not previouly support life
eg bare rocks, sand dunes, volcanic flows
Describe the seral stages of succession
- weathering creates small cracks in the rocks and small particles
- mossess and lichens begin to colonise organic matter builds up slowly
- legume begin to grow as they are able to fix atmospheric nitrogen to supplement the poor nutrient soil as they die soil becomes enriched
- grasses and ferns start to grow sheltering the soil from the elements soil and its moisture content increases
- large shrubs and small trees colonise leaf litter greatly increases fertility and humus content of the soil habitats created fro nesting birds and soil invertebrates so diverisity increases
- climax woodlands is reached this is usually oak,beech,hazel or lime species but is largely deciduou in southern uk ground flora includes backen shrubs and bluebells
What changes as succession progresses
- soil depth increases
- nutrient content increases
- humus content increases therfore water content increases
- species diversity increases
- stability of community increases
What is secondary succestion
secondary succession is the reintroduction of organims into a habitat previously occupied by plants and animals
Describe when secondary succession occur
- soil is present
- disrupted from succession by event such as fire/flooding/cultivation
climax community
a stable community that undergoes no further change
Describe what a pioneer species is
the first species to colonisse a new area in an ecological succession eg mosses and lichens in prumary succession
When does a deflected or diclimax arise
- when the climax community is not reached due to practices such as monoculture or graxing eg intervention
What encourages pioneer species
- heather moors are maaged to increase grouse numbers by routinley burnine large area every twelve years to remove old growth and encourage new pioneer specie which provide food for grouse
Compare primary succession and seconday succession
Primary succession
* surface is bare
* pioneer organisms are lichens and mosses
* takes a long time to reach climax community because soil must be created through physcial and biotic interactions
Secondary succession
* soil present
* pioneer organisms are typically small weedy plants
* quicker to reach climax community
niche
the role and position a species has in its environment including all interactions with biotic and abiotic factors of its environment
mutualism
an interaction between organisms of two species from which both derive benefit
commensalism
an interaction between organisms of two species from which one benefits but the other is not affected
Why are immigration of spores and seeds into an area are important
- in recolonisartion of an area
- new species are introduced, competition for resources at all the seral stages eg legumes can outcompete mosses as the soil content increases
Where does competition exist between
- different species (interspecific competition ) where each may occupy a ddifferent niche
- individuals of the same species (intraspecific competition) which is density dependent competition increases with population size
What is the competitive exclusive principle
states that when two specie occupy the same habitat one will out compete the other - to species cannot occupy the same niche
What is mutualism and give an example
- some species exist in a relationship which is beneficial to both
- nitrogen fixing bacterium rhizobium which inhabits the root nodules of leguminous plants
- it recieves a source of carbon from plant and supplies plant with nitrogen compounds from whcih it can synthesis nucleotides and proteins
What is commensalism and give an example
- some species are able to obtain benefit from one species whilst the other is unaffected
- the small fish that attach themselves to larger fish for locomotion and food scraps
Describe why carbon is important and what it is used for
- building block of life major component of carbohydrates, fats and protiens found in many other molecules
Describe two processes involving carbon
- it is abosrbed from the atomsphere during photosynthesis and returned during respiration
Why are Co2 levels rising
- carbon dioxide is added to the air during combustion of fossil fuels but decreasing amount are being removed by photosynthesis as large areas of the forest are being removed and the land are used for other purposes resulting in ynprecendented rises in atmospheric carbon dioxide levels
How is carbon dioxide returned to the atmospheres by detritivores and decomposers
feed on every trophic level and as they respire carbon dioxide is returned to the atmosphere
deforestation
the removal of trees and subsequent ue of land for another purpose
Describe how carbon dioxide eters aquatic systems
- dissolved in aquatic ecosystems as hydrogen ccarbonate ions and forms calcium carbonate in mollusc shells and arthropod skeletons
- when these organims die their shells settle on the ocean bed compression over million of years form chalk, limestone and marble
- from these carbonates which act as a long term store, or sink for carbon
- erosion of these rocks return carbon dioxide back to the atmosphere
Describe the human impact on the carbon cycle
- deforestation has resulted in up to 40 reduction in tree reducing the volume of carbon dioxide removed from the amosphere through photsynthesis
- burning fossil fuels accounts for the majority of the increases in atmospheric carbon dioxide levels
- methane comes from rice production in paddy fields and from cattle and other lifestock
Describe why carbon dioxide is harmful to our earth
- it is a greenhouse gas which absorbed infra red radition and reradiates it back toward the eathers surface rather than allowing it to escape into space
- increase in co2 levels can cause temperatures to fluctuate too widley to support life
- ehancing the grrenhouse effect
Name some greenhouse gases and why are they harmful
- methane, nitrous oxide, ozon, water vapour and CFCs act as a strong greenhouse gases and their levels have been increasing
- some of these are more warming molecules
- but therre are stil high levels of carbon dioxide
What is the effect of photosynthesis on global CO2 levels
decreases
What is the effect of respiration on global CO2 levels
increases
What is the effect of combustion on global CO2 levels
increases
What is the effect of deforestation on global CO2 levels
increeases
Deescribe how CO2 levels lead to global warming
- result of the enhanced greenhouse effect
- as global temperatures rise, polar ice will melt resulting in sea levels rising and coastal flooding and high temperatures increase the incidence of forest fires and lead to desertification
describe what are the consequences of global warming
- Climate change is a consequence of global warming as changes to regional climate patterns, average temperature, wind patterns and rainfall become more noticeable, and extreme weather conditions, e.g. drought and hurricanes, become more frequent.
- As the climate changes, plants and animals may not be able to adapt or migrate and many will become
extinct. - There is a risk from both global warming and the associated change in climate that many areas will suffer crop yield reductions and failed harvests, unless farming practices are changed, e.g. through use of drought- tolerant crops.
- Acidification of oceans due to increasing dissolved carbon dioxide will affect many aquatic organisms: fish gills produce mucus in response to increasing acidity which reduces gas exchange, and crustaceans
lose calcium carbonate from their exoskeletons as it is soluble in acid.
global warming
the increase of average global temperatures in excess
of the greenhouse effect caused by the atmosphere’s
historical concentration of carbon dioxide.
desertification
the process by which fertile land becomes desert as it
loses water, vegetation and wildlife.
carbon footprint
is the equivalent amount of carbon dioxide generated
by an individual, product or service in one year.
what is the main contributiont to a carbon footprint and how can reduce it
- agriculture, whilst removing carbon dioxide via photosynthesis, incurs a carbon footprint as
energy is needed to produce insecticides and fertilisers, fossil fuels power farming machinery, and produce needs to be transported to market. - To meet consumer needs for out of season produce, some crops travel thousands of miles, e.g. blueberries from Chile, roses from Kenya.
- By firstly reducing use of products, then reusing products more, and finally recycling (the three R’s) we can all reduce energy consumption and hence our carbon footprints.
what is carbon footprint
- The carbon footprint represents the equivalent amount of carbon dioxide produced in one year by an individual or activity.
what is the nitrogen cycle
- The nitrogen cycle involves the flow of nitrogen atoms between the atmosphere and inorganic and organic nitrogen compounds in the soil or water.
nitrificatio
the addition of nitrogen to the soil, most commonly as nitrite and nitrate ions.
nitrogen fixation
the reduction of nitrogen atoms in nitrogen molecules
to ammonium ions by prokaryotic organisms.
why is nitrogen needed in plants
synthesise nucleic acids and proteins
How do animals obtain their source of nitrogen
Animals obtain a source of nitrogen by digesting plant and animal proteins.
why does nitrogen gas have to be absorbed by plants in some other form such as nitrate ions in solution via their roots
nitrogen gas is inert
what are the four main proceses in the nitrogen cycle
- ammonification
- nitrification
- denitrification
- nitrogen fixation
describ the process of ammonification
- Ammonification (putrefaction): bacteria and fungi digest extracellularly dead organisms, faeces and urine.
- Proteases hydrolyse proteins to amino
acids and deaminases reduce the amino groups to ammonium ions (NH4+)
decribe the process of nitrfication
- the addition of nitrates to the soil by the conversion of ammonium ions to nitrites by Nitrosomonas bacteria
- and then the conversion of nitrites to nitrates by Nitrobacter bacteria.
- The first reaction involves the loss of hydrogen atoms and both result in the gain of oxygen, meaning both reactions are oxidation and require aerobic conditions.
decribe the process of denitrification
the loss of nitrate from the soil by anaerobic bacteria Pseudomonas, to atmospheric nitrogen.
describe the process of nitrogen fixation
the reduction of atmospheric nitrogen molecules to ammonium ions. This is accomplished by two genera of bacteria:
what are the functions of the two bactieria for nitrogen fixation
- Azotobacter free living in the soil accounts for most nitrogen fixation.
■ Rhizobium is a mutualistic bacterium found in the root nodules of - leguminous plants, e.g. pea and clover. Nitrogen gas diffuses into the
nodules where nitrogenase enzyme produced by the bacteria reduces
nitrogen (N2) to ammonium ions (NH4+) in an anaerobic process. - The ammonium ions are converted to organic acids and amino acids for the
bacteria, and some enter the phloem for use by the plant.
eutrophication
the artificial enrichment ofaquatic habitats by excess nutrients, often caused by
run-off fertilisers.
Describe what farmers do that increase their yields yet affect the nitrogen cycle
- To maximise yields, farmers use pesticides to reduce damage to crops, and use nitrogen-based fertilisers, e.g. ammonium nitrate, to improve plant
growth. - Farmers regularly plough and drain soils to increase soil aeration, which favours the aerobic processes of nitrogen fixation and nitrification, whilst inhibiting denitrification, which is anaerobic.
- This also allows air to reach the roots of plants, as nitrates and other minerals are taken up by active transport, which requires ATP (from aerobic respiration). Manure and slurry are also added to soils to improve soil structure and nitrogen content.
what is the major consequence of using water soluble nitrate fertilisers
- A major consequence of using water-soluble nitrate fertilisers is that they can
be washed off (leached) into water courses, e.g. rivers and streams, - which increases the ion content – this is called eutrophication
- Phosphates used in washing powders entering the water course further compound the problem.
what happens to the increase of nitrates and phosphates in eutrophication
- The increase in nitrates and phosphates leads to an algal bloom which blocks
out light to aquatic plants. - As plants and algae die, they form detritus, which is decomposed aerobically, using up dissolved oxygen in the water, which causes other aerobic organisms, e.g. fish, to die, further adding to the detritus.
- Eventually all the oxygen is used up and only anaerobic bacteria survive,
releasing ammonia, methane and hydrogen sulphide into the water creating
an environment toxic to most aerobic organisms.
what can farmers do to reduce fertiliser running off
- Apply fertilisers when plants are actively growing. This increases their
uptake reducing build up in the soil. - Not apply fertilisers within 10 metres of watercourses.
- Dig drainage ditches to collect any run off.
