Topic 7C - Populations in Ecosystems Flashcards
What can quadrats be used for?
To measure the frequency or percentage cover if a particular species.
Explain how you would use a quadrat to estimate the number of dandelion plants in a field measuring 100m by 150m
- Randomly placed quadrats (using random number generator to pick coordinates)
- Valid method of obtaining number of dandelions in the given area ( mean n⁰ per quadrat ÷ number of quadrats )
- Multiply to give a total estimate for total field area
What’s the 50% rule for percentage cover samples?
if 50 percent or more in then you count it as part of the percentage cover (in relation to within squares)
what are common sampling rules
- large sample size (minimum 20) in order to:
- give reliable representation
- so mean and standard deviations can be calculated
- so stats tests to see if any significant differences or correlations - random sampling to avoid bias
- calc a running mean to see when it stabilises ( e.g calc mean of 3 quadrats you may have already taken along the way and when you get 4 etc)
When are transects used?
To see how organisms are distributed across an area along a changing fact usually… e.g. from shore to grassy area of beach
2 types of transects and why would you use them?
Belt transects: (1m²) quadrats placed next to each other along transect to calc frequency and percentage cover along transect.
- you can set up the belt transect again throughout area and calculate a mean at each distance of a given transect to show if there’s a correlation along the transect.
Interrupted belt transect: (both using guiding poles) where samples taken at regular intervals, Luke every 2 metres.
- this may be used over longer distances as more useful and easier.
when to use mark release recapture
on mobile animals
what tools should you use for mark release recapture on different types of animals?
flying insects : sweep net (on a pole)
aquatic ones: a general net
walking insects: a pitfall trap (with a container sunken into the ground and covered by a raised lid so walking insects can fall)
how to perform mark release recapture?
- Sample is caught and marked in a way that doesn’t affect survival, such as if it would be toxic to them or make them more visible to predators (so usually use UV reactive powder).
- Then release back into habitat to reintegration for some time, like a week.
- Second sample captured band number of marked individuals counted.
how to estimate total population size from mark release recapture?
total pop. = (n⁰ of first sample × n⁰ of second sample) / number marked in the second sample
- all after reintegrating back into population
what are some assumptions of the mark release recapture method?
- questions may be worded as was the experiment provided in the question accurate?↓
- enough time and opportunity given for marked species to mix back into population.
- marking hasn’t affected chance of survival.
- no changes to population size due to births, deaths, or migration during study.
- stress to organisms is minimised to avoid reducing chance of survival
Scientists may be unable to prove that salt spray from the road is responsible for absence of species B (compared to abundance of species C) between 0 to 20 m from the road. Explain why.
Other factors like interspecific competition between species like for water or light intensity or even space.
reasons a population may rise
births as more mating (seasonal?)
natural selection
immigration (look up)
favourable changes, abiotic factors
reasons a population may fall
deaths
natural selection
emigration
predation (predator prey cycle)
unfavourable change , abiotic factors
intraspecific competition
competition within the sAme species.
What’s the difference between an adaptation being for biotic or abiotic conditions?
Abiotic conditions is when the organism is adapting to it’s environment and landscape and weathers.
Biotic is for more living conditions like mating and eating (prey decreasing could be a factor affecting population in question, for example) or competing
Bacteria grow exponentially. What’s an equation you could use to work out present number of bacteria (cells) in a population?
initial number of cells × 2^n
where n is the number of divisions
In an experiment involving growing populations of bacteria in a broth culture, why might the numbers level off and then decline?
As all the nutrients available are used up, and then there’s no more for the bac. so they start to die.
- possible build up of waste products (CO² dissolves in water, lowers pH and could impact bacteria)
- could also mention space is limited but unlikely as cells are small really.
Investigating population growth of bacteria:
1. liquid broth?
2. broth culture?
3. name of equipment that can estimate bacteria culture population?
4. relationship between absorbance values and bacteria population?
5. why is plotting the log10 number of bacteria against time better than plotting absorbance value?
- liquid substance containing nutrients
- a liquid broth with bacteria mixed in
- spectrophotometer / colorimeter
- ^ absorbance value (cloudier it is) = ^ population
- (Log allows to see exponential increase in smaller values) so bacteria number increases hugely so can be used as small numbers; can draw line of best fit to see population at any time.
