TOPIC 10: ECOSYSTEMS Flashcards
Define Ecosystem
A self-contained environment containing all the abiotic and biotic factors. Ecosystems range in sizes
Define Trophic level
The trophic level of an organism is the position it occupies in a food web. (feeding level)
Describe the advantages and disadvantages of the pyramid of number
They are easy to measure
counting the actual numbers for a whole ecosystem can be time consuming . The main drawback is that the bars simply compare the counts of organisms but the organisms are of very different sizes oak trees and insects also choosing scales to plot one axis will be difficult as the organisms are so largely different in sizes
Describe the advantages and disadvantages of the pyramid of biomass
Different components of biomass have very different energy contents per kilogram.It is also very time consuming to weigh each organism concerned. As we need the dry biomass the animal has to be dehydrated and dried out so it will be dead this may be deemed unethical
Describe the advantages and disadvantages of the pyramid of energy
The amount of energy at each trophic level is measured and a pyramid is drawn. The units for energy are expressed as kJ m^-2 yr^-1.
The pyramid of energy is accurate but it is hard to measure and uses a single set of measurements ,a single set of measurements gives us the situation at one snapshot in time but we know that ecosystems are subject to lots of fluctuations.
Describe ways to measure abundance of species
- Quadrats can be used they make sure that the sampling areas are the same size
- Estimates of percentage cover
- light traps to attract flying insects
- Capture/recapture techniques for animals that move around
- Beating of branches to collect what falls out
What is the subjective scale for animals
ACFORN
- Abundant
- Common
- Frequent
- Occasional
- Rare
- None
What is the subjective scale for plants
DAFORN
- Dominant
- Abundant
- Frequent
- Occasional
- Rare
- None
Describe ways to measure distribution
collecting data about distribution needs to be done in a systemic way
- Line transect
- Belt transect
- Interrupted belt transect
What is a line transect
Record organisms touching a line between two points
What is a belt transect
Record organisms in quadrats along a line between two points
What is an interrupted belt transects
Sample at regular intervals rather than recording a whole belt
When are transects used
Most often used to discover correlations between species distribution and environmental factors along a gradient
What is systematic sampling
Systematic sampling is sampling matching a pattern or sampling at periodic intervals from a large area
What is random sampling
Random sampling is sampling at random this eliminates bias; a number coordinate generator or dice can be used to make it random.
What are frame quadrats used for and how are they used
- used to collect frequency data
- Each plant is identified and then the number of squares the plant is identified in is counted
- Data collection is objective ( everyone looking at the sample should get the same answer)
What are point quadrats used for
- used to estimate percentage occurrence of individuals
- Useful when plant live in a mixed community and it is hard to identify distinct individuals
- More likely to miss rare or small plants as you are sampling a very small proportion of the population
- Less prone to random error
- Objective
What are the three things to consider when using quadrats
- The size of the quadrat - This will depend on the size of the organisms being investigated
- The number of samples being taken in the area- The more samples you take in the habitat the more reliable the results will be
- The position of each quadrat- its best to make it as unbiased and as quick as possible
List some abiotic factors
Wind Temperature Soil PH Humidity Soil moisture Light intensity
List some biotic factors
Competition Predation Diversity Parasites Disease
Equation for estimated mean density
Total number of individuals counted / Number of quadrats x Area of quadrat
Define null Hypothesis
The null hypothesis, states that there is no effect or difference (e.g. no difference between groups, or no correlation between variables).
What is the P value
The probability that our results would be obtained if the null hypothesis were true
When do we reject the null hypothesis
If P < 0.05 this means there is a less than 5% probability that the observed effect is due to chance and we reject the null hypothesis and conclude there is a significant effect
When do we accept the null hypothesis
If P > 0.05 OR P is equal to 0.05 this means that there is more than 5% probability that the observed effect is due to chance we accept the null hypothesis and conclude there is no significant effect
How do we determine whether the p value is greater or less than 0.05
- Calculate a test statistic
- Compare it wit the critical value in the table
- Use this to determine whether the P-value is greater or less than 0.05
When do we reject the null hypothesis
Critical value < the calculated value, means the P< 0.05 we reject the null hypothesis
When do we accept the null hypothesis
Critical value > the calculated value, means the P > 0.05 we accept the null hypothesis
What is the Standard Deviation
The standard deviation measures the dispersion of the raw data around the mean. The standard deviation is more representative than the range as it is calculated from replicate data. The larger the standard deviation the larger the spread of the data about the mean the less reliable the sample
Equation for Standard deviation
s=square root of sum of (value-mean)^2 /number of values-1
What is the unpaired t-test
The unpaired t-test tests for differences between two sets of independent data.
The unpaired t-test tests the null hypothesis that there is no difference between the means of two sets
Equation for Unpaired t-test
t= mean of set data 1 -mean of set data 2/square root of standard deviation 1^2/number of repeats of set data 1 + standard deviation 2^2/number of repeats of set data 2
When do you use the mean and standard deviation test
For summarisation of quantative (numeric) data
When do you use the unpaired t-test (independent samples)/ Paired t-test ( matched samples)
To compare two sets of quantative numeric data ( bar chart)
When do you use the Spearman correlation coefficient test
To correlate two sets of quantative numeric data (scatter graph)
What do you use to summarise qualitative categoric data
Tally frequencies
What do you use to compare two sets of qualitative categoric data
Chi-squared data
What is gross primary productivity
The amount of light energy fixed by photosynthesis in a given area and fixed time
The units are: KJ/m^2/year
What is net primary productivity
The total amount of light energy fixed by photosynthesis in a given area and fixed time after losses and uses by producer KJ/m^2/year
Equation linking GPP and NPP
NPP= GPP-R R= energy lost in plant respiration
Describe the ways in which energy can be used or lost in food webs?
- Through movement of the animal (respiration)
- Through excreted matter
- Through storage in cells and tissues
What are Detritivores?
Animals that feed off dead and decaying organic materials. They are important recyclers in all ecosystems
What are Sapratrophs?
Mainly fungi or bacteria; feeding by secreting extracellular enzymes to break down dead organic matter and reabsorb products
What are Scavengers?
Opportunist feeders on the remains of dead animals and faeces
What is a Carbon Sink?
A natural or artificial reservoir that accumalates and stores some carbon-containing chemical compound for an indefinate period
What is the removal of carbon dioxide from the atmosphere known as ?
Carbon Sequestation
Why are nitrates so important for plants ?
Plants take nitrates from the soil to produce amino acids and therefore proteins, and to produce the nucleotides used to build DNA and RNA
What do Nitrifying bacteria do ?
They convert the ammonium compounds that were produced during decomposition into nitrates
What does Nitrogen-fixing bacteria do ?
They convert inert nitrogen gas from the atmosphere into ammonia
What does Denitrifying bacteria do ?
They release nitrogen gas from nitrates, making the nitrogen unavailable to plants
What effect does ploughing have on anaerobes like denitryfying bacteria?
Ploughing:
- Aerates the soil
- More nitrates formed (nitrification)
- Less denitrification to lessen the nitrogen back into the atmosphere
What is the point in crop rotation ?
Crop rotation can be used to replenish nitrogen concentrations in the soil
legumes with nitrogen fixing nodules increase nitrification and increase nitrogen in the soil
What is the null hypothesis for a paired t-test
Null Hypothesis: The mean of the paired differences is zero (or there is no difference between the two conditions)
What is a paired t-test
The paired t-test tests the null hypothesis that the mean of the paired differences is zero, in other words that there is no difference between the two groups. Note that this is a different test from the unpaired t-test, so it has a slightly different null hypothesis.
The paired t-test is for experiments where the data is “matched”, eg in a before and after experiment were the same location is investigated but at different times
Equation for paired t-test
t= absolute mean of the differences x square root of the number of pairs / the standard deviation of the differences
What does the Spearmans rank correlation coefficient tell us
The spearman rank correlation coefficient gives us the strength of a correlation on a scale of -1 to +1.
-1 is the perfect negative correlation
+1 is the perfect positive correlation
What is the null hypothesis for Spearmans rank correlation
The null hypothesis is that there is no correlation between the two sets of data
Equation for Spearmans rank correlation
1- 6 x Difference in ranks ^2/ number of pairs cubed-number of pairs
