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程序代写案例-MATH3070-Assignment 5

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MATH3070 Assignment 5 – Size spectrum modelling

Assignment 5 is based on the ZooMSS (Zooplankton Model of Size Spectra) we are describing br>in class and using in tutorials. It is detailed in Heneghan et al. (2020) – see the MATH3070
Blackboard site under Learning Recourses/Weeks11-13/ZooMSS model publication.

In this assignment, you will conduct a sensitivity analysis, obtain outputs, and interpret your
answers. A sensitivity analysis is a study of how the inputs of a model affect its outputs – in
essence, which are the most and least important inputs to the model output. You can learn a
lot about a model by conducting a sensitivity analysis. We will conduct a simple sensitivity
analysis on a selection of model parameters by varying one parameter at a time while keeping
all others constant.

To answer the following questions, run the simulations then use the outputs and your
understanding from the equations in the lectures to explain the changes in zooplankton and
fish biomass. To help interpret your outputs, please report the wet weight biomass for total
zooplankton and total fish (you will need to sum the required elements in WWspecies – the
elements are ordered the same as in TestGroups.csv). In your answers, you can also use
output from the plots provided, with ggBiomassSizeSpec (ggplot of the Unnormalised
Biomass Size Spectrum) and ggBiomassTS (ggplot of biomass of the functional groups over
time) probably being the most useful.

For the sensitivity analyses in Questions 1-7, use a sea surface temperature (sst) of 15°C and
a chlorophyll-a (chlo) of 0.2 mg.m-3, close to the global mean for each. You will need to
modify the enviro_data object. So, in setup_RUN_NAME.R, you should set:

enviro_data <- fZooMSS_CalculatePhytoParam(data.frame(cellID = 1,
sst = 15,
chlo = 0.2,
dt = 0.01))

For the sensitivity analyses, change the parameter for all the zooplankton groups (Larvaceans,
Omnivorous copepods, Carnivorous copepods, Euphausiids, Chaetognaths, Salps, Jellyfish),
and keep all others (Flagellates, Ciliate, Small fish, Medium fish, Large fish) unchanged.

The base case simulation
All simulations will be run in comparison to the base case simulation with parameter values
provided in TestGroups.csv. If you think you might have changed the default values, download
another copy form Github: https://github.com/MathMarEcol/ZoopModelSizeSpectra.

For this assignment, you will only need to run the program setup_RUN_NAME.R – it calls all
other functions needed. To run the sensitivity analysis on a parameter, make sure you are
modifying the TestGroups.csv file, and that in setup_RUN_NAME.R you are calling this file:

Groups <- read.csv("TestGroups.csv", stringsAsFactors = FALSE)

2
Questions

1. Run the base case scenario. Describe the outputs. You will be able to use these
outputs to compare with the sensitivity analyses and projections below.

Sensitivity analysis: How does changing the search volume change the model output?
The search volume is the volume of water that an animal can search per unit time to ingest
food. The search volume is an allometric relationship, with a coefficient ( from lectures and
SearchCoef in TestGroups.csv) and exponent ( from lectures and SearchExp in
TestGroups.csv).

2. The default value for the coefficient of the search volume is 640. Run simulations
changing the search volume coefficient to 480 and then 800 for all zooplankton
groups. What happens to zooplankton and fish, and the size spectrum and how does
biomass change through time. Explain what is happening.
3. The default value for the search volume exponent is 0.8. Change this to 0.7 and then
0.9. What happens to zooplankton and fish and why? When interpreting what
happens, note that the weights for zooplankton are <1.
4. Which parameter do you think we would need to know more precisely in the model?
Explain your answer.

Sensitivity analysis: How do the Predator Prey Mass Ratios change the model output?
The Predator Prey Mass Ratios (PPMRs, called in lectures and PPMR in TestGroups.csv) is
the relative biomasses of the predator and their preferred prey. Changing PPMR in the model
is a bit more challenging than other parameters because the PPMR of some groups changes
with body size, rather than remaining constant as an organism grows. This is reflected in
TestGroups.csv by the NA for PPMR, and the PPMRscale parameter, which includes the non-
linear scaling with body size. To set the PPMR to be constant for each group across its body
size, change the PPMR value in TestGroups.csv from NA to any particular value, and change
the PPMRscale to NA (see below).

5. The lowest PPMR for zooplankton is about 3. So, let’s see what happens if we set the
PPMR of all zooplankton groups to 3. Describe the outputs. To run this simulation, the
relevant columns in your TestGroups.csv should look like this:


3
6. A high PPMR for zooplankton is 1,000,000 (they get even higher though!). Set the
PPMRs for all zooplankton groups to 1,000,000. What happens and why? Comment
on the stability of the system
7. How does PPMR generally impact the system. How would the PPMR change the slope
of the size spectrum?

Projections: How might climate change affect marine ecosystems, especially fish?
To answer this question, we will not conduct a sensitivity analysis, but instead make
projections for the future. You will now be changing the sst and chlo columns in the
envirodata object.

But before you do, make sure you change the TestGroups.csv back to its default values. You
can always redownload it from Github if needed…

8. Under a high emissions scenario in 2100, global mean sea surface temperature is likely
to increase by about 3°C, depending on the Earth System Model considered. Set the
temperature for the model to 3°C above the current global mean temperature we
have been using. Run a simulation with the default parameter values in
TestGroups.csv. How does global warming impact the marine ecosystem in ZooMSS?
Why?

9. Warming of the ocean surface layer increases the stratification in the ocean, decreases
nutrients in surface waters, and leads to declines in phytoplankton (chlorophyll-a).
Under a high emissions future scenario, chlorophyll-a is projected to decline by 25%
in many ocean regions. How does the impact of climate change on declining
chlorophyll-a affect the marine ecosystem modelled in ZooMSS? Why?

10. Finally, run a simulation with the temperature and Chl changes together, and see what
happens. Interpret your answer. What could this mean for fisheries globally and
human livelihoods?

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