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Modeling an Ecological
System
By: Alex(UW-La Crosse), Becca(KSU), Jessica(MU),
Justin(MU), and Victor(Bingrui)(UMASS Amherst)
California is currently experiencing a water crisis due to ● lack of annual rainfall ● overuse of groundwater from
aquifers● groundwater contamination ● fracking
Motivation: California Water Crisis
http://www.forbes.com/sites/williampentland/2014/02/04/as-water-supply-reaches-record-low-california-combats-drought-with-black-ops-weather-control-technology-from-vietnam-war/
Goals:
● To find a reasonable model that accurately depicts the relationship between farmers, plants, and water.
● Infer based on the data, how the water crisis may be affecting the system.
● Consider ways to solve the water crisis using mathematical and statistical techniques.
● Water has a seasonal component
● Plants depend on water
● Farmers are independent of water
● Farmers depend on plants
Our Story and Model Assumptions
Understanding the Variables
Farmer and water is not corrolated
Data Overview
LegendData1_lowData2Data3
Summary of Data
Original Data Set (Data1_Low)
1 = Water2 = Plants3 = Farmers
R2 Value: 0.9019
Second Data Set (Data2)
1 = Water2 = Plants3 = Farmers
Poor Models
R2 Value: 0.01242R2 Value: 0.02234
Bad Forms of Fit
● Linear Regression○ Doesn’t show flow of graph (highs and lows)
● Quadratic Regression○ Only represents frames of early data○ Does not accurately depict the data's trend well
(based on its continuous oscillating nature)
Using Fourier Series to Approx. Data
● Every continuous function can be written as a linear combination of sin and cos
● We used Fourier series, a combination of sines and cosines in order to fit the given data based on the amplitude and period of the curves.
● Advantage - derivative of the function has the same basis as the original function
R2 Value: 0.95
Model for Plants vs. Time
Model for Water vs. Time
R2 Value: 0.84
Model for Farmer vs. Time
R2 Value: 0.29
Best Fit Equations for Data
Graph of the Derivatives of the Best Fit Equations
Finding ODEs
● After using Fourier series to approximate the data of the water, plants, and farmers, we next determined coefficients to create differential equations which model the relationships between the three variables.
● We accomplished this using a computer program in R...
w’(t) = g (p, t)p’(t) = g (w, p, f)
f’(t) = g (p, f)
● Predator is dependent on a single prey ● Prey has an unlimited food supply*● There is no threat to the prey other than the predator
Lotka-Volterra Predator and Prey Model
x is the number of prey ;
y is the number of some predator ex: dx/dt = ax is the term from population dynamic -bxy is the death rate from interaction
Interrelationship
Results
Parameters: Estimate Std. Errora 4.967104 0.045907 b 2.069681 0.017873 c 2.925592 0.036546 d 4.565030 0.056859 e 2.570853 0.015306 f 0.200235 0.001184
dw=e*water*plant+0.04985*sin(1.745*t)+0.03364*cos(1.745*t)+f
dp = a*water*plant-b*plant*farmer
db = -c*farmer+d*plant*farmer
Residual standard error: 0.07783
Conclusions
● All variables are a function of time● There is a delayed change of plants as water
changes.● The farmers also have a delay in response.● We can’t change one without impacting the
others.
Limitations● Not able to capture all variables in
ecosystem● The assumptions are limiting
● Create plans to help deal with the water crisis that works best both financially and agriculturally
Future Research
Learning
From doing this project, we learned about the applications of math and statistics in real world environment. We learned how to take data and analyze it to form a differential equation that describes the system.
References● Aquifer. Digital image. Aquifer. Wikipedia, n.d. Web. 21
May 2015. <http://en.wikipedia.org/wiki/Aquifer>.● Foley, Kaye. "California's Water Crisis." Yahoo! News.
Yahoo!, n.d. Web. 21 May 2015. <http://news.yahoo.com/california-s-water-crisis-drought-katie-couric-explains-182006167.html>.
● Sternberg, Shlomo. "Lotka-Volterra." 19 Apr. 14. Lecture. <http://www.math.harvard.edu/library/sternberg/slides/11809LV.pdf>.
AcknowledgementsDr. Daniel Taylor-RodriguezDr. Kimberly KaufeldDr. Lea JenkinsThomas GehrmannNC State UniversitySAMSI
Thank You!
Questions?