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DRAFT 2 PRESENTATION
Dr. Pelesko
MATH 260
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Distribution of House and Bewick’s Wrens
HOUSE WREN BEWICK’S WRENhttp://www.roysephotos.com/zzBewicksWren6.jpghttp://www.sialis.org/images/nesteggsphotoalbum/images/28CarolinaWren.jpg
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Biological Problem
• House-Wren and Bewick’s Wren competition relatively new (within the last 10 years) – Didn’t share territory until recently (Kennedy et. al., 2007)
• How will this new interaction affect the population dynamics of both species?
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Bewick’s Wren Nest
X
http://byteshuffler.com/rospo/blog/uploaded_images/NestEggs-729160.jpg (nest)
http://www.suttoncenter.org/images/House-Wren-Carroll.jpg (wren)
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Egg Photo courtesy of The Nova Scotia Museum at http://museum.gov.ns.ca/mnh/nature/nsbirds/bns0276.htm
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Data Supporting Nest Vandalism
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Summary
• We want to analyze the consequences of the cohabitation of the House Wren and Bewick’s Wren on their populations
• Will this result in fewer Bewick’s Wrens? • Will this result in more House Wrens?
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Mathematical Problem
• How can build a mathematical model of the population dynamics of the Bewick’s Wren and the House Wren?
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Specific Aims
Aim 1: Examine single-species population model for both Bewick’s Wren and House Wren
Aim 2: Create two species model of competition between Bewick’s Wren and
House Wren
Aim 3: Compare Models with biological data from BBS
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HOUSE WREN BEWICK’S WREN
Aim 1: Single Species Model
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Model Assumptions
Interspecies competition with House Wrens is the only major contribution to the failing Bewick’s Wren population
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Single Species Model (Gina)
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HOUSE WREN
VS
BEWICK’S WREN
Aim 2: Two Species Model
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Model Equations
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Non-Dimensionalization
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Final Equations
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So what is a competition coefficient?
• Quantifies how every additional organism of species 1 fills the niche of species 2
€
dN2
dt= (r2)(N2)
K2 −N2 −N1α 21
K2
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Reproduction Rates
House Wrenr = .84
Of 36 nests 24 produced at least
one fledgling
Bewick’s Wrenr = .67
Of 535 nests 449 produced at least
one fledglingThis data was retrieved from The Birds of British Columbia - a reference work on 472 species of birds in the area.
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Calculate carrying capacity for each species
• Relate indiviual data and the logistic equation, growth rate
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Linear Stability at Critical Points of the Model
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4 Critical Points
• (0,0)• (0,1)• (1,0)• (n1
*,n2 *)
– n1 * = (1-alpha2/beta)/ (1-alpha1alpha2)
– n2 * = (1 – alpha1beta(1 – alpha2beta/(1-
alpha1alpha2)))
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Linear Stability
• We notice that similar to a scalar ODE– dx/dt = Ax ,x(0) = x0 where denotes vector
Has solution x(t) = x0 exp(At), where A is the Jacobian matrix
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Decomposing A• By writing • A = SDS-1
• Exp(At) = exp[(SDS-1)t] • then taylor expanding the following• sum{ (SDS-1 t)n / n! } from 0…inf• we can see that the eigenvalues of A determine the behavior
of the solution.• If Eig(A(criticalpt)) = both neg. then the point is stable• If Eig(A(criticalpt)) = both pos. then the point is unstable• If Eig(A(criticalpt)) = pos/ neg. then it is a saddle point
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Tedious details of Analysis
• This needs to be typed in latex• Show all A matrices evaluated at each critical
point• Eigenvalues of each matrix A• Phase plane behavior determined by above. A
couple plots for different cases of alphas, betas, etc. would be nice
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Aim 3: Compare Models with biological data from BBS
BBS has separated data by several classes, including Fish & Wildlife Service Regions
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• Species interactions have mostly taken place where “northern” and “southern” regions of the U.S. came together
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Physiographic Strata of the U.S.
• Areas of similar geographic and vegetation features
• Developed by modifying vegetation and soil distribution maps
• Allow for examination of bird species in a small area that experiences a specific climate
• Ignores state boundaries, concentrates on geographical boundaries
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Large Range Data
• Data from wider geographical regions allowed us to evaluate the behavior of each species' population somewhat individually
• This data from larger areas, reflected less of the effect of interaction with the other species
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Region 2: Southern Midwest U.S.• Bewick's wren and House wren populations stable
throughout BBS data collection• Average Bewick's population much lower than that of
House wren
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Region 6: Northern Midwest U.S.• Bewick's wren population: slowly increasing• House wren population: slowly increasing until early
1990's before stabilizing
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Region 3: Northern Central U.S.• Bewick's wren population: decreasing• House wren population: slowly increasing
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Region 4: Southern Central U.S.• Bewick's wren population: decreasing rapidly until
around 1980 and then stable• House wren population: increasing rapidly
throughout survey
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Wren Population Patterns
• Bewick’s Wren populations seem largest in the southwest
• Strongest areas with no House Wrens are in southern Texas, in Strata 53, 54, 56
• House Wren populations seem largest in the northern US
• Strongest areas with no Bewick’s Wrens are in the north and midwest, in Strata 31,32,40
• Overlap between the two is most prevalent in southwestern California, in Strata 92,94, and 83
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Strata 54 – Rolling Red Plains- Texas
Bewick’s Wren House Wren
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Strata 31 –Till Plains - Midwest
Bewick’s Wren• No data for species
House Wren
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Strata 92 – California Foothills – Southern California
Bewick’s Wren House Wren
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Pending Questions• Do both the birds coexist (did you mean can they coexist for infinitely
large t given their competitive nature)?
• There is no data given in the BBS, where the two birds over lap (?).
Looking at all the data , it seems that the House wrens exist at the central
and east where as the Bewicks wren at the west. There is no data that
shows their existence together. The possible problem that House Wrens
and Bewicks Wrens compete might be true as there are certain states where
the, population changes inversely. While the Bewicks Increase the House
Wren decreases.
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Do BBS data reflect populations?
€
B
A(R ×D)
• Convert to density• Extrapolate for region• Detection adjustments
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Interpreting Data From BBS Graphs
• The vertical axis of population graphs from the BBS website was labeled “count”.
• Clearly, this was not the raw number of birds counted because there were often data points that appeared to show fractional birds being observed
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Vertical Axis: Relative Abundance
• The vertical axis of these graphs is not the raw number of birds of a given species counted
• BBS has calculated the relative abundance (R.A.) for each species and region – the number of birds per route
• According to BBS, “[…] an approximate measure of how many birds are seen on a route in the region.”
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Example: House Wren data for region 87 – R.A. = 0.28