User:Carl Boettiger/Notebook/Stochastic Population Dynamics/2010/05/26

From OpenWetWare

Jump to: navigation, search
Stochastic Population Dynamics Main project page
Previous entry      Next entry

Rethinking Beetles Noise

  • Noise in the larval class is damped by  \partial_L f_L and grows proportional to its intrinsic variation and the contribution of other classes through their derivatives of fL, that is,  \partial_E f_l as well as the sum of its intrinsic rates (essentially whichever is larger). Taking E dynamics to be fast we might reduce to a continous time LPA model:

\begin{align}
& \dot L = a_e \frac{bA - c_{ea} A - c_{el} L}{a_e + \mu_e} - a_l - \mu_l \\
& \dot P = a_l L - \mu_p P - a_p P \\
& \dot A = a_p P - \mu_a A
\end{align}

and the larval fluctuations are essentially:


\begin{align}
\sigma^2_L &= \frac{\nu + \beta_L}{2 \partial_L f_L} \\
\nu &= \frac{ 2(\partial_A f_L)^2 \sigma_A^2 }{\partial_L f_L + \partial_A f_A} \\
\partial_A L &= \frac{a_e (b - c_{ea} ) }{a_e + \mu_e} 
\end{align}

where βi is the intrinsic noise of the age class. Hence a class i which propagates large noise to another class j has a large  \partial_i f_j . If this term is a linear transition λXi, then the same term appears in fi and hence damps the noise  \sigma_i^2 and cancels out. Hence noise must propagate into a class through nonlinear transition rates OR through an asymmetry in the transition (i.e. the c_1, c_2 large noise example in the generalized crowley).


Compare to noise in Eggs:

 
\sigma^2_E = \frac{ \frac{ (\sigma_L^2 c_{el} +\sigma_A^2 c_{ea} )E^2 }{\mu_A + \mu_L + a_L}+ \beta_E/2}{\mu_E + c_{ea} A + c_{el} L + a_e}


Adding age delay to beetle dynamics

Current formulation has used exponential waiting times between stages. By subdividing the classes (increasing the system dimension size) and creating single jump within-state transitions, these become gamma-distributed waiting times. Adding ten steps to each phase and a little parameter fiddling introduces sustained oscillations. (Version-stable code).



beetle_pars <- c(b=5, ue= 0, ul = 0.001, up = 0.00001, ua = 0.01, ae = 1.3, al = .1, ap = 1.5, cle = .2, cap = .1, cae = 5, V=100)

Xo[1] = 100

  • Implementation still needs trouble-shooting, variance dynamics don't seem to be being computed correctly. done
  • Adult class doesn't need multiple stages. done
  • Code should allow for a general k classes rather than a fixed 10 classes. done

and now we have noise in oscillatory, gamma-waiting model:


Misc / Code notes

  • R-evolution parallelizes the variance dynamics calculation (perhaps the matrix multiplication step?) and is probably responsible for the openmp parallelization working.
  • article on cloud computing vs grid. reminds me to include questions on cloud computing in the CSGF survey.
  • Should also take a closer read of the recent: Kendall BE, Wittmann ME. A stochastic model for annual reproductive success. The American naturalist. 2010;175(4):461-8. Available at: http://www.ncbi.nlm.nih.gov/pubmed/20163244.



Personal tools