similar to: Not sure how to handle hazard in my survival model

Hi, I wonder if anyone can help me with specifying a right model for my analysis. I am a beginner to lme methods and though have spent already many hours studying from various books an on-line helps, I was unfortunately not able to find a solution to my problem on my own. Data structure: I studied escape behavior of three species of a prey to a predator. The prey specimens (many) were in a

Dear R-users, I am currently modifying a previously developed predator prey model and was curious if there was a way to add in a disturbance to the model (let's say at time t=100). The disturbance can be the introduction of 40 prey (N=40) and 10 predators (Pred = 10). I would like to see my model go from a state of equilibrium (up to t = 99), show this disturbance (at t = 100) and then

Hello there I have the following model based on the hollings disc equation for the type II functional response for 2 data sets: nls(eaten~(a*suppl)/(1+a*h*suppl) where eaten is the number of prey eaten by a predator and suppl is the number of prey initially supplied to the same predator. I have parameter estimates of 'a' and 'h' for the two populations studied and would like

Dear list, I´m using the mgcv package to model the proportion by weight of certain prey on the stomach content of a predator. This proportion is the ratio of two weights (prey weight over stomach weight), and ranges between 0 and 1. The variance is low when proportion is close to 0 and 1, and higher at intermediate values. It seems that the best way to go is to model this using the

Hello, I have a syntactic problem with ode. How do I specify vectors of equations in ordinary differential equation systems. (i.e. in my case I want to simulate an a priory undefined number of species that have different parameters but the same behaviour) I demonstrate this using the Lotka Volterra example. The code below does not work and I have not a good idea how to specify this right. ##

I'm fairly new to R, and I'm trying to write out a population model that satisfies the following; the system consists of s species, i= 1, 2,...,s network of interactions between species is specified by a (s x s) real matrix, C[i,j] x[i] being the relative population of the "ith" species (0 =< x[i] =< 1, sum(x[i]=1) the evolution rule being considered is as follows;

Hello, I am writing a package with a collection of several models. In order to allow users to play interactively with the models (in contrast to hacking lengthy scripts), I want to put all what is needed to run a particular model into a single list object for each model. Then there will be a collection of functions to run the model or to modify parameters, time steps, integration method ...,

Greetings I'm using R 2.8 with recent (last month) versions of the packages I need to use at present. I'm interested in examining hierarchical spatio-temporal patterns in a data set. The data consist of 94 points (X, Y, UTM coordinates) at which catch rates for a fish were recorded and there are also estimates of prey available for these fish at the same locations.

Hi, I have data on stomach contents. Possible prey species are in the hundreds, so a list of prey codes has been in used in many labs doing this kind of work. When comes time to do analyses on these data one often wants to regroup prey in broader categories, especially for rare prey. In SAS you can nest a large number of "if-else", or do this more cleanly with "select"

Hi, I'm trying to move to R the last few data handling routines I was performing in SAS. I'm working on stomach content data. In the simplified example I provide below, there are variables describing the origin of each prey item (nbpc is a ship number, each ship may have been used on different trips, each trip has stations, and individual fish (tagno) can be caught at each

Dear useRs, A new version of the package GillespieSSA (0.3-1) has been uploaded to CRAN. The GillespieSSA package (Gillespie's Stochastic Simulation Algorithm) provides a simple to use, versatile, and extensible interface to a number of Monte Carlo implementations of the stochastic simulation algorithm (SSA) and is intended for scientists, teachers, and students alike. The SSA is a

Dear useRs, A new version of the package GillespieSSA (0.3-1) has been uploaded to CRAN. The GillespieSSA package (Gillespie's Stochastic Simulation Algorithm) provides a simple to use, versatile, and extensible interface to a number of Monte Carlo implementations of the stochastic simulation algorithm (SSA) and is intended for scientists, teachers, and students alike. The SSA is a

Dear all, I studied in tank prey fish behavior. Using the design described below (and R code), I want to test the effects of both habitat and predator (and interaction) on prey fish's vertical distribution, which was recorded (with repeated measures) as a categorical variable. I found that package mlogit might fit to my need but I don't know how to specify my complex design in the

Hello there, Suppose you want to solve the following system of ODE's (a simple Lotka-Volterra predator prey model) dP/dt = beta*P*V - mu*P dV/dt = r*V - beta*P*V where P and V are the numbers of predators and prey. Now, this is easy to do, but suppose you have a system of equations like this, dP1/dt = beta1*P1*V1 - mu1*P1 dP2/dt = beta2*P2*V2 - mu2*P2 dV1/dt = r1*V1 - beta1*P1*V1

Dear R friends- I'm attempting to generate a regression tree with one gradient predictor and multiple responses, trying to test if change in size (turtle.data$Clength) acts as a single predictor of ten multiple diet taxa abundances (prey.data) Neither rpart or mvpart seem to allow me to do multiple responses. (Or if they can, I'm not using the functions properly.) > library(rpart)

I have installed Prey onto my pc running PCLinuxOS following the instructions in http://frankscorner.org/index.php?p=prey or http://appdb.winehq.org/objectManager.php?sClass=application&iId=3465 and tried running it. I then found I needed the nocd patch, which I downloaded and applied. I then tried cd to the app folder, then wine prey.exe with the following result: Prey 1.0.103 win-x86 Jun 10

Hi I am struggling with the correct code syntax to generate xyplots that are different from the default graphics option. This is simplified version of my data: site size dnaconc prey A 44 22.6 1 A 47 18.2 1 B 38 25.6 0 B 47 20.5 1 C 45 30.5 0 C 32 18.5 0 D 45 15.0 1 D 22 20.1 0 So I am using xyplot(dnaconc~size|site,data=bug,groups=prey) to generate 4 panels (one for each site). My

Hello, I am trying to model a type II functional response of number of prey eaten (Ne) against number supplied (No) with a non-linear least squares regression (nls). I am using a modification of Holling's (1959) disc equation to account for non-replacement of prey; Ne=No{1-exp[a(bNe-T)]} where a is the attack rate, b is the handling time, and T is the experimental period. My script is as

*Thanks* all those who took the time to help me (even if the "question" was not related to - the use of - R). Now I think I can soundly make my point w/ the referee (can I use your replies? If so I intend to properly cite its use?!?). Regards, Eduardo Esteves ps - Sorry for not explaining the "biological details" of my posting: RNA/DNA is the ratio of RNA content to

Hi all, we found, that R is not only *the* superior data analysis, graphics and statistics package, but it is also a general tool for implementing, running and teaching ecological models. Last week we held our second course "Modelling in Limnology" using R. Some material (code and docs) was produced for this purpose and may be interesting to someone else, so I put the tutorial