Inverse Survivorship Models in the Fossil Record
This function replicates the model-fitting procedure for forward and reverse survivorship curve data, described by Michael Foote in a series of papers (2001, 2003a, 2003b, 2005). These methods are discrete interval taxon ranges, as are used in many other functions in paleotree (see function arguments). This function can implement the continuous time, pulsed interval and mixed models described in Foote (2003a and 2005).
A 2 column matrix with the first and last occurrences of taxa given in relative time intervals (i.e. ordered from first to last). If a list of length two is given for timeData, such as would be expected if the output of binTimeData was directly input, the second element is used. See details. Unsampled taxa (e.g. from a simulation of sampling in the fossil record, listed as NAs in the second matrix) are automatically dropped from the timeList and from groups simultaneously. Living taxa observed in the modern day are expected to be listed as last observed in a special interval (0,0), i.e. begins and ends at 0 time. This interval is always automatically removed prior to the calculation intermediary data for fitting likelihood functions.
Either NULL (the default) or matrix with the number of rows equal to the number of taxa and the number of columns equal to the number of 'systems' of categories for taxa. Taxonomic membership in different groups is indicated by numeric values. For example, a dataset could have a 'groups' matrix composed of a column representing thin and thick shelled taxa, coded 1 and 2 respectively, while the second column indicates whether taxa live in coastal, shelfal or deep marine settings, coded 1-3 respectively. Different combinations of groups will be treated as having independent sampling and extinction parameters in the default analysis, for example, thinly-shelled deep marine species will have separate parameters from thinly-shelled coastal species. Grouping systems could also represent temporal heterogeneity, for example, categorizing Paleozoic versus Mesozoic taxa. If groups are NULL (the default), all taxa are assumed to be of the same group with the same parameters. Unsampled taxa (e.g. from a simulation of sampling in the fossil record, listed as NAs in timeData or timeList) are automatically dropped from groupings and the time dataset (either timeData or timeList) and from groups simultaneously.
If TRUE (the default), then origination is assumed to be a continuous time process with an instantaneous rate. If FALSE, the origination is treated as a pulsed discrete-time process with a probability.
If TRUE (the default), then extinction is assumed to be a continuous time process with an instantaneous rate. If FALSE, the extinction is treated as a pulsed discrete-time process with a probability.
The probability of sampling a taxon after the last interval
included in a survivorship study. Usually zero for extinct groups,
although more logically has the value of 1 when there are still extant
taxa (i.e., if the last interval is the Holocene and the group is
still alive, the probability of sampling them later is probably 1...).
Should be a value of 0 to 1, NULL, or can be simply "fixed", the default option.
This default "fixed" option allows make_inverseSurv to decide the value
based on whether there is a modern interval (i.e. an interval that is
The probability of sampling a taxon before the first interval included in a survivorship study. Should be a value of 0 to 1, or NULL. If NULL, PB_1 is treated as an additional free parameter in the output model.
The number of taxa that enter an interval (b is for 'bottom'). This is an arbitrary constant used to scale other values in these calculations and can be safely set to 1.
Drops all extant taxa from a dataset, w
The design of this function to handle mixed continuous and discrete time models means that parameters can mean very different things, dependent on how a model is defined. Users should carefully evaluate their function arguments and the discussion of parameter values as described in the Value section.
A function of class "paleotreeFunc", which takes a vector equal to the number
of parameters and returns the *negative* log likelihood (for use with optim and
similar optimizing functions, which attempt to minimize support values). See the
functions listed at
modelMethods for manipulating and examining
such functions and
constrainParPaleo for constraining parameters.
The function output will take the largest number of parameters possible with respect to groupings and time-intervals, which means the number of parameters may number in the hundreds. Constraining the function for optimization is recommended except when datasets are very large.
Parameters in the output functions are named 'p', 'q' and 'r', which are respectively the origination, extinction and sampling parameters. If the respective arguments 'p_cont' and 'q_cont' are TRUE, then 'p' and 'q' will represent the instantaneous per-capita origination and extinction rates (in units of per lineage time-units). When one of these arguments is given as FALSE, the respective parameter (p or q) will represent per-lineage-interval rates. For p, this will be the per lineage-interval rate of a lineage producing another lineage (which can exceed 1 because diversity can more than double) and for q, this will be the per lineage-interval 'rate' of a lineage going extinct, which cannot be observed to exceed 1 (because the proportion of diversity that goes extinct cannot exceed 1). To obtain the per lineage-interval rates from a set of per lineage-time unit rates, simply multiply the per lineage-time-unit rate by the duration of an interval (or divide, to do the reverse; see Foote, 2003 and 2005). 'r' is always the instantaneous per-capita sampling rate, in units per lineage-time units.
If PA_n or PB_1 were given as NULL in the arguments, two additional parameters will be added, named respectively 'PA_n' and 'PB_1', and listed separately for every additional grouping. These are the probability of a taxon occurring before the first interval in the dataset (PB_1) and the probability of a taxon occurring after the last interval in a dataset (PA_n). Theses will be listed as 'PA_n.0' and 'PB_1.0' to indicate that they are not related to any particular time-interval included in the analysis, unlike the p, q, and r parameters (see below).
Groupings follow the parameter names, separated by periods; by default, the parameters will be placed in groups corresponding to the discrete intervals in the input timeList, such that make_inverseSurv will create a function with parameters 'p.1', 'q.1' and 'r.1' for interval 1; 'p.2', 'q.2' and 'r.2' for interval 2 and so on. Additional groupings given by the user are listed after this first set (e.g. 'p.1.2.2').
Calculating The Results of an Inverse Survivorship Model
Because of the complicated grouping and time interval scheme, combined with the probable preference of users to use constrained models rather that the full models, it may be difficult to infer what the rates for particular intervals and groups actually are in the final model, given the parameters that were found in the final optimization.
To account for this, the function output by
inverseSurv also contains
an alternative mode which takes input rates and returns the final values along with
a rudimentary plotting function. This allows users to output per-interval and per-group
parameter estimates. To select these feature, the argument
be TRUE. This function will invisibly return the rate values for each
group and interval as a list of matrices, with each matrix composed of the
p, q and r rates for each interval, for a specific grouping.
This plotting is extremely primitive, and most users will probably find the
invisibly returned rates to be of more interest. The function
used to play plots for different groupings in sequence, and this may lead to
plots which are either hard to read or even cause errors (because of too many
groupings, producing impossible plots). To repress this, the argument
can be set to FALSE.
This capability means the function has more arguments that just the
par argument that accepts the vector of parameters for running an
optimization. The first of these additional arguments,
this alternative mode, instead of trying to estimate the negative log-likelihood
from the given parameters. The other arguments augment the calculation and plotting
To summarize, a function output by inverseSurv has the following arguments:
A vector of parameters, the same length as the number of parameters needed. For plotting, can be obtained with optimization
If FALSE (the default) the function will work like ordinary model-fitting functions, returning a negative log-likelihood value for the input parameter values in
par. If TRUE, however, the input parameters will instead be translated into the by-interval, by-group rates used for calculating the log-likelihoods, plotted (if plotPar is TRUE) and these final interval-specific rates will be returned invisibly as described above.
If TRUE (the default) the calculated rates will be plotted, with each grouping given a separate plot. This can be repressed by setting plotPar to FALSE. As the only conceivable purpose for setting plotPar to FALSE is to get the calculated rates, these will not be returned invisibly if plotPar is FALSE.
If FALSE, the default option, the rates plotted and returned will be in units per lineage-time units, if those rates were being treated as rates for a continuous-time process (i.e. p_cont=TRUE and q_cont=TRUE for p and q, respectively, while r is always per lineage-time units). Otherwise, the respective rate will be in units per lineage-interval. If ratesPerInt is TRUE instead, then all rates, even rates modelled as continuous-time process, will be returned as per lineage-interval rates, even the sampling rate r.
If FALSE (the default) rates are plotted on a linear scale. If TRUE, rates are plotted on a vertical log axis.
If TRUE (default) the sampling rate and extinction rate will be plotted slightly ahead of the origination rate on the time axis, so the three rates can be easily differentiated. If false, this is repressed.
The position of a legend indicating which line is which of the three rates on the resulting plot. This is given as the possible positions for argument 'x' of the function
legend, and by default is "topleft", which will be generally useful if origination and extinction rates are initially low. If legendPosition is NA, then a legend will not be plotted.
This function is an entirely new rewrite of the methodology derived and presented by Foote in his studies. Thus, whether it would give identical results cannot be assumed nor is it easy to test given differences in the way data is handled between our coded functions. Furthermore, there may be differences in the math due to mistakes in the derivations caught while this function was programmed. I have tested the function by applying it to the same Sepkoski genus-level dataset that Foote used in his 2003 and 2005 papers. Users can feel free to contact me for detailed figures from this analysis. Overall, it seems my function captured the overall pattern of origination and sampling rates, at least under a model where both origination and extinction are modeled as continuous-time processes. Extinction showed considerably more variability relative to the published figures in Foote (2005). Additional analyses are being run to identify the sources of this discrepancy, and the function is being released here in paleotree on a trial basis, so that it can be more easily loaded onto remote servers. Users should be thus forewarned of this essentially 'beta' status of this function.
David W. Bapst, with some advice from Michael Foote.
Foote, M. 2001. Inferring temporal patterns of preservation, origination, and extinction from taxonomic survivorship analysis. Paleobiology 27(4):602-630.
Foote, M. 2003a. Origination and Extinction through the Phanerozoic: A New Approach. The Journal of Geology 111(2):125-148.
Foote, M. 2003b. Erratum: Origination and Extinction through the Phanerozoic: a New Approach. The Journal of Geology 111(6):752-753.
Foote, M. 2005. Pulsed origination and extinction in the marine realm. Paleobiology 31(1):6-20.
This function extensively relies on
A similar format for likelihood models can be seen in
For translating between sampling probabilities and sampling rates, see
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# let's simulate some taxon ranges from an imperfectly sampled fossil record set.seed(444) record <- simFossilRecord(p=0.1, q=0.1, nruns=1, nTotalTaxa=c(30,40), nExtant=0) taxa <- fossilRecord2fossilTaxa(record) rangesCont <- sampleRanges(taxa,r=0.5) #bin the ranges into discrete time intervals rangesDisc <- binTimeData(rangesCont,int.length=5) #apply make_inverseSurv likFun<-make_inverseSurv(rangesDisc) #use constrainParPaleo to make the model time-homogenous #match.all~match.all will match parameters so only 2 pars: p=q and r constrFun<-constrainParPaleo(likFun,match.all~match.all) results <- optim(parInit(constrFun), constrFun, lower=parLower(constrFun), upper=parUpper(constrFun), method="L-BFGS-B", control=list(maxit=1000000)) results #plot the results constrFun(results$par, altMode=TRUE) #unconstrained function with ALL of 225 parameters!!! # this will take forever to converge, so it isn't run optim(parInit(likFun),likFun,lower=parLower(likFun),upper=parUpper(likFun), method="L-BFGS-B",control=list(maxit=1000000))