trps (version 0.1.0)

two_source_priors_params: Adjust Bayesian priors - Two Source Trophic Position

Description

Adjust priors for two source trophic position model derived from Post 2002.

Usage

two_source_priors_params(
  a = NULL,
  b = NULL,
  c1 = NULL,
  c1_sigma = NULL,
  c2 = NULL,
  c2_sigma = NULL,
  n1 = NULL,
  n1_sigma = NULL,
  n2 = NULL,
  n2_sigma = NULL,
  dn = NULL,
  dn_sigma = NULL,
  tp_lb = NULL,
  tp_ub = NULL,
  sigma_lb = NULL,
  sigma_ub = NULL,
  bp = FALSE
)

Value

stanvars object to be used with brms() call.

Arguments

a

($\alpha$) exponent of the random variable for beta distribution. Defaults to 1. See beta distribution for more information.

b

($\beta$) shape parameter for beta distribution. Defaults to 1. See beta distribution for more information.

c1

mean ($\mu$) prior for the mean of the first ${\delta }^{13}$C baseline. Defaults to -21.

c1_sigma

variance ($\sigma$)for the mean of the first ${\delta }^{13}$C baseline. Defaults to 1.

c2

mean ($\mu$) prior for or the mean of the second ${\delta }^{13}$C baseline. Defaults to -26.

c2_sigma

variance ($\sigma$)for the mean of the first ${\delta }^{13}$C baseline. Defaults to 1.

n1

mean ($\mu$) prior for the mean of the first ${\delta }^{15}$N baseline. Defaults to 8.

n1_sigma

variance ($\sigma$)for the mean of the first ${\delta }^{15}$N baseline. Defaults to 1.

n2

mean ($\mu$) prior for or the mean of the second ${\delta }^{15}$N baseline. Defaults to 9.5.

n2_sigma

variance ($\sigma$) for the mean of the second ${\delta }^{15}$N baseline. Defaults to 1.

dn

mean ($\mu$) prior value for $\mathrm{\Delta }$N. Defaults to 3.4.

dn_sigma

variance ($\sigma$) for ${\delta }^{15}$N. Defaults to 0.25.

tp_lb

lower bound for priors for trophic position. Defaults to 2.

tp_ub

upper bound for priors for trophic position. Defaults to 10.

sigma_lb

lower bound for priors for $\sigma$. Defaults to 0.

sigma_ub

upper bound for priors for $\sigma$. Defaults to 10.

bp

logical value that controls whether informed priors are supplied to the model for both ${\delta }^{15}$N and ${\delta }^{15}$C baselines. Default is FALSE meaning the model will use uninformed priors, however, the supplied data.frame needs values for both ${\delta }^{15}$N and ${\delta }^{15}$C baseline (c1, c2, n1, and n2).

Details

We will use the following equations from Post 2002:

1. $${\delta }^{13}{C}_c=\alpha \ast ({\delta }^{13}{C}_1-{\delta }^{13}{C}_2)+{\delta }^{13}{C}_2$$

2. $${\delta }^{15}N=\mathrm{\Delta }N\times (tp-{\lambda }_1)+n_1\times \alpha +n_2\times (1-\alpha )$$

3. $${\delta }^{15}N=\mathrm{\Delta }N\times (tp-({\lambda }_1\times \alpha +{\lambda }_2\times (1-\alpha )))+n_1\times \alpha +n_2\times (1-\alpha )$$

• The random exponent ($\alpha$; a) and shape parameters ($\beta$; b) for $\alpha$. This prior assumes a beta distribution.

• The mean (c1; $\mu$) and variance (c1_sigma; $\sigma$) of the mean for the first ${\delta }^{13}C$ for a given baseline. This prior assumes a normal distributions.

• The mean (c2;$\mu$) and variance (c2_sigma; $\sigma$) of the mean for the second ${\delta }^{13}C$ for a given baseline. This prior assumes a normal distributions.

• The mean (n1; $\mu$) and variance (n1_sigma; $\sigma$) of the mean for the first ${\delta }^{15}N$ for a given baseline. This prior assumes a normal distributions.

• The mean (n2;$\mu$) and variance (n2_sigma; $\sigma$) of the mean for the second ${\delta }^{15}$N for a given baseline. This prior assumes a normal distributions.

• The mean (dn; $\mu$) and variance (dn_sigma; $\sigma$) of $\mathrm{\Delta }$N (i.e, trophic enrichment factor). This prior assumes a normal distributions.

• The lower (tp_lb) and upper (tp_ub) bounds for priors for trophic position. This prior assumes a uniform distributions.

• The lower (sigma_lb) and upper (sigma_ub) bounds for variance ($\sigma$). This prior assumes a uniform distributions.

See Also

two_source_priors(), two_source_model(), and brms::brms()

Examples

two_source_priors_params()