two_source_model {trps} | R Documentation |
Bayesian model - Two Source Trophic Position
Description
Trophic position using a two source model derived from Post 2002 using a Bayesian framework.
Usage
two_source_model(bp = FALSE, lambda = NULL)
Arguments
bp |
logical value that controls whether informed priors are
supplied to the model for both |
lambda |
numerical value, |
Details
We will use the following equations from Post 2002:
-
\delta^{13}C_c = \alpha \times (\delta ^{13}C_1 - \delta ^{13}C_2) + \delta ^{13}C_2
-
\delta^{15}N = \Delta N \times (tp - \lambda_1) + n_1 \times \alpha + n_2 \times (1 - \alpha)
-
\delta^{15}N = \Delta N \times (tp - (\lambda_1 \times \alpha + \lambda_2 \times (1 - \alpha))) + n_1 \times \alpha + n_2 \times (1 - \alpha)
For equation 1)
where \delta^{13}C_c
is the isotopic value for consumer, \alpha
is the ratio between baselines and consumer \delta^{13}C
,
\delta^{13}C_1
is the mean isotopic value for baseline 1, and
\delta^{13}C_2
is the mean isotopic value for baseline 2
For equation 2) and 3)
\delta^{15}
N are values from the consumer,
n_1
is \delta^{15}
N values of baseline 1, n_2
is
\delta^{15}
N values of baseline 2,
\Delta
N is the trophic discrimination factor for N (i.e., mean of 3.4
),
tp is trophic position, and \lambda_1
and/or
\lambda_2
are the trophic levels of
baselines which are often a primary consumer (e.g., 2
or 2.5
).
The data supplied to brms()
when using baselines at the same trophic level
(lambda
argument set to 1
) needs to have the following variables, d15n
,
c1
, c2
, n1
, n2
, l1
(\lambda_1
) which is usually 2
.
If using baselines at different trophic levels (lambda
argument set to 2
)
the data frame needs to have l1
and l2
with a numerical value for
each trophic level (e.g.,2
and 2.5
; \lambda_1
and \lambda_2
).
Value
returns model structure for two source model to be used in a
brms()
call.
See Also
Examples
two_source_model()