dt_growth_soVB: Discrete seasonally oscillating von Bertalanffy growth...

In marchtaylor/fishdynr: Fisheries science related population dynamics models

Description

dt_growth_soVB calculates length at time 2, given length at time 1 according to the seasonally oscillationg von Bertalanffy growth function

Usage

dt_growth_soVB(Linf, K, ts, C, L1, t1, t2)

Arguments

Linf	Infinite length
K	growth constant
ts	summer point. Time of year (between 0 and 1) when growth oscillation cycle begins (sine wave term becomes positive). Note that this definition differs from some interpretations of the model (see Somers 1998)
C	oscillation strength. Varies between 0 and 1
L1	Length at t1
t1	time 1
t2	time 2

References

Somers, I. F. (1988). On a seasonally oscillating growth function. Fishbyte, 6(1), 8-11.

Examples

# Growth parameters
Linf = 100
K = 0.5
ts = 0.5
C = 0.75

# create dataframe
df <- data.frame(t = seq(0,5,0.2), L=NaN)
df$L[1] <- 10 # intial size

# run iterative model
for(i in 2:nrow(df)){
  df$L[i] <- dt_growth_soVB(
    Linf, K, ts, C, 
    L1=df$L[i-1],
    t1=df$t[i-1],
    t2=df$t[i]
  )
}

# plot result
plot(L ~ t, df)
arrows(
  x0 = df$t[-nrow(df)], y0 = df$L[-nrow(df)],
  x1 = df$t[-1], y1 = df$L[-1],
  col = 8, length = 0.15
)

marchtaylor/fishdynr documentation built on May 21, 2019, 11:27 a.m.