Spatially explicit models for distance sampling data

Practical 3: Multiple smooths and model selection

Aims

By the end of this practical, you should feel comfortable:

• Fitting DSMs with multiple smooth terms in them
• Selecting smooth terms by \(p\)-values
• Using shrinkage smoothers
• Inspecting Q-Q plots select response distribution
• Selecting between models using AIC
• Investigating sensitivity and path dependence

Load data and packages

library(Distance)

## Loading required package: mrds

## This is mrds 2.2.3
## Built: R 4.0.2; ; 2020-08-01 10:33:56 UTC; unix

## 
## Attaching package: 'Distance'

## The following object is masked from 'package:mrds':
## 
##     create.bins

library(dsm)

## Loading required package: mgcv

## Loading required package: nlme

## This is mgcv 1.8-33. For overview type 'help("mgcv-package")'.

## Loading required package: numDeriv

## This is dsm 2.3.0
## Built: R 4.0.2; ; 2020-07-16 23:56:50 UTC; unix

library(ggplot2)
library(patchwork)
library(knitr)

Load the data and the fitted detection function objects from the previous exercises:

load("spermwhale.RData")
load("df-models.RData")

Exploratory analysis

We can plot the covariates together using the following code (don’t worry too much about understanding what that code is doing at the moment).

# make a list to hold our plots
p <- list()

# make a plot for each covariate
for(covname in c("Depth", "SST", "NPP", "DistToCAS", "EKE")){
  # make
  p[[covname]] <- ggplot() +
    # covariates are plotted as tiles
    geom_tile(aes_string(x="x", y="y", fill=covname), data=predgrid) + 
    geom_point(aes(x=x, y=y, size=size),
               alpha=0.6,
               data=subset(obs, size>0))+
    # remove grey background etc
    theme_minimal() +
    # remove axis labels and fiddle with the legend
    theme(axis.title.x=element_blank(),
          axis.text.x=element_blank(),
          axis.ticks.x=element_blank(),
          axis.title.y=element_blank(),
          axis.text.y=element_blank(),
          axis.ticks.y=element_blank(),
          legend.position="right", legend.key.width=unit(0.005, "npc")) +
    # make the fill scale be colourblind friendly
    scale_fill_viridis_c()
}

# using patchwork to stick the plots together
p[["Depth"]] + p[["SST"]] + p[["NPP"]] + p[["DistToCAS"]] + p[["EKE"]]  + plot_layout(ncol = 3, nrow=3)