Assessing the contribution of recorder effort to the occurrence of JTM
In order to assess whether recorder effort affected the distribution of known occurrences of JTM throughout the study region, four generalised linear mixed models (GLMMs; one for each data source) were constructed. GLMMs were constructed for the years 2016–2018, with the presence/pseudo-absence of JTM throughout the study region as a binary response variable. Recorder effort, habitat suitability from the historic model, and the interaction between the two were predictor variables in each model. Year was included as a random effect to account for a lack of independence between years. As above, AIC selection was then implemented to select the best model. Habitat suitability and recorder effort were both standardised by subtracting their mean and dividing by their standard deviation. GLMMs were constructed using theglmmTMB package and had a binary error structure and a logit link function.
All analyses were conducted in R version 4.0.037. Code is available from https://github.com/nis38/JTM.