Species Distribution models
The multivariate structure test performed with the MSVF.test function on the multiclass model containing all three groups reveals that all classes have an observed error, which is significantly lower (p< 0.05) than random error (null model). This means that there is significant multivariate structure to differentiate between the three lineages using the chosen predictor variables. The multiclass model had an out-of-bag training error of 4.35%. All 161 instances of lineage I-III were correctly classified (class error = 0). Lineage IV had an error of 6.6% in which one instance out of 15 was wrongly assigned to lineage V. Lineage V had an error of 25.8%, in which eight instances out of 31 were wrongly classified as lineage IV.
The prediction of the winner class of the model is depicted (Figure 6). Lineage I-III is distributed in the northern part of Iceland, from the shelf regions to the abyssal plains, having its southern distribution barrier along the GIF Ridge with an additional predicted occurrence south of the GIF Ridge. Lineage IV is present in the upper slope and shelf regions south of the GIF Ridge and extends into the Reykjanes Ridge at depths of around 1000 m. It is possible that this lineage extends into the deeper areas of the North Sea and further to the north along the coast of Norway. Lineage V extends from the abyssal plains of the North Atlantic to the north until a depth of around 1000 m to 2000 m, and is absent in the upper slope and shelf regions. Small disjunct areas are located on the west coast of Norway. The error rates of the presence/absence models were 0%, 6.7%, and 2.4% for lineages I-III, IV and V, respectively. The predictions for the single group models are depicted in Figures 7-9. Lineage I-III (Figure 7) shows basically the same predicted distribution as in the multiclass model. Lineage IV, however, displays an important extension into the abyssal areas in the North Atlantic, but with low probability of 0.5 to 0.6. On the other hand, lineage V shows an extension into the slope areas south of Iceland up to the 500 m isobath. The single lineage models show considerable overlap in the probability of occurrence between lineages IV and V in the slope areas. In this model, lineage V is not predicted to be present in the west coast of Norway.
The niche partitioning of the groups within the water masses is depicted in the temperature-depth plot (Figure 10). Lineage I-III occupies the northern water mass characterized by low temperature across all depths. This lineage is mainly distributed at bottom water temperatures below 2 °C. Lineage V is mainly distributed in southern water masses at temperatures between 2 °C and 3 °C and depths below 1,000 m. Lineage IV is mainly distributed at bottom water temperatures above 3 °C and depth above 3,000 m, with its core distribution above 1,000 m depth.