Figure 2: Diagram of two-way cluster analysis.

The horizontal matrix axis consists of 113 avian species coded by scientific name (former two letters) and AHR1 genotype (latter two letters), and the vertical axis is the ecological factors. For example, the herring gull (Larus argentatus), which has the Val_Ala type, was coded LAVA. In case that the initial of the scientific species name overlapped with others, the second letter of the name was used for coding. The matrix was constructed depending on presence (black) and absence (white) according to ecological factors affecting each species. The branch length indicates the percentage of information that shows the data coverage by ecological factors. A total of 113 species were grouped into 3 clusters (cluster 1, 2, and 3) and 3 subclusters (3-1, 3-2, and 3-3) according to ecological factors. The Val_Ala genotype was dominant in avian species that inhabit marine and wetland ecosystems (cluster 1) or are carnivorous (cluster 3-1). The Ile_Ala type prevailed in avian species that inhabit terrestrial ecosystems (clusters 2, 3-2, and 3-3). Each cluster is shaded according to the dominant genotype (blue for Val_Ala type and yellow for Ile_Ala type). Ecological factors formed 3 clusters (A, B, and C). Cluster A consisted of factors linked to the forest habitat while cluster B was composed of marine and wetland species. The remaining ecological factors were included in cluster C. Ecological factors are indicated according to color, with green, mint, and pink boxes.