2. Model selection
In the full model, interactions between filter pore size and water
temperature and between target gene and water temperature were
statistically significant (both P < 0.05), and effects
of the filter pore size and interaction between fragment size and water
source were marginally significant (both P < 0.1)
(Table 2). All supported models resulting from model selection included
the effects of filter pore size, target gene, and water source, whereas
the effects of fragment size and temperature were uncertain, owing to
their small coefficient and large SE. However, we focused on the effects
of the interactions among variables; all supported models included
interactions between filter pore size and temperature (Figure 1) and
between target gene and temperature (Figure 2). In addition, 11 of the
13 models included the interaction between target gene and water source
(Figure 3), and four models included the interaction between filter pore
size and water source (Figure S1). Other interactions were included in
less than three supported models, and the uncertainties of the
corresponding coefficients were relatively large.
Although DNA fragment size was included in most supported models, its
effect was relatively small due to its high variability (Table 2).
Considering the smaller number of eDNA decay rate constants targeting
longer DNA fragments as mentioned previously, we instead assessed the
relationship between the eDNA decay rate and shorter DNA fragment size
(<200 bp). Consequently, the fragment size was found to have a
significantly positive effect on the decay rate (P <
0.01; Figure S2).