Performance of a species distribution model based on presence/absence for various population sizes in the amphidromous fish species Sicyopterus japonicus

We formulated a species distribution model (SDM) for the amphidromous fish Sicyopterus japonicus on the basis of presence/absence data and confirmed its performance at various population densities. The best-fit SDM selected several environmental factors, including water depth and velocity, and performed validated prediction of presence/absence of various densities. The predicted probability of occurrence was positively correlated with the observed density. The density was positively related to habitat occupancy, suggesting that this species occupied a wide range of habitats under high densities, but only optimal habitat under low densities. Therefore, the threshold value for predicting presence/absence increased with decreasing densities.