Delineating freshwater fish biogeographic regions in the Philippine archipelago

The Philippines, a biodiversity hotspot with a complex geological history, presents an ideal setting to study freshwater fish biogeography in archipelagos. Despite its ecological significance, analyses of freshwater fish distribution patterns across the archipelago remain lacking. This study addresses this knowledge gap by delineating native freshwater fish biogeographic regions in the Philippines and investigating the factors influences these patterns. This research integrates extensive native freshwater fish occurrences data with environmental variables and historical biogeography. Species distributions, diversity and endemism were analyzed using cluster analysis of Simpson's beta (βsim) dissimilarity matrix and Generalized Dissimilarity Modeling (GDM). The analysis identifies five distinct biogeographic provinces across the archipelago: Northern Luzon, Central/Southern Luzon, Greater Visayas, Palawan-Mindoro, and Mindanao. Geographic distance and Pleistocene Aggregate Island Complex (PAIC) grouping emerged as key drivers of fish species turnover. Indicator species analysis characterized the unique faunal composition of each province. This study provides the first comprehensive biogeographic framework for Philippine freshwater fishes, offering crucial insights for understanding evolutionary processes, guiding conservation planning, and informing management strategies in this megadiverse yet understudied region. The findings contribute to understanding freshwater biogeography in complex island systems while highlighting the importance of integrating historical and contemporary factors in explaining biodiversity patterns.